Immunohistochemical distribution of S-100 alpha-positive cells in bovine mycobacterial and non-mycobacterial granulomas.

By means of immunohistochemistry, the distribution of the alpha-subunit (S-100 alpha) and the beta-subunit (S-100 beta) of S-100 protein was studied in bovine granulomas caused by Actinomyces bovis, Actinobacillus lignieresi, Actinomyces (Corynebacterium) pyogenes, Pseudomonas aeruginosa, Staphylococcus aureus, Mycobacterium bovis and Mycobacterium paratuberculosis. S-100 alpha-positive epithelioid cells or dendritic cells were scattered among the predominantly S-100 alpha-negative cells of the mononuclear phagocyte system (MPS). S-100 beta was not found in the MPS cells of granulomas but was observed in the endothelial cells of blood vessels. A positive reaction to S-100 was also seen in normal cells in the lymphoid and mammary tissues. Mycobacterial granulomas contained more S-100 alpha-positive cells than did non-mycobacterial ones.