Influence of pre-ovulatory insemination and early pregnancy on the distribution of CD2, CD4, CD8 and MHC class II expressing cells in the sow endometrium

The aim was to investigate the distribution of CD2+, CD4+ and CD8+ lymphocyte subpopulations and MHC class II expressing cells in the sow endometrium following pre-ovulatory insemination and during early pregnancy. Crossbred multiparous sows (Swedish Landrace × Swedish Yorkshire) were inseminated once at 15-20 h before ovulation. The sows were slaughtered at 5-6 h (group I, n=4) after AI or at 20-25 h (group II, n=4) and 70 h (group III, n=4) after ovulation, day 11 (group IV, day 1=first day of standing oestrus, n=3) and day 19 (group V, n=3). Uterine horns were flushed to control for the presence of spermatozoa and neutrophils (groups I-IV) and/or for recovery of oocytes and/or embryos (groups II-IV, control of pregnancy). Cryofixed mesometrial uterine samples were analysed by immunohistochemistry with an avidin-biotin-peroxidase method using monoclonal antibodies to lymphocyte subpopulations and MHC class II molecules. The surface (SE) and glandular (GE) epithelia as well as connective tissue layers in subepithelial (SL) and glandular (GL) areas were examined by light microscopy. Taking all groups and different tissue layers together, the most commonly observed positive cells were CD2+ cells (Pless than 0.001). The largest number of CD2+ cells within the SE was observed in groups I and II, and the smallest number in group V. In the SE and GE, more CD8+ (T cytotoxic) cells were observed than CD4+ (T helper) cells. In the SL and GL, the largest numbers of CD2+, CD4+ and CD8+ cells were found in group V. Taking all groups together, a larger number of CD4+ cells compared with CD8+ cells were found. For the proportion of (CD4+ + CD8+)/CD2+ cells, there were significantly (P≤0.001) lower proportions in the SE and GE than in the SL and GL. A larger number of MHC class II expressing cells in the SE was observed in groups I, II and III compared with the other groups. In the SL, a larger number of MHC class II expressing cells was observed in groups II and V compared with the other groups. In conclusion, the immunomodulation illustrated by the distribution of CD2+, CD4+, CD8+ and MHC class II expressing cells at the attachment sites on day 19, i.e. the low numbers in the surface epithelium and the high numbers in the subepithelial layer, shows that the porcine trophoblast may influence the endometrium to develop the conditions required for embryonic attachment and survival in pigs.