Competitive inhibition of cytotoxic T lymphocyte-target cell conjugation. A direct evaluation of membrane antigens involved in cell-mediated immunity.

A method to determine directly the antigenic similarity of target cells (TCs) involved in cytotoxic T lymphocyte (CTL)-TC interactions is described. When fluorescently labeled TC (FL-TCs) are bound (conjugated) to CTLs in the presence of antigenically similar but unlabeled TCs, the percentage of CTL-TC conjugates containing unlabeled TCs corresponds linearly to the number of unlabeled TCs in the TC population. This assay is specific, permits direct observation of individual CTLs and TCs which interact to form conjugates, can be completed within 10 min, eliminates complications attributable to CTL recycling, and the degree of competition observed fits that theoretically expected. The results of this paper provide the theoretical basis for "cold" (unlabeled) target inhibition of radioactive assays of lymphocyte-mediated cytolysis.