Immunologically specific direct T lymphocyte-mediated killing of Nocardia asteroides

Macrophage-depleted populations of splenic lymphocytes obtained from immunized and nonimmunized BALB/c mice were tested to determine their ability to kill Nocardia asteroides GUH-2 in vitro. Nocardia-primed lymphocytes, but not normal lymphocytes, killed N. asteroides. The ability of these lymphocytes to kill N. asteroides could be further enhanced by in vitro activation of the lymphocytes with nocardial cell wall fragments 12 to 48 hr before challenge. The nocardicidal activity of the lymphocytes was greater in populations enriched in T cells and was eliminated by lysing the lymphocytes with anti-Thy-1.2 plus C. N. asteroides-primed T cells were unable to kill a distantly related actinomycete, Rothia dentocariosa, and killed other species of Nocardia (N. brasiliensis and N. caviae) poorly or not at all, indicating that the microbicidal activity was immunologically specific. Light microscopy and electron microscopy revealed a close association between the T cell membrane and the cell wall of N. asteroides, with possible damage to the latter structure. The ability of immunologically specific T cells to recognize, bind, and kill Nocardia may be an important mechanism of host defense, because these microorganisms often are able to escape intracellular killing by macrophages.