Phenotypic characterization of the cells of the inflammatory response in ovine encephalitic listeriosis.

The brainstem (pons cerebri and medulla oblongata) of 22 sheep aged between 6 months and 3 years which had developed clinical signs of central nervous system dysfunction were examined. Histopathological changes characterized by microabscesses, focal gliosis and perivascular cuffing compatible with natural infection with Listeria monocytogenes were present. The brains were examined by lectin histochemistry and immunohistochemistry with markers for T lymphocytes (CD4+ and CD8+ subsets), B lymphocytes, mononuclear phagocytes (including macrophages, ramified microglia, activated microglia and amoeboid microglia), astroglia and L. monocytogenes. These methods allowed semiquantitative analyses of the frequency of the different cell types in the brain lesions. The distribution of listerial antigen in the lesions was variable but always sparse. Mononuclear phagocytes and neutrophils appeared to be the most numerous inflammatory cells in the affected areas of the brainstem. T lymphocytes (CD8+ and CD4+ subsets) and B lymphocytes also played a part in the inflammatory process, in addition to activated astrocytes.