In vitro studies of cell-mediated immunity. I. Induction of lymphocyte transformation by a soluble "mitogenic" factor derived from interaction of sensitized guinea-pig lymphoid cells with specific antigen

Abstract

Guinea-pigs were immunized with emulsions of protein antigens in Freund's complete adjuvant. Draining lymph node cells were cultured for 20 hours together with the immunizing antigen; after harvesting, the culture supernatants were added to fresh lymphocytes from allogeneic or autochthonous guinea-pigs, and these `recipient' cells were maintained in culture for 3 days. Uptake of [<sup>3</sup>H]thymidine was measured during the last 18 hours of culture, and revealed that the lymphocyte culture supernatants induced greater thymidine uptake by the `recipient' lymphocytes than could be expected from the amount of antigen present in the cultures. The soluble factor which mediates this effect was termed `mitogenic factor'.

Analysis of this phenomenon revealed that the mitogenic factor was only generated by interaction between sensitized lymphocytes and the specific antigen used for sensitization; but that once induced, the soluble mitogenic factor was equally active on non-sensitized and sensitized lymphocytes. It is suggested that the mitogenic factor contributes towards the expression of cell-mediated immunity and that it may participate in regulation of the immunological response.