Human Monoclonal Antibodies to Escherichia coli Outer Membrane Protein A Porin Domain Cause Aggregation but Do Not Alter In Vivo Bacterial Burdens in a Murine Sepsis Model

Escherichia coli is one of the most frequent human pathogens, increasingly exhibits antimicrobial resistance, and has complex interactions with the host immune system. E coli exposure or infection can result in the generation of antibodies specific for outer membrane protein A (OmpA), a multifunctional porin. We identified four OmpA-specific naturally occurring antibodies from healthy human donor B cells and assessed their interactions with E. coil and OmpA. These antibodies are highly specific for OmpA, exhibiting no cross-reactivity to a strain lacking ompA and retaining binding to both laboratory and clinical isolates of E. coil in enzyme-linked immunosorbent assay (EUSA) and immunofluorescence assays. One monoclonal antibody (Mab), designated ECOL-11, is specific for the extracellular N-terminal porin domain of OmpA and induces growth phase-specific bacterial aggregation. This aggregation is not induced by the fragment antigen binding (Fab) form of the MAb, suggesting the importance of bivalency for this aggregating activity. KOL-11 decreases adhesion and phagocytosis of E. coil by RAW 264.7 macrophage-like cells, possibly by inhibiting the adhesion functions of OmpA Despite this in vitro phenotype, organ E. coil burdens were not altered by antibody prophylaxis in a murine model of lethal E. coil septic shock Our findings support the importance of OmpA at the host-pathogen interface and begin to explore the implications and utility of E. coli-specific antibodies in human hosts.