Previously we showed that certain T cell lines and clones from a lepromatous leprosy patient displayed a dose‐dependent suppression of the proliferation of autologous T cells to Mycobacterium leprae (M. leprae) but not mitogen or an unrelatedantigen. The latter cells were also cloned and did not display this suppressive activity, were CD4⁺ and proliferated vigorously to M. leprae presented by autologous HLA‐DR molecules. We shall refer to these cells as T helper (T_h) cells. Most of the suppressive T cell clones (T_s) were also CD4⁺ and also proliferated to M. leprae presented by HLA‐DR, but much less strongly than T_h cells.

In this study we report on our search for (a) the mechanism of this apparently antigen‐specific suppression by T cells, and (b) a possible phenotypic difference between T_h and T_s clones. The two main conclusions are that T_s clones possess a lytic machinery, but that M. leprae‐specific suppression and cytotoxicity can be clearly dissociated, and that the only phenotypic difference between T_h and T_s is the presence of the CD28 marker on T_h and its absence on T_s clones.