Evidence for NK cells in equine endometrial cups (43.29)

Abstract

Abstract Placentation during equine pregnancy is distinguished by a unique subset of trophoblast cells that invade the endometrium and form discrete structures termed the endometrial cups. Shortly after the trophoblasts invade, there is a dramatic infiltration of maternal leukocytes which accumulate around the cups. Our lab has previously characterized the infiltrating leukocytes as primarily CD3+ cells with substantial CD4+ and CD8+ subpopulations. Here, we identify expression of the NK cell marker NKp46 in peripheral blood mononuclear cells (PBMC) and endometrial cup lymphocytes (ECL). PCR primers were developed to detect the equine homolog of NKp46 and expression was detected in resting and stimulated lymphocytes using standard PCR. Quantitative real-time PCR primers and standards were used to quantitate expression in CD3+ and CD3- sorted lymphocytes. NKp46 gene expression in CD3- lymphocytes was 10-fold higher than in CD3+ cells. Levels comparable to CD3-depleted lymphocytes were detected in frozen tissue sections of endometrial cups. The highest levels of expression were detected in leukocytes isolated from the endometrium surrounding the cups of five mares during early pregnancy (days 43-46). NKp46 expression levels were 7-43 fold higher in ECL compared to paired PBMC (p=0.04). Coincident CD3γ expression was lower in all ECL compared to paired PBMC (p=0.03). These data provide the first evidence for the presence of NK cells in the equine endometrium during pregnancy.