Passive intraperitoneal transfer of sera from Fasciola hepatica-infected sheep, cattle or rats can protect naive rats from F. hepatica infection, suggesting a parasite killing mechanism within the peritoneal cavity that is dependent on the presence of parasite-specific antibody. We investigated antibody-dependent cell-mediated cytotoxicity by resident peritoneal lavage cell populations, containing large numbers of monocytes/macrophages, as a potential host resistance mechanism by which juvenile flukes could be killed within the peritoneal cavity of naive rats. Comparative studies were conducted using cell populations containing large numbers of monocytes/macrophages from sheep. The results demonstrate that monocyte/macrophage-rich lavage cell populations from rat and sheep differ substantially in their ability to generate nitric oxide. Only resident rat peritoneal lavage cells were able to mediate antibody-dependent cell-mediated cytotoxicity against newly excysted juvenile liver fluke. The mechanism of cytotoxicity was dependent on, and directly proportional to, the production of nitric oxide and required attachment of effector cells to the newly excysted juvenile liver fluke tegument, which occurred following the addition of sera from F. hepatica-infected animals. This is the first report demonstrating a mechanism of cell-mediated cytotoxicity to newly excysted juvenile liver fluke.
The lupane triterpenoid lupeol, the ursane triterpenoid alpha-amyrin and esters of these compounds are present in the bark of roots of Alstonia boonei (Apocynaceae) and have anti-inflammatory properties. alpha-Amyrin is a competitive inhibitor of bovine trypsin and chymotrypsin (Ki values 29 microM and 18 microM, respectively). Lupeol linoleate, lupeol palmitate and alpha-amyrin linoleate are non-competitive inhibitors of trypsin (Ki values 7 microM, 10 microM and 16 microM, respectively). alpha-Amyrin linoleate is also a non-competitive inhibitor of chymotrypsin (Ki value 28 microM). Lupeol is a competitive inhibitor of both trypsin and chymotrypsin (Ki values 22 and 8 microM, respectively). alpha-Amyrin palmitate is a potent non-competitive inhibitor of chymotrypsin (Ki 6 microM). Lupeol, alpha-amyrin and the palmitic and linoleic acid esters of these compounds are ineffective or very weak as inhibitors of porcine pancreatic elastase and of Lucilia cuprina and Helicoverpa punctigera leucine aminopeptidases. These hydrophobic triterpenoids represent further examples of anti-inflammatory triterpenoids that are PKA inhibitors as well as being selective protease inhibitors.
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