In vitro demonstration of serological cross-reactivity between Ichthyphthirius multifiliis foquet and Tetrahymena pyriformis lwoff

The antigenic relation between $\text{Tetrahymena pyriformis}$ (Ehrenberg, 1830) Lwoff 1947 and $\text{Icthyophthirius multifiliis}$ Fouquet 1876 was investigated using various $\text{in vitro}$ immunologic tests. Tomites of $\text{I. multifiliis}$ exposed to dilutions of rabbit anti-tetrahymena serum were immobilized in 24 hours. $\text{Tetrahymena}$ 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 rabbit anti-tomite serum. In heterologous crosses, titers of 1:1024 were obtaibed using the passive hemagglutination test. These results indicate that an antigenic relationship does exist between these two organisms, cross-reacting antigens appear to be localized on the cilia.