A new antigen of Cryptosporidium parvum micronemes possessing epitopes cross-reactive with macrogamete granules.

Three monoclonal antibodies (mAbs) raised against purified excysted oocysts and sporozoites of Cryptosporidium parvum reacted in an immunofluorescent assay with antigens located at the apical pole of the sporozoites. On Western blots of oocyst extract, an antigen of 100 kDa was recognized by the three mAbs. Periodic acid treatment abolished this reactivity, suggesting that the corresponding epitopes are carbohydrates. As determined by immunoelectron microscopy, the three mAbs reacted with micronemes in sporozoites and merozoites and recognized a heterogeneous population of granules in the developing macrogametes. Gold particles were also detected in the parasitophorous vacuole of the macrogametes and sporulating oocysts. The detection of a microneme antigen in a family of macrogamete granules has not previously been reported in coccidia. The significance of this observation and the nature of these macrogamete inclusions are discussed.