Monoclonal antibody that recognizes an epitope of the sperm equatorial region and specifically inhibits sperm-oolemma fusion but not binding

Balb/c mice were immunized with purified hamster sperm heads for induction of antisera and the production of monoclonal antibodies that recognize pref erentially the equatorial segment. Twenty-six hybridoma clones secreted mon oclonal antibodies with strong affinity for spermatozoa. The supernatants o f 16 clones contained antibodies against the equatorial segment, of which 1 1 were specific to this region. Five supernatants (M1-M5) containing antibo dies that bind to various regions of the sperm head were selected and asses sed for the ability to inhibit hamster fertilization in vitro using intact and zona-free oocytes. All the supernatants inhibited fertilization compare d with the control. However, M1 supernatant specifically inhibited sperm-eg g fusion in a concentration-dependent manner, while sperm-oolemma binding a nd sperm motility remained unaffected. M1 supernatant recognized an epitope that is exclusive to the equatorial segment and expression of this epitope increased after capacitation and the acrosome reaction. Preliminary immuno blot analysis indicated that M1 monoclonal antibody recognized two protein bands of 37.5 and 34.0 kDa.