Distribution and activation of T-lymphocyte subsets in tuberculous bovine lymph-node granulomas

The immune response against mycobacterial infections is dependant upon a complex interaction between T lymphocytes and macrophages in the context of the granuloma. For this study, we performed the analysis of 18 stage I or II, and 13 stage III or IV granulomas found in lymph nodes from 8 experimentally and 2 naturally infected cattle. T-cell subpopulations (CD3⁺, CD4 ⁺, CD8⁺, WC1⁺, CD25⁺) were investigated by immunohistochemistry. In the majority of stage I/II lesions, CD8⁺ and CD25⁺ cells were predominantly found in the lymphocytic outer region of the granuloma, suggesting a possible role for activated CD8⁺ cells in the initial attempt to restrain the granuloma growth. CD4⁺ T cells appeared equally distributed in the lymphocytic mantle and in the internal areas of the granulomas. WC1⁺ cells appeared interspersed among the macrophages. We speculated that this could indicate a role for these 2 subsets in the maintenance and the maturation of the granuloma. In stage III/IV lesions, all of the T-cell subsets investigated appeared interspersed among the mononuclear component of the granulomas. In general terms, there was a higher density of CD8⁺ cells compared with CD4⁺ cells. However, there was no sense of rimming effect for any of the investigated cell populations.