Targeting a conserved flagellin D1 epitope with 16G10 confers cross-serotype protection in murine <i>Pseudomonas aeruginosa</i> infection models

Escalating resistance in Pseudomonas aeruginosa (PA) underscores the need for resistance-agnostic immunotherapies. In this study, we generated a panel of 20 monoclonal antibodies against the flagellin protein FliC and identified 16G10 as a high-affinity lead. Epitope mapping revealed a conserved linear site within the D1 domain (Gly71–Ile88), a region essential for filament assembly. In vitro, 16G10 induced bacterial aggregation, suppressed swimming motility, and significantly reduced adhesion to and invasion of A549 cells, while limiting biofilm biomass by SEM and confocal 3D imaging. In vivo, in murine pneumonia, where 16G10 administered either after pre-incubation with imipenem-resistant PA strain or as post-infection therapy, it improved survival, lowered lung bacterial loads, reduced IL-6 and TNF-α concentrations, and attenuated histologic inflammation. Protection extended across serotype A and B flagellated strains, indicating broad coverage. These data nominate 16G10 as a promising candidate for immunotherapy of drug-resistant PA lung infections and establish a druggable flagellin epitope for future vaccine and antibody designs.