Estrous cycle-dependent activity of neutrophils in the porcine endometrium: possible involvement of heat shock protein 27 and lactoferrin.

Neutrophil infiltration into the porcine endometrium is thought to be a specific feature during the follicular phase of the estrous cycle. To specify the localization and distribution of neutrophil granulocytes at different stages of the estrous cycle, porcine uterine samples were evaluated by immunohistochemical methods using anti-bovine lactoferrin (LF) antibody. Additionally, blood samples were collected from 30 pigs at different stages of the estrous cycle with a special focus on peri-estrous phase. Manual 100-cell differential counts were performed on routinely stained blood smears and evaluated statistically. Finally, the expression of granulocyte-colony-stimulating factor (G-CSF) and heat shock protein 27 (HSP 27), which are known to influence activation of the neutrophilic granulocytic lineage, was analyzed in porcine uteri using immunohistochemistry. Results show that LF is expressed regularly in the cytoplasm of neutrophil granulocytes. An increasing infiltration of subepithelial neutrophils was detected in the follicular phase. The highest number of intra- and subepithelial LF-positive cells was found on d 2 of the estrous cycle. Maximum level was followed by a strong decrease on d 3. Blood analysis revealed that the percentage of neutrophil granulocytes was significantly lower at d 2 (26.2+/-11.1%) than d 1 (42.1+/-11%) of the estrous cycle. HSP 27 staining was predominantly localized to luminal epithelium (LE) and glandular epithelium (GE) depending on stage of the estrous cycle. Strong immunostaining of HSP 27 is only found in LE during estrus. At d 2 of the estrous cycle, HSP 27 immunoreactivity in LE and superficial GE is reduced but moderate staining is found in deep GE. G-CSF immunostaining is uniformly not detected in endometrial cells of cyclic pigs. In conclusion, there is a clinically relevant relationship between neutrophil count in the blood and neutrophil infiltrate in the endometrium of the pig during the estrous cycle. This association may reflect the possibility of translocation of neutrophils from the blood to the endometrium up to d 2 of the estrous cycle. Additionally, HSP 27 could be a good candidate involved in migration and/or function of neutrophils within the porcine endometrium.

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