Lymphocytes in the bronchoalveolar space reenter the lung tissue by means of the alveolar epithelium, migrate to regional lymph nodes, and subsequently rejoin the systemic immune system

Lymphocytes in the bronchoalveolar space are routinely obtained and examine d in lung diseases such as asthma or sarcoidosis. In a pig model, labeled l ymphocytes were found in regional lymph nodes after intrabronchial instilla tion, indicating that reentry of lymphocytes from the bronchoalveaolar spac e into the body is possible. In the present study, the route and kinetics o f the reentry of bronchoalveolar lymphocytes were investigated in a congeni c rat model using immunohistochemistry on cryostat and semithin sections an d confocal laser scanning microscopy. As early as 15 min after intratrachea l instillation lymphocytes were found to leave the bronchoalveolar space by transmigration through alveolar but not bronchial epithelium and were obse rved in interstitial alveolar tissue. At 6 hr after intratracheal instillat ion, T and B lymphocytes appeared in the draining lymph nodes of the lung w ith an increase after 24 and 48 hr. The kinetic pattern clearly differed in nondraining lymph nodes and other organs. After 6 hr, only single cells we re found in nondraining lymph nodes, spleen, and blood with a slight increa se after 24 hr, and only occasionally were single cells seen in the liver, thymus, or Peyer's patches 24 and 48 hr after instillation. In conclusion, T and B lymphocytes can leave the alveolar space by reentry into the lung t issue through alveolar epithelium. They reach regional lymph nodes by means of lymphatic vessels and are then distributed all over the body to rejoin the systemic immune system. Coming into contact with environmental antigens , these lymphocytes could perform an important function in the lung immune system and might be a target for inhalative therapy. Anat Rec 264:229-236, 2001. (C) 2001 Wiley-Liss, Inc.