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Updated: Aug 7, 2026

Medium-throughput Screening Assays for Assessment of Effects on Ca2+-Signaling and Acrosome Reaction in Human Sperm
05:44

Medium-throughput Screening Assays for Assessment of Effects on Ca2+-Signaling and Acrosome Reaction in Human Sperm

Published on: March 1, 2019

The complement regulatory proteins CD55 (decay accelerating factor) and CD59 are expressed on the inner acrosomal

J A Cummerson1, B F Flanagan, D G Spiller

  • 1Division of Immunology, School of Infection & Host Defence, University of Liverpool, Liverpool, UK. joc@liv.ac.uk

Immunology
|July 11, 2006
PubMed

Insights

Complement regulatory proteins CD55 and CD59 are expressed on the inner acrosomal membrane (IAM) of human sperm. This finding, observed on unfixed sperm, suggests potential functional cooperation with CD46 during fertilization.

Area of Science:

  • Reproductive Biology
  • Immunology
  • Cell Biology

Background:

  • Complement regulatory proteins CD55 and CD59 are typically found on the sperm plasma membrane.
  • CD46 is localized to the inner acrosomal membrane (IAM), exposed after the acrosome reaction.
  • Previous studies suggested CD55 and CD59 presence in the acrosomal region of fixed sperm, but not on unfixed cells.

Purpose of the Study:

  • To investigate the precise localization and characteristics of CD55 and CD59 on fresh, unfixed human spermatozoa.
  • To determine if CD55 and CD59 are glycosylphosphatidylinositol (GPI)-anchored proteins on the IAM.
  • To explore the potential functional relationship between CD55, CD59, and CD46 on the IAM.

Main Methods:

  • Dual-labeling immunofluorescence and confocal microscopy on fresh, unfixed human spermatozoa.
  • Treatment with Phosphatidylinositol-specific phospholipase C (PI-PLC) to assess GPI-anchoring.
  • Western blotting analysis of acrosome-reacted sperm to characterize CD55.

Main Results:

  • CD55 and CD59 are significantly expressed on the IAM of unfixed human spermatozoa, with CD55 showing patchy staining and CD59 exhibiting a granular pattern.
  • Both CD55 and CD59 on the IAM were released by PI-PLC, confirming their GPI-anchored nature.
  • CD55 on the IAM was localized within GM1-containing lipid rafts, and Western blot revealed a novel 55 kDa form lacking significant glycosylation.
  • Significant coexpression of CD55 and CD46 on the IAM was observed.

Conclusions:

  • CD55 and CD59 are GPI-anchored proteins present on the inner acrosomal membrane of human spermatozoa, with distinct localization patterns.
  • The presence of CD55 within lipid rafts and its unique biochemical profile suggest specific regulatory mechanisms.
  • Coexpression of CD55 and CD46 on the IAM indicates potential functional cooperation in regulating complement activity during fertilization.

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