Detection of a CBG-like protein in human Fallopian tube tissue

The acrosome reaction (AR), a modified exocytotic process, is prerequisite for successful mammalian fertilization. The protein component that is responsible for the AR-inducing activity of human follicular fluid, has been found to be immunologically identical with corticosteroid-binding globulin (CBG), which is well characterized and serves as a transport protein for progesterone and cortisol in the plasma. Our findings have shown that the CBG-like protein is expressed by endothelial cells of the Fallopian tube depending on the hormonal cycle. In the culture medium of human epithelial tubal cells, the CBG-like protein was detected by Western blot analysis. The protein was also found in biologically active form in human tubular fluid. Our investigations strongly indicate that human Fallopian tube cells actively express and secrete a CBG-like progesterone-binding protein, which might play a role in the in vivo modulation of human sperm AR.