Efficacy of serine protease inhibitors against Cryptosporidium parvum infection in a bovine fallopian tube epithelial cell culture system.

The anticryptosporidial potential of the protease inhibitors alpha-1-antitrypsin (AAT), antipain, aprotinin, leupeptin, methoxysuccinyl-ala-ala-pro-valine chloromethylketone (MAAPVCK), soybean trypsin inhibitor (SBTI), and phenylmethylsulfonyl fluoride (PMSF) was evaluated in a bovine fallopian tube epithelial (BFTE) cell culture system. Protease inhibitor concentrations of 5, 10, 50, 100, and 500 micrograms/ ml (PMSF at 1, 2, and 3 mM) in RPMI medium were mixed with Cryptosporidium parvum oocysts and used to inoculate BFTE cell monolayers. At 24 hr postinoculation (candlejar/37 C), cells were rinsed with RPMI medium, fixed in methanol, and stained with Giemsa. Parasites were enumerated in cell monolayers by brightfield microscopy. The mean number of parasites counted in each protease inhibitor treatment group was expressed as a percentage of the mean number of parasites counted in an infection control group. Leupeptin and SBTI reduced parasite numbers to 40-50% of the control mean at 500 micrograms/ml: AAT, antipain, and aprotinin reduced parasite numbers to 10-15% at the same concentration. PMSF reduced parasite numbers to 40% of the control mean at 3 mM. MAAPVCK did not significantly inhibit cryptosporidial infection. These findings suggest that a protease component of C. parvum may be essential for host cell infection.