T-cell-mediated cytotoxicity against Mycobacterium antigen-pulsed autologous macrophages in leprosy patients

Abstract

The involvement of CD4+ T lymphocytes in the defense mechanisms against intracellular pathogens is widely recognized. Little information is available on the generation and specificity of the cytotoxic cells that eliminate human monocytes/macrophages infected with mycobacteria. In this work, we tested whether mononuclear cells from leprosy patients could generate cytotoxic T-cell activity against autologous macrophages pulsed with Mycobacterium leprae or purified protein derivative (PPD) in a 4-h 51Cr release assay. Peripheral blood mononuclear cells from normal Mycobacterium bovis BCG-immunized controls or from leprosy patients stimulated with antigen for 7 days were used as effector cells. Paucibacillary (PB) patients and normal controls yielded more active effector cells in this system than multibacillary (MB) patients. MB patients were able to develop cytotoxicity against M. leprae, BCG, or PPD, in contrast with the immunological anergy widely described. We did not find cytotoxicity against unpulsed macrophages. Cross-reactivity was observed between PPD, BCG, and M. leprae. Only antigen-pulsed autologous macrophages were suitable as target cells. M. leprae-induced cytotoxic cells were found in both CD4+ CD8- and CD4- CD8+ T-cell subsets, whereas CD4+ cells were the main component of PPD-induced cytotoxicity. In MB patients, BCG-induced cytotoxic cells were better killers of M. leprae-pulsed macrophages than cells induced by M. leprae. This is an interesting finding in view of the ongoing vaccination trials. The involvement of CD4- or CD8-mediated cytotoxicity may be important in the balance between protection and tissue or nerve damage.