Membrane retrieval in neutrophils during phagocytosis: inhibition by M protein-expressingS. pyogenesbacteria

Abstract

During phagocytosis and phagosome maturation, complex membrane traffic events must be coordinated. We have observed, using fluorescent fluid-phase and membrane markers, that in the human neutrophil, internalization of nonopsonized, Gram-positive bacteria, but not of latex beads, is accompanied by a rapid and localized formation of pinosomal structures. This pinocytic response is calcium-dependent but insensitive to actin cytoskeleton disruption and wortmannin treatment. Contrary to what we observe, endosomal structures usually are considered to participate in phagosome formation by providing necessary membrane to forming phagosomes. Instead, our results show a coupling between neutrophil secretory and membrane-retrieval processes during phagosome maturation, and we suggest that the observed, localized pinocytic response is linked to the secretion of azurophilic granules toward nascent phagosomes. Accordingly, M and M-like protein-expressing Streptococcus pyogenes bacteria, which are able to survive inside neutrophil phagosomes, inhibit both the secretion of azurophilic granules to phagosomes and pinosome formation.

Streptococcus pyogenes bacteria modulate membrane traffic in human neutrophils and selectively inhibit azurophilic granule fusion with phagosomes

“…However, it should be noted that the interpretation of these data is not straightforward because of a concomitant stimulation of pinosomal re‐uptake of the granule markers. Stimulation of pinosome formation was recently described and shown to be less efficiently triggered by live AP1 bacteria than the mutant strain, BMJ71 (Bauer and Tapper, 2004). Most likely, the reduced ability of live AP1 bacteria to trigger pinosome formation is coupled to the relative inability of AP1 to trigger secretion of azurophilic granules, as observed in the present study.…”

“…However, when we compared live and heat‐killed bacteria, we found that the live AP1 bacteria were more attenuated in their ability to stimulate phagosome–azurophilic granule fusion. It should be noted that similar observations were made regarding stimulation of pinosome formation by live and heat‐killed AP1 bacteria (Bauer and Tapper, 2004). If, as suggested, azurophilic granule secretion precedes induced pinosome formation, it is likely that the modulation of phagocyte membrane traffic by AP1 bacteria involves primarily azurophilic granules.…”

Phagocytosis of Streptococcus pyogenes by All-Trans Retinoic Acid-Differentiated HL-60 Cells: Roles of Azurophilic Granules and NADPH Oxidase

“…A potential drawback is that we used heat-killed bacteria for this. However, we have earlier reported that effects on intracellular trafficking persist even after heat treatment of bacteria, albeit to a lesser degree [23], [42]. The reduced amount of azurophilic granule-marker found on phagosomes containing wild-type bacteria as compared to those containing the mutant provided further evidence to the hypothesis that wild-type S.pyogenes bacteria interfere with phagosome maturation.…”

Understanding how leading bacterial pathogens subvert innate immunity to reveal novel therapeutic targets

“…77 GAS M protein was found to inhibit the fusion of azurophilic granules with the phagosome and other membrane trafficking events required for phagosome maturation. 78,79 Leukocidal toxins Staphylococcus aureus and GAS elaborate a variety of potent cytotoxins, and another important mechanism for innate immune resistance may involve triggering the death of the phagocytic cell types before bacterial killing can be accomplished. SA produces a family of 2-subunit heteroheptameric toxins capable of oligomerizing in the membrane of target leukocytes to produce pores and promote hypo-osmotic cell lysis.…”