Investigation of lymphocyte subpopulations and hypersensitivity skin tests during the menstrual cycle and pregnancy.

Cell-mediated immune responses were examined during the menstrual cycle of 10 healthy females and in 90 pregnant females, 10 for each month of gestation, and in 10 females 2--4 weeks after normal delivery. Lymphocytes and their subpopulations and PPD hypersensitivity skin tests were investigated. The lymphocyte subpopulation T-cells showed statistically significant depression at the time of ovulation (P less than 0.01) and during the entire period of gestation (P less than 0.001) with recovery in the post-partum period. There was borderline PPD skin response during pregnancy which became positive after parturition. These changes were demonstrated to be specific to conception but the exact mechanism of the T-cell depression is not known. There was a corresponding rise in the B-cell count.