Expression of progesterone receptor and progesterone-induced blocking factor in the spleen during early pregnancy in ewes

The spleen plays a key role in immune regulation. Progesterone (P4) exhibits different immunological effects through binding to different types of receptor. In the present study, splenic samples were obtained at day 16 of non-pregnancy and days 13, 16, and 25 of pregnancy to study the expression of P4 receptor (PGR) and P4-induced blocking factor (PIBF) in ewes through quantitative real-time PCR, Western blot and immunohistochemistry analysis. Our results showed that the relative expression levels of PGR and PIBF mRNA increased from day 13-16 in pregnant ewes, but decreased from day 16-25, and the 26 kDa isoform of PGR and the 22 kDa variant of PIBF were down-regulated in the spleens at day 25 of pregnancy compared with expression at day 16 of the oestrous cycle and days 13 and 16 of pregnancy. The immunohistochemistry test results confirmed that PGR and PIBF proteins were localized in the cytoplasm of cells in the capsule, trabeculae and splenic cords. This paper reports for the first time that the 26 kDa isoform of PGR and the 22 kDa variant of PIBF were down-regulated during early pregnancy, which may be essential for normal pregnancy in ewes.