A small ciliary surface glycoprotein of the monogenean parasite Neobenedenia girellae acts as an agglutination/immobilization antigen and induces an immune response in the Japanese flounder Paralichthys olivaceus.

The capsalid monogenean Neobenedenia girellae, a parasite of seawater fishes, was found to express an antigen that elicits antibodies in rabbits, and these antibodies had agglutination/immobilization activity against N. girellae larvae (oncomiracidia) in vitro. Indirect immunofluorescence staining of N. girellae oncomiracidia showed that this agglutination/immobilization antigen was expressed on the surface of cilia. An intraperitoneal injection of ciliary proteins (either sonicated or intact) with adjuvant also elicited agglutinizing/immobilizing antibodies in sera from Japanese flounder, Paralichthys olivaceus. These antisera showed a clear correlation between anti-ciliary antibody levels (measured by enzyme-linked immunosorbent assays) and their agglutination/immobilization activity. Anti-ciliary antibody levels in Japanese flounder reached a plateau at 39 days after booster immunization and were significantly higher in the two immunized groups (injection of sonicated or intact cilia) as compared with control fish (injection of bovine serum albumin; ANOVA, Tukey's test, P < 0.01). Anti-ciliary antibodies were also found in fish mucus; however, there was no correlation between fish serum anti-ciliary antibody levels and mucus antibody levels. A Triton X-114-soluble 8 kDa glycoprotein of the ciliary integral membrane fraction is a plausible candidate for the agglutination/immobilization antigen based on SDS-polyacrylamide gel electrophoresis and immunoblot analyses with rabbit and fish antisera.