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Updated: Aug 17, 2026
Human Blastocyst Biopsy and Vitrification
Published on: July 26, 2019
Complement-binding proteins are strongly expressed by human preimplantation blastocysts and cumulus cells as well as
1Reproductive Medicine Unit, Liverpool Women's Hospital, UK.
Insights
Human reproductive cells and early embryos express complement-binding proteins CD46, CD55, and CD59. These proteins protect gametes and embryos from complement-mediated damage, potentially aiding reproductive success.
Area of Science:
- Reproductive immunology
- Cellular biology
- Complement system
Background:
- The complement system is crucial for innate immunity but can harm reproductive cells.
- Complement regulatory proteins (CRPs) like CD46, CD55, and CD59 are known to protect host cells from complement attack.
- The expression and role of these CRPs in human gametes and preimplantation embryos are not fully understood.
Purpose of the Study:
- To investigate the expression of complement-binding proteins CD46, CD55, and CD59 on human gametes, cumulus cells, and preimplantation embryos.
- To determine the localization of these proteins on the cellular and subcellular levels.
- To assess the potential role of these proteins in protecting reproductive cells from complement-mediated damage.
Main Methods:
- Immunohistochemical analysis using monoclonal antibodies.
- Detection of complement regulatory proteins (CD46, CD55, CD59) and complement receptors (CR1, CR2, CR3).
- Study of human oocytes, spermatozoa, cumulus cells, and preimplantation embryos (zygotes to blastocysts).
Main Results:
- CD55 and CD59 were expressed on the plasma membrane and zona pellucida of oocytes and early embryos.
- CD46 was localized to the plasma membrane of oocytes and embryos, and the inner acrosomal membrane of spermatozoa.
- CD55 and CD59 were also found on the plasma and inner acrosomal membranes of spermatozoa.
- Cumulus cells showed variable CD55 expression but consistent CD46 and strong CD59 expression.
- Complement receptors CR1, CR2, and CR3 showed minimal or no reactivity on reproductive cells and embryos.
Conclusions:
- Human gametes and preimplantation embryos express complement regulatory proteins CD46, CD55, and CD59.
- These proteins likely provide protection against complement-mediated attack, crucial for reproductive success.
- The presence of these proteins suggests additional roles beyond complement regulation in reproductive events.
Abstract:
Human preimplantation embryos, gametes and cumulus cells were studied for expression of the complement-binding proteins CD46 (membrane cofactor protein), CD55 (decay accelerating factor) and CD59 (membrane attack complex inhibitory factor) as well as complement receptors type 1 (CRI), type 2 (CR2) and type 3 (CR3). Both the CD55 and CD59 glycosyl phosphatidylinositol (GPI)-anchored proteins were expressed by the plasma membrane and zona pellucida of oocytes, early embryos and expanded preimplantation blastocysts; in contrast, CD46 was expressed only on the plasma membrane. Cumulus cells consistently expressed CD46 and, most strongly, CD59 whereas CD55 expression was variable. Monoclonal antibodies (mAbs) to CRI, CR2 and CR3 epitopes gave only occasional reactivity on oocytes and were unreactive with blastocysts, spermatozoa and cumulus cells. CD46 is expressed only on the spermatozoal inner acrosomal membrane, and CD59 on the plasma membrane; CD55 expression was confirmed on the plasma membrane as well as the inner acrosomal membrane. Control mAbs specific for factor H were usually unreactive with gametes, blastocysts and cumulus cells. These data support the concept that gametes and early embryonic cells are protected from complement-mediated attack by expression of CD46, CD55 and CD59, although these complement-binding proteins may have additional roles in reproductive events.
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