Molecular mimicry between spermatozoa and bacteria.

PURPOSE Sperm immobilization factor isolated from Staphylococcus aureus immobilizes human spermatozoa as well as motile bacteria, showing that sperm immobilization factor receptor might be shared by bacteria and human spermatozoa. Thus, we sought to identify a common sperm immobilization factor binding receptor on spermatozoa and bacteria. MATERIALS AND METHODS Sperm immobilization factor was isolated from S. aureus. Sperm immobilization factor binding receptors were isolated from spermatozoa and bacteria. RESULTS Antisperm antibodies in humans cross-reacted with bacteria antibodies. Thus, molecular similarities between determinants of spermatozoa and pathogenic microorganisms can be inferred. Sperm immobilization factor isolated from S. aureus immobilized spermatozoa (150 μg/ml) and motile bacteria, including Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis (500 μg/ml). This showed the presence of a common sperm immobilization factor binding conformation on spermatozoa and bacteria. Furthermore, receptors binding sperm immobilization factor were extracted and purified from spermatozoa, E. coli, P. aeruginosa and P. mirabilis. Molecular mimicry between spermatozoa and bacteria was confirmed by observing the blockage of spermatozoa immobilization by sperm immobilization factor in the presence of receptors isolated from spermatozoa, E. coli, P. aeruginosa or P. mirabilis. Also, a higher concentration of sperm immobilization factor (200 μg/ml) caused sperm death. Blocking the death of spermatozoa induced by sperm immobilization factor in the presence of these receptors provided further evidence for a common receptor. CONCLUSIONS Results provide evidence for molecular similarity between bacteria and spermatozoa.