Conjugate Formation by Primary and Secondary Populations of Murine Immune T Lymphocytes

Primary (1°) and secondary (2°) murine immune T lymphocyte populations generated in vivo and in vitro exhibit differences in the rate of target cell-specific conjugate formation. Populations containing secondary CTL reached maximum conjugate formation after 10 to 15 min when mixed with target cells (1:1) and centrifuged at 4°C followed by incubation at 37°C, whereas primary alloimmune T lymphocytes required 20 to 30 min of incubation. Cytolytic activity was measured concurently during the incubation period by a 51Cr release-EDTA assay. Although populations of 1° and 2° immune T lymphocytes reached similar levels of maximum conjugate formation during incubation, cytolytic activity at the time of maximum conjugate formation was insignificant compared to that obtained after 3.5 hr of incubation. Also, long-term 1° MLC cells that exhibit very little cytolytic activity formed specific conjugates, as did all effector cell populations in the presence of EGTA, a Ca++ chelating agent that inhibited cytotoxicity 100%. This suggests that the expression of T lymphocyte alloantigen-specific membrane receptors and the binding of immune T cells to target cells are necessary but not sufficient for cytolysis. Repetitive killing of target cells by 2° CTL was suggested by the cytolytic activity after 3.5 hr when compared with the observed levels of maximum conjugate formation. Variations in the number, distribution, or affinity of alloantigen-specific receptors between 1° and 2° immune T lymphocyte populations may account for the observed differences in rates of conjugate formation.