Abstract:
Ichthyophthirius rnultifliis. a parasitic ciliate of freshwater fishes, was found to have surface antigens (Ag) which elicited
immobilizing antibodies (Ab) when injected into rabbits. An effort was made to purify and characterize these Ag (referred to as
immobilization Ag) because of their potential role in protective immunity in fishes. Mice immunized with theront cilia were used for
production of immobilizing monoclonal antibodies (MAb). Hybridomas were screened by indirect irnmunofluorescent light microscopy
and immobilization of live parasites. Six hybridomas producing immobilizing MAb were cloned. Immobilizing MAb were used to
affinity purify Ag solubilized with Triton X-114 and Na deoxycholate. Two membrane protein Ag of approximately 48 and 60 kDa
were identified. Immobilizing MAb failed to react with these Ag on Western blots and, conversely, MAb that reacted with the Ag on
Western blots did not immobilize live organisms. These results suggest that immobilization required native conformational epitopes
which were altered by Western blotting procedures. Individual MAb reactive on Western blots recognized both the 48- and 60-kDa
proteins indicating the presence of common epitopes. Affinity purified Ag elicited immobilizing antisera when injected into rabbits,
mice, and channel catfish.