Role of TLR4 in Environmental Asthma
Condition: Asthma
MeSH terms: Asthma
Study type: Interventional
Phase: Phase 1

Summary: 
      The overall goal of this project is to identify genes that are involved in the development of
      airflow obstruction and airway inflammation in asthmatics, and to determine whether
      polymorphisms in these differentially expressed genes predispose individuals to develop
      asthma. In this project, we hypothesize that polymorphisms of genes expressed by the airway
      epithelia in asthmatics following specific airway challenges predispose individuals to the
      development of asthma.
    

Detailed description: 
      The overall goal of this project is to identify genes that are involved in the development of
      airflow obstruction and airway inflammation in asthmatics, and to determine whether
      polymorphisms in these differentially expressed genes predispose individuals to develop
      asthma. Asthma is a complex genetic disorder that is caused by a number of unique gene-gene
      and gene-environment interactions. The search for asthma susceptibility genes has been
      complicated by the broad clinical phenotype of asthma, the polygenic inheritance pattern of
      this disease, and the substantial role of environmental exposures in the development and
      progression of asthma. Inhaled environmental agents induce several biologic responses in
      asthmatics; including the induction of acquired and innate immunity that leads to acute and
      chronic forms of airway inflammation and airway remodeling. Acquired immune responses to
      protein antigens, such as house dust mite allergen, often induce type 2 T lymphocyte-driven
      responses (Th2) which appear to be important in atopic asthma. Recent studies by our group
      and others demonstrate that innate immunity, initiated by inhalation of bacterial and viral
      pathogens, organic dusts, endotoxin or lipopolysaccharide (LPS), air pollution particulate
      matter, and ozone, can also cause acute and chronic forms of airflow obstruction, airway
      inflammation, and even airway remodeling. Emerging evidence indicates that both acquired and
      innate immune responses in the lung may be influenced by polymorphic genes. For instance,
      functional polymorphisms in the IL-4 receptor gene are thought to preferentially stimulate
      acquired Th2 immune responses to inhaled allergens, and we have recently shown that common
      co-segregating mutations in TLR4 (a transmembrane receptor for LPS) are associated with
      diminished airway responsiveness to inhaled LPS. These observations suggest that
      environmental challenges can be used to narrow the phenotype of asthma and investigate
      genetic susceptibility in biologically specific forms of asthma.

      In this project, we hypothesize that polymorphisms of genes expressed by the airway epithelia
      in asthmatics following specific airway challenges predispose individuals to the development
      of asthma. To test this hypothesis, we plan to identify the genes that are differentially
      expressed by airway epithelial cells following challenge with stimuli that induce acquired
      (house dust mite) or innate (LPS) immune responses, and then determine whether polymorphisms
      in these genes are associated with the development of asthma in a separate, well
      characterized, familial cohort of asthmatics. This is a powerful approach that is designed to
      identify novel genes that are associated with both asthma pathogenesis (differentially
      expressed in the exposure-response study) and asthma susceptibility (genetically associated
      with asthma in a linkage/association study).

      We hypothesize that individuals with the co-segregating Asp299Gly and Thr399Ile mutations in
      the TLR4 gene will exhibit a defective immune response to LPS, and that specific components
      of altered immunity in these individuals are linked to characteristic airway responses to
      LPS.

      Specific Aim 1: Approximately 1000 individuals will be genotyped in order to establish 3
      study groups: 10 subjects homozygous for the TLR4 299/399 mutation; 10 subjects heterozygous
      for the TLR4 299/399 mutation; and 10 subjects homozygous for wild type TLR 4.

      Specific Aim 2: Ten individuals with wild type TLR4, 10 individuals heterozygous for mutant
      TLR4 and 10 individuals homozygous for mutant TLR4 will be phenotyped for airway
      responsiveness to inhaled LPS.

      Specific Aim 3: In vitro immune responses to LPS will be measured in peripheral blood
      monocytes and PMNs from 10 individuals with wild type TLR4, 10 individuals heterozygous for
      mutant TLR4 and 10 individuals homozygous for mutant TLR4.

      Specific Aim 4: The in vivo immune response to inhaled LPS will be assessed in
      bronchoalveolar lavage (BAL) fluid and cells, and airway endobronchial brush biopsy cells in
      10 individuals with wild type TLR4, 10 individuals heterozygous for mutant TLR4 and 10
      individuals homozygous for mutant TLR4.
    

Intervention name(s): Lipopolysaccharide endotoxin
Intervention type(s): Biological
Intervention description(s): Delivered in nebulized form expressed in activity units(endotoxin units -EU).
Subjects receive each dose 30 min after completing the previous dose, dose duration is approximately 10 minutes:
Challenge One first saline then 5000 EU 10,000 EU 20,000 EU
Challenge 1 and 2 must be at least 2 weeks apart.
Challenge 2 Saline 40,000 EU 80,000 EU
Other intervention name(s): (CCRE)LPS endotoxin from E. Coli 0:113 maintained by NIH
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: LPS endotoxin; asthma