Immune response to first mating in the female rat.

The iliac and popliteal lymph nodes were removed from 110 Sprague Dawley female rats taken from a closed colony. All were killed at age 12-13 wk in groups of 10 animals; one group of virgin controls, the others at 2-day intervals during the first 10 days of either inbred or allogeneic poregnancy. Every tenth section of the lymph nodes was stained with methyl green pyronin and counts were made of the large pyroninophilic cells in the thymus-dependent area of the cortex for evidence of T cell proliferation and the plasma cells in the medulla for evidence of B cell proliferation. After allogeneic mating significant T cell proliferation was evident in both the iliac and popliteal lymph nodes by the second post-coital day and this proliferative response was sustained until the sixth postcoital day and recurred on the tenth post-coital day. After inbred mating transient T cell proliferation was observed on the fourth post-coital day in the iliac lymph nodes. Significant B cell proliferation occurred in the iliac lymph nodes on the second day of allogeneic pregnancy and on the fourth day of inbred pregnancy, being sustained in both until the end of the observation period. These results suggest that allogeneic mating and possibly semi-allogeneic implantation induce an immune response in the female rat.