Nitric oxide-induced membrane tubulovesicular extensions (cytonemes) of human neutrophils catch and hold Salmonella enterica serovar Typhimurium at a distance from the cell surface

Nitric oxide (NO) plays an important role in host defense against bacterial infections such as salmonellosis. NO and 4-bromophenacyl bromide (BPB) induce the formation of long tubulovesicular extensions (TVE, cytonemes, membrane tethers) from human neutrophils. These TVE serve as cellular sensory and adhesive organelles. In the present study, we demonstrated that in the presence of the NO donor, diethylamine NONOate or BPB human neutrophils bound and aggregated Salmonella enterica serovar Typhimurium bacteria extracellularly by TVE. In contrast, inhibition of NO-synthase activity by N-omega-nitro-l-arginine methyl ester stimulated neutrophil phagocytosis (ingestion) of bacteria. Neutrophil TVE consisted of membrane-covered cytoplasm as was shown by the fluorescent cytoplasmic dye 2',7'-bis(2carboxyethyl)-5,(6)-carboxyfluorescein, and the fluorescent lipid, BODIPY-labeled sulfatide. Disruption and shedding of TVE were accompanied by the appearance of specific invaginations (porosomes) on neutrophil cell bodies. These invaginations corresponded to the variations in diameter of TVE (160-240 nm). We hypothesized that TVE represented protrusions of neutrophil exocytotic trafficking through special structures on the neutrophil surface. In conclusion, we propose a novel mechanism by which NO-induced TVE formation enables neutrophils to bind and aggregate bacteria at a distance.