Effect of Theophylline on Endotoxin and Tumor Necrosis Factor Induced Airway Changes in an in vivo Animal Model.

We have previously reported that exposure to aerosolized endotoxin causes bronchial hyperresponsiveness in rats. This is at least partly due to secondary release of tumor necrosis factor (TNF). In this study, we evaluated the effect of pretreatment with aminophylline on these lipopolysaccharide-induced airway changes. Compared to placebo-pretreated animals aminophylline (20 mg/kg i.p.) significantly inhibited the lipopolysaccharide-induced increase in responsiveness without influencing neutrophil counts or TNF levels in bronchoalveolar lavage fluid. In a second part of the study, aminophylline- or placebo-pretreated rats were exposed to aerosolized recombinant human TNF. Compared to saline-exposed animals, TNF caused a significant increase in 5-hydroxytryptamine responsiveness which was inhibited by pretreatment with aminophylline. We conclude that the attenuating effect of aminophylline on lipopolysaccharide-induced airway hyperresponsiveness is not due to inhibition of TNF release, but could be explained by its inhibitory effect on TNF-induced hyperresponsiveness.

Role of IFN-gamma in the inhibition of the allergic airway inflammation caused by IL-12.

T-helper 2 (Th2)-like cells are thought to play a crucial role in the pathogenesis of the eosinophilic airway inflammation observed in asthma. In a murine model of allergen-induced airway eosinophilia and bronchial hyperresponsiveness (BHR), we have shown that interleukin (IL)-12 can suppress antigen-induced airway changes despite the presence of circulating specific IgE. In the present study, we investigated the role of interferon-gamma (IFN-gamma) in the inhibitory effects of IL-12 on allergic airway inflammation. Repeated daily exposure of actively immunized mice to aerosolized ovalbumin (OVA), as compared with aerosolized saline (SAL), induced a significant increase in bronchoalveolar lavage fluid (BALF) eosinophilia and OVA-specific serum IgE in both IFN-gamma-receptor-deficient (IFN-gammaR KO) and wild-type mice. As compared with placebo (PLAC), administration of recombinant murine IL-12 (rmIL-12) during the daily aerosol exposure (but not at the time of immunization) significantly inhibited BALF eosinophilia in both IFN-gammaR KO mice and wild-type controls, without influencing the production of specific IgE. In contrast, administration of rmIL-12 during the active immunization inhibited both BALF eosinophilia and specific IgE in wild-type mice as compared with littermates given PLAC; however, treatment with rmIL-12 during immunization, in comparison with PLAC, caused a significant increase in BALF eosinophilia and specific IgE in IFN-gammaR KO mice. These results demonstrate that inhibition of the allergen-induced eosinophil influx in murine airways by IL-12 is IFN-gamma-dependent during the initial sensitization, but becomes IFN-gamma-independent during the secondary response.

Attenuation of allergic airway inflammation in IL-4 deficient mice.

To investigate the role of IL-4 in vivo in allergic asthma, we developed a murine model of allergen-induced airway inflammation. Repeated daily exposures of actively immunized C57BL/6 mice to aerosolized ovalbumin (OVA) induced a peribronchial inflammation and an increase in eosinophils and lymphocytes in bronchoalveolar-lavage (BAL) fluid. In IL-4 deficient (IL4-/-) mice, treated in the same way, there were substantially fewer eosinophils in BAL and much less peribronchial inflammation compared with wild type mice. In this model, mast cell deficient (W/Wv) mice developed a similar degree of BAL eosinophilia and peribronchial inflammation as wild type mice, demonstrating that the mast cell is not required for the induction of chronic airway inflammation. In contrast, BAL eosinophilia and airway inflammation were absent in OVA-treated MHC ClassII deficient (B6.Aa-/-) mice which lack mature CD4+ T lymphocytes. In conclusion, these results indicate that IL-4 is a central mediator of allergic airway inflammation, regulating antigen-induced eosinophil recruitment into the airways by a T cell dependent mechanism.

Importance of interleukin-4 and interleukin-12 in allergen-induced airway changes in mice.

T helper 2 (Th2)-like cells are thought to play a crucial role in the pathogenesis of atopic asthma. In this study, we attempted to evaluate the in vivo effect of suppressing Th2 cell development on allergen-induced airway changes. Repeated exposure of actively sensitized C57Bl/6 mice to aerosolized ovalbumin (OA) causes, in comparison to saline-exposed control animals, synthesis of specific IgE, increase of eosinophils in bronchoalveolar lavage fluid and airway hyperresponsiveness. These effects are not observed in OA-exposed, sensitized IL-4-knockout mice. Likewise, these effects are inhibited in OA-exposed C57Bl/6 mice treated with IL-12 during initial antigen exposure. These results suggest that suppressing Th2 cell development in vivo might have profound inhibitory effects on allergen-induced airway changes.

Interleukin-12 inhibits antigen-induced airway hyperresponsiveness in mice.

The airway inflammation observed in allergic asthma is thought to be orchestrated by an antigen-driven T-helper-2 (Th2) lymphocyte response. In vitro data indicate that the presence of interleukin-12 (IL-12) during the primary stimulation of T-lymphocytes with antigen favors the development of Th1 cells. The aim of the present study was to examine the effect of IL-12 in vivo on antigen-induced airway changes in a murine model. C57BL/6 mice were actively sensitized to ovalbumin; 14 d later, they were exposed daily for 7 d to aerosolized ovalbumin. This resulted in airway eosinophilia, production of ovalbumin-specific IgE, and airway hyperresponsiveness to carbachol. Administration of recombinant murine IL-12 (rmIL-12) during the active immunization prevented these antigen-induced changes. In contrast, administration of rmIL-12 to actively immunized mice during the daily aerosol exposure (but not at the time of immunization) abolished airway eosinophilia and hyperresponsiveness without influencing the production of specific IgE. These results suggest that IL-12 can suppress antigen-induced airway changes despite the presence of circulating specific IgE.