Identification of the dominant non-neutralizing epitopes in the
haemagglutinin of H7N9 avian influenza virus
Abstract
H7N9 avian influenza vaccines induce high levels of non-neutralizing
(nonNeu) antibodies against the haemagglutinin (HA). However, the
antigenic epitopes underlying this particular antibody response are
still undefined. In this study, a panel of 15 monoclonal antibodies
(mAbs) against the HA protein of H7N9 virus was generated and 14 of them
had no hemagglutination inhibition and virus neutralizing activities.
Four antigenic epitopes, including one linear and three conformational
epitopes, in HA were identified using peptide-based enzyme-linked
immunosorbent assay and biopanning of phage display random peptide
library. More importantly, two mAbs (4B7 4D5 and 1B10 1D1) strongly
inhibited HA-binding of chicken nonNeu antisera against viral-vectored
H7N9 vaccine, whereas lower inhibition was observed for chicken
neutralizing antisera. In contrast, there was weak competition between
the mAb and murine nonNeu antisera against inactivated H7N9 antigen. The
epitopes targeted by these two mAbs were defined as the immunodominant
epitopes underpinning the elicitation of nonNeu antibodies by
viral-vectored H7N9 vaccine. Additionally, the identified stalk epitopes
were conserved among the H1-H17 subtypes and the stalk-reactive mAbs
exhibited cross-reactivity with different subtypes. In conclusion, four
novel nonNeu epitopes in H7N9 HA were identified, and two dominant
epitopes underlying the induction of nonNeu antibodies by viral-vectored
H7N9 vaccine were identified. Our results add new knowledge to the
molecular basis for antibody immunity against H7N9 vaccines and provide
useful implications for vaccine design and modification.