Synergistic effect of albumin and transferrin on the mitogen stimulation of human mononuclear leukocytes in serum-free medium.

It is well known that optimal lymphocyte proliferation in vitro requires the supplementation of the culture medium with serum, the usual concentration varying between 5% and 20%. In an attempt to reduce the serum requirement of lymphocytes in culture, we have found that supplementation of RPMI 1640 medium with as low as 1% human serum allows an adequate proliferation of human peripheral blood lymphocytes cultured in microtiter plates in a CO2 atmosphere and stimulated by phytohemagglutinin. In serum-free cultures, the addition of albumin (4 mg/ml) or transferrin (10 micrograms/ml) allows a significant proliferation of lymphocytes. This permissive effect was cell concentration-dependent, being maximal at 2 X 10(5) cells/well. The simultaneous addition of albumin and transferrin produced a synergistic effect, the phytohemagglutinin-induced proliferation being higher than expected from the addition of the two proteins separately. This synergistic effect was observed in 89% of the subjects studied (8 out of 9). These results suggest that albumin and transferrin are required for optimal lymphocyte proliferation and that the serum can be partially substituted by these two proteins.