Distribution patterns of leucocyte subpopulations expressing different cell markers in the cumulus - oocyte complexes of pregnant and pseudopregnant mice

Abstract

The nature of leucocyte subpopulations expressing different cell markers around the cumulus–oocyte complex (COC) of pregnant and pseudopregnant mice was investigated in the present study. Immunolabelling for CD4, CD8, CD14, CD45 and CD163 and transmission electron microscopy were used to determine whether leucocytes differ between pregnant and pseudopregnant mice. Sexually mature female BALB/c mice (n = 36; 18 pregnant, 18 pseudopregnant) were stimulated to superovulate with pregnant mare’s serum gonadotropin and human chorionic gonadotrophin, then mated with either fertile or vasectomised males. Postovulatory oocytes were collected after mating. The cumulus cell masses of the pregnant group contained spermatozoa between cells and were more variable than COCs of the pseudopregnant group. Streptavidin–biotin–peroxidase immunohistochemical labelling of the cell markers CD4, CD8, CD14, CD45 and CD163 showed that there were fewer leucocytes in the COCs of the pseudopregnant group compared with the pregnant group. Transmission electron microscopy revealed that often there were macrophage-like cells containing spermiophagic bodies between the cumulus cells. These observations suggest that, together with other cumulus cells and oviducal cells, these macrophage-like cells may be involved in removing unsuitable or excess spermatozoa and, therefore, in maintaining a suitable microenvironment for normal fertilisation.