Identification of previously unknown antigenic epitopes on the S and N proteins of avian infectious bronchitis virus

Abstract

This paper describes mapping of antigenic and host-protective epitopes of infectious bronchitis virus proteins by assessing the ability of defined peptide regions within the S1, S2 and N proteins to elicit humoral, cell-mediated and protective immune responses. Peptides corresponding to six regions in the S1 (Sp1-Sp6), one in the S2 (Sp7) and four in the N protein (Np1-Np4) were synthesized and coupled to either diphtheria toxoid (dt) or biotin (bt). Bt-peptides were used to assess if selected regions were antigenic and contained B- or T-cell epitopes and dt-peptides if regions induced an antibody response and protection against virulent challenge. All S1 and S2 peptides were antigenic, being recognised by IBV immune sera and also induced an antibody response following inoculation into chicks. Three S1-and one S2-bt peptides also induced a delayed type hypersensitivity response indicating the presence of T-cell epitopes. The S2 peptide Sp7 (amino acid position 566-584) previously identified as an immundominant region, was the most antigenic of all peptides used in this study. Two S1 (Sp4 and Sp6) and one S2 peptide (Sp7), protected kidney tissue against virulent challenge. From four N peptides located in the amino-terminal part of the N protein, only one, Np2 (amino acid position 72-86), was antigenic and also induced a delayed type hypersensitivity response. None of the N peptides induced protection against virulent challenge. The results suggest that the S1 glycoprotein carries additional antigenic regions to those previously identified and that two regions located in the S1 and one in the S2 at amino acid positions 294-316 (Sp4), 532-537 (Sp6) and 566-584 (Sp7) may have a role in protection.

The Protective Immune Response against Infectious Bronchitis Virus Induced by Multi-Epitope Based Peptide Vaccines

“…SP 540{564 epitopes have been shown to recognize neutralizing monoclonal antibodies and to provide protection against IBV. 14,35) As expected, we found that EpiA composed of the SP 540{564 epitope elicited neutralizing antibody, and prevented IBV from infecting SPF eggs. However, the humoral responses were not the only parameter of the protective responses to the virus.…”

Development of a multi-epitope antigen of S protein-based ELISA for antibodies detection against infectious bronchitis virus

“…The epitope E3 (Sp7, 566-584 aa) was also largely conserved in all IBV strains. 14) Additionally, the epitopes of the SE protein harbored were mainly linear but not conformational as the epitopes of S protein identified in the literature were mostly short peptides to be conformation independent, and a number of software tools developed and applied in recent years were mainly focused on linear B-cell epitope prediction. 19,20,30−33) We designed the SE by taking into account both the identified antigenic sites and the predicted epitopes to make it more reliable and perfect as the defined epitopes of S1 and S2 protein are not enough.…”

“…Thus the cut-off value using the mean ± 3 S.D was defined at 0.332. Heterologous serums to the viruses of 11,34) A conformation-independent Sp7 (566-584 aa), largely conserved in all IBV strains 14) Prediction results of ABCpred ND, IBD, and AI were shown negative by SE-ELISA (OD 450 0.164-0.178). By testing 10 selected serum samples in quadruplicate, the inter-assay CV was observed to range from 2.75 to 5.49%, with a median value of 4.23%, and the intra-assay CV was observed to range from 1.66 to 5.32%, with a median value of 3.17%.…”

“…While it also showed clearly that only two antigenic sites (S1-F and S2-G) contained in the S-fg protein (381-555 aa) made contribution to the antigenicity and the cross-reactivity of the S-fg ELISA, which were located with the region of S1 subunit C terminus and S2 subunit N terminus. Otherwise, additional antigenic regions of S protein were identified in subsequent researches, 12,14) and these findings enable the designation of the S protein fragment with improved versions and with enhanced detection potential.…”

“…It was designed by arranging the three fragments in tandem in the order of E1-E2-E3 and was expressed in Escherichia coli BL21(DE3). It harbored several antigenic sites in the conserved regions, including Sp1 (194-209 aa), Sp2 (209-228 aa), and Sp3 (245-260 aa, QYNTGNFSDGLYPFTN), 14,18) as well as two conformation-independent epitopes Sp5 (518-532 aa) and Sp7 (566-584 aa). 14) Therefore, the aim of this study was to establish an indirect ELISA based on the multi-epitope antigen SE and to evaluate its potential in the detection of IBV antibodies.…”