Characterization of cross-reactive, non-neutralizing monoclonal antibodies against a pandemic GII.4 norovirus variant.

Unlabelled: Antibodies are thought to play a major role in protection against human norovirus infection. Mouse humoral responses closely mimic those of humans; thus, mouse models are used to characterize norovirus epitopes on the major viral capsid protein, VP1. We have developed a panel of mouse monoclonal antibodies (mAbs) produced against the last pandemic variant to emerge, Sydney 2012. While most mAbs (25/44) were mapped to variable antigenic sites on VP1, 19 of the mAbs were cross-reactive against multiple genotypes or GII.4 variants. Most (12/19) of the cross-reactive mAbs bound to the Shell domain and were cross-reactive with different GII noroviruses. Interestingly, mAb 30A11 exhibited cross-reactivity against all tested norovirus genotypes (GI, GII, GIV, and GIX). This mAb was mapped to a highly conserved region of the Shell domain (PIDPWII) using peptide ELISA and immunofluorescence. Of those mapping to the Protruding (P) domain, two (19C10 and 14B11) showed cross-reactivity with GII noroviruses. Using hydrogen-deuterium exchange mass spectrometry, we mapped 19C10 to a conserved region of the P domain near the P/Shell interface, which explains its cross-reactivity with different GII noroviruses and lack of histo-blood group antigen-blocking activity. Binding and mutational analyses showed that residues 518, 519, and 525 are important for 19C10 and 14B11 epitope recognition. While the antibodies described here are mostly non-neutralizing, they can be useful tools for research and diagnostics of noroviruses. The role of non-neutralizing, cross-reactive antibodies targeting different areas of the viral capsid merits further research to facilitate our understanding of immunity to norovirus infection and disease.

Importance: To gain insights into the overall immune responses to human norovirus, we characterized non-neutralizing, cross-reactive monoclonal antibodies (mAbs) developed against a pandemic GII.4 norovirus. We determined the binding epitope of an antibody that exhibited cross-reactivity against all tested noroviruses, which makes it a useful tool for research and diagnostics. The epitope of two additional non-neutralizing mAbs was mapped to a less conserved region on the viral capsid protein, explaining their cross-reactivity patterns. Often overlooked, the role of non-neutralizing, cross-reactive mAbs merits further research to facilitate our understanding of immunity to norovirus infection and disease.