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Surface Expression of Complement Receptor gC1q-R/p33 Is Increased on the Plasma Membrane of Human Spermatozoa after Capacitation¹

^a Departments of Medicine ^b Obstetrics and Gynecology, State University of New York, Stony Brook, New York 11794-8161

Evidence is increasing that complement components might play a role in fertilization. C1q, the first component of the classical complement cascade, has the ability to promote sperm agglutination in a capacitation-dependent manner as well as an effect on sperm-oolemma binding and fusion. We have previously detected gC1qR, the receptor for the globular head portion of C1q, on the surface of capacitated sperm. In this study, we examined the expression of gC1qR in both fresh and capacitated human spermatozoa. We performed immunoprecipitation for gC1qR and analyzed biotinylated sperm membrane by Western blot to illustrate an increase in receptor density after overnight capacitation. These results were confirmed by flow cytometric analysis of spermatozoa using fluorescein isothiocyanate-labeled monoclonal anti-gC1qR antibody. Confocal, indirect immunofluorescence microscopy revealed an increase in receptor expression over the rostral portion of the sperm head after capacitation. In addition, the ability of live spermatozoa to bind to monoclonal anti-gC1qR antibody-coated microtiter wells was also increased after capacitation. These results suggest that gC1qR may play a role in human fertilization.

First decision: 14 September 2001.

¹ Supported in part by grants RPG-95068-03-CIM and RPG-95068-06 from the American Cancer Society, by a generous gift from Larry and Sheila Dalzell (B.G.), and by training grant GM 08444 from the National Institutes of Health. This publication represents part of K.S.G.'s work, performed in partial fulfillment of the Ph.D. Degree in Molecular and Cellular Biology.

² Correspondence: Berhane Ghebrehiwet, Department of Medicine, Health Sciences Center, T-16-040, SUNY-Stony Brook, NY 11794-8161. FAX: 631 444 2493; berhane{at}mail.som.sunysb.edu

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