The parasitic ciliate Ichthyophthirius multifiliis induces expression of immune relevant genes in rainbow trout, Oncorhynchus mykiss (Walbaum).

Abstract During an infection with the parasitic ciliate Ichthyophthirius multifiliis, expression of genes encoding complement factor C3, inducible nitric oxide synthase (iNOS), immunoglobulin (IgM) and major histocompatibility complex (MHC-II) was examined in the skin, head kidney and spleen of rainbow trout using semi-quantitative reverse transcriptase-polymerase chain reaction. Induction of C3 transcription levels was evident in the skin and spleen showing extra-hepatic production of C3. MHC-II and IgM levels were increased in both head kidney and skin suggesting a production of antibodies at the site of infection, as well as in the lymphoid organs. iNOS expression was only increased briefly in the skin during the infection. These data suggest that complement is involved in immune reactions against I. multifiliis and that mucosal antibodies might be produced at the site of infection.