Mechanisms of immunity to rickettsial infection: characterization of a cytotoxic effector cell.

Rickettsiae, as other intracellular bacteria, are relatively sequestered from the effects of antibody and local antibody-independent responses. Considering the obligate intracellular nature of rickettsia, the exact mechanisms by which lymphocytes and macrophages encounter rickettsial antigens and eliminate the infection depends upon the appropriate presentation of antigen to the immune system. We demonstrate here that cells taken from the spleens of Rickettsia typhi- or R. tsutsugamushi-infected mice are able to lyse specifically tissue culture targets infected with the homologous organism. This effect was eliminated upon treatment of the spleen cells with anti-Thy-1.2 + complement. Furthermore such T cells exhibit H-2-restricted killing when tested on infected targets of different genetic backgrounds. We propose that a T cell-mediated cytotoxic immune mechanism exists that may play an important role in the elimination of rickettsial organisms during infection.