Alloreactive cytolytic T-cell clones preferentially recognize conformational determinants on histocompatibility antigens: analysis with genetically engineered hybrid antigens.

Hybrid genes were constructed for the localization of allodeterminants on murine class I antigens recognized by antibodies and cytolytic T lymphocytes. By using deletion subclones of the H-2Kd and H-2Kk genes, homologous regions were exchanged between the two alleles. The altered genes were introduced and expressed in mouse fibroblast and fibrosarcoma cells. Cells expressing hybrid antigens were analyzed with 29 monoclonal anti-H-2Kd and anti-H-2Kk antibodies and with 150 short-term alloreactive cytolytic T-cell clones. When only the first or only the second amino-terminal domain was exchanged, most T cells and 60% of the antibodies lost their reactivity to the H-2K antigen. No T-cell clone was directed against the third extracellular domain, whereas three antibodies could bind to this domain. This implies that nearly all determinants essential for a cytolytic T-cell response or for antibody binding lie on the two external domains and are conformational structures generated by the interaction of these two domains.