HUMAN SEMINAL PLASMA INHIBITION OF COMPLEMENT

  • 1 January 1980
    • journal article
    • research article
    • Vol. 96  (4) , 582-591
Abstract
Human seminal plasma contains chemically and biologically distinct factors which inhibit lymphocyte functions and the serum bactericidal and opsonic activities associated with the killing of gram-negative organisms. Because of the direct association between complement (C) action and serum bactericidal and opsonic activities, inhibition of C may be one of the possible mechanisms of action of seminal plasma immunoinhibitory factors. C component hemolytic activity was measured for C3 and C4 in serum Neisseria gonorrhoeae and Escherichia coli bactericidal reaction mixtures with and without addition of seminal plasma. In the presence of seminal plasma, where there was no bactericidal action, C3 titers wwere were reduced to .apprx. 50% of the titers in the reactions with C donor serum. The C3 titers were lower than in the reaction mixtures with immune serum and C donor serum, where N. gonorrhoeae bactericidal activity occurred. Individual human seminal plasma specimens depressed CH50 [hemolytic whole complement] activity of pooled normal human sera up to 50% of normal levels. There were no differences in inhibition by seminal plasma specimens from normal or vasectomized men. Treatment with seminal plasma depressed the functional activity of C1 and C3 by > 50%. Seminal plasma also inhibited alternate pathway activity. Cleavage of factor B was demonstrated. The seminal plasma factor which inhibited C was of low MW. DPF [diisopropyl-fluorophosphate] blocked the seminal plasma C-inhibitory factor. Amidolytic activity for serine protease substrate could not be demonstrated. It is likely that the seminal plasma C inhibitor is a protease and/or a protease inhibitor acting singly or in combination.