Lymphocyte-activating factors released in vitro by sensitized and nonsensitized human lymphocytes

Abstract

Supernatants from mixed cultures between nonsensitized allogeneic human lymphocytes were competent to initiate DNA synthesis in normal lymphocyte cultures. Supernatants from lymphocyte cultures of single individuals did not have this ability. Based on determination of the HL-A phenotype it was concluded that the production of stimulating antibodies or the release of soluble HL-A antigens were probably not responsible for the effect, but rather the release of nonspecific mitogens. Mitogens were also released when lymphocytes specifically sensitized to HL-A antigens were confronted with the corresponding antigens. In addition, supernatants from the latter cultures were competent to inhibit migration of lymphocytes from capillary tubes and to transform normal lymphocytes into a cytotoxic state expressed on fibroblast targets. However, the supernatants by themselves were not cytotoxic to the fibroblasts. When the mixed lymphocyte cultures used for production of the supernatants were contaminated with granulocytes a supernatant was obtained that by itself damaged the fibroblast monolayers.