Cellular immunity during pregnancy. I. Proliferative and cytotoxic reactivity of paraaortic lymph nodes.

The possibility of changes in immune reactivity during pregnancy was studied by measuring cellular immunity in vitro of the paraaortic (PA) lymph nodes, which drain the uterus in pregnant mice. The proliferation of PA lymph node cells from primiparous pregnant C57Bl/6J mice, in mixed lymphocyte cultures (MLC) against alloantigens, was lower in magnitude, but had the same kinetics, as the response of virgins. This was observed in syngeneic and allogeneic (to DBA/2J) pregnancies, and using the paternal as well as third party allogeneic stimulators. The response was depressed by day 8 of gestation and returned to normal two days after delivery. The decrease was not due to an active suppressor mechanism, as assayed by mixing experiments. Irradiation (1500R) of the lymphocytes from pregnant mice, prior to mixing with cells from virgins, did not reveal the presence of a radioresistant suppressor cell. In contrast to the MLC results, no differences were found between lymphocytes from pregnant and virgin mice in their ability to develop MLC-generated cell-mediated lympholysis (CML) against alloantigens, as measured in a chromium release assay. The PA lymph node cells from pregnant animals bearing allogeneic fetuses also did not show evidence of in vivo sensitization to the paternal alloantigens. Therefore, the local nodes draining the uterus from primiparous pregnant animals bearing syngeneic or allogeneic fetuses show a nonspecific decrease of MLC proliferation while retaining the capacity to generate normal CML activity.