Characterization of the lymphocytic alveolitis in visna-maedi virus-induced interstitial lung disease of sheep.

In order to investigate the contribution of lymphocytes to interstitial lung disease in animals with visna-maedi infection, we studied in parallel bronchoalveolar cells and lung tissue from slaughter-house animals (n = 29) and from colostrum-deprived lambs transtracheally inoculated with field isolates of visna-maedi virus (n = 9) or saline (n = 6). Lymphocyte subpopulations were identified in bronchoalveolar lavage by immunofluorescence and flow cytometry analysis and in lung tissue using indirect immunohistochemistry. In infected animals a lymphocytic alveolitis containing CD4 and CD8 lymphocytes was observed. Peribronchovascular lymphoid nodules comprise mostly CD4 lymphocytes. Alveolar lymphocytes of both subsets displayed increased expression of MHC class II antigens in animals with naturally occurring maedi but not in experimentally infected ones. A sequential process of lymphocyte attraction and activation is likely to occur in vivo as part of the alveolitis.