Non-major histocompatibility complex-restricted cytotoxic activity of blood mononuclear cells stimulated with secreted mycobacterial proteins and other mycobacterial antigens

Several observations indicate that non-major histocompatibility complex (MHC)-restricted cytotoxicity, mediated for example by natural killer cells and lymphokine-activated killer cells, may serve as an important antimicrobial defense mechanism. The purpose of the present study was to investigate the influences of different mycobacterial antigens on non-MHC-restricted cytotoxicity and further to investigate the ways by which various lymphocyte subpopulations contribute to the development of this cytotoxicity. Non-MHC-restricted cytotoxicity was induced following stimulation of mononuclear cells with tuberculin purified protein derivative, Mycobacterium bovis bacillus Calmette-Guérin (BCG), short- and long-term culture filtrates of virulent Mycobacterium tuberculosis H37Rv, and 30-31-kDa secreted mycobacterial protein. These antigens also induced proliferation and production of gamma interferon. The CD4+ cells proliferated and expressed interleukin-2 receptors following stimulation with mycobacterial antigens. Depletion studies after antigen stimulation showed that the cytotoxic effector cells were CD16+ CD56+ and CD4-; the CD4+ cells alone did not mediate non-MHC-restricted cytotoxicity. To evaluate the influence of CD4+ cells on the development of non-MHC-restricted cytotoxicity, blood mononuclear cells were depleted of CD4+ cells before antigen stimulation. When mononuclear cells were incubated with purified protein derivative or short-term culture filtrate in the absence of CD4+ cells, cytotoxic activity was reduced. This reduction was abolished by interleukin-2 but not by gamma interferon. We conclude that several mycobacterial antigens are able to induce non-MHC-restricted cytotoxicity. This study indicates that non-MHC-restricted cytotoxicity following stimulation with mycobacterial antigens is induced by cytokines released by antigen-specific activated CD4+ cells.