Glycoprotein-based enzyme-linked immunosorbent assays for serodiagnosis of infectious laryngotracheitis

Glycoprotein D peptide-based diagnostic approach for the detection of avian infectious laryngotracheitis antibodies

Infectious laryngotracheitis (ILT) is a highly contagious respiratory disease of chickens, pheasants, and peafowl. It is caused by the alpha herpesvirus, infectious laryngotracheitis virus (ILTV). Glycoprotein D (gD) of ILTV is immunogenic and helps in its binding to the susceptible host cell receptor. In the present study, a recombinant gD protein was expressed in a prokaryotic system to develop a single serum dilution ELISA. In addition, two immunogenic peptides, corresponding to regions 77-89 and 317-328, were identified in gD protein. The peptides were synthesized using solid-phase peptide synthesis, purified using reversed-phase HPLC, and characterized using mass spectrometry. The peptides displayed a good titre and were found to be promising antigens to coat the ELISA plate to detect the ILTV antibodies in the serum sample. The developed ELISA showed 96.9% sensitivity, 87.5% specificity, and 95.3% accuracy as compared to OIE referenced standard indirect ILTV ELISA (whole viral coated). The assay may not differentiate vaccinated from infected birds when the flocks are administered with live attenuated vaccines. However, the assay could be useful to detect the disease condition in birds vaccinated with recombinant vaccine expressing glycoproteins other than gD. The developed ILTV single serum dilution ELISA could be an alternative to the existing diagnostics for the detection of ILTV antibodies.

Investigation onto the correlation between systemic antibodies to surface glycoproteins of infectious laryngotracheitis virus (ILTV) and protective immunity

Infectious laryngotracheitis virus (ILTV) is an alphaherpesvirus that causes upper respiratory tract disease in chickens and significant losses to the poultry industry worldwide. Both antibody and cell-mediated responses are generated against ILTV infection; however, the correlation of humoral immune response with protection against ILTV infection is debatable. To examine if whether antibody responses to individual ILTV glycoproteins are correlated with disease and protection, four ILTV glycoproteins (gD, gE, gG and gJ) were expressed as recombinant proteins and used in conjunction with commercially available recombinant gC and gI in indirect ELISAs to measure post-vaccination and/or post-challenge chicken serum antibodies. Serum optical density (OD) values detected by the whole virus, gC, gI and gJ were significantly higher in birds vaccinated with the Serva vaccine strain compared to the SA2 vaccine strain. However, the mean ODs detected by gD, gE and gG were not significantly different between the vaccine strains. Examination of post-ILTV vaccination sera found that gE was the most antigenic glycoprotein and that gC ODs were strongly correlated with those of gI and gJ, while ODs to gG had a relatively poor correlation with those of other glycoproteins. Moderate to poor correlations were found between microscopic tracheal lesion scores and ODs to individual glycoproteins. Examination of post-vaccination pre-challenge antibodies to individual glycoproteins did not find a strong correlation with protective immunity as measured by the severity of clinical signs, gross lesions, and tracheal viral load. Results from this study demonstrated that systemic antibody titers to individual ILTV glycoproteins C, D, E, G, I and J had a relatively poor correlation to protective immunity.