Molecular cloning of the human
complement inhibitor SP-40,40, has revealed strong homology to a major rat and ram Sertoli cell product,
sulfated glycoprotein-2, known also as
clusterin. This study reports the purification and characterization of human seminal
clusterin. Two-dimensional gel electrophoresis revealed charge differences between
clusterin purified from semen and the serum-derived material. Both preparations demonstrate comparable hemagglutination (clustering) activity and inhibition of
C5b-6 initiated
hemolysis. The average
clusterin concentration in normal seminal plasma is considerably higher than that found in serum. Mean seminal plasma
clusterin concentrations were significantly lower in
azoospermia caused by obstruction or seminiferous tubule failure than with
oligospermia or normospermia. Only men with vasal agenesis had undetectable seminal
clusterin, suggesting that some of the seminal
clusterin is produced by the seminal vesicles. Immunofluorescence of human spermatozoa revealed that
clusterin was detected on 10% of spermatozoa, predominantly those that were immature or had abnormal morphology. A pilot study of 25 patients suggests that seminal
clusterin concentration, together with sperm motility and morphology, is correlated with the fertilization rate in vitro. The function of seminal
clusterin is unknown. Its extensive distribution in the male genital tract and its high concentration in seminal plasma suggests an important role in male fertility.