Cellular Cooperation and Stimulatory Factors in Antibody Responses: Limiting Dilution Analysis in Vitro

Abstract

Abstract Limiting dilution analyses with the Poisson model were performed on normal mouse spleen cells alone or in the presence of added cells or soluble factors. When a constant number of T cells activated to sheep red blood cells were added to cultures of diluted spleen cells the mean frequency of response to sheep red blood cells was 5- to 30-fold greater than that of spleen cells diluted alone. Adding a constant number of B cells did not produce a significant change in the mean frequency of response of diluted spleen cells. Since a responding unit is thought to be composed of T cells and B cells, these results indicate that antigen-specific T cells normally limit the generation of responding units when normal spleen cells are subjected to limiting dilution analysis alone. Conversely, B cells appear to be in relative excess. Culture medium supernatants from mixed cultures of T cells activated to histocompatibility antigens and target cells bearing the antigens to which the T cells have been activated enhance antibody responses in vitro. When spleen cells were diluted in the presence of added supernatants the mean frequency of response was increased relative to that of spleen cells alone. This is interpreted to mean that the supernatants contain a factor, or factors which replace the requirement for T cells and enhance in vitro antibody responses by enabling more B cells to participate in the response.