THE PRESENCE OF A C1-INHIBITOR-LIKE MOLECULE (C1-INH-L) ON HUMAN SPERM - ITS INVOLVEMENT IN SPERM MOTILITY

PROBLEM: An 88-92-kDa C1-inhibitor-like molecule (C1-INH-L) was previo usly identified to elicit cytotoxic sperm antibody response in inferti le men and women. Here, we document that it is present on the human sp erm surface and could be detected by an enzyme-labeled immunoglobulin G (IgG) fraction of anti-human C1-INH antibody. METHOD OF STUDY: Weste rn blot analysis, enzyme-lined immunoadsorbent assay (ELISA) and compu terized sperm motion analysis. RESULTS: The existence of C1-INN-L on t he sperm surface is calcium independent. Phosphatidylinositol-specific phospholipase C (PIPLC), EDTA, and acid (pH 3.0) could not remove the C1-INH-L from sperm, but trypsin did, Activated C1s was able to bind to the sperm surface. Immunofluorescence studies localized the protein to the head and midpiece of the sperm membrane. The C1-INH-L exists o n both uncapacitated and capacitated sperm surfaces, which suggests th at this protein is a sperm-surface protein. The heat-treated (56 degre es C, 30 min) IgG fraction of anti-C1-INH greatly reduced the percenta ge of motile spermatozoa and the progressive and path velocities in th e absence of complement, CONCLUSION: Our data suggest that C1-INH is a sperm membrane-anchored protein that may have complement and sperm mo tility regulatory function.