Selection and identification of a new adhesion protein of Cryptosporidium parvum from a cDNA library by ribosome display

In this study, we described a novel display method to identify surface adhesion proteins of Cryptosporidium parvum. A cDNA library of the sporozoite and oocyst stages of C. parvum was expressed on ribosome and selectively and specifically screened with intestinal epithelial cells (IECs) from newborn Cryptosporidium-free Holstein calves. Proteins were then enriched using a multi-step panning procedure. A new surface adherence protein of C. parvum was selected, named Cp20. Sequence analyses showed that Cp20 has a N-terminal signal peptide and four transmembrane regions. Indirect immunofluorescence assay (IFA) using an antibody specific for rCp20 demonstrated that the antibody specifically bound to the surface of sporozoites and oocysts. The recombinant plasmid pVAX1-Cp20 was constructed to examine the potential of the Cp20 gene as a target for specific preventive and therapeutic measures for cryptosporidiosis. The in vivo efficacies of the DNA vaccine was tested in BALB/c mice. The results indicated that the DNA vaccine elicited significant antibody responses and specific cellular responses when compared to control mice that received vector only or PBS. The DNA vaccine induced strong protective immune response against C. parvum and lower level of the oocysts shedding after challenge infection. This study suggested that Cp20 could serve as an effective target for specific preventive and therapeutic measures for cryptosporidiosis.