Interaktionen von Spermien mit Immunzellen des Rinderuterus

It is well known in porcine and equine species that there is a prominent influx of immune cells into the uterus during estrus after insemination and that these cells play a role in the selection of sperm. The goal of this study was to investigate the influx of immune cells, particularly polymorphonuclear neutrophils (PMNs) and mononuclear cells (MNCs), into the bovine uterus after artificial insemination, to clarify their role in the selection of sperm, and to determine the role of these immune cells in producing the reduced fertility rates observed after insemination with reduced numbers of sperm, as is necessary with sex sorted sperm. In the framework of this project, we inseminated 147 preovulatory cows and heifers with various preparations of sperm and evaluated individual experimental groups separately. The sperm preparations used included: fresh sperm, cryopreserved sperm, sex sorted fresh sperm, sex sorted cryopreserved sperm, epididymal sperm, and cryopreserved epididymal sperm. Following insemination, uteri were flushed with a physiological salt solution and the cells recovered from the uteri were identified and counted. Each animal was subjected to a blank flushing (without insemination) prior to the experimental insemination and the cell counts from this blank flushing were compared to those from the same animal flushed after insemination. In addition, cell counts resulting from the different sperm preparations were compared with each other. The flushings were also evaluated with respect to bacterial contamination. A subgroup of 60 animals were inseminated with fresh sperm and flushed at different time points following insemination to determine if there was a point of maximal PMN infiltration. In the remaining 87 animals, uteri were flushed after six hours, the time of maximal response in horses. A total of 136 biopsies were taken from the corpus uteri and uterine horns and these were examined by scanning electron microscopy. In addition, 27 of the biopsies were examined histologically under the light microscope. The results of the examination of the animals inseminated with unmanipulated fresh sperm and flushed at different intervals revealed no time point at which an influx of leukocytes was evident. Results from the 86 flushings following insemination with preparations used for biotechnological manipulation also showed no influx of immune cells with fresh sperm. Cryopreserved sperm and higher volumes of epididymal sperm (6 ml) did result in low but detectable levels of leukocyte infiltration; however, the ratio of leukocytes to sperm cells was so low that there could not have been any effect on sperm selection. In heifers, none of the preparations caused measurable leukocyte infiltration. Scanning electron microscopy and the light microscope analysis gave no evidence of immune infiltration in the endometrium and only a small number of secretory cells and mobile immune cells in interstitial connective tissue, which is physiological during estrus. Therefore porcine and equine uteri are different not only anatomically but also functionally from the bovine uterus. The bull ejaculates in the vagina and the sperm cells must pass through the cervix where they are selected both physically and biochemically. This takes place at the uterotubal junction in other species, including the boar and stallion, which ejaculate in the uterus and exhibit immunological sperm selection. Sperm induced leukocyte infiltration in the bovine uterus is not sufficiently strong to affect sperm selection and can not be responsible for the decreased fertility rates observed with sexed sperm.