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

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) 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.