Immunodominant IgM and IgG Epitopes Recognized by Antibodies Induced in Enterovirus A71-Associated Hand, Foot and Mouth Disease Patients

Abstract

Enterovirus A71 (EV-A71) is one of the main causative agents of hand, foot and mouth disease (HFMD). Unlike other enteroviruses that cause HFMD, EV-A71 is more frequently associated with severe neurological complications and fatality. To date, no effective licensed antivirals are available to combat EV-A71 infection. Little is known about the immunogenicity of viral non-structural proteins in humans. Previous studies have mainly focused on characterization of epitopes of EV-A71 structural proteins by using immunized animal antisera. In this study, we have characterized human antibody responses against the structural and non-structural proteins of EV-A71. Each viral protein was cloned and expressed in either bacterial or mammalian systems, and tested with antisera by western blot. Results revealed that all structural proteins (VP1-4), and non-structural proteins 2A, 3C and 3D were targets of EV-A71 IgM, whereas EV-A71 IgG recognized all the structural and non-structural proteins. Sixty three synthetic peptides predicted to be immunogenic in silico were synthesized and used for the characterization of EV-A71 linear B-cell epitopes. In total, we identified 22 IgM and four IgG dominant epitopes. Synthetic peptide PEP27, corresponding to residues 142–156 of VP1, was identified as the EV-A71 IgM-specific immunodominant epitope. PEP23, mapped to VP1 41–55, was recognized as the EV-A71 IgG cross-reactive immunodominant epitope. The structural protein VP1 is the major immunodominant site targeted by anti-EV-A71 IgM and IgG antibodies, but epitopes against non-structural proteins were also detected. These data provide new understanding of the immune response to EV-A71 infection, which benefits the development of diagnostic tools, potential therapeutics and subunit vaccine candidates.

Immune responses against enterovirus A71 infection: Implications for vaccine success

“…The N‐terminal half of VP1 protein also induced a poly‐reactive anti‐enterovirus IgG response . The well‐reported anti–EV‐A71 IgG epitopes SP70 and VP2‐28, identified by mice and rabbit sera respectively, were not recognized by human sera, suggesting that human sera target different linear or discontinuous conformational epitopes compared with animal sera . Nonetheless, all the identified immunogenic epitopes in humans or animals induced neutralizing activities, suggesting the importance of neutralization responses during EV‐A71 infection …”

Identification and characterization of neutralization epitopes at VP2 and VP1 of enterovirus A71

“…10 We recently also showed that even at high dilutions, acutely-infected patient sera with EV-A71-specific IgM antibody responses had high neutralization titers. 11 These findings suggest that IgM is particularly important for virus neutralization during acute EV-A71 infection. To examine this, we (Table 1).…”

“…On the VP2 protein, only anti‐EV‐A71 IgM epitopes were recognized within the VP2 neutralization epitope, vp2‐50 (148‐159: YKQTQPGADGFE) . We recently also showed that even at high dilutions, acutely‐infected patient sera with EV‐A71‐specific IgM antibody responses had high neutralization titers . These findings suggest that IgM is particularly important for virus neutralization during acute EV‐A71 infection.…”

“…Identification of neutralization epitopes are also important for therapeutic, vaccine, and diagnostics development. Several studies have identified neutralization epitopes, mainly in animals, and two recent studies described B‐cell epitopes in humans . The major neutralizing epitope is found on the capsid protein VP1, spanning amino acids at positions 208‐222, and recent studies have also identified neutralizing epitopes on VP2, VP3, and VP4 capsid proteins .…”

“…B-cell epitopes in humans. [10][11] The major neutralizing epitope is found on the capsid protein VP1, spanning amino acids at positions 208-222, 4 and recent studies have also identified neutralizing epitopes on VP2, VP3, and VP4 capsid proteins. [5][6][7][8][9] In this study, we further determined other neutralizing epitopes by generating EV-A71 neutralization escape mutants with a widely used commercial monoclonal antibody, MAB979 (Merck, Millipore, Darmstadt, Germany).…”