title: Complement-inhibiting activity of seminal plasma.
abstract: Human seminal plasma has an anticomplement effect that can be measured by a standard immune hemolytic assay. We found that about 20% of samples lack complement-inhibiting activity. To determine the anatomical origin of a complement inhibitor, inhibition of hemolysis was measured in seminal plasma samples that were primarily of prostatic, vesicular, or epididymal/testicular origin, as well as in seminal plasma from vasectomized men. All samples contained complement-inhibiting activity, although epididymal fluid showed nearly twice the amount. Therefore, the factor (or factors) is ubiquitous in secretions of the male reproductive tract. Complement-inhibiting activity is eluted in two high-molecular-weight peaks upon gel filtration. We found evidence that the inhibitory factor is not lactoferrin, a proteinase, or one of the proteinase inhibitors known to be present in human seminal plasma. It seems likely that the complement inhibitor in seminal plasma protects gametes and reproductive tissues from complement-mediated damage.
mesh_terms: D002850:Chromatography, Gel; D003169:Complement Inactivator Proteins / Q000032:analysis*; D010450:Endopeptidases / Q000032:analysis; D006801:Humans; D007781:Lactoferrin / Q000032:analysis; D008297:Male; D008970:Molecular Weight; D011863:Radioimmunoassay; D012661:Semen / Q000276:immunology*
chemical_list: D003169:Complement Inactivator Proteins; D010450:Endopeptidases; D007781:Lactoferrin