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.

An Overview of the Immunological Defenses in Fish Skin

“…Until recently there had been little direct evidence of innate immune mechanisms against parasites associated with mucosal epithelium [285]. The active immunological role of skin against parasitic infection has been shown recently [286][287][288], and now mucosal immunity against them start to be elucidated. The physicochemical characteristics of skin mucus, the presence of bioactive molecules (lysozyme, complement, C-reactive protein, haemolysins, and lectins) and epidermal migration of inflammatory cells and their secretion may affect the establishment and proliferation of parasites [289].…”

“…The expression profiles of some cytokines and their receptors (IL-1β, IL-8, TNFα, and IL-1-Receptor 1) in the skin have also been examined in several fish species, and they are upregulated by infection of mechanical injury to the skin [288,[347][348][349]. IL-1b gene 1 is significantly expressed in many tissues (liver, head kidney, spleen, intestine, and muscle, but minimally in stomach, brain, and ovary) and skin of pufferfish.…”

Differences in virulence between two serotypes of Ichthyophthirius multifiliis

“…Induction of adaptive immune responses to I. multifiliis has been observed within days following initial exposure. The earliest response correlated with infection is an increase in the level of total IgM mRNA, detected by reverse transcription-PCR, in skin or head kidney samples 4 d after infection of rainbow trout Onchorhynchus mykiss with I. multifiliis (Sigh et al 2004). In channel catfish, antibodies specific for I. multifiliis can be detected in serum within 7 to 12 d following infection and within 12 d in the skin , Xu et al 2004).…”

Effect of gamma irradiation on inactivation of Ichthyophthirius multifiliis trophonts and its efficacy on host response in experimentally immunized rainbow trout (Oncorhynchus mykiss)

“…Thus, vaccination against I. multifiliis can be considered an alternative to chemical treatments to prevent mortality (2) in fish. A number of studies have indicated that whole-cell trophonts, theronts, and ciliary protein preparations or recombinant i-antigen proteins of this parasite are able to induce an acquired immune response in numerous fish species, including the channel catfish (Ictalurus punctatus), trout (Salmo gairdneri), and carp (Cyprinus carpio) (2)(3)(4)(5). Trophonts are commonly inactivated by using 1%-4% formalin (5) or freezing (5) and used for immunization at different doses (5).…”