Immunohistochemical characterization of bovine tuberculous granuloma

Tuberculous granuloma is a complex host-protective structure generated in response to persistent mycobacterial stimuli with focal accumulation of inflammatory cells. In the present study, tuberculous granulomas of lungs and lymph nodes from 16 cases were characterized. Majority of the granulomas were encapsulated lesions with multiple areas of caseous necrosis and dystrophic mineralization which were graded from I to IV. Masson's Trichrome staining was done to score the intensity of encapsulation in the granulomas. Acid fast bacilliwere demonstrated within the granulomas. The thickness of encapsulation surrounding the granuloma negatively correlated with the presence of Mycobacterium bacilli, indicating an attempt to limit the infection. Further, the granulomas were characterized for T- cell subpopulations and macrophages by immunohistochemistry using anti-CD4, CD8, CD68 and iNOS antibodies. There was a higher intensity of reactivity for CD8+ as compared to CD4+ in seven cases (43.75%). CD8+ cells were predominantly found in the lymphocytic outer region of the granuloma while CD4+ cells were distributed diffusely in both internal and external areas of the granuloma. iNOS and CD68+ cells were distributed in regionsurrounding the necrotic areas and marked the activated macrophages, giant cells and epithelioid cells.There was a weak correlation between inflammatory score and the pathology severity score, while a negative correlation between inflammatory score and the encapsulation of the granuloma.The present study showed that the granulomas were composed of different T cell subsets and CD68+and iNOS positive macrophages which invariably showed acid fastbacilli.