Failure of the human autologous mixed lymphocyte reaction in the absence of foreign antigens.

The autologous mixed lymphocyte reaction (AMLR) is thought to represent the in vitro proliferation of T cells in response to stimulation by autologous histocompatibility antigens present on non-T cells. We have investigated the possibility that xenogeneic determinants act as the stimulating antigens in the human AMLR. Exposure of lymphocytes to fetal calf serum and/or sheep red blood cells during fractionation triggers substantial proliferation of T cells, plaque-forming cell responses, and interleukin 2 production. In contrast, lymphocytes isolated and cultured in the absence of any known foreign substances failed to respond in the AMLR, yet responded significantly when cultured in the presence of fetal calf serum. These results suggest that without exposure to foreign antigens, the human AMLR is difficult to demonstrate in vitro.