Receptor/ligand interactions between Cryptosporidium parvum and the surface of the host cell.

The ability of membrane antigens on sporozoites of the intestinal pathogen, Cryptosporidium parvum, to bind host cell surface antigens was investigated. A novel membrane-associated protein of approximately 47 kDa, designated CP47, was found to possess significant binding affinity for the surface of both human and animal ileal cells. This protein was purified by a combination of anion-exchange chromatography on FPLC and immunoaffinity chromatography. Purified CP47 demonstrated competitive binding with parasite-associated membrane antigens to membranes of HCT-8 and ileal cells in a dose-dependent manner. Furthermore, the binding activity of CP47 was found to be Mn2+-sensitive, and was completely inhibited in the presence of 10 mM MnCl2. These results were consistent with earlier findings demonstrating the inhibitory effect of Mn2+ ions on Cryptosporidium infection both in vitro and in vivo (Nesterenko et al., Biol. Trace Elem. Res. 56 (1997) 243-253). Immunoelectron microscopy using gold-conjugated antibodies revealed CP47 to be localized at the apical end of the sporozoites. A single protein with an electrophoretic mobility of 57 kDa was purified from host cell membranes using CP47-Affigel. Similarly, affinity purification of this protein was abrogated in the presence of Mn2+. These data suggest that a novel parasite protein, CP47, may play an important role in sporozoite/host cell attachment.