EFFICACY OF SERINE-PROTEASE INHIBITORS AGAINST CRYPTOSPORIDIUM-PARVUMINFECTION IN A BOVINE FALLOPIAN-TUBE EPITHELIAL-CELL CULTURE SYSTEM

The anticryptosporidial potential of the protease inhibitors alpha-1-a ntitrypsin (AAT), antipain, aprotinin, leupeptin, methoxysuccinyl-ala- ala-pro-valine chloromethylketone (MAAPVCK), soybean trypsin inhibitor (SBTI), and phenylmethylsulfonyl fluoride (PMSF) was evaluated in a b ovine fallopian tube epithelial (BFTE) cell culture system. Protease i nhibitor concentrations of 5, 10, 50, 100, and 500 mu g/ml (PMSF at 1, 2, and 3 mM) in RPMI medium were mixed with Cryptosporidium parvum oo cysts and used to inoculate BFTE cell monolayers. At 24 hr postinocula tion (candlejar/37 C), cells were rinsed with RPMI medium, fixed in me thanol, and stained with Giemsa. Parasites were enumerated in cell mon olayers by brightfield microscopy. The mean number of parasites counte d in each protease inhibitor treatment group was expressed as a percen tage of the mean number of parasites counted in an infection control g roup. Leupeptin and SBTI reduced parasite numbers to 40-50% of the con trol mean at 500 mu g/ml; AAT, antipain, and aprotinin reduced parasit e numbers to 10-15% at the same concentration. PMSF reduced parasite n umbers to 40% of the control mean at 3 mM. MAAPVCK did not significant ly inhibit cryptosporidial infection. These findings suggest that a pr otease component of C. parvum may be essential for host cell infection .