Specific Cell-Surface Glycans on Phagocytes Mediate Binding of Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is a Gram-negative bacterium that, as an opportunistic pathogen, substantially contributes to high morbidity and mortality rates in susceptible individuals such as those with cystic fibrosis or neutropenia. Previous studies identified that the downregulation or loss of bacterial flagellar motility, typically observed within chronic infections, enables bacteria to evade interactions with phagocytic cells that would result in phagocytic uptake. Our recent work demonstrated that exogenous addition of a negatively charged lipid, PIP3, induces binding and phagocytosis of non-motile strains of P. aeruginosa. Based on this work, we hypothesized that the engagement of P. aeruginosa by host innate cells, and subsequent phagocytosis, is mediated by motility-dependent interactions with cell-surface polyanions. We now report that endogenous polyanionic N-linked glycans and heparan sulfate mediate bacterial binding of P. aeruginosa by human monocytic cells. These specific cell-surface interactions result in P. aeruginosa phagocytosis, bacterial type 3 secretion system (T3SS)-mediated cellular intoxication and the IL-1β inflammatory response of the host innate immune cells. Concomitantly, inhibition of host cell N-glycan synthesis reduces T3SS-mediated cytotoxicity and the IL-1β response induced by the bacteria. Importantly, the bacterial interactions with the glycans were motility-dependent and could be recapitulated with purified, immobilized glycans. Therefore, this work describes novel interactions of P. aeruginosa with specific phagocyte cell-surface glycans that modulate relevant host innate immune responses to the bacteria, including phagocytosis, inflammation and cytotoxicity.