NOX2 mediates quiescent handling of dead cell remnants in phagocytes

Abstract

The phagocyte NADPH oxidase (the NOX2 complex) generates superoxide, the precursor to reactive oxygen species (ROS). ROS possess both antimicrobial and immunoregulatory function. Inactivating mutations in alleles of the NOX2 complex cause chronic granulomatous disease (CGD), characterized by an enhanced susceptibility to infections and autoimmune diseases such as Systemic lupus erythematosus (SLE). The latter is characterized by insufficient removal of dead cells, resulting in an autoimmune response against components of the cell's nucleus when non-cleared apoptotic cells lose their membrane integrity and present autoantigenic molecules in an inflammatory context. Here we aimed to shed light on the role of the NOX2 complex in handling of secondary necrotic cells (SNECs) and associated consequences for inflammation and autoimmunity during lupus. We show that individuals with SLE and CGD display accumulation of SNECs in blood monocytes and neutrophils. In a CGD phenotypic mouse strain ( Ncf1** mice) build-up of SNECs in Ly6C HI blood monocytes was connected with a delayed degradation of the phagosomal cargo and accompanied by production of inflammatory mediators. Treatment with H 2 O 2 or activators of ROS-formation reconstituted phagosomal abundance of SNECs to normal levels. Induction of experimental lupus further induced increased antibody-dependent uptake of SNECs into neutrophils. Lupus-primed Ncf1** neutrophils took up more SNECs than wild type neutrophils, whereas SNEC-accumulation in regulatory Ly6C −/LO monocytes was lower in Ncf1** mice. We deduce that the inflammatory rerouting of immune-stimulatory necrotic material into inflammatory phagocyte subsets contributes to the connection between low ROS production by the NOX2 complex and SLE.

Neutrophils—Important Communicators in Systemic Lupus Erythematosus and Antiphospholipid Syndrome

“…The LE-cell is a blood granulocyte in which the nucleus after excessive phagocytosis of opsonized apoptotic cell remnants, closely resembling SNEC, become outstretched and pushed toward the edges of the cell (70, 71). A combination of antibodies to several different histone proteins promotes this phenomenon, increasing the uptake of nuclear material (72, 73).…”

“…In NOX2 expressing cells such as neutrophils, ROS produced by the NOX2 complex are important for regulation of autophagy (91), clearance associated LC3 (microtubule-associated protein 1 light chain 3α)-mediated phagocytosis (92), pH-regulation in endosomes and phagosomes for quiescent handling of necrotic material (73, 93), as well as degranulation (94) and release of NETs (95, 96). Perhaps even more important are the use of ROS as a messenger molecule.…”

Neutrophil cytosolic factor 2 (NCF2) gene polymorphism is associated with juvenile‐onset systemic lupus erythematosus, but probably not with other autoimmune rheumatic diseases in children

“…As regards SLE, the macrophages of patients with SLE show a decrease in the efficiency of efferocytosis, that is phagocytosis of apoptotic bodies (Gaipl et al, 2007; Hahn et al, 2019), including at the level of the phagocytosis‐related genes expression (Majai et al, 2014). A similar phenomenon is observed in murine macrophages isolated from CGD animals (Bagaitkar et al, 2018).…”

“…Moreover, there is evidence that the NADPH oxidase is involved in the formation of patterns of major histocompatibility complex class II‐restricted epitopic repertoires by controlling phagosome acidification (Allan et al, 2014; Bagaitkar et al, 2018). The pathogenetic mechanism associated with a decrease in the ROS production by neutrophils and the development of SLE is more likely to be a deficient clearance of apoptotic cells due to a decrease in the efferocytosis efficiency and impaired digestion of apoptotic debris (Hahn et al, 2019). In lupus‐prone genetic background, this may lead to the production of autoantibodies and chronic inflammation, which are characteristic of SLE.…”

Reactive Oxygen Species in Autoimmune Cells: Function, Differentiation, and Metabolism

“…It is well-known that autoantigen triggered autoantibody plays a vital role in pathology of SLE, and this process is dramatically enhanced in experimental lupus in NOX2 deficient mice ( 48 , 49 ). Failure in timely clearance of apoptotic cells that is founded in NOX2 deficient lupus mice contributes to accumulation of secondary necrotic cells leading to increased secretion of inflammatory cytokines and chemokines ( 50 ).…”