Genetic

and

Environmental

Influences

on

Individual

Differences

in

Attitudes

Toward

Homosexuality

An

Australian

Twin

Study

Previous

research

has

shown

that

many

heterosexuals

hold

negative

attitudes

toward

homosexuals

and

homosexuality

-LRB-

homophobia

-RRB-

Although

a

great

deal

of

research

has

focused

on

the

profile

of

homophobic

individuals

this

research

provides

little

theoretical

insight

into

the

aetiology

of

homophobia

To

examine

genetic

and

environmental

influences

on

variation

in

attitudes

toward

homophobia

we

analysed

data

from

twins

who

completed

a

questionnaire

concerning

sexual

behaviour

and

attitudes

including

attitudes

toward

homosexuality

Results

show

that

in

accordance

with

literature

males

have

significantly

more

negative

attitudes

toward

homosexuality

than

females

and

non-heterosexuals

are

less

homophobic

than

heterosexuals

In

contrast

with

some

earlier

findings

age

had

no

significant

effect

on

the

homophobia

scores

in

this

study

Genetic

modelling

showed

that

variation

in

homophobia

scores

could

be

explained

by

additive

genetic

-LRB-

-RRB-

shared

environmental

-LRB-

-RRB-

and

unique

environmental

factors

-LRB-

-RRB-

However

corrections

based

on

previous

findings

show

that

the

shared

environmental

estimate

may

be

almost

entirely

accounted

for

as

extra

additive

genetic

variance

arising

from

assortative

mating

for

homophobic

attitudes

The

results

suggest

that

variation

in

attitudes

toward

homosexuality

is

substantially

inherited

and

that

social

environmental

influences

are

relatively

minor

Introduction

Homophobia

can

be

defined

as

the

fear

of

aversion

to

or

discrimination

against

homosexuality

or

homosexuals

-LRB-

Merriam

Webster

's

Medical

Dictionary

-RRB-

Although

the

social

and

cultural

status

of

homosexuality

has

improved

Kite

and

Whitley

-LRB-

-RRB-

concluded

from

their

meta-analyses

of

studies

that

many

heterosexuals

still

hold

very

negative

attitudes

toward

homosexuals

and

their

sexual

behaviour

A

great

deal

of

research

has

focused

on

the

personality

and

demographic

features

of

homophobic

individuals

Numerous

studies

indicated

that

men

tend

to

hold

more

negative

attitudes

toward

homosexuals

than

women

especially

toward

gay

men

-LRB-

e.g.

Davies

Herek

Herek

and

Gonzalez-Rivera

Kite

and

Whitley

LaMar

and

Kite

Lingiardi

et

al.

Steffens

and

Wagner

-RRB-

The

most

common

explanation

for

this

sex

difference

in

homophobic

attitudes

is

that

men

tend

to

hold

more

traditional

gender

beliefs

which

encourage

them

to

be

more

negative

toward

homosexuality

particularly

toward

gay

men

-LRB-

Kite

and

Whitley

-RRB-

Furthermore

homophobic

individuals

in

general

seem

to

be

higher

in

authoritarianism

are

more

religious

hold

traditional

attitudes

toward

family

and

gender

roles

have

relatively

low

levels

of

education

and

have

had

fewer

interactions

with

homosexuals

-LRB-

Herek

Herek

and

Gonzalez-Rivera

-RRB-

As

Kite

and

Whitley

-LRB-

-RRB-

stated

these

data

offer

some

insight

into

the

profile

of

homophobic

individuals

but

the

existing

research

is

only

descriptive

in

nature

and

hence

provides

little

theoretical

insight

into

prejudices

regarding

sexual

orientation

There

is

considerable

support

for

the

existence

of

generalized

prejudice

-LRB-

see

Ekehammar

et

al.

-RRB-

Different

types

of

prejudice

-LRB-

e.g.

racism

sexism

and

prejudice

toward

homosexuals

-RRB-

have

been

shown

to

be

highly

correlated

-LRB-

e.g.

Bierly

Ekehammar

and

Akrami

-RRB-

implying

that

people

who

reject

one

out-group

will

also

tend

to

reject

others

As

Ekehammar

et

al.

-LRB-

-RRB-

describe

in

their

article

two

major

theories

have

risen

to

explain

why

some

individuals

are

more

prejudiced

than

others

In

the

first

theory

individual

differences

in

prejudice

are

considered

to

be

due

to

stable

factors

within

the

individual

-LRB-

their

personality

characteristics

-RRB-

in

this

case

prejudice

is

seen

as

an

expression

of

personality

-LRB-

Ekehammar

and

Akrami

Heaven

and

St.

Quintin

-RRB-

The

second

theory

implies

that

individual

differences

in

prejudice

are

caused

by

factors

linked

to

the

outside

world

like

intergroup

relationships

and

social

life

-LRB-

see

e.g.

Guimond

et

al.

Guimond

Reynolds

et

al.

-RRB-

Earlier

twin

studies

have

demonstrated

that

individual

differences

in

personality

are

substantially

heritable

-LRB-

e.g.

Jang

et

al.

Loehlin

et

al.

-RRB-

and

therefore

it

is

possible

that

there

are

genetic

influences

on

homophobia

as

well

On

the

other

hand

a

study

concerning

personality

and

social

attitudes

-LRB-

including

general

conservatism

and

attitude

to

sex

and

politics

-RRB-

in

a

large

sample

revealed

that

besides

genetic

effects

family

-LRB-

shared

-RRB-

environment

also

has

a

considerable

contribution

to

social

attitudes

-LRB-

Eaves

et

al.

-RRB-

Consequently

shared

environmental

influences

on

attitudes

toward

homosexuality

can

also

be

expected

Such

results

would

fit

the

second

theory

that

emphasizes

social

processes

Accordingly

the

aim

of

the

present

study

is

to

determine

the

contribution

of

both

genes

and

shared

environment

to

individual

differences

in

attitudes

to

homosexuality

using

data

from

a

large

twin

sample

Findings

will

result

in

further

insight

into

the

aetiology

of

variation

in

homophobia

Methodology

Participants

All

participants

were

drawn

from

the

Australian

National

Health

and

Medical

Research

Council

Twin

Registry

-LRB-

ATR

-RRB-

Subjects

for

this

study

were

recruited

in

two

phases

from

a

large

twin-family

study

of

alcohol

use

and

abuse

In

phase

one

all

twin

pairs

-LRB-

N

aged

between

and

years

-RRB-

participating

in

an

extensive

Health

and

Lifestyle

Questionnaire

-LRB-

HLQ

-RRB-

were

asked

whether

they

were

willing

to

participate

in

an

anonymous

study

about

sexual

behaviour

and

attitudes

All

those

who

agreed

were

mailed

the

sex

questionnaire

between

July

and

October

To

ensure

anonymity

twins

were

not

asked

about

their

name

or

date

of

birth

but

to

make

up

a

digit

number

Both

twins

of

a

pair

had

to

use

the

same

number

which

made

it

possible

to

connect

the

responses

of

both

twins

Additionally

informed

consent

was

obtained

separate

from

the

questionnaires

In

the

second

phase

an

additional

group

of

twin

pairs

in

an

older

cohort

-LRB-

aged

between

and

years

old

-RRB-

was

asked

to

participate

in

the

sexual

behaviour

and

attitudes

study

Procedures

for

this

data

collection

were

the

same

as

for

the

younger

cohort

as

described

above

Twins

who

expressed

willingness

to

participate

were

mailed

the

questionnaire

between

April

and

August

For

a

more

extensive

description

of

the

data

collection

procedure

the

study

sample

and

the

pairing

of

the

returned

questionnaires

-LRB-

see

Kirk

et

al.

-RRB-

In

total

complete

pairs

and

twins

from

incomplete

pairs

completed

the

questionnaire

-LRB-

male

and

female

individuals

-RRB-

However

due

to

missing

data

and

ambiguous

zygosities

the

effective

study

sample

used

for

the

homophobia

analyses

is

lower

than

as

described

in

the

result

section

Zygosity

The

zygosity

of

the

same-sex

twins

was

determined

during

completion

of

the

HLQ

based

on

their

response

to

standard

items

about

physical

similarity

and

being

mistaken

for

each

other

Ambiguous

replies

were

clarified

by

telephone

call

According

to

Ooki

et

al.

-LRB-

-RRB-

and

Martin

and

Martin

-LRB-

-RRB-

concurrence

on

zygosity

between

discriminant

analyses

of

questionnaire

scores

and

DNA

typing

is

at

least

and

telephone

clarification

will

have

increased

accuracy

In

the

present

study

the

zygosity

of

the

twin

pairs

was

premarked

on

their

questionnaire

and

the

twins

were

asked

whether

they

did

or

did

not

agreed

with

the

assessment

Measures

Data

used

in

this

study

were

items

from

a

larger

part

of

the

sexual

behaviour

and

attitudes

questionnaire

called

Your

Present

Personality

This

part

of

the

questionnaire

contained

items

selected

from

three

former

instruments

namely

Inventory

of

Attitudes

to

Sex

-LRB-

items

Eysenck

-RRB-

Attitudes

to

Homosexuality

-LRB-

items

Klassen

et

al.

-RRB-

and

Adult

Gender

Nonconformity

-LRB-

seven

items

Finn

The

structure

of

masculinity

and

femininity

self

ratings

Unpublished

manuscript

-RRB-

A

principal

components

analysis

of

these

items

-LRB-

performed

in

for

Windows

-RRB-

revealed

nine

factors

for

males

and

for

females

The

most

apparent

factor

for

both

sexes

explaining

of

the

total

variance

for

both

sexes

was

a

factor

regarding

attitudes

to

homosexuality

comprising

all

items

of

the

Attitudes

to

Homosexuality

scale

created

by

Klassen

et

al.

-LRB-

-RRB-

Each

item

showed

a

high

factor

loading

for

both

males

and

females

-LRB-

between

and

-RRB-

Accordingly

in

the

present

study

homophobia

was

measured

using

the

items

of

this

Attitudes

to

Homosexuality

scale

which

comprised

statements

like

Homosexuality

is

obscene

and

vulgar

and

Homosexual

men

should

be

allowed

to

work

as

schoolteachers

-LRB-

see

Appendix

A

for

the

total

scale

-RRB-

Twins

were

asked

to

either

tick

YES

if

they

agreed

with

the

statement

or

NO

if

they

disagreed

If

a

participant

filled

out

both

answers

on

an

item

-LRB-

both

YES

and

NO

-RRB-

the

item

was

coded

as

missing

To

enhance

unbiased

answering

a

preamble

to

the

section

explained

that

there

are

no

right

or

wrong

answers

and

no

trick

questions

and

they

were

encouraged

to

work

quickly

and

not

to

think

too

long

about

the

exact

meaning

of

questions

To

maximise

the

number

of

twin

pairs

available

for

genetic

analysis

missing

item

responses

were

imputed

where

possible

by

using

the

imputation

methods

in

PRELIS

-LRB-

Jöreskog

and

Sörbom

-RRB-

Missing

values

were

substituted

with

values

from

other

cases

with

similar

response

patterns

but

without

missing

data

Note

that

it

was

only

possible

to

impute

items

in

PRELIS

if

participants

had

only

one

missing

value

and

that

imputation

depended

on

the

response

patterns

from

other

cases

A

total

of

responses

were

imputed

-LRB-

of

the

total

item

responses

-RRB-

increasing

the

available

twins

for

structural

equation

modelling

from

to

a

gain

of

in

the

total

available

sample

size

A

total

homophobia

score

was

calculated

by

summing

the

answers

on

all

statements

where

a

homophobic

response

was

counted

as

one

and

a

non-homophobic

response

as

zero

To

further

maximise

the

number

of

twin

pairs

available

for

genetic

analysis

participants

missing

one

-LRB-

N

-RRB-

or

two

-LRB-

N

-RRB-

responses

were

included

in

further

analyses

Their

homophobia

score

was

corrected

by

adding

their

mean

item

score

for

each

missing

item

This

resulted

in

another

gain

of

of

the

available

sample

size

As

the

distribution

of

the

homophobia

data

showed

significant

skewness

and

kurtosis

scores

were

grouped

into

four

ordinal

categories

with

roughly

equal

sample

sizes

Individuals

scoring

on

the

continuous

scale

were

given

an

ordinal

score

of

while

individuals

scoring

or

were

given

score

individuals

scoring

score

and

individuals

scoring

score

To

determine

the

participants

sexual

orientation

twins

were

asked

the

following

question

in

another

part

of

the

questionnaire

called

Sexual

Feelings

and

Behaviour

Do

you

consider

yourself

to

be

heterosexual

-LRB-

straight

-RRB-

bisexual

or

homosexual

-LRB-

lesbian

or

gay

-RRB-

For

the

present

study

sexual

orientation

was

only

subdivided

into

heterosexual

and

non-heterosexual

The

latter

includes

both

bisexual

and

homosexual

individuals

Data

analysis

As

the

homophobia

scale

analysed

in

this

study

is

an

ordinal

scale

the

data

were

analysed

using

a

threshold

model

-LRB-

Falconer

-RRB-

For

these

analyses

it

is

assumed

that

there

is

an

underlying

continuum

of

liability

which

is

normally

distributed

in

the

population

Upon

this

normal

distribution

three

thresholds

are

placed

to

delimit

the

four

categories

Variation

in

liability

can

be

modelled

as

a

function

of

genetic

and

environmental

influences

Descriptive

statistics

for

the

homophobia

scores

are

obtained

using

for

Windows

Subsequently

Structural

Equation

Modelling

-LRB-

SEM

-RRB-

is

applied

to

estimate

thresholds

polychoric

correlations

between

twins

and

components

of

variance

First

the

effects

of

gender

age

and

sexual

orientation

on

the

thresholds

is

tested

Next

heterogeneity

of

polychoric

twin

pair

correlations

was

assessed

as

a

function

of

sex

and

zygosity

and

finally

the

importance

of

different

sources

of

familial

aggregation

-LRB-

i.e.

shared

genes

and

shared

environment

-RRB-

was

tested

SEM

is

conducted

using

Mx

b

a

matrix

algebra

calculator

that

fits

structural

equation

models

to

observed

data

-LRB-

Neale

et

al.

-RRB-

All

analyses

were

conducted

using

maximum-likelihood

estimation

for

raw

ordinal

data

in

Mx.

Models

were

compared

with

a

likelihood

ratio

χ2

test

To

determine

the

effects

of

age

sexual

orientation

and

sex

on

the

thresholds

different

-LRB-

nested

-RRB-

submodels

are

tested

against

a

full

model

in

which

all

parameters

were

estimated

By

looking

for

differences

in

model

fit

after

constraining

these

effects

to

zero

in

a

stepwise

manner

the

significance

of

parameters

that

contribute

to

explaining

differences

in

thresholds

can

be

determined

Heterogeneity

of

twin

pair

correlations

is

tested

by

determining

the

change

in

model

fit

when

twin

pair

correlations

-LRB-

for

sex

and/or

zygosity

-RRB-

were

equated

Genetic

model

fitting

of

twin

data

allows

for

decomposition

of

the

observed

variance

in

homophobia

scores

into

its

genetic

and

environmental

components

Additive

genetic

variance

-LRB-

A

-RRB-

denotes

the

variance

resulting

from

the

sum

of

allelic

effects

across

multiple

genes

while

D

symbolizes

non-additive

genetic

effects

including

dominance

and

epistasis

Common

environmental

variance

-LRB-

C

-RRB-

is

that

resulting

from

environmental

influences

shared

within

twin

pairs

whereas

unique

environmental

variance

-LRB-

E

-RRB-

results

from

non-shared

environmental

influences

and

includes

measurement

error

Estimates

of

A

C

D

and

E

can

be

derived

from

the

resemblance

between

monozygotic

-LRB-

MZ

-RRB-

twins

who

are

genetically

identical

and

dizygotic

-LRB-

DZ

-RRB-

twins

who

share

on

average

of

their

segregating

genes

Accordingly

if

MZ

twins

resemble

each

other

more

than

DZ

twins

on

a

particular

trait

this

is

an

indicator

that

it

is

partly

influenced

by

genetic

effects

Further

if

the

DZ

within-pair

correlation

is

higher

than

half

the

MZ

within-pair

correlation

this

implies

that

common

environmental

effects

contribute

to

individual

differences

in

the

homophobia

scores

By

means

of

SEM

different

combinations

of

A

C

D

and

E

can

be

evaluated

to

obtain

the

most

parsimonious

explanation

for

the

observed

pattern

of

MZ

and

DZ

twin

pair

correlations

Note

however

that

C

and

D

can

not

be

estimated

simultaneously

-LRB-

Martin

et

al.

-RRB-

and

that

the

choice

for

an

ACE

or

ADE

model

depends

on

the

pattern

of

MZ

and

DZ

correlations

Results

Descriptive

statistics

Of

the

respondents

to

the

questionnaire

were

omitted

as

they

had

more

than

two

missing

values

on

the

homophobia

items

and

an

additional

single

twins

were

deleted

due

to

ambiguous

zygosity

Hence

the

total

number

of

individuals

utilised

for

the

analyses

is

comprising

twin

families

-LRB-

pairs

and

singletons

-RRB-

Complete

twin

pairs

included

MZ

males

DZ

males

MZ

females

DZ

females

and

DZ

opposite

sex

pairs

The

age

range

of

the

study

sample

was

years

for

both

sexes

with

a

mean

age

for

males

of

-LRB-

S.D.

-RRB-

and

for

females

of

-LRB-

S.D.

-RRB-

Descriptive

statistics

for

each

homophobia

statement

for

all

individuals

are

presented

in

Table

Table

of

agreement

-LRB-

yes

-RRB-

disagreement

-LRB-

no

-RRB-

and

missing

answers

on

the

homophobia

statements

for

males

and

females

separatelyMales

-LRB-

N

-RRB-

Females

-LRB-

N

-RRB-

YesNoMissingYesNoMissingHomosexuality

is

not

Allow

as

school

Allow

as

court

Allow

as

Allow

as

medical

Allow

as

government

Dangerous

as

Homosexuality

is

Homosexuality

is

social

Allow

to

dance

with

each

other

in

aNote

that

agreement

on

these

statements

indicate

a

homophobic

attitude

Using

the

imputed

data

set

item

scores

were

added

together

and

subsequently

recoded

into

a

four-point

ordinal

scale

ranging

from

-LRB-

not

homophobic

at

all

-RRB-

to

-LRB-

highly

homophobic

-RRB-

Table

shows

the

number

and

percentage

of

individuals

within

each

homophobia

category

Table

and

percentage

of

males

and

females

heterosexuals

and

non-heterosexuals

for

each

category

of

the

ordinal

homophobia

scale

-LRB-

is

least

is

most

homophobic

-RRB-

Homophobia

heterosexual

-LRB-

N

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Males

non-heterosexual

-LRB-

N

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Males

-LRB-

N

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Females

heterosexual

-LRB-

N

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Females

non-heterosexual

-LRB-

N

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Females

-LRB-

N

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

aNote

that

for

males

and

females

self-reported

sexual

orientation

is

missing

To

determine

whether

sexual

orientation

influences

homophobic

attitudes

individuals

were

asked

which

sexual

orientation

they

considered

themselves

Of

the

male

participants

-LRB-

-RRB-

rated

themselves

as

heterosexual

while

-LRB-

-RRB-

considered

themselves

to

be

non-heterosexual

-LSB-

responses

-LRB-

-RRB-

were

missing

-RSB-

Of

the

females

-LRB-

-RRB-

rated

themselves

to

be

heterosexual

while

-LRB-

-RRB-

considered

themselves

to

be

non-heterosexual

-LSB-

responses

-LRB-

-RRB-

were

missing

-RSB-

In

Table

the

number

and

percentage

of

heterosexuals

and

non-heterosexuals

within

each

homophobia

category

is

shown

Hypotheses

concerning

differences

in

threshold

parsimony

Within

sexes

thresholds

for

MZ

and

DZ

twins

could

be

equated

without

significant

deterioration

in

model

fit

-LRB-

P

-RRB-

indicating

no

evidence

for

social

interaction

between

twins

However

results

show

a

significant

difference

in

the

distribution

of

attitudes

toward

homosexuality

between

sexes

such

that

males

were

more

homophobic

than

females

-LRB-

P

-RRB-

Furthermore

a

significant

difference

in

distribution

of

thresholds

was

found

between

heterosexuals

and

non-heterosexuals

-LRB-

P

-RRB-

On

average

heterosexuals

were

more

homophobic

than

non-heterosexuals

Finally

it

was

tested

whether

age

had

a

significant

influence

on

the

distribution

of

the

thresholds

Removing

the

effect

of

age

from

the

model

did

not

lead

to

a

significantly

worse

model

fit

-LRB-

P

-RRB-

implying

that

age

has

no

appreciable

influence

on

individual

differences

in

attitudes

toward

homosexuality

Heterogeneity

of

twin

pair

correlations

Polychoric

twin

pair

correlations

for

each

zygosity

group

shown

in

Table

were

estimated

in

Mx

by

maximum-likelihood

Although

the

twin

pair

correlation

for

MZ

males

is

higher

than

for

MZ

females

they

were

not

significantly

different

-LRB-

P

-RRB-

Table

twin

pair

correlations

-LRB-

confidence

intervals

-RRB-

for

the

homophobia

score

for

each

zygosity

group

estimated

in

MxMZM

pairsDZM

pairsMZF

pairsDZF

pairsDZOS

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Furthermore

as

the

twin

pair

correlation

for

DZ

opposite

sex

twin

pairs

is

lower

than

for

the

DZ

same

sex

twin

pairs

qualitative

differences

in

sources

of

familial

aggregation

between

sexes

could

be

expected

However

the

difference

in

twin

pair

correlation

between

the

opposite

and

the

same

sex

DZ

twin

pairs

was

not

significant

-LRB-

P

-RRB-

The

inability

to

find

significant

differences

between

the

MZ

twin

pair

correlations

for

males

and

females

and

between

the

DZ

same

sex

and

opposite

sex

twin

pair

correlations

may

however

be

due

to

a

lack

of

power

to

detect

qualitative

and

quantitative

differences

between

the

groups

The

MZ

twin

pair

correlations

are

significant

higher

than

the

DZ

twin

pair

correlations

-LRB-

P

-RRB-

suggesting

that

genetic

effects

are

a

source

of

familial

aggregation

in

attitudes

toward

homosexuality

Genetic

modelling

Results

of

the

univariate

SEM

for

the

homophobia

scores

are

shown

in

Table

As

the

DZ

twin

pair

correlations

are

more

than

half

the

MZ

twin

pair

correlations

a

model

is

fitted

incorporating

additive

genetic

-LRB-

A

-RRB-

shared

environmental

-LRB-

C

-RRB-

and

unique

environmental

-LRB-

E

-RRB-

effects

Since

the

DZ

opposite

sex

correlation

is

lower

-LRB-

although

not

significantly

-RRB-

than

the

DZ

same

sex

correlations

a

general

sex-limitation

model

is

fitted

which

allows

for

qualitative

and

quantitative

differences

in

the

sources

of

variation

in

attitudes

toward

homosexuality

between

sexes

-LRB-

Neale

and

Cardon

-RRB-

To

model

the

qualitative

differences

in

genetic

effects

between

sexes

the

genetic

correlation

for

DZ

opposite

sex

twins

-LRB-

H

-RRB-

is

estimated

in

the

model

instead

of

fixed

at

as

it

is

for

same

sex

DZ

twin

pairs

Table

model

fitting

Comparison

of

different

genetic

modelsModel

sex-limitation

Common

effects

sex-limitation

General

ACE

Subsequently

a

common

effects

sex-limitation

model

is

fitted

by

fixing

the

genetic

correlation

for

DZ

opposite

sex

twins

at

Results

show

no

significant

deterioration

of

model

fitting

-LRB-

P

-RRB-

consistent

with

the

same

sets

of

genes

influencing

homophobia

scores

for

males

and

females

Third

the

fit

of

a

general

ACE

model

in

which

proportions

of

A

and

C

are

constrained

equal

in

males

and

females

is

compared

with

the

fit

of

the

common

effects

sex-limitation

model

Results

show

no

significant

deterioration

of

model

fit

-LRB-

P

-RRB-

indicating

there

are

no

magnitude

differences

in

effects

of

A

C

and

E

on

variance

in

homophobia

scores

between

sexes

Under

the

general

ACE

model

additive

genetic

and

common

environmental

effects

together

account

for

between

and

of

the

variance

in

homophobia

-LRB-

see

Table

-RRB-

It

is

impossible

to

distinguish

between

AE

and

CE

models

as

removing

the

effects

of

either

A

or

C

causes

significant

deterioration

in

model

fit

Table

of

variance

-LRB-

confidence

intervals

-RRB-

attributable

to

A

C

and

E

effects

for

both

sexes

for

the

general

sex-limitation

model

the

common

effects

sex-limitation

model

and

the

general

ACE

modelAmalesCmalesEmalesAfemalesCfemalesEfemalesHDZOSGeneral

sex-limitation

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Common

effects

sex-limitation

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

General

ACE

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Accordingly

the

most

parsimonious

explanation

for

the

observed

pattern

of

MZ

and

DZ

twin

pair

correlations

is

the

general

ACE

model

where

there

are

no

qualitative

and

quantitative

differences

in

sources

of

variance

between

sexes

The

twin

pair

correlations

however

point

to

possible

differences

in

the

sources

of

variance

between

sexes

The

inability

to

detect

these

qualitative

and

quantitative

differences

between

sexes

might

be

due

to

insufficient

power

from

using

a

threshold

model

necessitated

by

the

extreme

skewness

of

the

raw

data

-LRB-

Neale

et

al.

-RRB-

Based

on

the

general

ACE

model

estimates

of

the

influence

of

A

C

and

E

on

the

variance

in

homophobia

scores

for

both

sexes

are

and

-LRB-

see

Table

-RRB-

In

Fig.

the

graphical

illustration

of

the

general

ACE

model

-LRB-

a

-RRB-

and

the

general

sex-limitation

model

-LRB-

b

-RRB-

including

the

path

coefficients

are

presented

Fig.

presentation

of

the

general

ACE

model

-LRB-

a

-RRB-

and

the

general

sex-limitation

model

-LRB-

b

-RRB-

along

with

the

standardised

path

coefficients

In

the

general

sex-limitation

model

path

coefficients

for

males

are

presented

on

the

left

and

for

females

on

the

right

side

Note

that

in

the

general

sex-limitation

model

the

correlation

between

opposite

sex

twins

for

additive

genetic

effects

is

estimated

in

the

model

Discussion

Analyses

of

the

homophobia

scale

showed

that

in

accordance

with

former

literature

-LRB-

e.g.

Kite

and

Whitley

-RRB-

males

have

more

negative

attitudes

toward

homosexuality

than

females

and

heterosexuals

are

more

homophobic

than

non-heterosexuals

-LRB-

Jellison

et

al.

-RRB-

In

this

study

age

had

no

effect

on

attitudes

toward

homosexuality

whereas

some

others

have

found

that

younger

individuals

have

more

favourable

attitudes

regarding

homosexuality

than

older

persons

-LRB-

Herek

Steffens

and

Wagner

-RRB-

It

should

be

noted

however

that

the

distribution

of

age

in

this

study

was

highly

skewed

with

the

majority

of

participants

-LRB-

-RRB-

in

age

group

and

only

of

all

participants

aged

between

and

years

The

aim

of

the

present

study

was

to

determine

the

contribution

of

genes

and

environment

to

individual

differences

in

attitudes

toward

homosexuality

Based

on

the

general

ACE

model

estimates

of

the

influence

of

A

C

and

E

on

the

variance

in

homophobia

scores

are

and

However

although

no

significant

qualitative

and

quantitative

differences

in

sources

of

variation

between

males

and

females

were

found

twin

pair

correlations

do

suggest

possible

differences

between

the

sexes

Under

a

general

sex-limitation

model

estimates

of

the

influence

of

A

and

C

on

variation

in

homophobia

scores

are

and

for

males

and

and

for

females

respectively

The

additive

genetic

correlation

for

the

DZ

opposite

sex

twins

is

estimated

at

considerably

lower

than

the

assumed

for

DZ

same

sex

twins

This

finding

would

suggest

that

genes

influencing

homophobia

in

males

are

to

a

large

extent

different

from

those

in

females

However

since

both

A

and

C

effects

are

present

in

both

sexes

the

parameterisation

of

sex

limitation

as

genetic

in

origin

is

arbitrary

If

it

were

parameterised

as

a

lower

common

environmental

correlation

between

males

and

females

the

same

model

fit

would

be

obtained

Moreover

there

could

be

sex

limitation

of

both

A

and

C

influences

but

since

there

is

only

one

degree

of

freedom

to

estimate

them

obtained

from

the

DZ

opposite

sex

twin

pair

correlation

the

two

are

completely

confounded

In

either

case

differences

in

saliency

of

homosexuality

between

males

and

females

make

it

unsurprising

that

there

are

distinct

causes

of

variation

in

homophobia

in

the

two

sexes

A

limitation

to

our

confidence

in

the

variance

components

estimated

above

is

that

strong

assortative

mating

has

been

repeatedly

found

for

social

attitudes

-LRB-

e.g.

Eaves

et

al.

Hatemi

et

al.

Martin

et

al.

-RRB-

This

means

that

the

relative

genetic

variance

may

have

been

underestimated

If

spouses

are

correlated

for

homophobia

through

the

assortment

process

then

both

MZ

and

DZ

twin

correlations

will

be

raised

to

the

same

degree

Mimicking

the

effect

of

shared

environment

this

extra

resemblance

would

yield

higher

estimates

of

C

As

our

sample

does

not

include

spouses

we

rely

on

previous

estimates

of

assortative

mating

to

determine

its

effect

on

our

estimates

Recently

Hatemi

et

al.

-LRB-

-RRB-

investigated

spouse

correlations

on

social

attitudes

including

an

item

on

gay

rights

for

which

they

found

a

spouse

correlation

of

Assuming

that

this

value

is

a

reasonable

estimate

for

assortative

mating

in

our

sample

it

is

possible

to

correct

our

C

estimate

for

assortative

mating

by

using

a

procedure

described

by

Martin

-LRB-

-RRB-

After

correction

the

contribution

of

shared

environment

on

individual

differences

in

homophobia

scores

falls

from

to

while

the

genetic

estimate

increases

to

about

This

finding

suggests

that

variation

in

attitudes

toward

homosexuality

is

substantially

inherited

while

social

environmental

influences

are

relatively

minor

When

applying

the

assortative

mating

correction

to

the

results

of

the

general

sex-limitation

model

the

contribution

of

shared

environment

on

individual

differences

in

homophobia

scores

for

males

falls

from

to

and

for

females

from

to

while

the

genetic

estimate

increases

to

about

for

males

and

for

females

As

such

based

on

the

general

sex-limitation

model

familial

aggregation

for

homophobia

scores

for

males

might

be

almost

totally

accounted

for

by

genetic

effects

while

for

females

both

genes

and

shared

environment

seem

to

have

about

equal

effects

If

this

would

be

the

case

and

there

is

little

or

no

C

influence

on

homophobia

scores

for

males

sex

limitation

for

homophobia

scores

can

only

have

a

genetic

origin

Another

important

consideration

is

that

the

genetic

contribution

to

homophobia

might

partly

reflect

genetic

influences

on

related

traits

such

as

intelligence

personality

or

social

class

In

our

data

the

polychoric

correlation

of

the

homophobia

measure

with

educational

level

was

-LRB-

P

-RRB-

and

with

social

class

was

-LRB-

P

-RRB-

so

these

traits

would

only

account

for

a

modest

amount

of

variance

While

individuals

attitudes

toward

homosexuality

are

partly

influenced

by

genes

shared

environmental

factors

also

contribute

a

modest

proportion

of

variation

in

homophobic

attitudes

This

finding

suggests

that

shared

environmental

influences

such

as

norms

and

values

taught

by

parents

are

aspects

in

forming

positive

or

negative

attitudes

toward

homosexuals

and

possibly

also

toward

other

out-groups

The

main

source

of

variance

is

unique

environment

-LRB-

under

the

general

ACE

model

-RRB-

While

an

unknown

fraction

of

this

will

be

due

to

measurement

error

the

number

suggest

a

great

influence

on

attitudes

to

homosexuality

is

the

unique

experiences

of

the

individual

shaping

his

or

her

attitudes

independent

of

family

influences

This

study

shows

that

one

's

own

sexual

orientation

is

one

such

influence

although

previous

research

has

shown

that

sexual

orientation

itself

is

substantially

genetically

influenced

-LRB-

e.g.

Kendler

et

al.

Kirk

et

al.

-RRB-

Although

the

effect

of

sexual

orientation

on

homophobia

is

large

at

the

individual

level

the

percentage

of

non-heterosexuals

is

so

low

it

accounts

for

only

a

trivial

proportion

of

population

variance

in

attitudes

to

homosexuality

There

are

a

few

important

methodological

limitations

to

be

considered

for

this

study

As

already

mentioned

the

most

important

limitation

of

this

study

was

a

lack

of

statistical

power

Although

the

sample

size

is

fairly

large

due

to

the

fact

that

the

homophobia

scale

had

to

be

analysed

as

ordinal

data

it

is

still

insufficient

Neale

et

al.

-LRB-

-RRB-

showed

that

for

a

threshold

study

at

least

three

times

the

sample

size

needed

for

equivalent

power

to

a

study

using

continuous

data

is

required

Another

important

limitation

of

this

study

is

that

no

distinction

has

been

made

between

attitudes

toward

male

versus

female

homosexuals

Five

out

of

the

ten

questions

are

asked

in

gender

neutral

terms

while

the

other

five

statements

are

about

homosexual

men

The

term

homosexuals

will

by

most

individuals

be

interpreted

as

referring

to

gay

males

and

not

to

females

-LRB-

Haddock

et

al.

-RRB-

so

the

items

will

predominantly

measure

attitudes

toward

gay

men

As

previously

mentioned

heterosexuals

tend

to

have

quite

different

attitudes

toward

the

two

with

lesbians

generally

being

viewed

less

negatively

-LRB-

e.g.

Herek

Kite

and

Whitley

-RRB-

Hence

to

better

understand

individual

differences

in

attitudes

toward

homosexuality

researchers

should

distinguish

between

male

and

female

homosexuals

in

their

questions

-LRB-

Herek

and

Capitanio

LaMar

and

Kite

Kite

and

Whitley

-RRB-

A

further

consideration

is

whether

participation

biases

influenced

the

results

of

the

present

study

especially

as

this

survey

queried

participants

about

very

personal

information

Dunne

et

al.

-LRB-

-RRB-

have

examined

this

question

for

the

survey

used

in

the

current

study

by

comparing

the

social

psychological

and

behavioural

features

of

the

twins

who

explicitly

consented

to

join

the

present

study

-LRB-

-RRB-

with

those

who

either

explicitly

refused

-LRB-

-RRB-

or

initially

agreed

but

subsequently

did

not

return

the

consent

forms

-LRB-

-RRB-

Results

indicate

that

those

individuals

who

explicitly

consented

had

less

conservative

sexual

attitudes

and

were

more

likely

to

agree

with

gay

rights

However

the

effect

sizes

of

these

findings

were

small

indicating

the

participation

bias

probably

did

not

influence

the

results

to

a

great

extent

Another

limitation

to

consider

is

the

possibility

of

socially

desirable

responding

Although

it

is

not

possible

to

exclude

social

desirability

effects

twins

were

encouraged

to

be

honest

by

guaranteeing

anonymity

and

by

asking

them

to

fill

out

the

questionnaire

while

alone

with

sufficient

privacy

In

summary

this

study

concerning

the

aetiology

of

homophobic

attitudes

revealed

that

familial

aggregation

in

attitudes

toward

homosexuality

is

accounted

for

by

genes

as

well

as

by

shared

environmental

factors

However

when

the

plausible

effect

of

assortative

mating

on

our

estimates

is

taken

into

account

familial

aggregation

for

homophobia

scores

might

be

almost

totally

accounted

for

by

genetic

effects

More

research

is

necessary

to

further

unravel

the

sources

of

variance

in

homophobia

and

to

determine

whether

these

differ

between

sexes

This

future

research

will

need

greater

sample

sizes

preferably

including

spouses

and

should

analyse

attitudes

toward

male

and

female

homosexuals

separately

It

will

also

be

of

interest

to

compare

prejudice

toward

homosexuals

with

prejudice

toward

other

targets

-LRB-

like

racism

and

sexism

-RRB-

to

see

to

what

extent

similar

results

will

be

obtained

and

whether

the

same

genetic

and

environmental

sources

explain

individual

differences

in

prejudice

toward

different

out-groups

O O O O O O O O B O B O O O B I O O O O O O O O O B O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O B O O O O O O O O O O O O O O O B O O B O B O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

attitudes
homophobia
twin study
homosexuality


Lymphocyte subsets in peripheral blood of patients with moderate-to-severe versus mild plaque psoriasis In several studies peripheral blood T-cells have been quantified , yet few data are available on lymphocyte subsets in moderate-to-severe psoriasis -LRB- in terms of extent and activity of lesions -RRB- versus mild psoriasis . The objective is to compare lymphocyte subsets in peripheral blood of patients with moderate-to-severe disease -LRB- PASI-score ≥ 12 -RRB- to patients with mild disease -LRB- PASI-score < 12 -RRB- and to healthy subjects . By means of flow cytometry method , lymphocytes in peripheral blood of 27 patients with psoriasis and 10 healthy controls were characterized . The absolute number of total lymphocytes was markedly decreased in patients with moderate-to-severe psoriasis as compared to patients with mild disease and normal subjects . Cellcounts of all analysed subsets were found to be increased in more severe psoriasis , except for CD8 + CD45RO + cells . The under-representation of CD8 + CD45RO + cells is compatible with the dynamics of acquired immunity , which requires a time log after the relapse of the lesions to differentiate from CD45RA + naive cells . Introduction Psoriasis is a common inflammatory skin disease characterized by hyperproliferation of keratinocytes . It is a well established fact that T-cells play an important role in the pathogenesis of psoriasis -LSB- 6 , 9 -RSB- . Indeed , treatments such as anti-CD4 -LSB- 5 , 15 , 19 -RSB- , anti-CD11 -LSB- 5 , 13 -RSB- and anti-CD25 -LSB- 13 -RSB- , targeting at specific T-cells , have shown to be effective in psoriasis . Several T-cell subsets seem to play a primary role . Major classes are CD4 + , CD8 + , CD45RO + and CD45RA + T-cells . Recently , NK-T cells have been suggested to play an additional role in the regulation of immunity , through the release of cytokines -LSB- 3 , 14 , 16 -RSB- . NK-T cells are cells bearing both T cell receptors as well as natural killer-cell specific receptors such as CD161 . It has been shown that circulating NK-T cells are significantly reduced in some autoimmune diseases -LSB- 8 , 17 -RSB- . The large body of research on the role of T-cells in psoriasis has been focused on lesional T-cells . This has resulted in the hypothesis that there is a final common pathway responsible for the development of chronic plaque psoriasis , which may involve specific antigen recognition by T-cells that results in stimulation of keratinocyte proliferation . In psoriasis , CD4 + cells seem to be important mainly in the early phase of plaque development . These cells are found predominantly in the upper dermis , whereas CD8 + cells have proven to be relevant during chronic phases and are found predominantly in the epidermis -LSB- 21 -RSB- , although others have found a more early involvement of CD8 + T-cells in the development of psoriatic plaques -LSB- 22 -RSB- . A large number of activated T-cells have been shown in clinically involved skin of psoriatic patients , but also uninvolved skin contains a significant number of T-cells . In healthy skin , however , T-cells can hardly be found . It has been suggested that circulating T-cells are activated and subsequently recruited from the circulation during the development of psoriatic plaques -LSB- 2 , 10 -RSB- . Several studies have investigated peripheral blood T-cells of psoriatic patients -LSB- 1 -- 3 , 7 , 10 , 12 , 14 , 20 , 21 -RSB- . These studies indicated that the total amount of T-cells in patients is comparable or slightly increased as compared to that found in normal subjects . No relevant differences have been shown with respect to total T-cell counts and T-cell subsets including CD4 + , CD8 + , CD45RO + and CD45RA + cell counts . Only few studies comprise a comparison between mild and more severe forms of psoriasis , using clinical severity indicators such as the Psoriasis Area and Severity Index -LRB- PASI-score -RRB- -LSB- 4 , 18 -RSB- . The present study compares specific circulating lymphocyte subsets in patients with mild psoriasis , patients with moderate-to-severe psoriasis and normal subjects . Materials and methods Patients and controls Fifteen patients with moderate-to-severe psoriasis vulgaris -LRB- 12 male and three female aged 19 -- 66 , mean age 46.2 years -RRB- and 12 patients with mild psoriasis -LRB- seven male and five female , aged 34 -- 72 , mean age 52.8 years -RRB- from our outpatient department participated in this study . Mean PASI-scores in both groups were 20.97 ± 2.55 -LRB- mean ± SEM -RRB- and 6.11 ± 1.27 , respectively . Patients were classified into one of both groups based on their PASI-score . We considered all patients with a PASI-score < 12 as having a `` mild '' , and all patients with a PASI > 12 as having a `` moderate-to-severe '' psoriasis -LSB- 4 , 18 -RSB- . Patients were free of any systemic therapy for at least 4 weeks and did not use any topical therapy in the last 2 weeks . Peripheral blood was obtained from all subjects with their written informed consent . Control samples were collected from 10 healthy volunteers without any history or signs of skin disease -LRB- four male and six female aged 24 -- 49 , mean age 33.8 years -RRB- . Preparation of PBMC 's For each patient , the exact amount of blood withdrawn was determined by measuring the height of the column of blood in the tube , which was subsequently converted to the corresponding volume in microliter . PBMC 's were isolated from heparinized blood by density centrifugation on polyester gel -LRB- Becton Dickinson Vacutainer ™ CPT ™ , Franklin Lakes NJ , USA -RRB- . After filtering through a 70 μm cellstrainer , cells were washed twice . For flow cytometry , single-cell suspensions -LRB- concentration 5 × 105 cells ml − 1 -RRB- were stained in 1 % fetal calf serum in phosphate-buffered saline -LRB- PBS -RRB- at concentrations recommended by the manufacturer . Additionally , 450 μl propidium iodide -LRB- PI -RRB- in PBS was added to each sample in order to exclude non-viable cells from analysis . The following monoclonal antibodies were used : fluorescein isothiocyanate -LRB- FITC -RRB- - conjugated anti-CD4 , FITC-conjugated anti-CD8 , phycoerythrin -LRB- PE -RRB- - conjugated anti-CD4 , PE-conjugated anti-CD8 , PE-conjugated anti-CD94 and PE-conjugated anti-CD161 -LRB- all from Immunotech , Marseille , France -RRB- , as well as FITC-conjugated anti-CD45RA -LRB- Becton Dickinson , San Jose , CA , USA -RRB- and FITC-conjugated anti-CD45RO -LRB- DAKO , Glostrup , Danmark -RRB- . Flowcytometric analysis Cells were analyzed with an EPICS Elite flow cytometer -LRB- Coulter , Luton , UK -RRB- , using the forward scatter as a discriminator . Lymphocytes were identified by gating on CD45 and side and forward scatter properties . All samples were processed within 18 h of phlebotomy . The following -LRB- combinations of -RRB- PE and FITC-conjugated reagents were used to determine the expression of each antigen or antigen combination on lymphocytes derived from peripheral blood : CD4 + -LRB- marker for T-helper cells -RRB- , CD8 + -LRB- marker for cytotoxic T cells -RRB- , CD45RA + -LRB- marker for naïve T-cells -RRB- , CD45RO + -LRB- marker for memory T-cells -RRB- , CD94 + -LRB- marker for NK-cells , T cells -RRB- , CD161 + -LRB- marker for NK-cells , T-cells with memory phenotype -RRB- , CD4 + CD45RA + , CD4 + CD45RO + , CD8 + CD45RA + , CD8 + CD45RO + , CD8 + CD94 + and CD8 + CD161 + . Determination of absolute numbers of lymphocytes Enumeration of positive cells was performed by adding Flow Count Beads -LRB- Beckman Coulter , Fullerton , CA , USA -RRB- to the cell suspension of PBMCs . An automatic stop after a defined amount of beads was programmed on the flow cytometer . Absolute counts of lymphocyte subsets per blood sample were calculated by determining the ratio of the beads to the cell population and then multiplying this ratio by the number of beads in the tube . By dividing this count by the amount of microliters in the tube , a relative absolute lymphocyte count in cells μl − 1 blood withdrawn was obtained . Analysis was performed with Verity software . Ratios for CD4 + / CD8 + cells , CD45RO + / CD45RA + cells , CD4 + CD45RO + / CD4 + CD45RA + cells and CD8 + CD45RO + / CD8 + CD45RA + cells were calculated afterwards , with data derived from this analysis . Statistical analysis Data-entry and analysis was performed using Statistica 6.0 software . Means and standard deviations were calculated for each parameter and were tested with one-way ANOVA . Differences were considered statistically significant at p < 0.05 . Results In total , 27 patients with psoriasis and 10 normal subjects without signs or symptoms of skin disease were included in the present study . Table 1 summarizes the demographic details and psoriasis related characteristics of the patients with moderate-to-severe psoriasis , patients with mild psoriasis and normal subjects . Four out of 12 patients with mild psoriasis had shown a minimal increase in the extent of lesions ; in the others the skin abnormalities were stable . With respect to the 15 patients with moderate-to-severe-psoriasis , 12 had an increase of the extent of lesions during the previous 4 weeks , whereas the other three had been stable . Table 1Demographic and psoriasis related characteristics of patient and subjects participating in the study -LRB- mean ± SEM -RRB- Moderate-to-severe psoriasisMild psoriasisNormal subjectsDemographicsAge -LRB- years -RRB- 46.2 ± 3.4552.8 ± 3.4933.8 ± 3.1 Male : female ratio 12:37:54:6 Psoriasis related characteristicsPASI-score 20.97 ± 2.556.11 ± 1.27 NADuration -LRB- years -RRB- 16.7 ± 2.722.2 ± 2.5 NA Total cell counts The total amount of gated cells -LRB- per microliter blood withdrawn -RRB- in normal subjects was 2,220 ± 301 cells μl − 1 -LRB- mean ± SEM -RRB- . The cell-count in mild psoriasis was 1,923 ± 230 cells μl − 1 . In contrast , patients with moderate-to-severe psoriasis had cell counts of 498 ± 95 cells μl − 1 . No statistically significant difference was observed between normal subjects and patients with mild psoriasis . However , a highly significant difference -LRB- p < 0.0001 -RRB- was observed between mild and severe psoriasis . The CD4 + / CD8 + ratios in all three groups were in the same range , meaning no shift occurred in the distribution of these subgroups of peripheral blood lymphocytes . The total number of lymphocytes , and the CD4 + and CD8 + counts of the patients with moderate-to-severe disease were also routinely measured at the GLP certified Central Haematology Laboratory in our hospital , in which the whole blood lysing method is the standard . Comparison of both methods reveals an acceptable resemblance in results , with lower counts of maximum 10 % . Lymphocyte subsets Lymphocyte subsets as a percentage of total gated cells are summarized in Fig. 1 . CD4 + , CD8 + , CD45RA + and CD45RO + cells are increased in patients with severe psoriasis as compared to patients with mild psoriasis and normal subjects -LRB- p < 0.0001 in all cases -RRB- . Fig. 1CD4 , CD8 , CD45RO and CD45RA subpopulations , expressed as a percentage of total lymphocyte counts . Comparison between normal subjects , patients with mild - and patients with moderate-to-severe psoriasis . -LRB- * : p < 0.0001 -RRB- No significant differences were observed between patients with mild psoriasis and normal subjects . Double labeling of lymphocytes revealed that the percentages of CD4 + CD45RO + , CD4 + CD45RA + and CD8 + CD45RA + cells were significantly increased in moderate-to-severe versus mild psoriasis -LRB- p < 0.001 in all cases -RRB- , whereas the percentage of CD8 + CD45RO + cells was not increased significantly -LRB- Fig. 2 -RRB- . Cell ratios for CD4 + / CD8 + cells , CD45RO + / CD45RA + cells , CD4CD45RO + / CD4CD45RA + cells and CD8CD45RO + / CD8CD45RA + cells are summarized in Fig. 3 . Fig. 2Expression of CD4 + CD45RO + , CD4CD45RA + , CD8 + CD45RO + and CD8CD45RA + cells , as percentage of the total amount of lymphocytes , in three subgroups : moderate-to-severe psoriasis , mild psoriasis and normal subjects -LRB- * : p < 0.001 -RRB- Fig. 3Ratios of CD4/CD8 , CD45RO + / CD45RA + , CD4CD45RO + / CD4CD45RA + and CD8CD45RO + / CD8CD45RA + in normal subjects , mild and moderate-to-severe psoriasis -LRB- * : p < 0.05 -RRB- Lymphocytes expressing NK cell receptors CD94 + and CD161 + cells , expressed as a percentage of total cells were increased in patients with moderate-to-severe psoriasis , as compared to patients with mild psoriasis and normal subjects -LRB- p < 0.05 and p < 0.001 , respectively -RRB- . Figure 4 summarizes these observations . Again no statistically significant differences were observed between normal subjects and patients with a mild form of psoriasis . Fig. 4CD94 and CD161 subpopulations , expressed as a percentage of total lymphocyte counts . Comparison between normal subjects , patients with mild - and patients with moderate-to-severe psoriasis -LRB- * : p < 0.05 and p < 0.001 respectively -RRB- With respect to double stained cells , we observed an increase in the expression of both CD8 + CD94 + cells as well as CD8 + CD161 + cells -LRB- markers for NK T subpopulations -RRB- in patients with a more extensive form of psoriasis , expressed as a percentage of the total amount of cells , as compared to patients with mild psoriasis and normal subjects -LRB- p < 0.008 and p < 0.009 , respectively , results shown in Fig. 5 -RRB- . Fig. 5Cellcounts of CD8 + CD94 + and CD8 + CD161 + cells as percentage of total lymphocytes -LRB- * : p < 0.009 -RRB- Correlation between PASI-score and lymphocyte subsets and cells expressing NK receptors Linear regression analysis revealed no significant correlation between the individual PASI-scores and the quantifications of lymphocyte subsets or cells with NK-cell receptors . Correlation analysis between disease activity and peripheral lymphocytes did not reveal a difference between patients with spreading lesions and those with stable plaque psoriasis . Discussion The results of this study show marked differences in absolute cellcounts between the three patient groups . Our main goal was to investigate whether there is a difference in the occurrence of biomarkers on circulating lymphocytes in mild psoriasis versus more severe forms of the disease . One of the criteria to qualify for a treatment with major systemic therapies such as a biological is often a minimum PASI-score of 12 -LSB- 4 , 18 -RSB- . We were interested whether this cut-off point also implies a differentiation between mild versus moderate/severe psoriasis in terms of T-cell and NKT-cell subsets . The results of the present study have shown us that there are indeed marked differences between mild psoriasis and the more severe forms of disease defined by cut-off point PASI 12 . A decrease of total lymphocyte counts , as percentage of PBMC , and an increase in the percentage of CD4 + CD45RO + cells in patients with moderate-to-severe psoriasis has been reported before -LSB- 10 -RSB- . These patients -LRB- 32 subjects -RRB- had an average PASI of 25.7 -LRB- 10 -- 48 -RRB- , and all had had an exacerbation following infection . Patients had a mixed morphology , from guttata psoriasis to chronic plaque psoriasis . In the same study , however , a decrease in the amount of CD4 + cells was described , which is in contrast with the findings in our study . Other authors have reported no significant difference in total T-cells as percentage of PBMC counts between patients with psoriasis and normal subjects -LSB- 3 -RSB- . These patients -LRB- 14 subjects -RRB- had an average PASI of 23.5 ± 10.6 . However , no information was given whether these patients had relapsing psoriasis . In the present study , the patients with severe psoriasis had an extension of lesions during the wash out period -LRB- average increase in PASI : 4.9 -RRB- . Therefore , the severity in our patients not only comprises the extent of lesions but also activity of lesions with progression and therefore , approaches the characteristics of the patients reported by Lecewicz-Torún et al. -LSB- 10 -RSB- , who also reported a decrease of T-cells in peripheral blood in psoriasis -LRB- expressed as percentage of total PBMC -RRB- . The decrease of lymphocyte counts , expressed as a percentage , in peripheral blood in patients with moderate-to-severe psoriasis is the reverse of the substantial accumulation of lymphocytes in psoriatic skin . The most likely explanation for this paradox is an increased influx of cells into the skin of patients with severe disease . Further studies , in which simultaneous measurements of lesional and circulating T cells will be performed , need to be carried out to support this hypothesis . A striking observation is the increased percentage of both CD4 + cells and CD8 + cells in patients with moderate-to-severe psoriasis as compared to mild psoriasis and normal subjects , without a change in CD4/CD8 ratio . So far , reports on the CD4 + / CD8 + ratio in psoriasis have been at variance -LSB- 10 , 11 -RSB- . With respect to the double labeled lymphocytes , both the percentage of CD4 + CD45RO + cells as well as the percentage of CD4 + CD45RA + cells is increased in patients with moderate-to-severe psoriasis , in contrast to the absolute decrease of total lymphocytes . The relative count of both subsets is increased , whereas their ratio shows a tendency to decrease -LRB- p = 0.0509 -RRB- . Thus , with increasing severity of disease , the increase in CD4 + CD45RA + cells seems to exceed the increase in CD4 + CD45RO + cells . An explanation for this phenomenon is the preferential migration of CD4 + CD45RO + cells into lesional skin in extensive disease , resulting in a relative decrease of this subset of CD4 + lymphocytes in peripheral blood . This hypothesis supports earlier studies where CD4 + CD45RO + cells have been shown to be the major players in psoriatic plaques . Indeed , CD4 + cells appear in a very early phase of the psoriatic process . In a previous study , CD4 + cells have been detected in the distant uninvolved skin of patients with active psoriasis -LSB- 22 -RSB- . The percentage of CD8 + CD45RO + cells in patients with moderate-to-severe psoriasis approached the percentages in patients with mild psoriasis and normal subjects , in contrast with the CD8 + CD45RA + cells , which did show a significant increase in peripheral blood . The impressive under-representation of CD8 + CD45RO + lymphocytes as compared to CD8 + CD45RA + lymphocytes in moderate to severe psoriasis suggests a preferential influx of CD8 + CD45RO + cells into the skin . Both CD8 + cells , as well as CD45RO + cells are abundantly present in psoriatic lesional skin . Previously , we have shown that in the outer margin of the spreading psoriatic plaque the number of CD8 + cells and CD45RO + cells were increased -LSB- 22 -RSB- . Therefore , the relative under-representation in peripheral blood of CD45RO + cells , in particular the CD8 + CD45RO + cells , most likely reflect the influx of these cells into the skin in patients with moderate-to-severe psoriasis in an active phase of disease . However , further studies are needed to support this hypothesis . Lymphocyte counts , preferably T-cells , in skin as well as in the peripheral blood should be monitored during a longer period of time , e.g. , during exacerbation and during disease-free intervals . The CD8 + CD94 + cells and CD8 + CD161 + cells show a marked increase in patients with moderate-to-severe psoriasis as compared to mild psoriasis and normal subjects . The increases of these lymphocytes expressing NK receptors in peripheral blood are accompanied with increases of these cells in the psoriatic lesion . The results of the present study suggest that in peripheral blood of patients with moderate-to-severe psoriasis , in contrast to the vast presence of T-cells in skin lesions , the absolute lymphocyte counts are profoundly decreased , without any change of CD4/CD8 ratio . The relative under-representation of CD45RO + cells , as compared to CD45RA + cells , in peripheral blood most likely results from a massive influx of memory effector T-cells into the psoriatic lesions in an active phase of disease . Both in blood and skin of patients with moderate-to-severe psoriasis the percentages of CD94 + and CD161 + cells are increased . These results are compatible with the functions of these cells . CD45RO + cells differentiate from CD45RA + cells and represent acquired immunity , whereas NK-T cells are able to act without prior sensitization , representing innate immunity -LSB- 3 -RSB- . In further research , more selective lymphocyte markers are required in order to investigate the role of peripheral blood T-cells in the pathogenesis of psoriasis , and correlation studies between peripheral blood T-cells and T-cells in skin are required in order to understand the dynamics of compartmentalization of T-cell subsets belonging to either the acquired or the innate immunity system in psoriasis .

O O O B I O O O O O O O B O O O B I O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B I O O O O B O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I B O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O O B I O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O B O O O O O O O B O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O O O B O O O O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O

psoriasis
lymphocytes
peripheral blood
severity of disease
t cells