Occurrence of T lymphocytes in perivascular regions of the lung after intratracheal infection of swine with Pasteurella multocida.

The defence mechanisms of the lung acting against airborne antigens (bacteria) are not yet fully understood. Therefore, we investigated cell-derived immunological processes in porcine pulmonary tissue. The incidence and distribution of leukocyte subpopulations in lungs, lung lymph nodes and tonsils from eight animals intratracheally infected with Pasteurella multocida (P.m.) type A wild strain and from four non-infected control animals were established by immunohistochemistry, using a panel of monoclonal antibodies (mAbs) against specific porcine leukocyte antigens: MHC Class II (MHC II), SWC1, SWC3a, CD2a, CD4a, CD8b. In the test animals, a broad layer of SWC1+ cells and SWC3a+ cells emerged in the subsinusoidal region of lung lymph nodes and in the bronchoalveolar spaces of the lung as early as 4 and 24 h after infection, and in the subsinusoidal regions of the lung lymph nodes only very few cells could be stained with the mAb against the MHC II antigen. We could not detect any MHC Class II+ cells in the bronchoalveolar spaces at this time of the investigation. In the course of the disappearance of the SWC1+ cells and SWC3+ cells, CD2a+, CD4a+ and, in lower numbers, CD8b+ T lymphocytes seemed to concentrate in the perivascular and, partially, the peribronchial regions of the lung 72 h after infection. By means of the double immunostaining method, we could demonstrate an accumulation of CD4a+ cells and CD8b+ cells after infection which lacked the SWC1 antigen, indicating that these cells were activated T lymphocytes. The same cell types (SWC1-/CD4a+ and SWC1-/CD8b+ cells) as well as CD8b-/CD4a+ cells could be observed in the interstitium of the lung 72 h after infection.