INTERACTION OF THE HUMAN SERINE-PROTEASE INHIBITOR ALPHA-1-ANTITRYPSIN WITH CRYPTOSPORIDIUM-PARVUM

The protozoan parasite Cryptosporidium parvum was studied for interact ion with a human serine protease inhibitor (serpin), alpha-1-antitryps in (AAT). A C. parvum homogenate (CPH) prepared from oocysts was incub ated with purified human AAT and complexes formed between the serpin a nd CPH were detected using an enzyme-linked immunosorbent assay (ELISA ). The optical density read at 450 nm of AAT:CPH reactivity was signif icantly increased (P < 0.001) relative to CPH in the absence of AAT tr eatment. Additionally, ELISA reactivity was blocked by incubating AAT with a cognate target enzyme, porcine pancreatic elastase (PPE), prior to treatment of the CPH. Incubation of a partially excysted sample of C. parvum with AAT (37 C x 60 min) demonstrated preferential fluoresc ence labeling of sporozoites by indirect immunofluorescence assay; AAT complexes were not detected on intact oocysts. Localization of AAT in teractions with C. parvum sporozoites was visualized by transmission i mmunoelectron microscopy. Collectively, these data suggest that C, par vum sporozoites express a protease-like component that is recognized b y human AAT. The ability to block ELISA reactivity with PPE suggests t hat the AAT interactions we detected are functionally similar to the s erpin-enzyme complex AAT forms with a protease target.