The role of toll-like receptors 2 and 4 in the pathogenesis of feline pyometra.

Pyometra is the most common uterine disease in queens. To protect itself from infection, the female reproductive tract possesses several immune mechanisms that are based on germline-encoded pattern recognition receptors (toll-like receptors [TLRs]). The aim of our study was to examine endometrial immunolocalization of TLR2/4, study the influence of lipopolysaccharide (LPS) and tumor necrosis factor (TNF) α on messenger RNA expression of both receptors in pyometric queens, and compare these patterns between estrous cycling queens and those hormonally treated with medroxyprogesterone acetate (MPA). Thirty-six queens, ranging in age from 7 months to 11 years, were allocated into seven groups (anestrus, estrus, mid-diestrus and late diestrus, short-term and long-term hormonally treated queens, and pyometric queens). At the messenger RNA level, the real-time polymerase chain reaction was applied, whereas at the TLR2/4 protein level, the expression was tested by immunohistochemistry. In queens at estrus, gene expression of TLR2 was upregulated after stimulation of endometrial explants by TNF (P < 0.001) and by TNF together with the LPS (P < 0.01). Moreover, gene expression of TLR2 was significantly upregulated after stimulation by TNF (P < 0.001) and LPS (P < 0.01) explants derived from queens that had been long-term hormonally treated with MPA. Endometrial gene expression of TLR4 was significantly upregulated after incubation of explants with TNF (P < 0.001) in queens at estrus and with LPS (P < 0.05) in queens short-term hormonally treated with MPA. Immunolocalization reported that TLR2/4 receptors are mainly localized in the surface and glandular epithelia. These data show that short-term and especially long-term administration of progesterone derivatives impairs TLRs in the endometrial epithelium, presumably enabling pathogens to break through this first natural barrier and thereby increase the risk of pyometra development.