EXPRESSION OF COMPLEMENT REGULATORY PROTEINS ON HUMAN EGGS AND PREIMPLANTATION EMBRYOS

PROBLEM: To investigate the relation between the complement system and reproduction, expression of complement regulatory proteins (C3b recep tors and inhibitor of the membrane attack complex) were screened on un fixed human eggs and preimplantation embryos. METHODS: Unfixed unferti lized oocytes and preimplantation embryos obtained from an in vitro fe rtilization program were stained by indirect immunofluorescence using monoclonal antibodies raised against membrane cofactor protein, (MCP o r CD46), decay accelerating factor (DAF or CD55), protectin (CD59), hu man C3b/C4b receptor (CRI or CD35), and major histocompatibility compl ex class I antigen (MHC class I). RESULTS: CD55 and CD59 were both exp ressed by the plasma membrane of unfertilized oocytes and pre-implanta tion embryos. CD46 was not expressed by unfertilized oocytes but appea red at the 6-to-8 cell stage embryo when human gene expression first o ccurs. CD35 and MHC class I antigens were not expressed at all on oocy tes and preimplantation embryos. CONCLUSIONS: Selective expression of complement regulatory proteins (DAF and protectin) associated with the lack of MHC class I antigens may represent an immune protective mecha nism by which human oocytes and preimplantation embryos escape complem ent-mediated damage during their travel through the female genital tra ct. Furthermore, participation of these complement regulatory proteins including MCP in cell to cell interaction during fertilization and/or implantation cannot be excluded.