Gamma–delta T cell subsets are differentially associated with granuloma development and organization in a bovine model of mycobacterial disease

The characteristic lesion in bovine tuberculosis is well‐organized respiratory granulomas. This is typically associated with a strong T‐helper 1 biased cell‐mediated immune response and eventual containment of the infection. In bovine paratuberculosis, the classic lesion is unorganized granulomatous intestinal inflammation. Clinical paratuberculosis is associated with a T‐helper 2 biased humoral immune response and eventual death because of inability of the host to contain the infection. Recent reports have suggested that gamma–delta (γδ) T cells play a significant role in granuloma development and/or maintenance during initial stages of infection and may influence the subsequent adaptive immune response. The objective of this study was to use an in vivo bovine model to evaluate γδ T cells during the early host immune response to mycobacterial infection. We used immunofluorescent staining, hyperspectral microscopy, and computerized assisted morphometry to evaluate staining and distribution of γδ T cells during development of organized and unorganized granulomas. Our data suggest that bovine γδ T cell subsets are differentially recruited to early infection sites, and may be instrumental during the initial antimycobacterial host immune response as well as for granuloma organization.