Lymphoid response to pregnancy and pseudopregnancy in the rat.

Differences in weight, while cell density and differential white cell count of the thymus, spleen, iliac and popliteal lymph nodes of virgin, 10 days outbred pregnant, 10 days inbred pregnant, 10 days pseudopregnant, and 40 days outbred post-coitum rat were examined. Compared with virgin animals, significant weight gain occurred only in the thymus, spleen and iliac lymph nodes of the outbred group. Significant weight loss from the thymus and iliac nodes, and significant reductions in white cell density of the spleen and popliteal nodes occurred in delivered animals when compared with the virgin group. During pseudopregnancy significant weight loss occurred from the thymus, spleen and popliteal lymph nodes compared with the inbred group, and from the iliac lymph nodes compared with the virgin group. No significant differences were observed between the proportions of proliferating cells in the lymphocyte populations of the thymus, spleen, iliac and popliteal lymph nodes of the virgin group. In the outbred group the proliferating populations of all four tissues rose significantly above virgin levels, while in the inbred group only the iliac lymph nodes showed any significant rise above the virgin value. These findings are discussed in relation to the maternal immunological response to pregnancy.