Serum factors affecting the incorporation of [3H]thymidine by lymphocytes stimulated by antigen. IV. Comparison of enhancement by heated (56 degrees C) serum and by 2-mercaptoethanol.

Serum preheated to 56 degrees C and 2-mercaptoethanol (ME) both enhance the stimulation (%) by antigen of [3H]thymidine incorporation by lymph node cells from immunized rabbits. The enhancements show several similar features suggesting a common mechanism. Both enhancements show (i) non-specific components, affecting [3H]thymidine incorporation in control and antigen-treated cultures proportionately, and (ii) antigen-specific components, having a greater proportionate effect on antigen-treated cultures than on control cultures. The non-specific components, in combination, are approximately additive. The specific components, in combination, are non-additive (mutually exclusive). With both preheated serum and ME the specific component of the enhancement is most evident late in the culture period and is greater at high antigen concentrations. The ME concentration needed for optimum enhancement is reduced if the serum concentration is reduced or if serum is preheated.