Toll-like receptor 2 and 4 expression in the bovine corpus luteum during the different stages of the estrous cycle

The aim of this study was to elucidate the presence of components of the innate immune system in the bovine corpus luteum (CL) by detecting the expression and cell-specific localization of TLR2 and TLR4 during different stages of the estrous cycle in a control study design. Bovine CL samples were collected from a local slaughterhouse and assigned to three groups as follows: developing CL (dCL; n = 6, approx. days 3-6), mature CL (mCL; n = 5, approx. days 8-12), and regressing CL (rCL; n = 5, approx. days 17-19). An upregulation of TLR2 mRNA was detected only in rCL (P < 0.05). Localization of the TLR2 protein was particularly apparent in luteal cells and a prominent immunofluorescent signal corresponding to TLR2 was detected only in rCL. TLR4 mRNA were higher in mCL and rCL compared to dCL (P < 0.05). The presence of the TLR4 protein in bovine CL was clearly detected in the luteal cells of both mCL and rCL. The results of this study suggest a role for TLRs in the development, maintenance, and regression of bovine CL. TLR signaling mediated pathway in luteal cells may involve in the regression of CL via regulation of TLR2 and TLR4.