Leukocytes including monocyte/macrophages, granulocytes, and T lymphocytes were localized in the corpus luteum (CL) of pregnant and pseudopregnant rats using monoclonal antibodies reactive with lineage-specific antigens. Neutrophilic granulocytes and monocytes/macrophages were found to be the most abundant leukocyte populations in the CL during both pregnancy and pseudopregnancy. The density of neutrophilic granulocytes (MCA 149-reactive cells) increased approximately 2-fold after mating, to peak on Day 9 of pseudopregnancy (214 +/- 13 positive cells/0.125 mm2 grid area) and Day 10 of pregnancy (216 +/- 12/grid area), and then declined in later stages of CL life. In pregnant rats, monocytes/macrophages positive for the monoclonal antibody ED1 were most numerous during early CL life when they were approximately 6-fold more plentiful than at luteolysis (153 +/- 14/grid area at Day 5 vs. 25 +/- 2 at 2 days postpartum). In pseudopregnant rats, the density of ED1-positive cells declined approximately 5-fold during the life span of the CL (124 +/- 17/grid area at Day 2 vs. 20 +/- 2 at Day 13) prior to a second, somewhat lesser peak at luteal regression (84 +/- 12 at Day 15). Fewer monocyte/macrophages within the CL were found to express antigen reactive with the monoclonal antibody ED2, which is characteristically a marker for tissue-macrophages (7% of the density of ED1-positive cells at Day 5 in the pregnant group and 13% at Day 2 in the pseudopregnant group); and while there was an approximately 60% reduction in the number of ED2-positive cells during pregnancy, these cells were found not to fluctuate significantly in number over the course of CL life in pseudopregnant animals.(ABSTRACT TRUNCATED AT 250 WORDS)

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