A monoclonal antibody was raised against a human sperm protein of apparent molecular size of 40 kDa. Of the 6 hybridoma clones selected for study, one clone (B-12) was chosen for further investigations. The antibody secreted by the clone agglutinated human and rabbit spermatozoa in vitro. The antibody belonged to IgM class. In indirect immunofluorescence studies this antibody reacted to acrosome of living human and rabbit spermatozoa. On fixed sperm of the same species it recognized midpiece and parts of tail along with the acrosome. Mouse, hamster, guinea pig, monkey and rat sperm showed similar localization. Interaction between rabbit sperm and oocyte was inhibited in vitro by this antibody. On western blots of human and rabbit sperm extracts the antibody recognized more than one epitope.

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