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Published on: February 8, 2016
The expression of the complement regulators CD46, CD55, and CD59 by human sperm does not protect them from antisperm
1Department of Obstetrics and Gynecology, University of Oklahoma Health Sciences Center, Oklahoma City.
Insights
Human sperm express complement (C) regulators that offer limited protection against C-mediated injury. This suggests limitations in using serum C for diagnosing cytotoxic antisperm antibodies in infertile couples.
Area of Science:
- Immunology
- Reproductive Biology
- Complement System
Background:
- The complement system plays a crucial role in innate and adaptive immunity.
- Complement regulators on cell surfaces are essential for preventing self-damage.
- Human sperm express complement regulators, but their role in sperm protection is not fully understood.
Purpose of the Study:
- To determine the expression of complement regulators on human sperm.
- To assess the protective effects of these regulators against antisperm antibody and complement-mediated injury.
- To evaluate the implications for diagnosing infertility.
Main Methods:
- Indirect immunofluorescence flow cytometry was used to quantify complement regulators (CR1, CD46, CD55, CD59) on human sperm.
- Sperm surface complement inhibitors were detected on acrosome-intact and acrosome-reacted sperm.
- Sperm motility loss was assessed in the presence of antisperm antibodies and complement.
Main Results:
- Decay-accelerating factor (CD55) and P18 (CD59) were detected on both acrosome-intact and acrosome-reacted sperm.
- Membrane cofactor protein (CD46) was found only on acrosome-reacted sperm; CR1 was not detected.
- Sperm motility loss was enhanced by complement in the presence of anti-CD55 and/or anti-CD59, but unaffected by complement regulators in C-fixing antisperm antibody-positive sera.
Conclusions:
- Human sperm possess complement regulators (CD46, CD55, CD59) with limited potency against serum complement.
- The effectiveness of serum complement in traditional assays for cytotoxic antisperm antibodies may be limited.
- The inefficiency of these regulators suggests a potential role in preventing proteolytic damage during fertilization.
Objectives:
To investigate whether membrane-bound regulators of the initial (C3) and terminal (C5b-9) complement (C) pathway components are expressed on human sperm and to evaluate the protective effects of these regulators in restricting antisperm antibody and C-mediated injury.
Design:
Sperm surface C inhibitors were quantitated by indirect immunofluorescence flow cytometry using murine monoclonal antibodies to detect C3 regulatory proteins, C3b/C4b receptor type (CR1, CD35), membrane cofactor protein (CD46), and decay-accelerating factor (CD55), and C5b-9 inhibitor, P18 (CD59) on acrosome-intact human sperm and sperm induced to undergo acrosomal loss. The susceptibility of sperm to antisperm antibody- and C-mediated immobilization was evaluated by sperm motility loss in the presence of antidecay-accelerating factor and/or anti-P18.
Setting:
University of Oklahoma Health Sciences Center, a tertiary care referral center.
Results:
Both decay-accelerating factor and P18 were detected on acrosome-intact and sperm induced to undergo acrosomal loss; neither expressed CR1. Membrane cofactor protein was detected on only acrosome-reacted sperm. The time course of sperm motility loss in antisperm antibody-negative sera in the presence of antidecay-accelerating factor, anti-P18, or both had a cumulative effect and brought about a time-dependent enhancement of sperm motility loss by serum C. However, sperm motility loss in C-fixing antisperm antibody-positive sera was unaffected by sperm membrane bound C3 and C5b-9 regulators.
Conclusions:
The susceptibility of human sperm to antisperm antibody- and C-induced motility loss may reflect a low potency of the sperm membrane C regulators membrane cofactor protein, decay-accelerating factor, and P18 in inhibiting serum C. Therefore, the use of serum C in the traditional assay for the diagnosis of cytotoxic antisperm antibody in infertile couples may have limitations. The inefficiency of these proteins in restricting serum C activity also suggested a secondary function in restricting localized proteolytic damage at the site of fertilization.
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