Systemic and cutaneous mucus antibody responses of channel catfish immunized against the protozoan parasite Ichthyophthirius multifiliis

Antibody response of bluegill sunfish during development of acquired resistance against the larvae of the freshwater mussel Utterbackia imbecillis

The larvae of freshwater mussels in the order Unionoida are obligate parasites on fishes, on which they metamorphose into juveniles. Bluegill sunfish (Lepomis macrochirus) acquire resistance against glochidia of the freshwater mussel Utterbackia imbecillis after 2 infections. In order to study the systemic and mucosal antibody response associated with acquired resistance, sera from experimentally infected fish were collected at 10-d intervals during 4 sequential infection periods and from naïve fish. Enzyme-linked immunosorbant assays (ELISA) revealed that fish exhibited a humoral and mucosal antibody response around day 20 after the 1st infection which was followed by second antibody response beginning at day 60 (day 20, 3rd infection) that persisted until the end of the collection period. Western blots of glochidial proteins probed with the sera revealed that the profile of proteins recognized by antibodies produced by fish changed over the course of multiple infections. Serum collected from fish at day 20 (peak of primary response) contained antibodies against approximately 39 and 91 kDa proteins. Immunohistochemical studies on whole-mount glochidia probed with serum from these fish demonstrated that the antibodies recognize granular structures located between the larval mantle and shell. Serum collected from fish during the secondary antibody response (days 60-80) bound additional protein bands in Western blots. Those antibodies recognized other cells of the larval mantle, most prominently in a ciliated region that contains the primordia of the gills and organs of the juvenile and adult mussel.

Amoebic gill disease (AGD)-affected Atlantic salmon, Salmo salar L., are resistant to subsequent AGD challenge

There is inconsistent evidence of resistance of Atlantic salmon, Salmo salar L., to amoebic gill disease (AGD). Here, evidence is presented that demonstrates that Atlantic salmon exposed and subsequently challenged with AGD are more resistant than naïve control fish. Seventy-three per cent of Atlantic salmon previously exposed to AGD survived to day 35 post-challenge compared with 26% exposed to Neoparamoeba sp. for the first time, yet the gill pathology of surviving naïve control or previously exposed fish was not significantly different. Development of resistance to AGD is associated with anti-Neoparamoeba sp. antibodies that were detectable in serum of 50% of surviving Atlantic salmon previously exposed to AGD. However, anti-Neoparamoeba sp. antibodies were not detectable in cutaneous mucus of resistant fish. Increased resistance of Atlantic salmon after secondary Neoparamoeba sp. infection and detection of specific serum antibodies provides support for the development of a vaccine for AGD.

Response and function of cutaneous mucosal and serum antibodies in barramundi (Lates calcarifer) acclimated in seawater and freshwater

Mucosal and serum antibody responses were studied in sibling barramundi (Lates calcarifer) acclimated in either seawater or freshwater following vaccination by intraperitoneal injection or direct immersion in an inactivated Streptococcus iniae vaccine. As expected, route of vaccination had a marked effect on immune response, with direct immersion resulting in low serum antibody levels against S. iniae by ELISA detected 21 days post vaccination at 26 degrees C, whilst a significant response was detected in mucus. A strong specific antibody response was detected in both mucus and serum 21 days following intraperitoneal injection. Fish acclimated in seawater prior to vaccination showed a markedly higher specific mucosal antibody response than sibling fish acclimated in freshwater, regardless of the route of vaccination, whilst the serum antibody response was not affected by salinity. Both mucosal and serum antibodies from fish in seawater and freshwater were capable of binding antigen at salinities similar to full strength seawater in a modified ELISA assay. These results indicate that this euryhaline fish species is not only able to mount significant specific antibody response in cutaneous mucus, but that these antibodies will function in the marine environment.

A small ciliary surface glycoprotein of the monogenean parasite Neobenedenia girellae acts as an agglutination/immobilization antigen and induces an immune response in the Japanese flounder Paralichthys olivaceus

The capsalid monogenean Neobenedenia girellae, a parasite of seawater fishes, was found to express an antigen that elicits antibodies in rabbits, and these antibodies had agglutination/immobilization activity against N. girellae larvae (oncomiracidia) in vitro. Indirect immunofluorescence staining of N. girellae oncomiracidia showed that this agglutination/immobilization antigen was expressed on the surface of cilia. An intraperitoneal injection of ciliary proteins (either sonicated or intact) with adjuvant also elicited agglutinizing/immobilizing antibodies in sera from Japanese flounder, Paralichthys olivaceus. These antisera showed a clear correlation between anti-ciliary antibody levels (measured by enzyme-linked immunosorbent assays) and their agglutination/immobilization activity. Anti-ciliary antibody levels in Japanese flounder reached a plateau at 39 days after booster immunization and were significantly higher in the two immunized groups (injection of sonicated or intact cilia) as compared with control fish (injection of bovine serum albumin; ANOVA, Tukey's test, P < 0.01). Anti-ciliary antibodies were also found in fish mucus; however, there was no correlation between fish serum anti-ciliary antibody levels and mucus antibody levels. A Triton X-114-soluble 8 kDa glycoprotein of the ciliary integral membrane fraction is a plausible candidate for the agglutination/immobilization antigen based on SDS-polyacrylamide gel electrophoresis and immunoblot analyses with rabbit and fish antisera.

Ichthyophthirius multifiliis Fouquet and Ichthyophthiriosis in Freshwater Teleosts

The ciliate Ichthyophthirius multifiliis is an important pathogen of freshwater teleosts occurring in both temperate and tropical regions throughout the world. The disease, ichthyophthiriosis, accounts for significant economic losses to the aquaculture industry, including the ornamental fish trade, and epizootics in wild fish populations can result in mass kills. This review attempts to provide a comprehensive overview of the biology of the parasite, covering the free-living and parasitic stages in the life cycle, host-parasite interactions, and the immune response of host and immune evasion strategies by the parasite. Emphasis on the immunological aspects of infection within the fish host, including molecular studies of i-antigens, reflects the current interest in this subject area and the quest to develop a recombinant vaccine against the disease. The current status of methods for the control of ichthyophthiriosis is discussed, together with new approaches in combating this important disease.