INTERACTION OF THE HUMAN EPIDIDYMAL PROTEIN CD52 (HE5) WITH EPIDIDYMAL SPERMATOZOA FROM MEN AND CYNOMOLGUS MONKEYS

A monoclonal antibody (CAMPATH-1G) against the human lymphocyte surfac e protein CD52, which is similar to the epididymal secretion HE5, was used to ascertain the presence of this protein on maturing primate spe rmatozoa by flow cytometry. The percentage of human viable spermatozoa stained specifically with this antibody increased from sperm in sperm atocoeles (0.5%), to the efferent ducts (3.8%), corpus (47.2%), and ca uda (85.7%) epididymidis. Positive cells revealed staining mainly over the whole tail and postacrosomal region of the sperm head. Spermatozo a (similar to 10%) from both the efferent ducts and corpus epididymidi s took up additional antigen when incubated with human distal cauda ep ididymidal plasma as a source of CD52, and 12-22% of human testicular sperm (from spermatocoeles) took up CD52 from human seminal plasma. In the cynomolgus monkey, nonspecific binding of control IgG was greater than that in human males and net CD52 staining was measurable only on similar to 30% of corpus sperm where it was mainly on the principal p iece. Neither caput nor cauda sperm took up human CD52 upon incubation with human seminal plasma, but an additional 27% of corpus sperm expr essed CD52. Such uptake of CD52 was drastically reduced, or did not oc cur, when seminal plasma had been fractionated by filtration through 0 .1 mu m filters (filtrate II) or 300,000 Da cutoff filters (filtrate I II), respectively. Western blots revealed that CD52 contents were much reduced in filtrate II and nondetectable in filtrate III of seminal p lasma. Similar reduction of CD52 in the filtrate of cauda epididymidal plasma indicates the association of this epididymal secretion with la rge molecular factors and suggests their involvement as carriers in th e in vivo transfer of the secretion onto the epididymal sperm surface. The in vitro uptake of CD52 by some but not all immature sperm and th e detection by Western blotting of much less CD52 in the corpus than t he cauda luminal plasma suggest that the acquisition of this epididyma l secretion by spermatozoa depends on their maturation status as well as the availability of the protein in the epididymal lumen. (C) 1997 W iley-Liss, Inc.