Immune reactions between excretory-secretory antigens and specific antibodies of Clonorchis sinensis before and after praziquantel treatment in experimentally infected rabbits

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Abstract
This study was designed to evaluate the humoral immune reactions in clonorchiasis before and after praziquantel treatment. Rabbits were infected with 150 or 450 metacercariae, treated on 4 and 8 1/2 months after infection, and observed for 13 months of posttreatment. Infection controls were maintained for 22 months. Antigen was the metabolic product of worms incubated in physiologic saline. The immune reactions of anti-Clonorchis IgG were observed using SDS-PAGE/immunoblot. During the infection and posttreatment, the antigenic proteins of 66, 63, 54, 52, 50, 47, 42, 40, 38, 34, 33, 30, 27, 25, 23, 20, 19, 18, 17, 16, 15, 14, 13, 12.5 and 11.5 kDa were detected. Of them, 33, 27, 13, and 12.5-kDa antigens were highly antigenic and observed predominantly in infection controls. After the treatment, 13 and 12.5-kDa antigens faded in 6 months after the second treatment, but 33 and 27-kDa antigens were detected until 13 months of posttreatment. The results clearly demonstrate that 13 and 12.5-kDa antigens represent attenuated host immune reactions by praziquantel treatment. As the 12.5-kDa antigen had a large amount of protein in SDS-PAGE, it was designated as 'K2-Ag' of C. sinensis.