POSSIBLE PROTECTIVE IMMUNITY IN HUMAN OPISTHORCHIASIS

Chronic infections with the liver flukes Opisthorchis viverrini and Cl onorchis sinensis affect over 30 million people in southeastern Asia, With ongoing exposure, reinfection readily occurs following curative t reatment and cumulative infections result in significant morbidity and a predisposition to cholangiocarcinoma. Though protective immunity ha s never been described in human opisthorchiasis, heterogeneity in worm burden occurs and a small number of exposed residents of endemic area s remain apparently uninfected. To explore the nature of this heteroge neity, we compared levels of serum antibody (Ab) to O. viverrini measu red by an enzyme-linked immunosorbent assay in 83 stool egg-positive a nd 49 stool egg-negative residents of an O. viverrini-endemic area in Thailand. Compared to the egg-positive residents, the egg-negative gro up had significantly higher levels of immunoglobulin (Ig)G, IgA and Ig M to adult worm homogenate (AWH) and total Ab to metacercaria homogena te (MH). Furthermore, immunoblot analyses revealed that a significantl y higher proportion of sera from the egg-negative residents had IgA re activity against a 38-kDa AWH antigen and IgM reactivity against carbo hydrate epitopes of a 42-kDa AWHN glycoprotein antigen. These findings support a hypothesis that the egg-negative group includes individuals who may be immunologically, resistant to this usually chronic infecti on.