Cellular changes in the bronchoalveolar lavage (BAL) of pigs, following immunization by the enteral or respiratory route.

Normal young pigs were immunized by the oral or aerogenic route with the viable or inactivated lung-pathogenic bacterium Actinobacillus (Haemophilus) pleuropneumoniae. Three weeks later the cellular composition as well as the lymphocyte subset composition of the bronchoalveolar space were examined by BAL. Lymphocytes in the lavage increased significantly, including CD4+ and CD8+ T cells. After oral immunization a dramatic increase of plasma cells and lymphoid blasts was found. Among immunoglobulin-positive lymphocytes IgG+ cells showed the most pronounced increase. For most lymphocyte subsets there was no difference between viable and inactivated bacteria. Oral immunization with a lung-pathogenic bacterium results in increased numbers of lymphocytes in the bronchoalveolar space and might play a critical role in protection against lower respiratory tract infections.