Characterization of a teleost immunoglobulin: the immune macroglobulin from the channel catfish, Ictalurus punctatus

Physiology and immunology of mucosal barriers in catfish (Ictalurus spp.)

The mucosal barriers of catfish (Ictalurus spp) constitute the first line of defense against pathogen invasion while simultaneously carrying out a diverse array of other critical physiological processes, including nutrient adsorption, osmoregulation, waste excretion, and environmental sensing. Catfish depend more heavily on mucosal barriers than their terrestrial counterparts as they are continuously interacting with the aquatic microbiota. Our understanding of these barriers, while growing, is still limited relative to that of mammalian model systems. Nevertheless, a combination of molecular and cellular studies in catfish over the last few decades, and particularly within the last few years, has helped to elucidate many of the primary actors and pathways critical to their mucosal health. Here we describe aspects of innate and adaptive immune responses in the primary mucosal tissues (skin, gill, and intestine) of catfish, focusing on mucus-driven responses, pathogen recognition, soluble mediators, and immunoglobulin and T-cell derived immunity. Modulation of mucosal barriers will be critical moving forward for crafting better diets, improving vaccine delivery, enhancing water quality, and ensuring sustainable production practices in catfish.

Isolation, Purification, and Molecular Weight Determination of Serum Immunoglobulin from Gulf Menhaden: Development of an Enzyme-Linked Immunosorbent Assay to Assess Serum Immunoglobulin Concentrations from Atlantic Menhaden

An immunoglobulin M (IgM)-like immunoglobulin was isolated by polyethylene glycol precipitation from pooled serum collected from healthy gulf menhaden Brevoortia patronus. The immunoglobulin (Ig) was purified by Sephacryl-400 gel filtration chromatography. The molecular weight of unreduced, purified Ig was determined to be 850 kilodaltons (kD) by high-performance liquid chromatography. A goat antiserum against the purified Ig was produced and determined to react with the serum Ig of both gulf and Atlantic menhaden B. tyrannus by double gel diffusion. When reacted with sera from taxonomically unrelated species of fish, sheepshead minnow Cyprinodon variegatus, striped mullet Mugil cephalus, gulf flounder Paralichthys albigutta, and hybrid striped bass (white bass Morone chrysops × striped bass M. saxatilis), no precipitation bands developed. Furthermore, the specificity of the goat antiserum was shown by Western blot analysis to be for the 77,000-molecular-weight heavy chain of reduced and alkylated gulf and Atlantic menhaden Ig. An indirect enzyme-linked immunosorbent assay (ELISA) was developed for the assessment of Ig concentrations in Atlantic menhaden serum. To illustrate the applicability of the ELISA, we assessed the Ig concentration in the serum of 542 healthy Atlantic menhaden collected from inland bays of Delaware and Maryland in 2000 and 2001. The amount of Ig was estimated to be in the range 0.26-23.50 mg/mL, with a mean of 7.37 and a standard deviation of 5.12 mg/mL. The ELISA was reproducible, as determined by the inter- and intra-assay coefficients of variation (100·SD/mean) of 11.2% and 6.8%, respectively, and used very small amounts (1-2 μL) of serum to assess the Ig concentrations from menhaden.

Isolation and molecular weight determination of two immunoglobulin heavy chains in the channel catfish, Ictalurus punctatus

Channel catfish (Ictalurus punctatus), a teleost fish, were immunized over a 4 month period with 4 intraperitoneal injections of bovine serum albumin (BSA) in Freund's adjuvant. The catfish anti-BSA antibody was purified by affinity chromatography and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). By elution of catfish anti-BSA antibody from BSA-affinity columns with 3.0 M KSCN and subsequent SDS-PAGE, two immunoglobulin heavy chains were demonstrated in the channel catfish. The molecular weights and the relative percentages found of the two immunoglobulin heavy chains were 72,000 (94%) and 56,000 (6%). The molecular weight of the single light chain found was 23,000. Using the 72,000 mol. wt heavy chain and 23,000 mol. wt light chain and including a molecular weight of 15,000 for the J-chain, the molecular weight of the predominant channel catfish tetrameric IgM immunoglobulin molecule was calculated to be 775,000. Using the 56,000 low mol. wt heavy chain, the molecular weight of a second subclass of the channel catfish tetrameric IgM molecule was calculated to be 647,000. After Sephadex G-200 gel filtration, anti-BSA antibody activity was found only in the 14S globulin fraction by indirect hemagglutination testing.

Distinctive subpopulations of catfish serum antibody and immunoglobulin

High molecular weight antibodies and immunoglobulin of the channel catfish were found to be composed of heterogeneous mixtures of covalent subpopulations. Although these proteins appeared tetrameric in physiological buffers (mol. wt approximately 700,000), molecular weight estimates in the presence of the detergent sodium dodecyl sulfate indicated that they dissociated into eight distinct subpopulations. Each dissociative subpopulation was found to be stable under the conditions of electrophoretic analysis, and furthermore each was apparently composed of equimolar H and L chains. Based upon relative mobilities it seems probable that the catfish antibody was composed of various combinations of covalent linkages between covalently-linked H-L chain pairs, i.e. 8, 7, 6, 5, 4, 3, 2 and 1. Further studies suggest the presence of size heterogeneity in catfish light chains. Whether or not this distinction represents isotypic L chain differences is not yet known but these findings coupled with the complex architecture of the physiological tetramer suggest an unusual and previously unappreciated level of complexity present in fish antibody.

Alternate pathway of complement and bactericidal response of the channel catfish to Salmonella paratyphi

Fresh channel catfish (Ictalurus punctatus) serum from unimmunized catfish exhibited 100% bactericidal activity against Salmonella paratyphi. Components responsible for bactericidal activity could be absorbed from the fresh catfish serum with S. paratyphi. The bactericidal system of the fresh catfish serum showed a need for magnesium rather than for calcium after EDTA treatment. The addition of salicylaldoxime or ammonium hydroxide to catfish serum indicated the alternate rather than the classical pathway of complement activation to be important in bactericidal activity against S. paratyphi. Bactericidal activity of catfish serum was labile when incubated at 47 degrees C for 30 min., stable for at least 4 mo. at -80 degrees C and could be absorbed with S. paratyphi at 25 degrees C. Very minimal bactericidal activity was present in the descending portion of the first 13.7S peak with most activity being found in the descending portion of the second 7.1S peak and throughout the entire 3.4S peak after Sephadex G-200 catfish serum fractionation.