Biology of Reproduction, Vol 25, 1091-1097, Copyright © 1981 by Society for the Study of Reproduction

Binding of a Marker for Immunoglobulins to the Surface of Rabbit Testicular, Epididymal, and Ejaculated Spermatozoa

¹ Department of Biology, Department of Urology, and Department of Anatomy, University of Virginia, Charlottesville, Virginia 22908

The Cowan I (CI) stain of the bacterium Staphylococcus aureus was used to detect the presence of immunoglobulins on rabbit spermatozoa. The acrosomal and postacrosomal regions of 86 ± 4.5% of motile ejaculated spermatozoa were labeled with CI bacteria. In contrast, Wood 46 strain bacteria, which lack protein A, labeled very few spermatozoa. Binding was blocked by pretreating CI bacteria with rabbit IgG. Spermatozoa were collected from the efferent ducts of the testis and the caput and caudal regions of the epididymis by micropuncture to avoid contamination by serum immunoglobulins. Only 5 ± 1.8% of efferent duct sperm bound CI bacteria, while 84 ± 7.1% of caput sperm and 40 ± 10.4% of caudal sperm were labeled. The hypothesis that the decrease in labeling of cauda samples could be attributed to the masking of binding sites by luminal fluid components was tested on ejaculated sperm: significantly fewer were labeled in the presence of seminal plasma. Neither the exposure of ejaculated samples to serum nor the contamination of micropuncture samples with blood affected the percentage of spermatozoa labeled by bacteria. Apparently an immunoglobulin-like molecule is produced in the caput epididymidis or becomes exposed on caput sperm. This ligand may then be masked by substances secreted into the lumen distal to the caput epididymidis.

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ACKNOWLEDGMENTS This work was supported by NIH Research Grant HD08573. S.S.S. is a recipient of an NIH Developmental Biology Training Grant HD07192 and B.T.H. is a recipient of a Rockefeller Foundation Fellowship.