Secondary cytotoxic cell response to lymphocytic choriomeningitis virus. I. Kinetics of induction in vitro and yields of effector cells.

Secondary (memory) cell-mediated cytotoxic responses in lymphoid cells from CBA/H mice pre-primed with lymphocytic choriomeningitis virus (LCM) 5-7 weeks previously were induced by culturing these cells in vitro with syngeneic, infected peritoneal cells at 37 degrees for periods of up to 5 days. Cytotoxic effectors were assayed against LCM infected, H-2 compatible target cells in a 51Cr release assay. Response was greater with a higher ratio (1:10) of infected peritoneal cells:pre-primed cells than with lower ratios (e.g. 1:250). Separating responders from infected cells by a 450 mmum nucleopore membrane (coarse enough to allow passage of virus particles) still permitted induction of a secondary response whilst interposition of a 50 mmum nucleopore membrane (which apparently prevented transit of virus particles) virtually abolished the secondary response. Removal of phagocytic cells from responders prior to setting up memory cultures greatly reduced responders' capacity to be induced. Fixed, infected stimulators still induced strong secondary responses. Secondary response was maximal with spleen cells, peripheral blood lymphocytes, or pooled iliac and lumbar lymph node cells. Thymocytes responded less well, whilst mesenteric lymphoid cells and peritoneal cells gave minimal responses. Effector cells from memory cultures killed targets with single-hit kinetics and a rectilinear log effectors: log targets lysed relation held. Memory spleen cells developed increasing cytolytic activity from 2 to 5 days in culture. Memory-generated effectors were markedly potent by day 5, e.g. giving 70 per cent specific release at a killer:target ratio of 0-8:1. Peak DNA synthesis occurred on day 4. We conclude that memory effectors as a population differ in kinetics and potency from effectors obtained by primary viral challenge in the mouse.