SEVERAL VASCULAR COMPLEMENT INHIBITORS ARE PRESENT ON HUMAN SPERM

We have previously reported that the complement inhibitor SP-40,40 is present in human seminal plasma. We also speculated that other inhibit ors of the vascular complement system may be present within semen for the purpose of providing protection for sperm against complement withi n the male and/or female genital tract. In this study, we examined hum an seminal plasma and spermatozoa for the presence of several major co mplement regulatory proteins. We detected the presence of decay-accele rating factor (DAF) and CD59 and have confirmed the presence of Membra ne Cofactor Protein (MCP) and SP-40,40 on human sperm. As an approach to the possible functional significance of these inhibitors on sperm m embranes, the presence of two key complement components, C3 and C9, in seminal plasma was used as a criterion for an active complement syste m. We failed to detect C9 in seminal plasma and showed that its concen tration was less than 5% of the level detected in blood plasma. C3 was also undetectable in seminal plasma; as assessed by Western transfer, its level was less than 0.3% of that in blood plasma. The low level o r indeed the absence of key components of the complement system in sem inal plasma-together with the finding that human sperm possess an exte nsive array of the vascular complement inhibitors, some of known physi ologic significance-strongly suggests that their role on sperm is to p rotect sperm from complement lysis in the female rather than the male genital tract.