EVALUATION OF A COMMERCIAL COMPETITIVE ENZYME-LINKED IMMUNOSORBENT ASSAY FOR DETECTION OF AVIAN INFLUENZA VIRUS SUBTYPE H5 ANTIBODIES IN ZOO BIRDS

A novel epitope-blocking ELISA for specific and sensitive detection of antibodies against H5-subtype influenza virus hemagglutinin

Background

H5-subtype highly pathogenic (HP) avian influenza viruses (AIVs) cause high mortality in domestic birds and sporadic infections in humans with a frequently fatal outcome, while H5N1 viruses have pandemic potential. Due to veterinary and public health significance, these HPAIVs, as well as low pathogenicity (LP) H5-subtype AIVs having a propensity to mutate into HP viruses, are under epidemiologic surveillance and must be reported to the World Organization for Animal Health (OIE). Our previous work provided a unique panel of 6 different monoclonal antibodies (mAbs) against H5 hemagglutinin (HA), which meets the demand for high-specificity tools for monitoring AIV infection and vaccination in poultry. In this study, we selected one of these mAbs to develop an epitope-blocking (EB) ELISA for detecting H5 subtype-specific antibodies in chicken sera (H5 EB-ELISA).

Methods

In the H5 EB-ELISA, H5 HA protein produced in a baculovirus-expression vector system was employed as a coating antigen, and the G-7-27-18 mAb was employed as a blocking antibody. The performance characteristics of the assay were evaluated by testing 358 sera from nonimmunized chickens and chickens immunized with AIVs of the H1–H16 subtypes or recombinant H5 HA antigen to obtain the reference and experimental antisera, respectively. The samples were classified as anti-H5 HA positive or negative based on the results of the hemagglutination inhibition (HI) assay, the gold standard in subtype-specific serodiagnosis.

Results

The H5 EB-ELISA correctly discriminated between the anti-H5 HA negative sera, including those against the non-H5 subtype AIVs, and sera positive for antibodies against the various-origin H5 HAs. Preliminary validation showed 100% analytical and 97.6% diagnostic specificities of the assay and 98.0% and 99.1% diagnostic sensitivities when applied to detect the anti-H5 HA antibodies in the reference and experimental antisera, respectively.

Conclusions

The H5 EB-ELISA performed well in terms of diagnostic estimates. Thus, further optimization and validation work using a larger set of chicken sera and receiver operating characteristic (ROC) analysis are warranted. Moreover, the present assay provides a valuable basis for developing multispecies screening tests for birds or diagnostic tests for humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01564-6.

Quantitative ELISA sandwich for a new vaccine against avian influenza virus H5N1

Analytical techniques are essential in the process of standardizing and validating vaccines. In this study we described a methodology to establish an ELISA sandwich for the quantification of a new vaccine against avian influenza virus H5N1 based on the main antigenic determinant of the virus, the extracellular domain of the glycoprotein hemagglutinin (HA), fused to the extracellular domain of the chicken CD154 glycoprotein (HACD). The chimerical proteins HA and HACD were produced in SiHa cells and the experiments were performed by using three monoclonal antibodies (MAb-HA1, MAb-HA2 and MAb-HA3), alone or conjugated to horseradish peroxidase (HRP-HA1, HRP-HA2 and HRP-HA3). The hemagglutination inhibition assay was carried out with a negative and a positive H5N2 reference serum, together with the antigen H5N1 A/Mallard/Italy/3401/05, all purchased from the "Istituto Zooprofilattico delle Venezie", Italy. After demonstrating the similar recognition pattern between the HA and the HACD proteins, the MAb-HA2 at a concentration of 2,5 μg/mL was selected as the capture antibody and the HRP-HA3 at a dilution of 1/20000 was selected as the detection antibody due to their optimal values of optical density at these conditions. The best dynamic range of the standard curve using the protein HACD was achieved at concentrations from 100 to 1,56 ng/mL. There were no significant differences when five batches of HACD were quantified by the ELISA sandwich and the bicinchoninic acid method linked to densitometry. In conclusion, the final parameters for the quantification of the chimeric protein HACD using an ELISA sandwich were described, which could contribute to develop a large-scale process for the final vaccine production.