Role of syngeneic Ia⁺ accessory cells in the generation of allospecific CTL responses

Under conditions in which antigen dose is suboptimal, the recognition of Ia determinants is a necessary component of the generation of allospecific CTL responses. With monoclonal anti-Ia antibodies used as blocking reagents, it is demonstrated that the recognition of alloantigens may proceed via two pathways. Alloantigens can be recognized in the context of syngeneic Ia determinants in a similar fashion to conventional antigens. If, however, the Ia⁺ cells are removed from the responder population, the generation of such responses involves the recognition of allogeneic Ia determinants directly. A non-T, non-B, adherent accessory cell was identified as the critical syngeneic Ia⁺ cell required for CTL responses in these cultures.