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ABSTRACT |
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INTRODUCTION
METHODS
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DISCUSSION
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In mice, respiratory syncytial virus (RSV) infection can enhance the
consequences of allergic airway sensitization, resulting in lung eosinophilia and the development of airway hyperresponsiveness (AHR)
to inhaled methacholine (MCh). To delineate a role for interleukin-5 (IL-5), interleukin-4 (IL-4), and interferon gamma (IFN-
) in mediating the effects of RSV infection on subsequent allergic sensitization, we treated BALB/c mice with anti-IL-5 during acute RSV
infection but not during subsequent exposure to ovalbumin (OVA). IL-5-deficient and IL-4-deficient mice were also treated with IL-5 either during acute RSV infection or during the sensitization period. Airway responsiveness to inhaled MCh was assessed
and numbers of lung eosinophils were monitored. Anti-IL-5 treatment during RSV infection reduced AHR and lung eosinophilia after subsequent exposure to allergen. In IL-5-deficient or IL-4-deficient mice lung eosinophilia and AHR after RSV infection and
allergen exposure were also markedly reduced. IL-5 administration
during RSV infection restored the responses to allergen in both
IL-5- and IL-4-deficient mice. However, IL-5 administration only
during sensitization restored these responses in IL-4-deficient but
not in IL-5-deficient animals. IFN--deficient mice developed AHR
and some lung eosinophilia after allergen exposure alone and
when RSV infection preceded allergen, these responses were enhanced. We conclude that both IL-5, particularly during acute infection, and IL-4 are critical in mediating the effects of RSV infection on allergic airway sensitization, resulting in the development
of AHR and lung eosinophilia.
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INTRODUCTION |
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
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Respiratory viruses, in particular respiratory syncytial virus
(RSV), have been associated with the development of asthma and allergic sensitization in children (1, 2). Recent epidemiological data suggest that RSV bronchiolitis is an important risk
factor for the presence of asthma in children age 3 to 7 yr (3,
4). In a murine model, RSV infection can aggravate the consequences of subsequent airway sensitization to allergen, resulting in airway hyperresponsiveness (AHR) and influx of eosinophils into the lungs, as we have reported recently (5). In
fact, RSV infection enhanced the response to allergen exposure via the airways even when begun after the resolution of
the acute RSV-induced disease, which by itself resulted in
transient lung eosinophilia and AHR lasting up to 14 d. Treatment of mice with anti-interleukin-5 (anti-IL-5) during acute
infection or during sensitization prevented development of
lung eosinophilia and AHR after acute infection and sensitization, respectively. The mechanism by which RSV infection induces development of airway inflammation and AHR after
airway sensitization have not been determined. Here, we use
this model to delineate the role of interleukin-5 (IL-5) and in
addition, the role of interleukin-4 (IL-4) and interferon gamma
(IFN-) in mediating these RSV-induced effects. Both the T
helper cell, type 2 (Th2) cytokines
including IL-4, which is
essential for immunoglobulin isotype switching to IgE (6), and
IL-5 which is critical for eosinophil recruitment, activation,
and survival (7)as well as IFN-, a T helper cell, type 1 (Th1) cytokine, have been implicated in the development of
human asthma (10) and of allergen-induced AHR in murine models (15). In addition, we have demonstrated a critical role for IL-5 in AHR induced by acute RSV infection (5).
To address the issue of cytokine involvement in RSV-induced
enhancement of the consequences of allergic airway sensitization, we used two different approaches: anti-IL-5 treatment of
mice during acute RSV infection but not during sensitization;
and RSV infection and subsequent airway sensitization in
mice genetically deficient in either IFN-, IL-4, or IL-5. After
airway sensitization, airway responsiveness to inhaled methacholine (MCh) was assessed using barometric whole-body
plethysmography, and influx of eosinophils into the lung was monitored.
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METHODS |
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INTRODUCTION
METHODS
RESULTS
DISCUSSION
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Animals
Female BALB/c mice, IL-5-deficient or IL-5-sufficient C57BL/6 mice
from our colony (initially derived at Max-Planck-Institut for Immunology, Freiburg, Germany), and both male and female IL-4-deficient and IFN--deficient BALB/c By mice and sex-matched cytokine-sufficient controls (Jackson Laboratory, Bar Harbor, ME), all 8 to 16 wk of age, free of specific pathogens, and maintained on ovalbumin (OVA)-free diets were used in this study. All animals used in this
study were under a protocol approved by the Institutional Animal
Care and Use Committee of the National Jewish Medical and Research Center.
Virus and Infection of Mice
Human RSV, group A (Long strain), free of Chlamydia or Mycoplasma contamination, was obtained from the Viral Diagnostic Laboratory, Health Sciences Center, University of Colorado (Denver,
CO). The virus was cultured on Hep2 cells from American Type Culture Collection (ATCC, Rockville, MD) in medium containing fetal
calf serum (FCS) from GIBCO (Grand Island, NY). It was purified as
described (18). Briefly, cells and supernatant were harvested, the cells
were disrupted by ultrasonic manipulation, and the suspension was
clarified by centrifugation (8,000 × g, 20 min). The supernatant was
layered over 30% sucrose in STEU buffer (sodium chloride 0.1 M,
Tris 0.01 M, ethylenediaminetetraacetic acid [EDTA] 0.001 M, and
urea 1 M, all obtained from Sigma [St. Louis, MO]) and centrifuged
(100,000 × g, 1 h, 10° C). The pellet was resuspended in 1.2 ml phosphate-buffered saline (PBS), aliquoted and frozen at 
70° C. The suspension was adjusted to contain 4 × 106 plaque-forming units (PFU)
of RSV/ml as assessed by quantitative plaque-forming assay.
Mice were infected under light anesthesia (Avertin 2.5%, 0.015 ml/g body weight) by intranasal inoculation of RSV (105 PFU in 50 µl PBS). Controls were sham-infected with PBS in the same way. Efficacy of this infection procedure was regularly tested by quantitative plaque-forming assays (19); briefly, on Day 4 postinfection mice were killed, the lungs were removed, homogenized, centrifuged, and the supernatant was added to Hep 2 cell cultures. Successful infection of all mice under each experimental condition was confirmed by quantitative plaque-forming assay in which all infected mice demonstrated cytopathic effects but not sham-infected animals. In the different groups on Day 4, the range of PFU/g fresh lung was 794 to 1,364, with no significant differences between any of the groups.
Experimental Protocols
As described previously in wild-type mice (5), to define the effect of
RSV on allergic responses mice deficient in either IFN-, IL-4, or IL-5
and their cytokine-sufficient controls were sham-infected or infected
with RSV. From Day 11 to Day 20 postinfection, mice were sensitized
by inhalation of OVA obtained from Sigma for 10 consecutive days
(1%, in 7 ml PBS, 10 min/d) using an Aerosonic Nebulizer 5000D
from Devilbiss (Somerset, PA) as described (5). Some IL-5- and IL-4-deficient mice were treated intravenously with 40 ng of murine IL-5
(kindly provided by Dr. James Lee, Mayo Clinic, Scottsdale, AZ) during acute RSV infection on Days 0 and 3 or during sensitization on
Days 11, 14, and 18 postinfection. Forty-eight hours after completion
of sensitization, airway responsiveness to inhaled MCh (Sigma) was
assessed and the following day animals were killed to harvest lungs.
In a second protocol using anti-IL-5, the initiation of allergen exposure on Day 21 was chosen, as in previous experiments the effects of anti-IL-5 were no longer evident. Mice (4 per treatment group in each experiment) were infected with RSV or sham-infected on Day 0 and treated intravenously with 150 µg/dose of anti-IL-5 (rat IgG) from clone TRFK-5 (DNAX, Palo Alto, CA; kindly provided by Dr. Robert Coffman) or of isotype control rat IgG1 (Sigma) on Days 0 and 3 postinfection. From Day 21 to Day 30 mice were sensitized by inhalation of OVA. As described previously (5), delaying the beginning of OVA exposure to Day 21 had little influence on the enhancement of allergic responses by RSV. Forty-eight hours after completion of sensitization, airway responsiveness to inhaled MCh (Sigma) was assessed and the following day animals were killed to harvest lungs.
To ensure that no detectable anti-IL-5 activity was left at the beginning of sensitization (Day 21 postinfection), noninfected mice were treated with anti-IL-5 or rat IgG1 on Days 0 and 3. These animals were infected with RSV on Day 15 or challenged with OVA aerosol on Days 19 to 21 after single intraperitoneal sensitization to OVA with alum on Day 9. Numbers of eosinophils were enumerated in lung cell isolates and did not differ between anti-IL-5- and rat IgG1- treated mice after either infection or sensitization: 6 d after RSV infection (rat IgG1 1.21 ± 0.43 × 106 versus anti-IL-5 1.37 ± 0.32 × 106, n = 8) or 48 h after the last challenge (rat IgG1 4.35 ± 1.18 × 106 versus anti-IL-5 4.19 ± 1.73 × 106, n = 8).
Determination of Airway Responsiveness
Airway responsiveness was assessed using a single-chamber whole-body plethysmograph obtained from Buxco (Troy, NY) as described (20). Enhanced pause (Penh) was used as the measure of airway responsiveness in this study. In the plethysmograph, mice were exposed for 3 min to nebulized PBS and subsequently to increasing concentrations of nebulized MCh (3 to 50 mg/ml in BALB/c mice; 6 to 100 mg/ml in C57BL/6 mice) from Sigma in PBS using an AeroSonic ultrasonic nebulizer (Devilbiss, Somerset, PA). After each nebulization, recordings were taken for 3 min. The Penh values measured during each 3-min sequence were averaged and are expressed for each MCh concentration as the percentage of baseline Penh values after PBS exposure.
Lung Cell Isolation
Lung cells were isolated by collagenase digestion as previously described (21) and counted with a hemocytometer. Cytospin slides were stained with Leukostat from Fisher Diagnostics (Pittsburgh, PA) and differential cell counts were performed in a blinded fashion by counting at least 300 cells under light microscopy. The data are presented as number of cells per lung for each individual animal.
Measurement of Allergen-specific Antibodies
Anti-OVA, IgE, IgG1, and IgG2a antibody concentrations in serum were measured by ELISA as described previously (21). The anti-OVA antibody titers of samples related to internal pooled standards and expressed as ELISA units (EU). Total IgG and IgE concentrations were calculated by comparison with known mouse IgG or IgE standards from Pharmingen (San Diego, CA). The limit of detection was 100 pg/ml for IgE and 1 mg/ml for IgG.
Statistical Analysis
For statistical analysis, data from 8-12 animals from two to three separate experiments were pooled. Values for all measurements are expressed as the mean ± SD except for values of airway responsiveness (Penh), which were expressed as mean ± SEM. Differences between groups of mice were compared by analysis of variance (ANOVA). Pairs of groups were compared by Student's t test. Individual differences between groups were tested by multiple comparison and analysis using the Tukey-Kramer honest significant difference (HSD) test. p Values for significance were set at 0.05.
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RESULTS |
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INTRODUCTION
METHODS
RESULTS
DISCUSSION
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Anti-IL-5 Treatment during Acute RSV Infection Reduces AHR and Prevents Lung Eosinophilia after Subsequent Allergen Exposure
BALB/c mice were infected with RSV and treated with anti-IL-5 or with rat IgG1 as a control during the acute infection. Twenty-one days after infection these mice and sham-infected controls were exposed to nebulized OVA via the airways for 10 d. After this period of sensitization, airway responsiveness to MCh was assessed by barometric whole-body plethysmography and numbers of eosinophils were enumerated in lung digests. Exposure to 10 d OVA preceded by RSV infection resulted in an influx of eosinophils into the lung and in AHR, whereas exposure to allergen in the absence of prior RSV infection did not. Penh in response to 50 mg/ml MCh increased 9.5 ± 0.7-fold over PBS in RSV-infected and allergen-sensitized mice compared with a 2.2 ± 0.3-fold increase in mice sensitized without prior infection. Numbers of eosinophils increased to 1.46 ± 0.6 × 106 compared with 0.49 ± 0.21 × 106 per lung after sensitization alone.
No AHR (Penh at 50 mg/ml MCh was 2.8 ± 0.4-fold over PBS, n = 8) or lung eosinophilia (0.41 ± 0.17 × 106 eosinophils/lung, n = 8) was observed in mice 32 d after RSV infection without subsequent exposure to allergen, confirming our previous findings (5). Treatment with anti-IL-5 but not rat IgG1 during acute infection prevented eosinophil influx into the lung and resulted in a significant reduction of AHR after allergen sensitization (Figures 1A and 1B). Control experiments ensured that no anti-IL-5 activity was left at the beginning of sensitization by demonstrating that eosinophil recruitment to the lung induced by either RSV infection or allergic sensitization and challenge was unimpaired 18 d after the last anti-IL-5 treatment on Day 3 (see METHODS).
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aIL5R/O versus CR/O, R/
O, and O. (B) Anti-IL-5 treatment during acute RSV infection prevents
eosinophil influx into the lungs after subsequent airway sensitization.
Lung cells were isolated from the same sham-infected, (O, n = 12) and
RSV-infected (R/O, n = 12) mice after airway sensitization and treatment with anti-IL-5 (aIL5R/O, n = 12) or rat IgG1 (CR/O, n = 12).
Numbers of eosinophils per lung were determined. Illustrated are
means ± SD of the numbers of these cells from three independent experiments. Significant differences, p < 0.05, *R/O versus O versus O,
RSV Infection Only Induces AHR and Lung Eosinophilia after Allergen Exposure in IL-5-deficient Mice if They Are Reconstituted with IL-5 during Acute Infection
C57BL/6 mice genetically deficient in IL-5 and IL-5-sufficient controls were sham-infected or infected with RSV and subsequently sensitized to OVA via the airways over 10 d. Some IL-5-deficient animals were reconstituted with IL-5 either during the acute RSV infection or only during the airway sensitization phase. After sensitization, airway responsiveness to MCh and numbers of eosinophils in the lung were assessed and serum levels of allergen-specific antibodies were monitored. In IL-5-sufficient mice, RSV infection before allergen exposure resulted in increased airway responsiveness to MCh (Figure 2A) and in increases in numbers of lung eosinophils compared with noninfected sensitized animals. Penh in response to 100 mg/ml MCh increased by 4.5 ± 0.7-fold and eosinophil numbers increased to 1.56 ± 0.2 × 106 per lung compared with a Penh of 2.3 ± 0.2-fold and 0.42 ± 0.1 × 106 eosinophils per lung in mice sensitized without prior infection. No AHR (Penh at 100 mg/ml was 2.2 ± 0.3-fold over PBS, n = 8) or lung eosinophilia was observed in C57BL/6 mice 21 d after RSV infection without subsequent sensitization (0.51 ± 0.22 × 106, n = 8), similar to the results in BALB/c mice.
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RSV infection in IL-5-deficient mice did not elicit these responses (Figure 2A). The small increase in airway responsiveness after RSV infection and sensitization to OVA was not statistically significant from those mice exposed to allergen alone. However, treatment with IL-5 at the time of acute RSV infection resulted in significant increases in AHR and numbers of lung eosinophils after subsequent allergic sensitization (Figures 2B and 2C). In contrast, IL-5 treatment of IL-5-deficient mice only during the airway sensitization period, after RSV infection in the absence of IL-5, did not result in AHR, although increases in lung eosinophil numbers were detected.
After OVA exposure in both IL-5-sufficient and IL-5-deficient mice, allergen-specific antibody was detectable (Table 1). RSV infection before sensitization via the airways did not significantly alter levels of allergen-specific antibodies or total immunoglobulins.
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RSV Infection Prior to Allergen Exposure Does Not Induce AHR and Lung Eosinophilia in Mice Deficient in IL-4 but IL-5 Treatment Reconstitutes These Responses
IL-4-deficient and IL-4-sufficient BALB/c mice were sham- infected or infected with RSV and subsequently sensitized to OVA via the airways. Whereas RSV infection before allergen exposure induced AHR and lung eosinophilia in IL-4-sufficient mice, it did not have these effects in IL-4-deficient animals (Figures 3A and 3B). IL-4-deficient mice were treated with IL-5 either during acute RSV infection or during airway sensitization. In contrast to the results in IL-5-deficient mice (Figure 2), IL-5 given to these IL-4-deficient mice at either time point restored development of AHR to MCh (Figure 3C) and resulted in increases in numbers of lung eosinophils (Figure 3D).
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Whereas allergen-specific IgE and IgG1 were detectable in IL-4-sufficient mice, only OVA-specific IgG1 and IgG2a were observed in IL-4-deficient mice after OVA exposure (Table 1). RSV infection before sensitization did not significantly alter concentrations of allergen-specific antibodies or total immunoglobulins.
Airway Exposure to OVA in IFN--deficient Mice
Results in Lung Eosinophilia and AHR, Both of Which
Are Further Enhanced after RSV Infection
INF--deficient and -sufficient mice were sham-infected or infected with RSV before airway sensitization to OVA. In contrast to IFN--sufficient mice, IFN--deficient mice developed
AHR and a small increase in lung eosinophil numbers that did
not reach statistical significance after exposure to OVA alone.
AHR was increased further and a significant increase in eosinophil numbers in the lung was observed if RSV infection
preceded airway sensitization (Figures 4A and 4B). Both IFN--sufficient and IFN--deficient mice developed allergen-specific antibody responses, which were not significantly influenced by prior RSV infection (Table 1).
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DISCUSSION |
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INTRODUCTION
METHODS
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DISCUSSION
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In the present study, we monitored airway responsiveness and
pulmonary inflammation in a murine model of RSV infection
before allergic airway sensitization. We recently reported that
RSV infection enhances the consequences of subsequent exposure to allergen, resulting in AHR and influx of eosinophils
into the lung. Here, we used this model to delineate the role of
the cytokines IL-5, IL-4, and IFN- in the RSV-induced enhancement of the response to allergic airway sensitization. To
address this issue, we monitored responses to allergen exposure in cytokine-sufficient BALB/c mice after anti-IL-5 treatment during acute RSV infection and we compared responses
to RSV infection and sensitization via the airways in IL-5-,
IL-4-, and IFN--deficient mice. Airway responsiveness to
aerosolized MCh was assessed using barometric whole-body
plethysmography, and pulmonary eosinophilic inflammation
was monitored. Allergen exposure via the airways resulted in
sensitization as demonstrated by production of allergen-specific antibodies in all mice used.
RSV infection before allergic airway sensitization resulted in AHR and the influx of eosinophils into the lung in cytokine-sufficient BALB/c and C57BL/6 mice, confirming our previous findings (5). Increases in airway responsiveness after MCh inhalation in C57BL/6 mice were smaller than in BALB/c mice as has been reported in allergen-induced AHR (22). To delineate the role of IL-5 in the development of AHR induced by RSV infection and subsequent allergen exposure, BALB/c mice were treated with anti-IL-5 during the acute infection. This treatment prevents lung eosinophilia and AHR but not lung neutrophilia after acute RSV infection as we reported (5). In the present study, it prevented lung eosinophilia and significantly reduced AHR induced by allergic sensitization after RSV infection. Control experiments demonstrated that these results were not a consequence of persistent anti-IL-5 activity during the phase of allergen exposure, because eosinophil recruitment to the lung induced either by allergic sensitization and airway challenge or by RSV infection was not impaired 18 d after the last anti-IL-5 administration, the time point when allergen exposure was begun. These data indicate that the presence of IL-5 during acute RSV infection plays a major role in the development of lung eosinophilia and the extent of AHR after subsequent sensitization via the airways. The results also indicate that RSV infection in the absence of IL-5 can nevertheless result in AHR after subsequent allergen exposure to a limited extent when allergen exposure is initiated after a sufficient period of time has elapsed and the effects of anti-IL-5 are no longer detectable.
These conclusions were further confirmed in IL-5-deficient C57BL/6 mice. RSV infection followed by allergic airway sensitization did not result in lung eosinophilia and only a limited increase in airway responsiveness in IL-5-deficient mice. Reconstitution of these mice with IL-5 during the phase of acute RSV infection fully restored these responses, supporting the critical role for IL-5 in the induction of enhanced responses to airway sensitization after RSV infection. In contrast, IL-5 treatment only during the phase of allergen exposure, but preceded by RSV infection in the absence of IL-5, did not result in significant AHR despite an increase in numbers of lung eosinophils. It is likely that exogenous IL-5 was present in the airways at higher concentrations than in cytokine-sufficient mice (endogenous IL-5), resulting in an influx of eosinophils into the lung in response to allergen exposure, not observed without IL-5 treatment. However, despite the presence of IL-5 and eosinophils in the lung, this only resulted in a small increase in airway responsiveness, suggesting that RSV infection in the absence of IL-5 was not able to fully "prime" the airways to develop AHR after allergen exposure. Assuming that eosinophils are involved in the development of virus-induced AHR as we have suggested (23), these data imply that lung eosinophilia alone is not sufficient for the development of AHR and that a second signal is required. Similar results were reported in T-cell-deficient (nude) mice where exogenous IL-5 and allergen exposure resulted in lung eosinophilia but not AHR (24). The mechanisms by which IL-5 is involved in the initiation of effects of RSV infection on subsequent allergic airway sensitization have not been defined in the present study. One possibility is that IL-5 is necessary for the mobilization and recruitment of eosinophils during acute RSV infection and eosinophils in turn are likely involved in the development of AHR (23). Activated eosinophils may result in damage to the airways, which predisposes to development of AHR at a later phase in response to allergen exposure, even when the apparent consequences of RSV infection have been resolved (5).
In addition to IL-5, IL-4 has also been implicated in the development of AHR in mice and in humans. IL-4, a Th2-type cytokine, has been detected in increased concentrations in bronchoalveolar lavage fluid (BALF) (10) and IL-4 messenger RNA (mRNA) was expressed at higher levels in bronchoalveolar lavage (BAL) cells (11) and bronchial biopsies (12) from patients with atopic asthma. In murine models of allergic sensitization and airway challenge, IL-4 has been found to be crucial for the development of allergic airway inflammation (25, 26) and AHR (15, 16) in some studies, whereas others demonstrated a partial inhibition of eosinophil recruitment to the lung but no inhibiton of AHR or histological damage of the airways in IL-4-deficient mice (27). In the present study, RSV infection followed by allergic sensitization via the airways did not result in AHR or lung eosinophilia in IL-4-deficient mice. Treatment with IL-5 either during the acute infection or during the allergen senitization phase restored the responses to the levels observed in IL-4-sufficient mice after RSV infection and sensitization. These findings indicate that IL-4 is critical for the development of AHR and lung eosinophilia after allergic airway sensitization and RSV infection. The data also show that administration of IL-5 can compensate for the lack of IL-4 in the development of AHR and lung eosinophilia in this model.
The finding that IL-5 treatment during acute infection of the IL-4-deficient mice restores the consequences of subsequent allergen exposure parallels our findings in IL-5-deficient mice and lends further support to the notion that IL-5 plays a critical role during the acute infection in inducing the effects of RSV infection on allergic airway sensitization. The observation that IL-5 also restores AHR and lung eosinophilia if given during sensitization only in IL-4-deficient mice is strikingly different from the observations in IL-5-deficient animals. One explanation for these findings is the ability of IL-4-deficient mice, in contrast to IL-5-deficient mice, to develop AHR and influx of eosinophils into the lung in response to acute RSV infection (23), indicating that in IL-4-deficient mice, sufficient IL-5 may be released to allow induction of these responses and "priming" of the airways for development of AHR after subsequent allergen exposure. IL-4 may be essential for the development of AHR and lung eosinophilia after airway sensitization and preceding RSV infection through several mechanisms. Our data are in keeping with the requirement for IL-4 in the development of IL-5-producing T cells (28, 29). In addition, IL-4 is involved in the upregulation of vascular cell adhesion molecule-1 (VCAM-1) on vascular endothelial cells (30), facilitating eosinophil and lymphocyte extravasation and thus development of allergic airway inflammation.
IFN-, a Th1-type cytokine, is produced in large amounts
during acute RSV infection in humans (31) and in mice (5, 32, 33). It may play a pivotal role in virus-induced inflammation (34). Increased amounts of IFN- have been observed in cells from BAL of atopic asthmatics (13, 14). The role of IFN- in
the development of allergen-induced AHR remains controversial. On one hand, administration of IFN- during allergic
airway sensitization has been shown to inhibit airway inflammation and AHR (35, 36). On the other hand, in a study employing an antibody against IFN-, this cytokine seemed to
play a critical role in the development of allergen-induced
AHR (17). In acute RSV infection, IFN- does not seem to be
involved in the development of AHR and airway inflammation (23). On the contrary, the presence of IFN- appears somewhat protective against these consequences of RSV infection. In the present study, IFN--deficient but not IFN--sufficient mice developed AHR and a small increase in numbers of lung eosinophils in response to allergen exposure via
the airways alone. Both AHR and lung eosinophilia were further increased in IFN--deficient mice if RSV infection preceded this sensitization. The data indicate that IFN- is not
critically involved in the development of AHR either after airway sensitization alone or after allergen exposure following
RSV infection. Moreover, the presence of IFN- could be inhibitory to the development of AHR, perhaps by regulating Th2-cytokine (IL-4 and IL-5) production (36).
In summary, we present a murine model of airway inflammation and AHR in response to allergic sensitization via the
airways after RSV infection. Using anti-IL-5 and mice deficient in either IL-5, IL-4, or IFN-, we show that IL-5 is critical for RSV-induced enhancement of lung eosinophilia and
AHR in response to allergic airway sensitization. The presence of IL-4, possibly by enhancing IL-5 production, is also essential for the development of AHR after RSV infection and
subsequent allergic airway sensitization. In contrast, IFN-,
the predominant cytokine in acute RSV infection, does not
seem to be required for the development of AHR in this model. In fact, in IFN--deficient mice the eosinophilic inflammatory response and airway responsiveness to inhaled
MCh after allergen exposure alone is enhanced. These data
begin to define the mechanisms whereby viruses such as RSV
impact allergic airway disease in either the initiation or exacerbation of heightened airway responsiveness to inhaled MCh
after allergen exposure.
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Footnotes |
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Correspondence and requests for reprints should be addressed to Erwin W. Gelfand, M.D., 1400 Jackson Street, Denver, CO 80206. E-mail: gelfande{at}njc.org
(Received in original form March 10, 1999 and in revised form January 11, 2000).
Acknowledgments: The authors thank Diana Nabighian for her assistance in the preparation of this manuscript.
Supported by Grants HL-61005, HL-36577, and AI-30389 (to E.W.G.) from the National Institutes of Health. J.S. was supported by the Deutsche Forschungsgemeinschaft (Schw 597/1-1); his current address is Rühr-Universität, Bochum, Germany.
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References |
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INTRODUCTION
METHODS
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DISCUSSION
REFERENCES
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