Characterization of a monoclonal antibody reacting with antigen-4 domain of gp900 in Cryptosporidium parvum invasive stages

Cryptosporidium parvum (Protozoa, Apicomplexa) infects the apical surface o f intestinal epithelial cells, where it grows and divides within a membrane -bound parasitophorous vacuole. gp900, an abundant glycoprotein of C. parvu m merozoites and sporozoites, is localized in micronemes and at the surface of invasive stages and participates in the invasion process. Here, we desc ribe a new monoclonal antibody (mAb) against gp900. As shown by immunofluor escence of excysted parasites and immunoelectron microscopy of infected tis sues, the mAb reacted with micronemes present in the apical pole of invasiv e stages. In immunoprecipitation experiments, the mAb was shown to react wi th a high molecular weight antigen co-migrating with gp900. Finally, three reactive clones were selected upon screening of a C. parvum genomic express ion library with the mAb; and sequencing of the insert from one of them sho wed a 596 bp sequence identical to the DNA region encoding a domain of gp90 0 identified as antigen 4.