Attachment of Cryptosporidium parvum sporozoites to MDCK cells in vitro.

The initial attachment of Cryptosporidium parvum sporozoites to host cells in vivo may be a critical event in the pathogenesis of this infection. The molecular basis of attachment and the conditions influencing this host-parasite interaction have not been studied systematically. Therefore, we have developed a sporozoite attachment model by using paraformaldehyde-fixed Madin-Darby canine kidney (MDCK) cells. Attachment of sporozoites to fixed MDCK cells was quantitated by indirect immunofluorescence and confirmed by transmission electron microscopy. Attachment in this system was time, temperature (37 degrees C), and pH (7.2 to 7.6) dependent. Dose-response studies demonstrated that the attachment of sporozoites to fixed MDCK cells was a saturable process. Attachment was enhanced in the presence of 10 mM manganese, 1 mM calcium, and 1 to 10 mM zinc. Attachment of sporozoites to MDCK cells was inhibited in a dose-dependent manner by polyclonal anti-Cryptosporidium antisera and by purified immunoglobulin G (IgG). This model will be useful for the study of parasite and host cell molecules involved in the initial interaction of C. parvum sporozoites with their target cell.