Capacity of purified Lyt-2(+) T cells to mount primary proliferative and cytotoxic responses to Ia(−) tumour cells

Allogeneic gene products of the major histocompatibility complex, the HLA complex in man and the H–2 complex in mice, induce T lymphocytes to exert powerful mixed lymphocyte reactions (MLR) and cell-mediated lympholysis (CML). In mice, the subset of T cells carrying the L3T4 surface antigen but lacking the Lyt-2 antigen responds predominantly to H–2 class II (la) differences whereas the L3T4(−) Lyt-2(+) subset reacts to class I (K/D) differences(1,2). For primary responses the stimulus for MLR and CML appears to be controlled by Ia(+) cells of the macrophage/dendritic cell lineages, for both L3T4(+) and Lyt-2(+) cells(3–6). The finding that la(+) cells are required for responses involving Lyt-2(+) cells has been taken to imply that triggering of these cells is controlled by la-restricted L3T4(+) cells(7,8). Lyt-2(+) cells have thus come to be regarded as crippled cells which are heavily dependent on ‘help’ from other T cells(9–11). This well-entrenched view is challenged by evidence presented here that purified Lyt-2(+) cells can give high primary responses to certain Ia(−) tumour cells in vitro.