Human serum-free mixed lymphocytes response: the stereospecific effect of insulin and its potentiation by transferrin.

We have established a serum-free human mixed lymphocyte response (MLR). Proliferative unidirectional responses are discerned using peripheral blood leukocytes obtained from unrelated individuals and family members mismatched for HLA while MLR conducted between HLA identical siblings are negative. Resting lymphocytes lack insulin and transferrin receptors; activated lymphocytes are known to express insulin and transferrin receptors. Interestingly, physiologic concentrations of insulin and transferrin synergistically potentiate DNA synthesis in serum-free allogeneic cultures. To verify that the insulin effect was due to a stereospecific interaction between insulin and classical, high-affinity insulin receptors, insulin and a series of insulin-like peptides were compared in their ability to bind to alloactivated T cells and amplify the MLR. The results demonstrate the stereospecificity of the insulin effect in the MLR and underscore the importance of lymphocytic insulin receptors in the process of lymphocyte activation.