EXPRESSION AND ROLE OF COMPLEMENT REGULAT ORY PROTEINS ON HUMAN GAMETES AND PREIMPLANTATION EMBRYOS

Human gametes and pre-implantation embryos express selectively several complement regulatory proteins, Membrane cofactor protein (MCP, CD46) and decay accelarating factor (DAF; CD55) are regulators for C3 conve rtases and protectin (CD59) is an inhibitor of the membrane attack com plex, These three proteins were identified on human sperm and found to be functionnal, CD55 and CD59 were both expressed by the plasmic memb rane of unfertilized oocytes and pre-implantation embryos. CD46 was no t present on unfertilized oocytes but appeared at the 6/8 cell-stage e mbryo when human gene expression first occurs, Complement receptor 1 ( CR1,CD35) and MHC class I antigens were not found on oocytes neither o n embryos. Such a selective expresssion of complement regulatory prote ins asociated with the lack of MHC class I antigens may represent an i mmune protective mechanism by which human gametes and pre-implantation embryos escape from complement-mediated damage during their travel th rough the female genital tract. Indeed uterin, tubal and follicular fl uids contain all the components of the complement cascade, including c lassical and alternative pathways, Neverthereless participation of CD4 6 and CD59 in cell to cell interaction during fertilization and/or imp lantation cannot be excluded, CD59 is an adhesive molecule involved in the rosette phenomena and CD46 has been described as the human recept or for measles virus, which binds through a fusion protein. Monoclonal antibodies raised against these two proteins (CD46 and CD59) are able to inhibit heterospecific fertilization between zona-free hamster ooc ytes and human spermatozoa suggesting the role of these proteins durin g fertilization,