Alpha-fetoprotein and human lymphocyte subpopulations.

Peripheral blood lymphocytes were incubated with varying concentrations of alpha-fetoprotein and enumerated for total and ""active'' T lymphocytes, B lymphocytes, and their proliferative responses to phytohemagglutinin. No significant effect was observed on total T or B lymphocyte proportions. However, there was a dose-related increase in proportions of the so called "active" T lymphocytes. The response of human lymphocytes to phytohemagglutinin was markedly depressed. The alteration in the proportion of active T cells and the inhibition of T lymphocyte response to phyto hemagglutinin by alpha-fetoprotein occurred at higher concentrations than are present in amniotic fluid, serum of pregnant women, or serum of adults, but well within the range reached in fetal serum. The immunoregulatory role of alpha-fetoprotein is discussed.