IN VITRO ACTION OF ANTISERA ON ADULTS OF CLONORCHIS SINENSIS

The action of immune sera on adult Clonorchis sinensis was studied in vitro in the “circumadult” test. Precipitates of various kinds were consistently demonstrated when the living parasites were incubated with heated or unheated immune sera from experimentally infected rabbits and guinea-pigs, and from rabbits and guinea-pigs artificially immunized with whole fluke extracts or adult metabolic products. Sera from 18 of 20 clonorchiasis patients and from 3 of 20 patients without Clonorchis eggs in the stools were also positive. There was no reaction when the living flukes were incubated with normal sera or with sera against Clonorchis eggs or other parasites, or when dead flukes were incubated with immune serum. When the positive sera were absorbed with metabolic products before incubation, the precipitates were greatly diminished or entirely abolished. Precipitates were located at the oral sucker, the genital pore and the cuticle, and also lay free and suspended in the serum. The parasites began to disintegrate after 24 hours' incubation, and died. In comparisons of normal with immune rabbit sera, and of human clonorchiasis antisera with sera from patients without Clonorchis eggs in the stools, it was found that the immune rabbit sera and the human clonorchiasis antisera possess parasiticidal effects in vitro. The differences between these two groups are statistically highly significant. The reaction develops remarkably early after infection, but is probably based on an immunological mechanism elicited in infection by absorption of metabolic products secreted by the flukes. The chief sites of these secretions are the oral sucker and genital pore, and to a less degree the cuticle. © 1969 Royal Society of Tropical Medicine and Hygiene.