T helper lymphocyte depression in early human pregnancy.

Peripheral blood lymphocyte subclasses were determined in 60 women with normal pregnancies, 20 from each trimester, and in 20 controls using automated flow cytofluorimetry. The cells were stained with the monoclonal antibodies OKT3, OKT4 and OKT8 to stain total T cells, T helper and T suppressor-cytotoxic lymphocytes, respectively. A polyvalent rabbit anti-human Ig serum was used to stain B lymphocytes. Absolute numbers of T lymphocytes were significantly reduced in both the first and second trimesters. This was due to a significant decrease in T helper lymphocytes and a smaller, statistically not significant, reduction in the number of T suppressor lymphocytes. There was no significant change in lymphocyte subclasses during the third trimester. Total lymphocyte numbers were normal throughout pregnancy.