AbstractThe biological activities of mycobacteria‐reactive Lyt‐2+T cells were characterizedin vitro.T cells from mice immunized with killedMycobacterium tuberculosisor viableM. boviswere restimulatedin vitroand cloned under limiting dilution conditions. Several L3T4−Lyt‐2+T cell lines, some of them KJ16+, were established. These T cell lines were capable of lysing mycobacteria‐primed macrophages in an antigen‐specific way. The cytolytic activity of some T cell lines was found to be class I restricted, whereas others showed antigen‐specific killing in the absence of apparent H‐2 restriction. Several T cell lines produced interferon‐γ after appropriate stimulation. Furthermore, these T cell lines could induce tuberculostatic macrophage capacities by apparently two different mechanisms, namely by secretion of lymphokines (most probably interferon‐γ) and by direct cell qontact. We conclude that CD8 T cells with antigen‐specific cytolytic potential are generated during tuberculosis and that these T cells are involved in the immune respo