BACKGROUND
numerous epidemiological studies conducted in different parts of the world have demonstrated a consistent association between levels of ambient air particles and various health outcomes, including mortality, cardiopulmonary disease, reduced lung function, and exacerbation of asthma and allergy-related symptoms .
some populations seem to be at particular risk, like the elderly, children or patients with diabetes, chronic obstructive pulmonary disease and asthma  <cit> .
furthermore, the genetic background has been associated with differences in human susceptibility to environmental agents including pesticides and infectious agents  <cit> , and may be of importance also with regard to biological effects of particles.
supporting a causal relationship between particles and increased allergic symptoms, particles have been shown to increase allergic responses both in humans and in animal models .
in rodent models, widely different particles have been shown to increase allergen-specific ige levels both after inhalation, intratracheal, intranasal, intraperitoneal and subcutaneous exposure  <cit> .
particle characteristics like particle size, particle composition and chemicals adsorbed to the particle surface have been shown to influence the adjuvant effect on allergic sensitization and airway inflammation and hyperreactivity in mice  <cit> .
for combustion particles, the insoluble particle core appears to play an important role in the adjuvant effect of particles in several mouse models  <cit> .
mouse strain differences in allergic airway inflammation and allergen-specific antibody levels have been reported after intratracheal instillation of diesel exhaust particles  and allergen  <cit> .
also with "clean" polystyrene particles  as a surrogate of the insoluble combustion particle core, granum et al.
<cit>  concluded that the particle adjuvant effect differed qualitatively with regard to th2- and th1-associated antibody responses, depending on the genetic background or induced immune status of the mice.
the overall aim of the present study was to investigate how the genetic background influences the responses to the allergen and particles alone and in combination.
we therefore examined the antibody and lymph node responses in various inbred strains of mice expected to display different responses to ova and particles.
balb/ca mice are regarded as a high ige responder strain to ova  <cit> .
nih mice were included because they in an intraperitoneal model responded differently from balb/ca mice to psp and ova  <cit> .
furthermore, we included c3h/hen mice, which have been shown to be ige low-responders to ova  <cit> .
balb/cj mice were included in the antibody experiments because this sub-strain has been reported to respond more strongly to ova than balb/ca mice in a subcutaneous model  <cit> .
the lymph node is a key site in the priming of t lymphocytes and ige production by b lymphocytes  <cit> .
therefore, in addition to serum antibody levels, we examined the primary cellular response in the draining popliteal lymph node  after footpad injection of polystyrene particles  and the allergen ovalbumin , alone and in combination.
the pln is the only lymph node draining the footpad  <cit> , and is therefore well suited for studies of responses in the lymph node cells.
we investigated how the selected inbred strains of mice differed qualitatively and quantitatively in their th2- and th1-associated serum antibody and pln cellular response patterns to ova+psp.
furthermore, we investigated if the background , ova-, psp- and ova+psp-induced cytokine patterns differed in the various mouse strains, and whether the cytokine patterns could explain the differences in the antibody responses to ova+psp.
we found that the susceptibility to the adjuvant effect of particles on both secondary antibody responses and primary cellular responses was influenced by genetic factors .
the ex vivo cytokine response patterns did not predict the in vivo antibody responses.
RESULTS
the antibody adjuvant activity of psp in different strains of mice
to examine the dose-response relationship of ova and psp with regard to antibody production, balb/ca and nih mice were immunized with various dose combinations of ova  and psp .
after a booster dose of ova on day  <dig>  the ova-specific ige, igg <dig> and igg2a antibody levels in serum were determined on day  <dig>  in balb/ca mice, psp given with ova strongly increased the levels of the th2-associated ige and igg <dig> antibodies compared to ova alone .
in contrast, the th1-associated igg2a levels did not differ between the groups given ova in the presence or absence of psp .
overall, there was an inverse relationship between the ova dose and both the ige and igg <dig> levels, with  <dig> μg of ova giving the highest antibody levels for all particle doses.
analyses of the factorial design showed that the dose of  <dig> μg ova, regardless of psp dose, induced significantly higher ige levels than the other ova doses, and higher igg <dig> levels than  <dig> μg ova .
irrespective of ova dose, the igg <dig> response increased significantly with each increase in psp dose .
a dose-response trend for particles was less clear for ige due to an absence of a difference between  <dig> and  <dig> μg psp.
in nih mice, psp also exerted an adjuvant effect on the antibody responses to ova, however nih mice responded differently from balb/ca mice in two ways.
first, the nih mice receiving the highest dose combinations of ova and psp experienced anaphylactic reactions and died within minutes after the ova booster injection .
secondly, also the ova-specific igg2a levels were increased by psp in nih mice, in contrast to balb/ca mice.
however, the responses in the surviving mice  suggest that ige and igg <dig> responses were similar in nih and balb/ca mice with regard to the dose-response relationship for particles.
also the igg2a levels were significantly higher for ova with all particle doses than for ova alone, and significantly higher antibody levels were observed with  <dig> μg psp than with  <dig> μg psp.
as  <dig> μg ova and  <dig> μg psp gave a medium but still pronounced response, these doses were used in further experiments.
next, we compared the allergen-specific antibody responses after immunization with ova+psp, ova and psp in balb/ca, balb/cj, nih and c3h/hen mice.
as shown in figure  <dig>  the response patterns for balb/ca and nih mice were similar to those shown in figure  <dig>  with increased ige production in both strains, whereas igg2a production was increased only in nih mice.
furthermore, in our system, balb/cj mice had specific ige and igg2a responses similar to balb/ca mice, however the igg2a levels tended to be slightly increased by ova+psp in balb/cj mice .
similar to the responses in nih mice, psp had an adjuvant effect on both ige and igg2a responses in c3h/hen mice, although the responses appeared weaker in c3h/hen than in nih and balb/c mice.
immunization with ova alone gave ige responses in some individual balb/ca, balb/cj and c3h/hen mice, but never in nih mice .
as expected, hbss and psp without allergen did not affect the specific antibody levels in any of the strains.
cell numbers and ex vivo cytokine responses in the draining lymph node during the primary response
to examine how the primary cellular response to ova and psp, alone or in combination, varied in balb/ca, nih and c3h/hen mice, we studied the cell numbers and the ex vivo cytokine secretion by the popliteal lymph node  cells.
five days after injection of ova+psp, ova, psp and buffer  into the footpad, the pln cell numbers were determined, and the amount of il- <dig>  ifn-γ and il- <dig> released from pln cells after con a stimulation ex vivo were determined.
for all three strains, the pln cell numbers were significantly increased by ova+psp compared to all three control groups .
interestingly, the cell number response to ova alone and psp alone  varied between the three strains.
in balb/ca mice, ova significantly increased the cell numbers, whereas psp significantly increased the cell numbers in nih mice.
c3h/hen mice took an intermediate position, as both ova and psp weakly but significantly increased the cell numbers compared to hbss.
with regard to the cytokines , ova+psp strongly increased the levels of il- <dig> and il- <dig> compared to the three control groups in balb/ca mice , whereas the ifn-γ levels were only marginally affected .
furthermore, ova tended to weakly  increase the il- <dig> levels in balb/ca mice.
the il- <dig> levels for the balb/ca control groups were relatively low compared to levels in nih mice.
in nih mice, ova induced no changes in cytokines or cell numbers, whereas psp significantly increased the il- <dig> and il- <dig> levels , and ova+psp also increased these "responsive" cytokines .
the ifn-γ levels in nih mice were not altered by psp.
again, the c3h/hen mice responded to both ova and psp.
all cytokines were significantly increased by ova and further increased by ova+psp in c3h/hen mice, although more pronounced for ifn-γ than for il- <dig> and il- <dig>  psp alone also significantly increased the levels of ifn-γ and il- <dig> in c3h/hen mice.
the levels of il- <dig> and il- <dig> were low and the levels of ifn-γ were high in c3h/hen mice compared to the levels in the other strains.
the background levels  of il- <dig> and ifn-γ were relatively low in balb/ca and relatively high in nih mice, whereas the levels in c3h/hen mice appeared low for il- <dig> and high for ifn-γ, respectively.
discussion
the genetic background appears to strongly influence whether an individual develops allergic immune responses to an allergen  <cit> .
in mice, this is illustrated by reports of strain differences in allergic responses to allergens  <cit> .
in agreement with granum et al.
<cit> , our data indicate that also the antibody-enhancing capacity of the "clean" insoluble particle is influenced by the genetic background.
this is consistent with reports of mouse strain differences in allergic airway inflammation and specific antibody levels after intratracheal instillation of dep and allergen  <cit> .
also the effects of particles on airway inflammation, epithelial permeability and alveolar macrophage phagocytic activity have been shown to vary between mouse strains  <cit> .
the dose-response relationship for particles appeared similar for balb/ca and nih mice, as the low ova dose  and the high particle doses  induced the strongest ige and igg <dig> antibody responses.
however, the nih mice immunized with a high concentration of both ova and psp were lost due to anaphylactic shock after the booster injection.
high booster antigen concentrations have earlier been shown to induce anaphylactic shock in mice after subcutaneous priming with horse gamma globulin covalently bound to cellulose particles  <cit> .
in mice, igg has been suggested to be as effective as ige in triggering anaphylactic reactions  <cit> .
the induced levels of ova-specific igg <dig> appeared to be about  <dig> times higher in the surviving nih mice than in balb/ca mice .
thus, nih mice may be more susceptible than balb/ca mice to experience anaphylactic shock either because of a stronger igg <dig> response, or because of an otherwise greater susceptibility to anaphylactic shock.
in the present study, the antibody adjuvant effect of psp differed between the different strains of mice, both with regard to the magnitude and whether a th <dig> or a mixed th1- and th2-associated antibody response was increased.
whereas the th1-associated igg2a response was markedly increased by psp only in nih and c3h/hen mice, psp enhanced the th2-associated ige response in all mouse strains examined.
psp seemed also to increase ige responses in pilot studies with c57bl/6j and c3h/hej mice .
also with regard to the adjuvant effect of psp, the balb/ca mice appeared to be a high ige-responder, whereas the c3h/hen mice seemed to be a relatively low responder for both ova-specific ige and igg2a antibody levels.
this responder status is in accordance with other studies of the ige responsiveness to ova in these strains of mice  <cit> .
also with regard to the primary cellular responses in the lymph node, psp increased the response to ova in both balb/ca, nih and c3h/hen mice .
however, while il- <dig> and il- <dig> cytokine responses were significantly increased by ova+psp in all three strains, in c3h/hen mice the levels were low and the increases may not be biologically significant.
on the other hand, ova+psp markedly increased the ifn-γ levels in c3h/hen mice, and marginally in balb/ca mice.
il- <dig> and ifn-γ cytokines are often used as indicators for a th <dig> and thl response, respectively  <cit> .
in this regard, the cytokine responses to ova+psp could be characterized as th2-, th2- and th1-biased for balb/ca, nih and c3h/hen mice, respectively, which would not, however, predict the balance between th2- and th1-associated antibody responses .
neither could the background  responses for il- <dig> and ifn-γ in the different strains explain the balance between th2- and th1- associated antibody responses to ova+psp.
the complexity in gene-environment interactions were illustrated by the highly varying responsiveness to ova and psp given separately in the three strains examined.
balb/ca mice responded with a non-significant but consistent increase in il- <dig> cytokine release in ova-treated mice, whereas nih mice responded with a significantly increased th2-biased  cytokine release in psp-treated mice.
c3h/hen mice responded with both th1- and th2-type cytokine secretion, although apparently th1-skewed due to low il- <dig> and il- <dig> levels, after both ova or psp treatments.
this suggests that the genetic background strongly influences the susceptibility to immunogens and irritative stimuli such as particles, also with regard to the th <dig> and th <dig> cytokine balance of the response.
interestingly, psp alone increased the th2-associated, but not the th1-associated, cytokine responses in nih mice.
if particles by themselves are able to induce il- <dig> production in the lymph nodes also in vivo, this might promote an allergic response to the allergen present.
taken together, psp exerted an adjuvant effect on ova-induced ige and il- <dig> levels in all three strains, while there was no association between the th1-associated parameters igg2a and ifn-γ.
thus, for the strains of mice used, the primary ex vivo cytokine pattern could not predict the th2- and th1-associated antibody pattern.
one reason could be that the con a-stimulation in vitro was not an optimal way to describe the actual in vivo cytokine secretion by the pln cells.
however, in vitro ova-stimulation of pln cells from ova+psp treated balb/ca mice gave similar il- <dig> and ifn-γ response pattern as con a-stimulation .
our findings are consistent with previous studies showing that cytokine expression was only in part correlated with airway disease and ige responses  <cit> , and our data illustrate that interpretation and extrapolation of in vitro data should be done with caution.
the description of the th2/th <dig> balance may explain parts of an immune response, however the immune regulation is more complex, involving other cytokines, cell surface molecules and regulatory t cells.
il- <dig> seems to play an important role in the development and function of certain regulatory t cells .
however, in the present study, il- <dig> secretion by the pool of pln cells was highly correlated with the secretion of il- <dig> .
although contribution from regulatory t cells could not be excluded, this indicates that il- <dig>  which are secreted to a higher degree by th <dig> than th <dig> cells  <cit> , in the pln at this stage was produced mainly by th <dig> cells.
in agreement with randolph et al.
<cit> , we have previously shown that both psp, dep and ambient air particles in the draining lymph node were located within acid phosphatase-, mhc class ii- and cd86-positive cells, most probably antigen-presenting cells   <cit> .
it is remarkable that psp, in the absence of allergen, affected the lymph node cells in both nih and c3h/hen mice.
in contrast, our present and previous data from balb/ca mice indicate that although the particles synergistically enhanced the cellular responses to ova, model particles  had no detectable effects neither on pln cell numbers, expression of lymphocyte surface molecules nor on ex vivo cytokine secretion by the pln cells  <cit> .
taken together, our data from balb/ca mice therefore suggest a role for solid particles as allergen carriers  <cit>  in the adjuvant effect on allergic sensitization.
our present data suggest that particles, in susceptible strains, additionally influence the immune response in the lymph node.
in our model it appears that the particles which induced cellular responses in the absence of allergen ) enhanced both th2- and th1-associated antibody responses, whereas the particles enhancing a th2-dominated antibody response  did not induce detectable cellular changes themselves.
this suggests that the insoluble particle core act by enhancing the inherent response to the allergen , and that genetic background and particle properties determine whether an additional th1-associated response is elicited.
the presence of a th <dig> response has been suggested to amplify th2-driven inflammation  <cit> .
our results therefore suggest that particles may both enhance the ige sensitization and, depending on genetically determined susceptibility, further aggravate allergic inflammation and thereby increase the allergic symptoms in some individuals.
CONCLUSIONS
psp enhanced the ova-specific ige antibody responses in all strains of mice examined, whereas the igg2a response was increased to varying degrees and only in some strains.
genetic factors  influenced the responsiveness to the adjuvant effect of psp on secondary antibody responses and the primary cellular responses to ova.
furthermore, genetic factors also influenced the lymph node cell responsiveness to both ova and psp given separately.
interestingly, psp alone induced different cytokine responses in the lymph node in some of the mouse strains.
furthermore, we found that the ex vivo cytokine patterns could not predict the in vivo th2- and th1-associated antibody response patterns in the different mouse strains.
the results indicate that the insoluble particle core acts by increasing the inherent response to the allergen, and that the genetic background may determine whether an additional th1-associated component is added.

 numerous epidemiological studies conducted in different parts of the world have demonstrated a consistent association between levels of ambient air particles and various health outcomes, including mortality, cardiopulmonary disease, reduced lung function, and exacerbation of asthma and allergy-related symptoms. some populations seem to be at particular risk, like the elderly, children or patients with diabetes, chronic obstructive pulmonary disease and asthma. furthermore, the genetic background has been associated with differences in human susceptibility to environmental agents including pesticides and infectious agents, and may be of importance also with regard to biological effects of particles. supporting a causal relationship between particles and increased allergic symptoms, particles have been shown to increase allergic responses both in humans and in animal models. in rodent models, widely different particles have been shown to increase allergen-specific ige levels both after inhalation, intratracheal, intranasal, intraperitoneal and subcutaneous exposure. particle characteristics like particle size, particle composition and chemicals adsorbed to the particle surface have been shown to influence the adjuvant effect on allergic sensitization and airway inflammation and hyperreactivity in mice. for combustion particles, the insoluble particle core appears to play an important role in the adjuvant effect of particles in several mouse models. mouse strain differences in allergic airway inflammation and allergen-specific antibody levels have been reported after intratracheal instillation of diesel exhaust particles and allergen. also with "clean" polystyrene particles as a surrogate of the insoluble combustion particle core, granum et al. concluded that the particle adjuvant effect differed qualitatively with regard to th2- and th1-associated antibody responses, depending on the genetic background or induced immune status of the mice. the overall aim of the present study was to investigate how the genetic background influences the responses to the allergen and particles alone and in combination. we therefore examined the antibody and lymph node responses in various inbred strains of mice expected to display different responses to ova and particles. balb/ca mice are regarded as a high ige responder strain to ova. nih mice were included because they in an intraperitoneal model responded differently from balb/ca mice to psp and ova. furthermore, we included c3h/hen mice, which have been shown to be ige low-responders to ova. balb/cj mice were included in the antibody experiments because this sub-strain has been reported to respond more strongly to ova than balb/ca mice in a subcutaneous model. the lymph node is a key site in the priming of t lymphocytes and ige production by b lymphocytes. therefore, in addition to serum antibody levels, we examined the primary cellular response in the draining popliteal lymph node after footpad injection of polystyrene particles and the allergen ovalbumin, alone and in combination. the pln is the only lymph node draining the footpad, and is therefore well suited for studies of responses in the lymph node cells. we investigated how the selected inbred strains of mice differed qualitatively and quantitatively in their th2- and th1-associated serum antibody and pln cellular response patterns to ova+psp. furthermore, we investigated if the background, ova-, psp- and ova+psp-induced cytokine patterns differed in the various mouse strains, and whether the cytokine patterns could explain the differences in the antibody responses to ova+psp. we found that the susceptibility to the adjuvant effect of particles on both secondary antibody responses and primary cellular responses was influenced by genetic factors. the ex vivo cytokine response patterns did not predict the in vivo antibody responses.  the antibody adjuvant activity of psp in different strains of mice to examine the dose-response relationship of ova and psp with regard to antibody production, balb/ca and nih mice were immunized with various dose combinations of ova and psp. after a booster dose of ova on day the ova-specific ige, igg and igg2a antibody levels in serum were determined on day in balb/ca mice, psp given with ova strongly increased the levels of the th2-associated ige and igg antibodies compared to ova alone. in contrast, the th1-associated igg2a levels did not differ between the groups given ova in the presence or absence of psp. overall, there was an inverse relationship between the ova dose and both the ige and igg levels, with μg of ova giving the highest antibody levels for all particle doses. analyses of the factorial design showed that the dose of μg ova, regardless of psp dose, induced significantly higher ige levels than the other ova doses, and higher igg levels than μg ova. irrespective of ova dose, the igg response increased significantly with each increase in psp dose. a dose-response trend for particles was less clear for ige due to an absence of a difference between and μg psp. in nih mice, psp also exerted an adjuvant effect on the antibody responses to ova, however nih mice responded differently from balb/ca mice in two ways. first, the nih mice receiving the highest dose combinations of ova and psp experienced anaphylactic reactions and died within minutes after the ova booster injection. secondly, also the ova-specific igg2a levels were increased by psp in nih mice, in contrast to balb/ca mice. however, the responses in the surviving mice suggest that ige and igg responses were similar in nih and balb/ca mice with regard to the dose-response relationship for particles. also the igg2a levels were significantly higher for ova with all particle doses than for ova alone, and significantly higher antibody levels were observed with μg psp than with μg psp. as μg ova and μg psp gave a medium but still pronounced response, these doses were used in further experiments. next, we compared the allergen-specific antibody responses after immunization with ova+psp, ova and psp in balb/ca, balb/cj, nih and c3h/hen mice. as shown in figure the response patterns for balb/ca and nih mice were similar to those shown in figure with increased ige production in both strains, whereas igg2a production was increased only in nih mice. furthermore, in our system, balb/cj mice had specific ige and igg2a responses similar to balb/ca mice, however the igg2a levels tended to be slightly increased by ova+psp in balb/cj mice. similar to the responses in nih mice, psp had an adjuvant effect on both ige and igg2a responses in c3h/hen mice, although the responses appeared weaker in c3h/hen than in nih and balb/c mice. immunization with ova alone gave ige responses in some individual balb/ca, balb/cj and c3h/hen mice, but never in nih mice. as expected, hbss and psp without allergen did not affect the specific antibody levels in any of the strains. cell numbers and ex vivo cytokine responses in the draining lymph node during the primary response to examine how the primary cellular response to ova and psp, alone or in combination, varied in balb/ca, nih and c3h/hen mice, we studied the cell numbers and the ex vivo cytokine secretion by the popliteal lymph node cells. five days after injection of ova+psp, ova, psp and buffer into the footpad, the pln cell numbers were determined, and the amount of il- ifn-γ and il- released from pln cells after con a stimulation ex vivo were determined. for all three strains, the pln cell numbers were significantly increased by ova+psp compared to all three control groups. interestingly, the cell number response to ova alone and psp alone varied between the three strains. in balb/ca mice, ova significantly increased the cell numbers, whereas psp significantly increased the cell numbers in nih mice. c3h/hen mice took an intermediate position, as both ova and psp weakly but significantly increased the cell numbers compared to hbss. with regard to the cytokines, ova+psp strongly increased the levels of il- and il- compared to the three control groups in balb/ca mice, whereas the ifn-γ levels were only marginally affected. furthermore, ova tended to weakly increase the il- levels in balb/ca mice. the il- levels for the balb/ca control groups were relatively low compared to levels in nih mice. in nih mice, ova induced no changes in cytokines or cell numbers, whereas psp significantly increased the il- and il- levels, and ova+psp also increased these "responsive" cytokines. the ifn-γ levels in nih mice were not altered by psp. again, the c3h/hen mice responded to both ova and psp. all cytokines were significantly increased by ova and further increased by ova+psp in c3h/hen mice, although more pronounced for ifn-γ than for il- and il- psp alone also significantly increased the levels of ifn-γ and il- in c3h/hen mice. the levels of il- and il- were low and the levels of ifn-γ were high in c3h/hen mice compared to the levels in the other strains. the background levels of il- and ifn-γ were relatively low in balb/ca and relatively high in nih mice, whereas the levels in c3h/hen mice appeared low for il- and high for ifn-γ, respectively. discussion the genetic background appears to strongly influence whether an individual develops allergic immune responses to an allergen. in mice, this is illustrated by reports of strain differences in allergic responses to allergens. in agreement with granum et al., our data indicate that also the antibody-enhancing capacity of the "clean" insoluble particle is influenced by the genetic background. this is consistent with reports of mouse strain differences in allergic airway inflammation and specific antibody levels after intratracheal instillation of dep and allergen. also the effects of particles on airway inflammation, epithelial permeability and alveolar macrophage phagocytic activity have been shown to vary between mouse strains. the dose-response relationship for particles appeared similar for balb/ca and nih mice, as the low ova dose and the high particle doses induced the strongest ige and igg antibody responses. however, the nih mice immunized with a high concentration of both ova and psp were lost due to anaphylactic shock after the booster injection. high booster antigen concentrations have earlier been shown to induce anaphylactic shock in mice after subcutaneous priming with horse gamma globulin covalently bound to cellulose particles. in mice, igg has been suggested to be as effective as ige in triggering anaphylactic reactions. the induced levels of ova-specific igg appeared to be about times higher in the surviving nih mice than in balb/ca mice. thus, nih mice may be more susceptible than balb/ca mice to experience anaphylactic shock either because of a stronger igg response, or because of an otherwise greater susceptibility to anaphylactic shock. in the present study, the antibody adjuvant effect of psp differed between the different strains of mice, both with regard to the magnitude and whether a th or a mixed th1- and th2-associated antibody response was increased. whereas the th1-associated igg2a response was markedly increased by psp only in nih and c3h/hen mice, psp enhanced the th2-associated ige response in all mouse strains examined. psp seemed also to increase ige responses in pilot studies with c57bl/6j and c3h/hej mice. also with regard to the adjuvant effect of psp, the balb/ca mice appeared to be a high ige-responder, whereas the c3h/hen mice seemed to be a relatively low responder for both ova-specific ige and igg2a antibody levels. this responder status is in accordance with other studies of the ige responsiveness to ova in these strains of mice. also with regard to the primary cellular responses in the lymph node, psp increased the response to ova in both balb/ca, nih and c3h/hen mice. however, while il- and il- cytokine responses were significantly increased by ova+psp in all three strains, in c3h/hen mice the levels were low and the increases may not be biologically significant. on the other hand, ova+psp markedly increased the ifn-γ levels in c3h/hen mice, and marginally in balb/ca mice. il- and ifn-γ cytokines are often used as indicators for a th and thl response, respectively. in this regard, the cytokine responses to ova+psp could be characterized as th2-, th2- and th1-biased for balb/ca, nih and c3h/hen mice, respectively, which would not, however, predict the balance between th2- and th1-associated antibody responses. neither could the background responses for il- and ifn-γ in the different strains explain the balance between th2- and th1- associated antibody responses to ova+psp. the complexity in gene-environment interactions were illustrated by the highly varying responsiveness to ova and psp given separately in the three strains examined. balb/ca mice responded with a non-significant but consistent increase in il- cytokine release in ova-treated mice, whereas nih mice responded with a significantly increased th2-biased cytokine release in psp-treated mice. c3h/hen mice responded with both th1- and th2-type cytokine secretion, although apparently th1-skewed due to low il- and il- levels, after both ova or psp treatments. this suggests that the genetic background strongly influences the susceptibility to immunogens and irritative stimuli such as particles, also with regard to the th and th cytokine balance of the response. interestingly, psp alone increased the th2-associated, but not the th1-associated, cytokine responses in nih mice. if particles by themselves are able to induce il- production in the lymph nodes also in vivo, this might promote an allergic response to the allergen present. taken together, psp exerted an adjuvant effect on ova-induced ige and il- levels in all three strains, while there was no association between the th1-associated parameters igg2a and ifn-γ. thus, for the strains of mice used, the primary ex vivo cytokine pattern could not predict the th2- and th1-associated antibody pattern. one reason could be that the con a-stimulation in vitro was not an optimal way to describe the actual in vivo cytokine secretion by the pln cells. however, in vitro ova-stimulation of pln cells from ova+psp treated balb/ca mice gave similar il- and ifn-γ response pattern as con a-stimulation. our findings are consistent with previous studies showing that cytokine expression was only in part correlated with airway disease and ige responses, and our data illustrate that interpretation and extrapolation of in vitro data should be done with caution. the description of the th2/th balance may explain parts of an immune response, however the immune regulation is more complex, involving other cytokines, cell surface molecules and regulatory t cells. il- seems to play an important role in the development and function of certain regulatory t cells. however, in the present study, il- secretion by the pool of pln cells was highly correlated with the secretion of il-. although contribution from regulatory t cells could not be excluded, this indicates that il- which are secreted to a higher degree by th than th cells, in the pln at this stage was produced mainly by th cells. in agreement with randolph et al., we have previously shown that both psp, dep and ambient air particles in the draining lymph node were located within acid phosphatase-, mhc class ii- and cd86-positive cells, most probably antigen-presenting cells. it is remarkable that psp, in the absence of allergen, affected the lymph node cells in both nih and c3h/hen mice. in contrast, our present and previous data from balb/ca mice indicate that although the particles synergistically enhanced the cellular responses to ova, model particles had no detectable effects neither on pln cell numbers, expression of lymphocyte surface molecules nor on ex vivo cytokine secretion by the pln cells. taken together, our data from balb/ca mice therefore suggest a role for solid particles as allergen carriers in the adjuvant effect on allergic sensitization. our present data suggest that particles, in susceptible strains, additionally influence the immune response in the lymph node. in our model it appears that the particles which induced cellular responses in the absence of allergen ) enhanced both th2- and th1-associated antibody responses, whereas the particles enhancing a th2-dominated antibody response did not induce detectable cellular changes themselves. this suggests that the insoluble particle core act by enhancing the inherent response to the allergen, and that genetic background and particle properties determine whether an additional th1-associated response is elicited. the presence of a th response has been suggested to amplify th2-driven inflammation. our results therefore suggest that particles may both enhance the ige sensitization and, depending on genetically determined susceptibility, further aggravate allergic inflammation and thereby increase the allergic symptoms in some individuals.  psp enhanced the ova-specific ige antibody responses in all strains of mice examined, whereas the igg2a response was increased to varying degrees and only in some strains. genetic factors influenced the responsiveness to the adjuvant effect of psp on secondary antibody responses and the primary cellular responses to ova. furthermore, genetic factors also influenced the lymph node cell responsiveness to both ova and psp given separately. interestingly, psp alone induced different cytokine responses in the lymph node in some of the mouse strains. furthermore, we found that the ex vivo cytokine patterns could not predict the in vivo th2- and th1-associated antibody response patterns in the different mouse strains. the results indicate that the insoluble particle core acts by increasing the inherent response to the allergen, and that the genetic background may determine whether an additional th1-associated component is added. 
psp in the presence of ova increased cell numbers and il- il- and ifn-γ levels in balb/ca, nih and c3h/hen mice, with the exception of ifn-γ in nih mice. furthermore, we found that the ex vivo cytokine patterns did not predict the in vivo th2- and th1-associated antibody response patterns in the different mouse strains. the results indicate that insoluble particles act by increasing the inherent response to the allergen, and that the genetic background may determine whether an additional th1-associated component is added to the response. there is increasing epidemiological and experimental evidence for an aggravating effect of particulate air pollution on asthma and allergic symptoms and, to a lesser extent, on allergic sensitization. genetic factors appear to influence not only the magnitude, but also the quality of the adjuvant effect of particles with respect to allergen-specific ige and igg2a responses. genetic factors influenced the susceptibility to the adjuvant effect of psp on both secondary antibody responses and primary cellular responses in the lymph node, as well as the cellular responses to both ova and psp given separately. we examined how polystyrene particles affected the ige and igg2a responses against the model allergen ovalbumin, after subcutaneous injection into the footpad of balb/ca, balb/cj, nih and c3h/hen mice, further, ex vivo il- ifn-γ and il- cytokine secretion by con a-stimulated cells from the draining popliteal lymph node five days after injection of ova and psp separately or in combination was determined. in the present study, we aimed to investigate how the genetic background influences the responses to the allergen and particles alone and in combination. interestingly, psp alone induced cytokine responses in the lymph node in some of the mouse strains. in contrast, the igg2a levels were significantly increased only in nih and c3h/hen mice. however, each mouse strain had their unique pattern of response to ova+psp, ova and psp, and also their unique background cytokine response.
 there is increasing epidemiological and experimental evidence for an aggravating effect of particulate air pollution on asthma and allergic symptoms and, to a lesser extent, on allergic sensitization. genetic factors appear to influence not only the magnitude, but also the quality of the adjuvant effect of particles with respect to allergen-specific ige and igg2a responses. in the present study, we aimed to investigate how the genetic background influences the responses to the allergen and particles alone and in combination. we examined how polystyrene particles affected the ige and igg2a responses against the model allergen ovalbumin, after subcutaneous injection into the footpad of balb/ca, balb/cj, nih and c3h/hen mice, further, ex vivo il- ifn-γ and il- cytokine secretion by con a-stimulated cells from the draining popliteal lymph node five days after injection of ova and psp separately or in combination was determined.  psp injected with ova increased the levels of ova-specific ige antibodies in all strains examined. in contrast, the igg2a levels were significantly increased only in nih and c3h/hen mice. psp in the presence of ova increased cell numbers and il- il- and ifn-γ levels in balb/ca, nih and c3h/hen mice, with the exception of ifn-γ in nih mice. however, each mouse strain had their unique pattern of response to ova+psp, ova and psp, and also their unique background cytokine response.  genetic factors influenced the susceptibility to the adjuvant effect of psp on both secondary antibody responses and primary cellular responses in the lymph node, as well as the cellular responses to both ova and psp given separately. interestingly, psp alone induced cytokine responses in the lymph node in some of the mouse strains. furthermore, we found that the ex vivo cytokine patterns did not predict the in vivo th2- and th1-associated antibody response patterns in the different mouse strains. the results indicate that insoluble particles act by increasing the inherent response to the allergen, and that the genetic background may determine whether an additional th1-associated component is added to the response. 