Development of a stringent ELISA protocol to evaluate anti-viral hemorrhagic septicemia virus-specific antibodies in olive flounder Paralichthys olivaceus with improved specificity

Development of an indirect ELISA for detection of the adaptive immune response of black carp (Mylopharyngodon piceus)

Black carp (Mylopharyngodon piceus) is an important fishery resource and the main breeding target in China. Due to the lack of an assay of immunoglobulin M (IgM) antibodies in black carp, there is no effective method to evaluate adaptive immune response, which limits immunological studies and vaccine development. The present study used mAbs (monoclonal antibodies) against serum IgM of grass carp as capture antibodies. The results of Western blot analysis indicated that these antibodies had strong affinity and specificity to IgM heavy chain in black carp serum and were used to detect the antibody titer, optimize the conditions, perform a sensitivity test, and develop an indirect ELISA (enzyme-linked immunosorbent assay) to detect specific IgM antibodies in the serum. This detection method has good specificity and is effective only for grass carp (Ctenopharyngodon idella) and black carp and not for crucian carp (Carassius aumtus), silver carp (Hypophthalmichthys molitrix), bighead carp (Hypophthalmichthys nobilis), mandarin fish (Siniperca chuatsi), black bream (Megalobrama skolkovii), or yellow catfish (Pseudobagrus fulvidraco). The lowest antigen detection level was 0.05 μg/ml. The error of experimental repetition in the same sample was 1.61-4.61%. The levels of specific IgM in black carp serum were steadily increased after immunization, peaked on day 28, and then slowly decreased. Indirect ELISA can be applied to detect the changes in specific antibodies in black carp serum. Moreover, indirect ELISA provides a convenient and reliable serological detection method for immunological research and evaluation of immune effects of a vaccine in black carp.

Detection of Salmonid IgM Specific to the Piscine Orthoreovirus Outer Capsid Spike Protein Sigma 1 Using Lipid-Modified Antigens in a Bead-Based Antibody Detection Assay

Bead-based multiplex immunoassays are promising tools for determination of the specific humoral immune response. In this study, we developed a multiplexed bead-based immunoassay for the detection of Atlantic salmon (Salmo salar) antibodies against Piscine orthoreovirus (PRV). Three different genotypes of PRV (PRV-1, PRV-2, and PRV-3) cause disease in farmed salmonids. The PRV outer capsid spike protein σ1 is predicted to be a host receptor binding protein and a target for neutralizing and protective antibodies. While recombinant σ1 performed poorly as an antigen to detect specific antibodies, N-terminal lipid modification of recombinant PRV-1 σ1 enabled sensitive detection of specific IgM in the bead-based assay. The specificity of anti-PRV-1 σ1 antibodies was confirmed by western blotting and pre-adsorption of plasma. Binding of non-specific IgM to beads coated with control antigens also increased after PRV infection, indicating a release of polyreactive antibodies. This non-specific binding was reduced by heat treatment of plasma. The same immunoassay also detected anti-PRV-3 σ1 antibodies from infected rainbow trout. In summary, a refined bead based immunoassay created by N-terminal lipid-modification of the PRV-1 σ1 antigen allowed sensitive detection of anti-PRV-1 and anti-PRV-3 antibodies from salmonids.

Production of a monoclonal antibody against of muskellunge (Esox masquinongy) IgM heavy chain and its use in development of an indirect ELISA for titrating circulating antibodies against VHSV-IVB

This study reports the development of a monoclonal antibody (designated 3B10) against the muskellunge (Esox masquinongy) IgM. The 3B10 monoclonal antibody (mAb) belongs to the IgG3 kappa isotype. Western blotting demonstrated that 3B10 mAb reacted primarily to muskellunge IgM heavy chain. 3B10 also reacted strongly with the IgM heavy chain of other esocids, including the northern pike (Esox lucius), tiger muskellunge (E. masquinongy x E. lucius), and, to a much lesser extent, the chain pickerel (E. niger). The 3B10 mAb did not bind to IgM from 10 other fish species resident in the Great Lakes basin. Using the 3B10 mAb, it was possible to determine the muskellunge Ig ability to bind to antigens. Using trinitrophenyl hapten conjugated to keyhole limpet hemocyanin (TNP-KLH) as the eliciting antigen, muskellunge Ig subclasses exhibited a range of affinities with log aK values 5.56-6.25 that is considered intermediate compared to other fish species. 3B10 mAb was used to develop and evaluate an indirect ELISA for the detection and quantitation of circulating antibodies against the viral hemorrhagic septicemia virus genotype IVb (VHSV-IVb). Using the newly optimized assay, anti-VHSV-IVb antibodies were detected in sera of VHSV-IVb vaccinated muskellunge as well as from those of wild muskellunge sampled from an endemic waterbody. In addition to its use in immunoassays, the developed 3B10 mAb will enable future investigation aiming at deciphering immune mechanism of this important fish species to pathogens.

Herpesvirus Infection Induces both Specific and Heterologous Antiviral Antibodies in Carp

IgM antibody diversity induced by viral infection in teleost fish sera remains largely unexplored despite several studies performed on their transcript counterparts in lymphoid organs. Here, IgM binding to microarrays containing ~20,000 human proteins was used to study sera from carp (Cyprinus carpio) populations having high titers of viral neutralization in vitro after surviving an experimental infection with cyprinid herpes virus 3 (CyHV-3). The range of diversity of the induced antibodies was unexpectedly high, showing CyHV-3 infection-dependent, non-specific IgM-binding activity of a ~20-fold wider variety than that found in sera from healthy carp (natural antibodies) with no anti-CyHV-3 neutralization titers. An inverse correlation between the IgM-binding levels in healthy versus infection-survivor/healthy ratios suggests that an infection-dependent feed back-like mechanism may control such clonal expansion. Surprisingly, among the infection-expanded levels, not only specific anti-frgII_CyHV-3 and anti-CyHV-3 IgM-binding antibodies but also antibodies recognizing recombinant fragment epitopes from heterologous fish rhabdoviruses were detected in infection-survivor carp sera. Some alternative explanations for these findings in lower vertebrates are discussed.

Validation of a serum neutralization test for detection of antibodies specific to cyprinid herpesvirus 3 in infected common and koi carp (Cyprinus carpio)

Cyprinid herpesvirus 3 (CyHV-3) is the aetiological agent of a serious infective, notifiable disease affecting common carp and varieties. In survivors, infection is generally characterized by a subclinical latency phase with restricted viral replication. The CyHV-3 genome is difficult to detect in such carrier fish that represent a potential source of dissemination if viral reactivation occurs. In this study, the analytical and diagnostic performance of an alternative serum neutralization (SN) method based on the detection of CyHV-3-specific antibodies was assessed using 151 serum or plasma samples from healthy and naturally or experimentally CyHV-3-infected carp. French CyHV-3 isolate 07/108b was neutralized efficiently by sera from carp infected with European, American and Taiwanese CyHV-3 isolates, but no neutralization was observed using sera specific to other aquatic herpesviruses. Diagnostic sensitivity, diagnostic specificity and repeatability of 95.9%, 99.0% and 99.3%, respectively, were obtained, as well as a compliance rate of 89.9% in reproducibility testing. Neutralizing antibodies were steadily detected in infected carp subjected to restrictive or permissive temperature variations over more than 25 months post-infection. The results suggest that this non-lethal diagnostic test could be used in the future to improve the epidemiological surveillance and control of CyHV-3 disease.

The amino-terminal domain of ORF149 of koi herpesvirus is preferentially targeted by IgM from carp populations surviving infection

Recombinantly expressed fragments of the protein encoded by ORF149 (pORF149), a structural protein from the common- and koi-carp-infecting cyprinid herpesvirus-3 (CyHV-3) that was previously shown to be antigenic, were used to obtain evidence that its amino-terminal part contains immunodominant epitopes in fish populations that survived the infection. To obtain such evidence, nonspecific binding of carp serum tetrameric IgM had to be overcome by a novel ELISA protocol (rec2-ELISA). Rec2-ELISA involved pre-adsorption of carp sera with a heterologous recombinant fragment before incubation with pORF149 fragments and detection with anti-carp IgM monoclonal antibodies. Only in this way was it possible to distinguish between sera from uninfected and survivor carp populations. Although IgM from survivors recognised pORF149 fragments to a lesser degree than whole virus, specificity was confirmed by correlation of rec2- and CyHV-3-ELISAs, inhibition of rec2-ELISA by an excess of frgIIORF149, ELISA using IgM-capture, Western blotting, and reduction of reactivity in CyHV-3-ELISA by pre-adsorption of sera with frgIIORF149. The similarity of IgM-binding profiles between frgIORF149 (amino acid residues 42-629) and frgIIORF149 (42-159) and their reactivities with previously described anti-CyHV-3 monoclonal antibodies confirmed that most pORF149 epitopes were localised in its amino-terminal part.