Peribronchial lymphocyte activation in bleomycin-induced lung injury

The role of lymphocytes in bleomycin (Bleo)-induced lung injury remains obscure. In normal hamsters, peribronchial lymphatic tissue (PBLT) has been found to contain a large population of T lymphocytes responsive to interleukin 2 (IL-2) but not to IL-4. Lung injury induced by a single intratracheal instillation of Bleo in hamsters has been ameliorated by cyclosporin A (CyA). In the present study, using this model, PBLT-derived lymphocyte function was explored for 28 days after Bleo instillation. Increase in PBLT lymphocytes occurred at five time points investigated, reaching highest values on day +7 (p < 0.0025). Cell proliferation in response to concanavalin A was enhanced, while IL-2 +/- the mitogen had no effect. In contrast to its inactivity in the normal hamster, in the Bleo-injured animal IL-4 alone induced T cell proliferation (p = 0.0077) on day +7. CyA therapy initially suppressed and delayed recovery of the number of lymphocytes and their activation. The results of this study suggest the existence of a vulnerable period in Bleo-induced lung injury and indicate that lymphocytes participate in the pathogenesis of the insult to the tissue. The unresponsiveness to IL-2 and the emergence of cellular response to IL-4 indicate immune deviation in PBLT-derived T cells.