Host-Derived Microvesicles Carrying Bacterial Pore-Forming Toxins Deliver Signals to Macrophages: A Novel Mechanism of Shaping Immune Responses

• Main Authors: René Köffel, Heidi Wolfmeier, Yu Larpin, Hervé Besançon, Roman Schoenauer, Viktoria S. Babiychuk, Patrick Drücker, Thomas Pabst, Timothy J. Mitchell, Eduard B. Babiychuk, Annette Draeger
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2018-07-01
• Series: Frontiers in Immunology
• Subjects: macrophage polarization; microvesicles; liposomes; bacterial pore-forming toxins; host-defense
• Online Access: https://www.frontiersin.org/article/10.3389/fimmu.2018.01688/full

Bacterial infectious diseases are a leading cause of death. Pore-forming toxins (PFTs) are important virulence factors of Gram-positive pathogens, which disrupt the plasma membrane of host cells and can lead to cell death. Yet, host defense and cell membrane repair mechanisms have been identified: i.e., PFTs can be eliminated from membranes as microvesicles, thus limiting the extent of cell damage. Released into an inflammatory environment, these host-derived PFTs-carrying microvesicles encounter innate immune cells as first-line defenders. This study investigated the impact of microvesicle- or liposome-sequestered PFTs on human macrophage polarization in vitro. We show that microvesicle-sequestered PFTs are phagocytosed by macrophages and induce their polarization into a novel CD14+MHCIIlowCD86low phenotype. Macrophages polarized in this way exhibit an enhanced response to Gram-positive bacterial ligands and a blunted response to Gram-negative ligands. Liposomes, which were recently shown to sequester PFTs and so protect mice from lethal bacterial infections, show the same effect on macrophage polarization in analogy to host-derived microvesicles. This novel type of polarized macrophage exhibits an enhanced response to Gram-positive bacterial ligands. The specific recognition of their cargo might be of advantage in the efficiency of targeted bacterial clearance.