ANTAGONISTIC EFFECT OF HUMAN ALPHA-1-ANTITRYPSIN ON EXCYSTATION OF CRYPTOSPORIDIUM-PARVUM OOCYSTS

This study evaluated the effects of the human serine protease inhibito r alpha-1-antitrypsin (AAT) on in vitro excystation and infectivity of Cryptosporidium parvum. Excystation was monitored at 37 C in RPMI med ium in the presence of 0, 100, 500, or 1,000 mu g/ml AAT. AAT signific antly inhibited (P < 0.05) excystation of bleach-decontaminated oocyst s in a concentration-dependent manner at incubation intervals from 15 to 90 min but did not alter the excystation dynamics of unbleached ooc ysts. Pleach-treated oocysts, suspended in RPMI containing 0, 1, 10, 1 00, 500, or 1,000 mu g/ml AAT, were used to inoculate bovine fallopian tube epithelial (BFTE) cell monolayers. Alternately, sporozoites, exc ysted at 37 degrees C and collected by filtration, were used to inocul ate BFTE cells under the same conditions. The mean number of parasites counted in AAT-treated, oocyst-inoculated cells was significantly les s (P < 0.01) than control mean values at 24 and 48 hr postinoculation (PI); longer PI intervals (72-96 hr) exhibited a decreased inhibitory effect. AAT did not inhibit parasite infection when cultures were inoc ulated with C. parvum sporozoites. The findings of this study show tha t the anticryptosporidial potential of AAT is primarily associated wit h an antagonistic effect on oocyst excystation.