Role of gd T Cells in Immunopathology of Pulmonary Mycobacterium avium Infection in Mice

Several studies have shown that gd T cells influence granuloma development after infection with intracellular pathogens. The role of gd T cells in controlling the influx of inflammatory cells into the lung after Mycobacterium avium infection was therefore examined with gene-disrupted mice (K/O). The mice were infected with either M. avium 724, a progressively replicating highly virulent strain of M. avium, or with M. avium 2-151 SmT, a virulent strain that induces a chronic infection. gd-K/O mice infected with M. avium 2-151 SmT showed early enhanced bacterial growth within the lung compared to the wild-type mice, although granuloma formation was similar in both strains. gd-K/O mice infected with M. avium 724 showed identical bacterial growth within the lung compared to the wild-type mice, but they developed more-compact lymphocytic granulomas and did not show the extensive neutrophil influx and widespread tissue necrosis seen in wild-type mice. These data support the hypothesis that isolates of M. avium that induce protective T-cell-specific immunity are largely unaffected by the absence of gd T cells. Whereas with bacterial strains that induce poor protective immunity, the absence of gd T cells led to significant reductions in both the influx of neutrophils and tissue damage within the lungs of infected mice.