Key Points• Neutrophilic granulocytes stimulated with opsonized particles produce microvesicles (MVs) that are able to impair bacterial growth.• Antibacterial effect correlates with number and size of aggregates between bacteria and MVs and depends on cytoskeletal reorganization of MVs.Cell-derived vesicles represent a recently discovered mechanism for intercellular communication. We investigated their potential role in interaction of microbes with host organisms. We provide evidence that different stimuli induced isolated neutrophilic granulocytes to release microvesicles with different biologic properties. Only opsonized particles initiated the formation of microvesicles that were able to impair bacterial growth. The antibacterial effect of neutrophil-derived microvesicles was independent of production of toxic oxygen metabolites and opsonization or engulfment of the microbes, but depended on ␤ 2 integrin function, continuous actin remodeling, and on the glucose supply. Neutrophil-derived microvesicles were detected in the serum of healthy donors, and their number was significantly increased in the serum of bacteremic patients. We propose a new extracellular mechanism to restrict bacterial growth and dissemination. IntroductionCell-derived vesicles (such as exosomes, ectosomes, microvesicles, shedding microvesicles, and microparticles) represent a recently discovered mechanism for cell-cell communication. [1][2][3] Exosomes are small (50-100 nm) vesicles released from multivesicular bodies. 4 They are involved in antigen presentation [5][6][7] and cell-tocell transfer of receptors 8 or RNA, 9,10 thereby influencing or reprogramming neighboring cells and often promoting tumorigenesis. 8,11 Exosomes also play a role in host defense against microorganisms: tracheobronchial epithelial cells produce exosome-like vesicles with antiviral activity, 12 and macrophage-derived exosomes are able to transfer pathogen-associated molecular patterns of opportunistic intracellular pathogens to uninfected cells. 13 Larger vesicles, called microvesicles (MVs) or microparticles express tissue factor on their surface that is capable of initiating coagulation. 14 Both exosomes and MVs of different cellular origin were detected in various body fluids and selective enrichment was related to specific diseases. [15][16][17][18][19] Neutrophilic granulocytes (PMNs) play a critical role in innate immune mechanisms by engulfing, killing, and degrading various microorganisms. PMNs produce larger vesicles (named by the authors alternatively as ectosomes, microparticles, or MVs) after incubation with various stimuli. [19][20][21][22] Microparticles obtained from PMNs stimulated by chemotactic agents or phorbol esters activated cytokine (IL-6) secretion from endothelial cells 23 and platelets, 24 thereby contributing to the procoagulant effect of leukocytederived microparticles. 25 Chemotactic peptide-induced PMNectosomes increase the secretion of the anti-inflammatory cytokine transforming growth factor ␤ 26 and interfere with the maturatio...

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Itaconate is a nonamino organic acid exhibiting antimicrobial effects. It has been recently identified in cells of macrophage lineage as a product of an enzyme encoded by immunoresponsive gene 1 (Irg1), acting on the citric acid cycle intermediate cis-aconitate. In mitochondria, itaconate can be converted by succinate-coenzyme A (CoA) ligase to itaconyl-CoA at the expense of ATP (or GTP), and is also a weak competitive inhibitor of complex II. Here, we investigated specific bioenergetic effects of increased itaconate production mediated by LPS-induced stimulation of Irg1 in murine bone marrow-derived macrophages (BMDM) and RAW-264.7 cells. In rotenone-treated macrophage cells, stimulation by LPS led to impairment in substrate-level phosphorylation (SLP) of in situ mitochondria, deduced by a reversal in the directionality of the adenine nucleotide translocase operation. In RAW-264.7 cells, the LPS-induced impairment in SLP was reversed by short-interfering RNA(siRNA)-but not scrambled siRNA-treatment directed against Irg1. LPS dose-dependently inhibited oxygen consumption rates (61-91%) and elevated glycolysis rates (>21%) in BMDM but not RAW-264.7 cells, studied under various metabolic conditions. In isolated mouse liver mitochondria treated with rotenone, itaconate dose-dependently (0.5-2 mM) reversed the operation of adenine nucleotide translocase, implying impairment in SLP, an effect that was partially mimicked by malonate. However, malonate yielded greater ADP-induced depolarizations (3-19%) than itaconate. We postulate that itaconate abolishes SLP due to 1) a "CoA trap" in the form of itaconyl-CoA that negatively affects the upstream supply of succinyl-CoA from the α-ketoglutarate dehydrogenase complex; 2) depletion of ATP (or GTP), which are required for the thioesterification by succinate-CoA ligase; and 3) inhibition of complex II leading to a buildup of succinate which shifts succinate-CoA ligase equilibrium toward ATP (or GTP) utilization. Our results support the notion that Irg1-expressing cells of macrophage lineage lose the capacity of mitochondrial SLP for producing itaconate during mounting of an immune defense.

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