Antiprotozoan immunization studies in the channel catfish, Ictalurus punctatus.

The antigenic relation between Tetrahymena pyriformis (Ehrenberg, 1830) Lwoff, 1947 and Ichthyophthirius multifiliis Fouquet 1876 was investigated using various in vitro immunologic tests. Tomites of I. multifiliis exposed to dilutions of rabbit anti-tetrahymena serum were immobilized in 24 hours. Tetrahymena in this test system were agglutinated at low dilutions and immobilized at higher dilutions. Using an indirect fluorescent antibody test, both organisms showed fluorescence when treated with either rabbit anti-tetrahymena serum or anti-tomite serium. In heterologous crosses, titers of 1:1024 were obtained using the passive hemagglutination test. These results indicate than an antigenic relationship does exist between these two organisms, cross-reacting antigens appearing to be localized on the cilia. Channel catfish Ictalurus punctatus Rafinesque were immunized with ciliary and whole cell preparations of I. multifiliis and subsequently challenged with I. multifiliis. Similar T. pyriformis preparations were used to determine if this heterologous immunization would elicit a protective immune response against I. multifiliis infestation. Results indicate that various degrees of protective immunity were induced with all antigen preparations. T. pyriformis ciliary antigens provided the greatest degree of protection. Four doses of antigen, ranging from 25 μg to 1.0 μg were used to determine if the immunizing dosage influenced the degree of protective immunity conferred.