Accessory cells in the in vitro generation of type C virus-specific T-killer lymphocytes. III. Two methods of antigen presentation of cytolytic T-lymphocyte precursors

F₁ hybrid mice primed in vivo with tumor cells bearing the virus-induced FMR antigen and the H-2 specificities of each parent are able to produce in vitro in secondary response cytolytic T lymphocytes (CTL) reacting with FMR in the context of the H-2 antigens of both parents. This suggests that the processing in vivo of the immunizing cells by f₁ macrophages results in the presentation of FMR antigens in the context of both H-2 specificities. It has also been suggested that FMR antigens are recognized by cytolytic T-lymphocyte precursors (CTL-P) at the surface of tumor cells and not of macrophages (4). The results reported here show that there are two methods of CTL-P priming: (a) in most cases, FMR antigens are presented directly by the tumor cells; (b) however, in the absence of antigen-presenting tumor cells in vivo or in vitro, macrophages present FMR to CTL-P. The presentation by macrophages appears less efficient but is probably sufficient to explain the priming of memory cells corresponding to both parental H-2.