Characterization and regional binding of human sperm monoclonal antibodies

Five monoclonal antibodies (MAb) with specific binding for tail, midpiece, equatorial region, and postacrosome of human sperm were selected. The reactivity of the MAbs was tested by three techniques: an ELISA with human sperm, an indirect immunostaining analyzed by a cell sorter, and immunofluorescence on the cell where the antigens were localized. The localization or exposure of the antigens changes throughout the in vitro capacitation. These antigens are distributed among other mammalian species: mouse, ram, and goat. Their presence was also analyzed in some human tissues: peripheral blood mononuclear cells, spleen, pancreas, thyroid, heart, skin, intestine, and lung. No cross-reactivity was detected. Some of the MAbs showing tail staining severely inhibited sperm motility after 5 hr of incubation with sperm, although no agglutination was present. This immobilizing activity of MAbs would prevent spermatozoa from reaching the oocyte in vivo.