Induction of secondary cytotoxic T lymphocytes by liposomes containing HLA-DR antigens [23]

It is evident that the gene products of the major histocompatibility complex (MHC) have a crucial role in the induction of cytotoxic T lymphocytes (CTLs) and as target antigens for CTLs^1-6. Assessment of the precise molecular requirements for CTL induction and recognition, however, is difficult when intact cells are used as targets. Recently, in several model systems, it has been demonstrated that, after detergent solubilisation, cell-surface antigens can be isolated that retain the ability to stimulate a secondary CTL response. CTL stimulating activity has been isolated by detergent solubilisation from murine tumour cell plasma membranes^7,8 which co-purified with H-2 antigens through lentil lectin affinity chromatography and gel filtration^9,10. Highly purified HLA-A and HLA-B antigens, from the human lymphoblastoid cell line JY, have been isolated and incorporated into well characterised liposomes¹¹. Spleen cells from mice primed to JY cells developed cytolytic activity, specific for JY targets, after co-culture with these HLA-liposomes¹². In these experiments it was observed that membranes which had been solubilised with deoxycholate and then dialysed to remove the detergent (reconstituted membranes) always stimulated greater cytolytic activity than did HLA-liposomes. At the time it was suggested that this disparity might reflect the loss of other antigens involved in CTL stimulation as a consequence of HLA-A and HLA-B purification. Data are presented here which demonstrate that other antigens are indeed able to induce secondary CTLs, independently of the HLA-A and HLA-B antigens. The results suggest that this activity is present on HLA-DR-associated molecules.