Pregnancy-induced morphologic changes in lymphocytes; an experimental study on materno-fetal tolerance in the rat

Morphological changes in lymphocyte nucleoli were examined in the course of pregnancy in rats. Small amounts of lymphocytes became activated, most of them producing micronucleoli. These findings show the same changes as found in the course of pregnancy in women. Subcutaneous administration of human placental eluate to non-pregnant rats induced a low degree of activation and high micronucleoli formation, dependent on the dose of placental antigen. Repeated administration of increasing doses of placental eluate revealed almost the same morphological changes in lymphocyte nucleoli as seen in normal pregnancy. This is considered an experimental verification that the morphological changes in lymphocyte nucleoli during pregnancy are due to permanent and gradually increasing doses of foreign antigen.