Background: Liver fluke infection caused by Opisthorchis viverrini is highly endemic in Northeast Thailand and is associated with several hepatobiliary diseases. Our previous study has shown that Opisthorchis antigens shedding into the bile duct epithelium can recruit inflammatory cell infiltration and induce biliary damage. Moreover, portions of the antigens are also observed in the surrounding tissue. We, therefore, further hypothesize that these liver fluke antigens may enter the circulation via the lymphatic or vascular plexus and can be detected in the blood or serum.

Objective: To detect and characterize Opisthorchis antigens in the serum of rabbits infected with Opisthorchis viverrini.

Design: Experimental study.

Setting: Faculty of Medicine, Khon Kaen University.

Materials and Methods: Five rabbits were infected with 1000 metacercariae of O. viverrini for 6 months. Serum was taken from each rabbit on month 1, 3 and 6 post-infection (p.i.). Pool infected sera from each time point was used for rabbit immunization and hyperimmune sera to the three infected sera were obtained. The hyperimmune sera were characterized for anti- O. viverrini antibody by indirect ELISA, immunoblotting and immunocytochemistry.

Results: Rabbit hyperimmune serum against O. viverrini infected serum contained parasite-specific antibody by indirect ELISA. Immunoblot analysis revealed an immunogenicity of at least 4 major protein bands encompassing the MW ranging from 18.3 kDa to 68 kDa for the infected serum. The proteins with M.W. of approximately 21 kDa and 68 kDa were predominant during early infection (month 1 and 3, p.i.) and were slightly less intense in chronic infection (month 6 p.i.). Immunocytochemically, antibody to infected serum mainly reacted with the tegument, miracidia and gut of the adult fluke. The biliary epithelium that lying in close contact with the fluke was also stained.

Conclusion: This study demonstrates the presence of Opisthorchis antigens with different protein components in the infected serum of rabbits. Majority of the proteins is derived from the tegument and gut epithelium of the fluke. It is promising in further development of serum antigen detection for diagnosis O. viverrini infection in conjunction with the conventional fecal egg examination.

*This work was supported by the Faculty of Medicine, Khon Kaen University, Thailand. Grant No. I44006