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

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Abstract
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) differences1,2. 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+ cells3–6. 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+ cells7,8. Lyt-2+ cells have thus come to be regarded as crippled cells which are heavily dependent on ‘help’ from other T cells9–11. 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.