COMPLEMENT REGULATORY PROTEINS ON THE SPERM SURFACE - RELEVANCE TO SPERM MOTILITY

PROBLEM: To determine whether complement regulatory proteins are prese nt on human spermatozoa and whether antibodies to these proteins adver sely affect sperm motility. METHOD OF STUDY: Human sperm membrane prot eins were solubilized and subjected to polyacrylamide gel electrophore sis followed by Western blot analysis against antibodies to complement component 1 inhibitor (C1-INH), decay-activating factor (DAF; CD55), membrane cofactor protein (MCP; CD46), and homologous restriction fact or (HRF; CD59). Spermatozoa, obtained by a swim-up technique, were inc ubated in medium (control 1) and medium supplemented with antibodies t o human albumin (control 2) and antibodies to these complement regulat ory proteins. We used a computerized sperm motion analysis to determin e the effect of these antibodies on sperm motion characteristics. RESU LTS: Complement regulatory proteins such as C1-INH, CD55, CD46, and CD 59 were found in the sperm extracts as shown by Western blot analysis. The heat-treated (56 degrees C, 30 min) IgG fraction of antibodies to these proteins significantly reduced sperm motility in general and ot her motion parameters. Addition of complement did not affect these res ults except in the antibodies to CD46 in which the reducing action was further amplified. CONCLUSIONS: Our data suggest that C1-INH, CD55, C D46, and CD59 are present on the sperm surface. These proteins may hav e biological functions, such as affecting sperm motility, besides the complement regulatory functions. In infertile men and women with antib odies that recognize one or more of these complement regulatory protei ns, there may be problems related to poor sperm motility and survival in the reproductive tracts.