Abstract
Mucus hyperproduction in asthma results from airway inflammation and contributes to clinical symptoms, airway obstruction, and mortality. In human asthmatics and in animal models, excess mucus production correlates with airway eosinophilia. We previously described a system in which TCR transgenic CD4 Th2 cells generated in vitro were transferred into recipient mice and activated in the respiratory tract with inhaled Ag. Th2 cells stimulated airway eosinophilia and a marked increase in mucus production, while mice that received Th1 cells exhibited airway inflammation without eosinophilia or mucus. Mucus could be induced by IL-4−/− Th2 cells at comparable levels to mucus induced by IL-4+/+ Th2 cells. In the current studies we dissect further the mechanisms of Th2-induced mucus production. When IL-4−/− Th2 cells are transferred into IL-4Rα−/− mice, mucus is not induced, and BAL eosinophilia is absent. These data suggest that in the absence of IL-4, IL-13 may be critical for Th2-induced mucus production and eosinophilia. To determine whether eosinophils are important in mucus production, IL-5−/− Th2 cells were transferred into IL-5−/− recipients. Eosinophilia was abolished, yet mucus staining in the epithelium persisted. These studies show definitively that IL-5, eosinophils, or mast cells are not essential, but signaling through IL-4Rα is critically important in Th2 cell stimulation of mucus production.
Asthma is a chronic inflammatory disease of the bronchial airways defined by intermittent episodes of airway obstruction. In patients with asthma, excess mucus production leads to wheezing and coughing and contributes significantly to airway obstruction (1, 2). Airway biopsies in asthmatics show infiltration of the mucosa and submucosa with lymphocytes, eosinophils, mast cells, and hyperplasia of goblet cells and submucosal glands. In autopsy specimens from patients who died in status asthmaticus, obstructing plugs of mucus and cellular debris have been identified in the small airways.
In asthma, mucus hypersecretion is associated with inflammation. A variety of inflammatory mediators have been shown to stimulate mucus secretion, including histamine, PGs, leukotrienes, platelet-activating factor, and eosinophil cationic (3, 4). More recently, the cytokines IL-4, IL-5, and IL-9 have been shown to influence mucus secretion (5, 6, 7). Despite multiple potential mechanisms, the precise inflammatory pathways that stimulate increased mucus production are not well defined.
Animal models of asthma have helped to define the critical importance of CD4 T cells and their cytokines in the development of airway inflammation and eosinophilia. In a mouse model we recently defined a system of CD4 Th2 cell-induced allergic airway inflammation (8, 9). We showed that stimulation of airway epithelial mucus production and airway hyperresponsiveness are dependent on local inflammation by Th2, but not Th1, cells. Despite previously described associations with IL-4, we showed that both mucus production and airway hyperresponsiveness could be stimulated in the absence of IL-4.
IL-4R and IL-13R share a common receptor chain, IL-4Rα, and common signal transduction mechanism through Stat6. In mice lacking in IL-4Rα or Stat6, many functions of IL-4 and IL-13 are inhibited, including Th2 cell differentiation, IgE production, and reduction in airway epithelial mucus (10, 11, 12, 13, 14, 15, 16). However, in these models Th2 cell development was impaired, and Th2 effector function in mucus production could not be determined.
In the current studies we dissect further the mechanisms of CD4 Th2-induced mucus production using Th2 cells generated in vitro from cytokine gene-deficient mice. After transfer into wild-type and cytokine receptor-deficient mice we assess the effector function of Th2 cells on airway mucus induction. We identify the critical importance of IL-4R/IL-13R signaling in Th2 cell stimulation of mucus production. Furthermore, we show definitively that IL-5, eosinophils, and mast cells are not essential for the induction of mucus production.
Materials and Methods
Mice
CD4 T cell donors were DO11.10 mice (BALB/c), which are transgenic for the TCR recognizing OVA peptide 323–339 (pOVA323–339;3 provided by K. Murphy, Washington University, St. Louis, MO) (17), DO11.10 IL-4−/− mice (bred in our facilities), and IL-5−/− (C57BL/6; provided by M. Kopf, Basel Institute for Immunology, Basel, Switzerland) (18). Transfer recipients were 6–12 wk of age and included BALB/c, C57BL/6, W/Wv ((WB/Rej-kitW/+ × C57BL6J-kitW-v/+)F1), and their wild type littermates, WBB6F1 (all from The Jackson Laboratory, Bar Harbor, ME), and IL-4Rα−/− mice (BALB/c).4
Generation of Th1 or Th2 cells
To generate Th2 cells from nontransgenic mice, C57BL/6 or IL-5−/− mice were injected i.p. with 100 μg of OVA (Sigma, St. Louis, MO) in 4.5 mg of alum (Immuject, Sigma). Five days after immunization, spleens and local draining lymph nodes were harvested, and CD4 T cells were isolated by negative selection as previously described (19), using mAbs to CD8 (clone 53-6.72 and clone 2.43) (20), class II MHC I-Ad (212.A1) (21), and anti-Ig-coated magnetic beads (Collaborative Research, Bedford, MA). To generate DO11.10 or DO11.10 IL-4−/− Th2 cells, CD4 T cells were isolated from spleens. Syngeneic T-depleted splenocytes were used as APC in all cultures and were prepared by negative selection using Abs to CD4 (GK1.5) (22), anti-CD8 and anti-Thy-1 (23), and treatment with rabbit complement. APCs were treated with mitomycin C. All cultures were set up in flasks containing equal numbers of CD4 T cells and APCs at a concentration of 0.5–3 × 106 cells/ml and OVA at 100 μg/ml for nontransgenic CD4 T cells or pOVA323–339 at 5 μg/ml for DO11.10 cells, IL-4 at 200 U/ml (Collaborative Research), and anti-IFN-γ (XMG1.2) (24) at an inhibitory concentration. Cultures were maintained for 4 days.
Transfer of cells and aerosol administration of OVA
Cultured Th2-like cells were harvested after 4 days and washed with PBS, and 5 × 106 cells were injected i.v. into syngeneic recipients. WBB6F1 and W/Wv mice received C57BL/6-derived Th2 cells. One day after transfer of cells, mice were challenged with inhaled 1% OVA/0.01% Tween-20 in PBS for 20 min daily for 7 days using an ultrasonic nebulizer (1- to 5-μm particles by manufacturer’s specifications, UltraAir NE-U07, OMRON, Vernon Hills, IL) as previously described (8).
Bronchoalveolar lavag (BAL)
BAL was performed by cannulation of the trachea and lavage with 1 ml of PBS. Cytospin preparations of BAL cells were stained with Diff-Quik (Baxter Healthcare, Miami, FL), and differentials were performed on 200 cells based on morphology and staining characteristics.
Cytokine assays
At the time of transfer, an aliquot of Th2-like cells was retained for restimulation. CD4 T cells (1 × 106/ml) and 1 × 106
FACS analysis
At the time of transfer, FACS (Becton Dickinson, Mountain View, CA) analysis was performed on Th2 cell preparations to determine the purity of transferred cell populations. Cells were stained with anti-CD4 (Quantum Red-L3T4, Sigma) and, in mice that received DO11.10 transgenic CD4 cells, with the biotinylated anticlonotypic Ab, KJ1-26 (25), and FITC-avidin D (Vector, Burlingame, CA). KJ1-26 is specific for the transgenic TCR in the DO11.10 mice. Transferred cells were uniformly >96% CD4 positive. After a period of inhalational exposure, BAL cells were also analyzed by FACS using these Abs.
Lung histology
Lungs were prepared for histology by perfusing the animal via the right ventricle with 20 ml of PBS. Lungs were then inflated with 1.0 ml of fixative instilled through a tracheostomy tube. Samples for paraffin sectioning were formalin fixed and sectioned in the coronal plane at 5 μm ensuring that central airways were visible. Sections were stained with hematoxylin and eosin and periodic acid-Schiff (PAS). The histological mucus index (HMI) was determined on PAS-stained sections on which marker dots in a grid with 2-mm spacing were placed over the entire lung section. The slide was examined at ×100 final magnification with a rectangular 10-mm square reticule grid (American Optical, Buffalo, NY) inserted into one eyepiece. Each marker dot was placed in the lower left corner of the field, and all intersections of airway epithelium with the reticule grid were counted in that field, distinguishing mucus-containing or normal epithelium. Approximately 25% of the total lung section was scored. The ratio of total number of mucus-positive intersections and the total of all intersections, which we call the HMI, is equivalent to the linear percentage of epithelium positive for mucus (26). This index was calculated for each mouse lung and then the mean HMI was calculated for each experimental group.
Results
Th2 cells stimulate mucus production in the absence of IL-4
We previously showed that when Th1 or Th2 cells were generated in vitro from TCR transgenic DO11.10 mice and transferred into recipient mice, and mice were exposed to inhaled OVA, only the mice that received DO11.10 Th2 cells exhibited eosinophilic airway inflammation and increased mucus staining in the bronchial epithelium (8). Mice that received Th1 cells showed inflammation without eosinophilia or mucus production. Thus, activated Th2 cells stimulated inflammation leading to mucus hyperproduction. In mice that received DO11.10 IL-4+/+ or IL-4−/− Th2 cells, mucus was induced at similar levels (Fig. 1⇓A). These data confirmed our previous findings and showed that in a TCR transgenic system Th2 cell production of IL-4 is not necessary for mucus induction (8). Mucus production was completely IL-4 independent, since transfer of IL-4−/− Th2 cells into IL-4-deficient mice still led to the induction of mucus (data not shown). In mice that received IL-4−/− Th2 cells, although there was a reduction in airway eosinophilia (Fig. 1⇓B), it was still possible that small numbers of eosinophils could stimulate mucus production.
Airway mucus staining and eosinophilia in mice after transfer of Th2 cells. DO11.10 cells (IL-4+/+; 2.5 × 106), DO11.10 IL-4−/− Th2 cells, or no cells (−) were transferred into BALB/c-recipient mice. All mice were exposed to inhaled OVA. A, An HMI was performed on lung sections stained with PAS. B, BAL eosinophils were recovered from mice. The mean HMI or number of eosinophils (±SEM) is shown (n = 4 mice/group). One experiment is shown and is representative of three experiments. Statistical significance was determined by unpaired Student’s t test. ∗, p < 0.0003, Th1 vs Th2, and Th2 vs IL-4−/− Th2.
Mucus production in response to Th2 cells requires IL-4Rα
To investigate further which factors secreted by Th2 cells stimulate increased mucus production, we asked whether IL-13 might substitute for IL-4 in mucus production. Since IL-13 and IL-4 have many overlapping functions due to the use of a common receptor chain, IL-4Rα, it was possible that in the absence of IL-4, IL-13 could stimulate mucus production. To test whether signaling via the IL-4R/IL-13R mediates mucus production by Th2 cells, we generated DO11.10 IL-4−/− Th2 cells in vitro and transferred the cells into BALB/c (IL-4Rα+/+) and IL-4Rα−/− mice. At the time of transfer, IL-4−/− Th2 cells produced high levels of IL-13 and IL-5 and minimal IFN-γ, but only IL-4Rα+/+-recipient mice and not IL-4Rα−/− mice could respond to IL-13 (Fig. 2⇓A). Mice were exposed to inhaled OVA and then assessed for inflammatory changes in the lungs. In IL-4Rα−/− mice that received IL-4−/− Th2 cells and inhaled OVA, mucus staining was absent, while IL-4Rα+/+-recipient mice exhibited extensive mucus staining in the bronchial epithelium (Fig. 2⇓B and Fig. 3⇓). Airway inflammation, as shown by the number of BAL cells recovered, was modestly reduced in IL-4Rα−/−-recipient mice compared with that in IL-4Rα+/+ mice (Fig. 2⇓C). There was no airway eosinophilia in the IL-4Rα−/− mice, while 20% of the BAL cells were eosinophils in IL-4Rα+/+ mice after transfer of IL-4−/− Th2 cells. CD4 expressing transgenic cells (KJ1.26+) were found in similar numbers in wild-type and IL-4Rα−/− mice (Fig. 2⇓C), indicating that the failure to observe mucus production and eosinophilia is not due to the absence of transgenic Th2 cells in the lung. These data show that in the absence of IL-4, IL-4Rα controls Th2-induced mucus production and airway eosinophilia, indicating a possible role for IL-13 in stimulating these processes.
Mucus production and BAL cells recovered from IL-4Rα−/− mice. BALB/c (IL-4Rα+/+) and IL-4Rα−/− mice received transfer of 5 × 106 IL-4−/− Th2 cells and inhaled OVA. A, Cytokine production by IL-4−/− Th2 cells. At the time of transfer into recipient mice, in vitro generated DO11.10 IL-4−/− Th2 cells were cultured with APCs and pOVA323–339. Supernatants were collected after 48 h, and cytokine ELISAs were performed. Typical DO11.10 Th1 populations generated with skewing cytokines produce between 100 and 1000 ng/ml of IFN-γ, while IL-4+/+ Th2 cells produce 8 and 120 ng/ml IL-4 (8, 9). B, An HMI was performed on lung sections stained with PAS. The mean HMI (±SEM) is shown. C, Total BAL cells and eosinophils (Eos) recovered from mice. Differential counts were performed on cytospins of cells recovered from BAL in individual mice. FACS analysis was performed on BAL cells stained with CD4 and KJ1.26 (anti-DO11.10 TCR) Abs. The mean (±SEM) number of cells per mouse per group that stained positive with both Abs is shown (n = 3–5 mice/group). One experiment is shown and is representative of two experiments. Statistical significance was determined by unpaired Student’s t test. ∗, p < 0.008, IL-4Rα+/+ vs IL-4Rα−/−.
Lung histology in mice that received transfer of IL-4−/− Th2 cells and inhaled OVA. A, BALB/c (IL-4+/+)-recipient mice. B, IL-4−/−-recipient mice. Small airways are shown (PAS stain, ×50 magnification). PAS-positive mucins within the epithelial cells stain dark gray (arrow).
Th2 cells induce mucus production in the absence of IL-5 and eosinophilia
Since the induction of airway eosinophilia and mucus were both blocked in IL-4Rα−/− mice, it was still unclear whether eosinophils were required for mucus induction by Th2 cells. IL-5 is essential for augmenting eosinophil recruitment to sites of inflammation (18). To determine the importance of lung eosinophils in mucus production, we generated OVA-specific IL-5−/− Th2 cells in vitro and transferred them into C57BL/6 (IL-5+/+)-recipient mice. At the time of transfer, IL-5+/+ Th2 cells and IL-5 −/− Th2 cells both produced high levels of IL-4 and IL-13, but only IL-5+/+ Th2 cells produced IL-5 (Fig. 4⇓A). Mice that received IL-5−/− Th2 cells exhibited decreased BAL eosinophilia compared with mice that received IL-5+/+ Th2 cells, yet airway epithelial mucus staining was similar in the two groups (Fig. 4⇓, B andC). C57BL/6 (IL-5+/+) and IL-5−/− mice that did not receive cells and were exposed to inhaled OVA alone exhibited mucus staining in <5% of airway epithelial cells, and eosinophils were not present in the BAL (data not shown). Although these experiments suggested that mucus staining did not correlate with airway eosinophilia, it was still possible that epithelial stimulation required only a small number of activated eosinophils to induce a threshold level of mucus. To completely eliminate IL-5 from this system, we transferred IL-5−/− Th2 cells into IL-5−/−-recipient mice. BAL eosinophilia was abolished when IL-5 is absent from both the transferred cells and recipient mice, yet mucus staining was induced at similar levels in mice that received IL-5+/+ or IL-5−/− Th2 cells. These studies show that Th2 cells can stimulate airway epithelial mucus production in the absence of IL-5 and airway eosinophilia.
Mucus production and eosinophilia induced by IL-5−/− Th2 cells after transfer into C57BL/6-recipient (IL-5+/+) and IL-5−/−-recipient mice. IL-5+/+ or IL-5−/− Th2 cells (5 × 106) were transferred into IL-5+/+- or IL-5−/−-recipient mice, and mice were exposed to inhaled OVA. A, Cytokine production by OVA-specific IL-5+/+ and IL-5−/− Th2 cells. At the time of transfer into recipient mice, in vitro generated IL-5+/+ and IL-5−/− Th2 cells were cultured with APCs and OVA. Supernatants were collected after 48 h, and cytokine ELISAs were performed. Typical Th1 populations generated from C57BL/6 mice with skewing cytokines produce between 200 and 300 ng/ml of IFN-γ. B, An HMI was performed on lung sections stained with PAS. The mean HMI (±SEM) is shown. C, BAL cells recovered from mice after exposure to inhaled OVA. Differential counts were performed on cytospins of cells recovered from BAL of individual mice. Mean cell counts (±SEM) are shown (n = 5 mice/group). C57BL/6 and IL-5−/− mice that received inhaled OVA alone had HMIs <5%, and eosinophils were not present in the BAL. One experiment is shown and is representative of three experiments. Statistical significance was determined by unpaired Student’s t test. ∗, p < 0.03, IL-5−/− Th2/IL-5−/−-recipient mice compared with other groups.
Taken together, these studies show that Th2 cell production of IL-13 and/or IL-4 is necessary for the stimulation of mucus production. This induction can occur independently of eosinophilia and IL-5.
Mast cells do not contribute to Th2-induced mucus production
Mast cells, upon activation, synthesize and secrete the cytokines IL-4 and IL-13 and mucus secretagogues such as histamine and leukotrienes (4, 27, 28). IL-4R/IL-13R are present on mast cells and are believed to be important for activation, and IL-4/IL-13 are critical for the production of IgE Abs (13, 29, 30, 31). To determine whether mucus production stimulated by Th2 cells was mediated through activation of mast cells, we generated OVA-specific Th2 cells and transferred them into wild-type and mast cell-deficient (W/Wv) mice. After exposure to inhaled OVA, both mast cell-deficient and wild-type mice exhibited equivalent mucus staining in the bronchial epithelium (Fig. 5⇓). Wild-type and W/Wv mice that were only exposed to inhaled OVA exhibited mucus staining in <5% of airway epithelial cells (data not shown). Thus, these experiments show that increased mucus production induced by Th2 cells is independent of mast cell activation.
Mucus production induced in mast cell-deficient mice after transfer of Th2 cells. Wild-type WBB6F1 (W.T.) and mast cell-deficient (W/Wv) mice received 5 × 106 OVA-specific Th2 cells and were exposed to inhaled OVA. An HMI was performed on lung sections stained with PAS. WBB6F1 and W/Wv mice that received inhaled OVA alone had HMIs <5%. The mean HMI (±SEM) is shown (n = 4–5 mice/group).
Discussion
Airway epithelial mucus production is stimulated by activated Th2 cells in the respiratory tract. A relationship between Th2-type inflammation and mucus has been shown in animals and humans. In mice, when Ag-specific CD4 effector Th1 or Th2 cells are recruited and activated in the lung, mucus is induced by Th2, but not Th1, cells (8). In the lungs of immunized, Ag-challenged animals, both IL-4 and eosinophils correlate with mucus hyperproduction (32, 33, 34, 35). In human asthmatics, the level of mucus production correlates with airway eosinophilia (36).
The cytokines secreted by Th2 cells determine their effector function in an inflammatory response. We studied the roles of IL-4, IL-5, and IL-13 to determine how Th2 cell activation resulted in the induction of mucus production. We generated Th2 cells from mice deficient in IL-4 and IL-5 and observed the effects in recipient animals after inhalational challenge. Although IL-4 is critical for the generation of Th2 cells, we previously determined that it was not required for the induction of airway epithelial mucus production (8). We now show that in the absence of IL-4, IL-4Rα signaling is required to stimulate mucus production. The lack of mucus staining in IL-4Rα−/− mice was not due to the absence of eosinophils, since mucus can be induced by Th2 cells in the absence of IL-5 and eosinophils. In these studies we have blocked the effects of individual Th2 cytokines to dissect the inflammatory pathways of IL-4, IL-5, and IL-13 in the induction of airway epithelial mucus production.
The cytokine microenvironment in which a naive CD4 T cell is stimulated determines whether it will differentiate into a Th1 cell, secreting IFN-γ, or a Th2 cell, secreting IL-4, IL-5, and IL-13. If stimulated in the presence of IL-4, a population of CD4 T cells will become Th2 cells, while in the absence of IL-4 and/or IL-13, they will differentiate into Th1 cells (13, 15, 30, 31). Previous studies in Stat6-deficient mice, which have defective signaling through both IL-4R and IL-13R, showed that when these mice were primed with Ag, predominantly IFN-γ-secreting Th1 cells were generated (10, 11, 12). When primed Stat6−/− mice were challenged with inhaled Ag (14), it was difficult to determine whether the inhibition of mucus production that was observed reflected a blockade of IL-4/IL-13 or the presence of activated Th1 cells in the lungs. Inflammation induced by mixed populations of Th1 and Th2 cells leads to a dominance of Th1 effects and reduced mucus production, as shown when we transferred both Th1 and Th2 cells together into recipient mice and challenged mice with inhaled Ag (L. Cohn, manuscript in preparation). By generating Th2 cells in vitro in these studies we have eliminated the problem of Th1 bias due to the in vivo priming environment and can assess specifically the effector functions of Th2 cells and their cytokines.
In IL-4Rα−/− mice, receptor signaling in response to both IL-4 and IL-13 is inhibited (13, 15). The IL-4R α-chain associates with the γc subunit to form the IL-4R or pairs with IL-13Rα to form a distinct IL-13R. The common receptor chain and signal transduction pathway are believed to be responsible for the overlapping functions of IL-4 and IL-13. Both cytokines prime CD4 T cells to become Th2 cells, stimulate Ig isotype switching to IgE, and induce suppression of immune responses (30, 31, 37). In IL-4Rα−/− mice there is no activation of Stat6, Th2 cell differentiation, or IgE production (13, 15). Since mucus can be stimulated in the absence of IL-4, and there is complete inhibition of mucus production in IL-4Rα−/− mice, one possible interpretation is that IL-13 is essential to activate the airway epithelium in the absence of IL-4. In studies published while this manuscript was in review, IL-13 was shown to play an important role in mucus production. In OVA-immunized, aerosol-challenged mice that were treated with an IL-13 inhibitor, goblet cell mucus staining was markedly decreased (38, 39). Furthermore, aerosol administration of IL-13 led to mucus induction. Because IL-4 and IL-13 appear to be coordinately regulated (40), it is not clear whether IL-4 alone can stimulate mucus production in the absence of IL-13. Although many redundant functions of IL-4 and IL-13 have been reported (41), there are clear examples of cytokine-specific responses. Recently, IL-13, but not IL-4, was identified as essential for worm expulsion in parasitic nematode infection (30, 42, 43), and differential epithelial cell responses to these cytokines have been described (44). Whether IL-4 and IL-13 have identical functions in the induction of mucus production awaits further study.
Eosinophil activation in the airways is associated with mucus production in both humans and animals. Eosinophil cationic protein has been shown to stimulate mucus production, as have other mediators from eosinophils that are released during activation (3). Yet, we have shown that eosinophils are not required for mucus induction by Th2 cells. Since there is no reduction in mucus production as airway eosinophils are progressively eliminated from the lung, eosinophils cannot contribute to mucus induction in this experimental system. Therefore, it is likely that the association of eosinophils and mucus production seen in mice is merely an association of eosinophils with activated Th2 cells secreting IL-5.
Mast cells are activated by IgE, have receptors for IL-4 and IL-13, express mRNA for IL-4 and IL-13, and thus may contribute to Th2 inflammation (27, 28, 29). Once activated, mast cells secrete a variety of mediators known to be mucus secretagogues, including histamine, leukotrienes, and platelet-activating factor (3). In systemically immunized and aerosol-challenged mast cell-deficient mice, Kung et al. showed a 60% reduction in airway eosinophilia, suggesting that Th2 responses were decreased in the absence of mast cells (45), while others showed that mast cells did not contribute to eosinophilia or airway hyper-responsiveness (46, 47). Thus, we wanted to test whether mast cells contributed to Th2-induced mucus production. W/Wv mice are genetically deficient in mast cells, showing <1% of mast cells at mucosal surfaces and no staining of mast cells in the airway submucosa (47, 48, 49). In our studies mast cell-deficient and wild-type mice that received Th2 cells and inhaled Ag had similar inflammatory responses. Both airway eosinophilia (not shown) and mucus production were equivalent. The reduction in eosinophils seen previously probably results either from a defect in Th2 cell priming in the absence of mast cells or from an effector mechanism that is evident only when inflammation is mild. However, these studies show definitively that Th2 cells can stimulate mucus production in the absence of mast cell-derived mediators.
IL-13 and/or IL-4 stimulate mucus production either by direct effects on mucus-secreting goblet cells or indirectly through mediators activated locally in the lung. Mucus is a mixture of proteins, mucus glycoproteins, glycosaminoglycans, water, and electrolytes that lines the upper and lower airways. Mucins, five of which have been shown to be expressed in the respiratory tract, are a heterogeneous group of richly glycosylated molecules secreted by epithelial cells that give mucus its viscous property (50). The mechanisms by which inflammatory stimuli lead to increased epithelial mucin production are unknown. IL-4Rα may signal an initial step in Th2-induced mucus production. Understanding these mechanisms may contribute significantly to our ability to reduce the morbidity from asthma.
Acknowledgments
We thank P. Ranney, N. Niu, and A. Marinov for technical assistance; S. Ziff for artwork; and D. Corry for helpful discussion.
Footnotes
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↵1 This work was supported by the Yale Cancer Center, the Howard Hughes Medical Institute, and National Institutes of Health Grants R01-HL54450 (to K.B.), K08HL03308 (to L.C.), and P50HL56389.
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↵2 Address correspondence and reprint requests to Dr. L. Cohn, Section of Pulmonary and Critical Care Medicine, Yale University School of Medicine, 333 Cedar St., P.O. Box 208057, New Haven, CT 06520-8057. E-mail address: lauren.cohn{at}yale.edu
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↵3 Abbreviations used in this paper: pOVA323–339, OVA peptide 323–339; BAL, bronchoalveolar lavage; PAS, periodic acid-Schiff; HMI, histologic mucus index.
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↵4 M. Mohrs, B. Ledermann, G. Koehler, A. Dorfmuller, A. Gessner, F. Brombacher. Differences between IL-4 and IL-4Rα deficient mice reveal a protective role for IL-13 receptor signaling in chronic Leishmania major infection. Submitted for publication.
- Received November 25, 1998.
- Accepted February 22, 1999.
- Copyright © 1999 by The American Association of Immunologists
References
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