New insights into the innate immune defences of the equine endometrium: in situ and in vitro expression pattern of beta-defensin

摘要

Equine endometrial diseases are a frequent cause of subfertility causing financial loss. Degenerative and inflammatory diseases are often associated with alterations of the innate immunity and beta-defensin has been identified within the equine endometrium. The aim of this study was to further characterize the expression of beta-defensin protein within in the equine endometrium by immunohistochemistry. For in situ investigations, endometrial samples were collected from 26 mares once at different stages of the oestrus cycle and from 3 mares repeatedly during the same oestrus cycle (days 0, 5, 10, 13, 16, 19 and 21; day 0 is defined as ovulation day). In vitro examinations were performed on cultured epithelial cells obtained from endometrial specimens of 15 mares. The following results were obtained: Endometrial tissue sections of the 26 mares were either without pathological alterations (n = 3) or showed varying degrees of endometritis, endometrosis and/or angiosclerosis. Beta-defensin protein was mainly expressed within the cytoplasm of epithelial cells lining the lumina! surface (100%, 26 mares) and glandular ducts (69%, 18 mares) and rarely within the nucleus of these cell populations (8% and 19%, respectively). The vast majority of cells showed either a cytoplasmic or a nuclear immunostaining. A simultaneous cytoplasmic and nuclear immunoreaction within the same cell was seldom observed (3 mares, up to 1% of the analyzed cells). Mid and basal glands without endometrosis were rarely immunopositive (nuclear immunostaining: 5 mares; cytoplasmic labelling: 1 mare). In contrast, endometrotic glands often contained small to moderate numbers of epithelial cells with a cytoplasmic immunosignal (15 of 19 cases; 79%). In regard to the repeatedly collected biopsies of three mares, the percentage of immunopositive cells and the calculated immunoreactive scores were highly variable over the course of the oestrus cycle and between individual mares. In regard to cultured endometrial epithelial cells (n=15 mares), a positive beta-defensin immunosignal was observed in almost all cells (97% of 521 analyzed cells) and was mainly located solely within the cytoplasm (76% of the analyzed cells), less frequently within the cytoplasm and nucleus (17%) and rarely only within the nucleus (4%). These results lead to the following conclusions: the antimicrobial peptide beta-defensin can be detected within the equine endometrium, the almost complete lack of beta-defensin immunostaining of unaltered glands could predispose to bacterial colonization of glandular lumina, the frequent beta-defensin immunoreaction of endometrotic glands indicates their functional alteration also in regard to the synthesis of beta-defensin, the variations in regard to the beta-defensin immunostaining between individual mares suggest a complex regulation of the beta-defensin expression, possibly under the influence of genetic factors, the beta-defensin immunostaining of cultured epithelial cells is similar to the in situ situation and therefore the cell culture system may be used to examine pathophysiological mechanisms that modulate the beta-defensin expression within equine endometrial epithelial cells. In particular, further studies should investigate if an association exists between the beta-defensin expression patterns within the endometrium and the susceptibility of a mare to develop endometritis and/or endometrosis.