<em>In Vitro</em> 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.

Guinea-pigs were immunized with emulsions of protein antigens in Freund&#39;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 &#39;recipient&#39; cells were maintained in culture for 3 days. Uptake of [&#179;H]thymidine was measured during the last 18 hours of culture, and revealed that the lymphocyte culture supernatants induced greater thymidine uptake by the &#39;recipient&#39; lymphocytes than could be expected from the amount of antigen present in the cultures. The soluble factor which mediates this effect was termed &#39;mitogenic factor&#39;. 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. [ABSTRACT FROM AUTHOR]