The response of iliac lymph nodes to the fetal allograft.

It is well known that large pyroninophilic cell proliferation in regional lymphoid tissue preceds and accompanies cell-mediated immunological reactions. In the present study of lymph node responses in the pregnant rat it was found that there were no significant differences between large pyronionphilic cell counts from iliac nodes (which drain the uterus) and popliteal lymph nodes, in either virgin or delivered rats. The iliac large pyronionphilic cell count, however, rose significantly in early pregnancy, fell in late pregnancy and returned to virigin levels after delivery, whereas the popliteal large pyronionphilic cell count showed no significant change during pregnancy. It is also well established that plasma cell proliferation in regional lymphoid tissue precedes and accompanies antibody synthesis. In the present studies the plasma cell count in iliac nodes rose significantly and progressively during pregnancy, while in popliteal nodes it rose significantly only in late pregnancy. There was no significant difference between the plasma cell counts of iliac and popliteal nodes in virgin animals. In delivered animals the iliac plasma cell count was significantly greater than the popliteal count, and both were significantly greater than the corresponding virgin counts. It is concluded that the mother possesses the capacity for rejecting the conceptus, but there is some mechanism which blocks rejection.