T cells are necessary for Th2 cytokine production and eosinophil accumulation in airways of antigen-challenged allergic mice.

In a murine model of pulmonary inflammation, aerosolized antigen challenge of sensitized B6D2F1 mice leads to eosinophil accumulation within the lungs. Little is known of the role of T cells and their cytokine products in these allergic animals. In this study, we show that T cells migrate into the lungs in response to antigen challenge and are necessary for local production of cytokines (IL-4 and IL-5) important in B and T cell development as well as eosinophil activation and differentiation. Flow cytometry revealed an increase in the percentage of Thy1+ T cells but not in B220+ B cells in bronchoalveolar lavage fluid after challenge when compared to unchallenged mice. Although there was an increase in both T cell subsets, there were twice as many CD4+ cells as CD8+ cells at 24 hr and after 48 hr the CD4+ subset predominated. The CD4+ T lymphocytes were CD44+ CD45RBlo indicating an activated/memory phenotype and tracheobroncheal lymph node cells obtained from challenged mice proliferated in a dose-dependent manner in response to antigen stimulation in vitro. Reverse transcriptase-polymerase chain reaction analysis of lung tissue-derived RNA indicated an increase in Th2-like cytokines. IL-4 and IL-5 steady-state mRNAs were at peak levels 6 hr after challenge, while no consistent increase was found for IFN-gamma mRNA levels. Treatment with the glucocorticoid betamethasone just prior to challenge reduced the levels of cytokine mRNA as well as the eosinophil influx. In vivo depletion of T cells from sensitized mice reduced pulmonary eosinophilia as well as the expression of IL-4, IL-5, and IFN-gamma steady-state mRNAs in the lungs of sensitized and challenged mice. These results indicate that T cells migrating into the lungs of mice after antigen challenge play an important role in the production of Th2-like cytokines and the accumulation of eosinophils in bronchial fluids.