EXPRESSION OF THE COMPLEMENT REGULATORY PROTEIN CD59 ON HUMAN SPERMATOZOA - CHARACTERIZATION AND ROLE IN GAMETIC INTERACTION

Protectin (CD59) is a complement regulatory protein which blocks the m embrane attack complex during complement activation. CD59 was identifi ed on the human sperm surface by means of H19, an IgG(1) anti-protecti n mouse monoclonal antibody. Using indirect immunofluorescence, flow c ytometry and immunoperoxidase, CD59 was found to be present on the who le plasma membrane including the head and tail of fresh ejaculated, ca pacitated and acrosome-reacted spermatozoa. Immunoperoxidase staining of normal testicular sections indicated that this protein was already present on intraluminal germ cells. Analysis of this sperm protein by gel electrophoresis and immunoblotting revealed that its molecular wei ght of 20 kDa was comparable to that of CD59 expressed on peripheral b lood cells (erythrocytes, lymphocytes) and that it was bound to the me mbrane through a glycophospholipid tail which could be released after treatment with phosphatidylinositol-specific phospholipase C. Associat ed to membrane cofactor protein (CD46) and decay accelerating factor ( CD55) located in the acrosomal membranes, CD59 may participate to the protection of male gametes against complement-mediated damage as they travel through the female genital tract. Moreover CD59, known as an ad hesion molecule involved in lymphocyte rosettes, may also participate in cell to cell adhesion during gametic interaction since H19 inhibite d sperm binding and reduced the penetration rate and index during the hamster egg penetration test. (C) 1994 Wiley-Liss, Inc.