Longitudinal studies showing alterations in the levels and functional response of T and B lymphocytes in human pregnancy.

Altered blood levels of T and B lymphocytes were found in the first half of human pregnancy. A total of twenty-two women were tested, using direct or indirect rosetting assays or the fluorescence-activated cell sorter, to determine the levels of peripheral blood T and B cells. In all cases, an inversion of T- and B-cell levels was observed, i.e. T-cell levels were decreased and B-cell levels (as measured by the presence of surface immunoglobulin or the presence of B-cell surface antigens) were increased. This inversion was exhibited as early as 1 week post-implantation. Lymphocytes from two fo the women were also examined for stimulation with phytohaemagglutinin (PHA) and pokeweed mitogen (PWM) at intervals during gestation, and the amount of [3H]thymidine uptake was compared to that of two non-pregnant women tested at each interval. The values obtained for the pregnant women with PHA were markedly lower, and with pokeweed mitogen slightly lower, than those of non-pregnant controls. However, the PHA and PWM values in the pregnant women returned to levels similar to those of the nonpregnant women shortly after the T- and B-cell levels returned to normal. Thus the decrease in the response of the lymphocytes to mitogens during early pregnancy appears to parallel the numerical deficiency of T cells.