Circulating Apoptotic Microparticles in Systemic Lupus Erythematosus Patients Drive the Activation of Dendritic Cell Subsets and Prime Neutrophils for NETosis

Abstract

Objective Circulating chromatin‐containing apoptotic material and/or neutrophil extracellular traps (NETs) have been proposed to be an important driving force for the antichromatin autoimmune response in patients with systemic lupus erythematosus (SLE). The aim of this study was to determine the exact nature of microparticles in the circulation of SLE patients and to assess the effects of the microparticles on the immune system. Methods We analyzed microparticles isolated from the plasma of patients with SLE, rheumatoid arthritis (RA), and systemic sclerosis (SSc), as well as from healthy subjects. The effects of the microparticles on blood‐derived dendritic cells (DCs) and neutrophils were assessed by flow cytometry, enzyme‐linked immunosorbent assay, and immunofluorescence microscopy. Results In SLE patients, we identified microparticles that were highly positive for annexin V and apoptosis‐modified chromatin that were not present in healthy subjects or in RA or SSc patients. These microparticles were mostly CD31+/CD45– (endothelial), partly CD45+/CD66b+ (granulocyte), and negative for B and T cell markers. Microparticles isolated from the plasma of SLE patients increased the expression of the costimulatory surface molecules CD40, CD80, CD83, and CD86 and the production of proinflammatory cytokines interleukin‐6, tumor necrosis factor, and interferon‐α by blood‐derived plasmacytoid DCs (PDCs) and myeloid DCs (MDCs). SLE microparticles also primed blood‐derived neutrophils for NETosis. Microparticles from healthy subjects and from RA or SSc patients exhibited no significant effects on MDCs, PDCs, and NETosis. Conclusion Circulating microparticles in SLE patients include a population of apoptotic cell–derived microparticles that has proinflammatory effects on PDCs and MDCs and enhances NETosis. These results underline the important role of apoptotic microparticles in driving the autoimmune response in SLE patients.

Cell death in the pathogenesis of systemic lupus erythematosus and lupus nephritis

“…Previous groups have successfully inhibited NETosis and reduced disease activity by using molecules that scavenge ROS, inhibit PAD activation, modulate intracellular and extracellular calcium pools, block MPO activation, and disrupt the stabilization of the actin cytoskeleton (170). Given the critical role of DNASE1L3 in the degradation of DNA in circulating apoptotic microparticles and prevention of autoimmunity in mice (126), examining the effect of DNASE1L3 in SLE patients should be explored. Finally, HDAC inhibitors have been shown to modulate renal disease in various mouse models of lupus and should be further investigated in SLE patients (279-281).…”

“…DNASE1L3 is a serum enzyme that is critical for the degradation of chromatin in microparticles precluding autoantibody recognition of microparticle DNA and humans and mice lacking DNASE1L3 develop SLE-like disease (127-131). Microparticles from SLE patients express apoptosis-related histone modifications while these were absent in microparticles from healthy individuals (126). Microparticles from SLE patients activate pDCs and myeloid DCs that results in the induction of proinflammatory cytokines and type I IFN and also primes neutrophils for neutrophil extracellular trap (NET) formation (126).…”

“…Microparticles from SLE patients express apoptosis-related histone modifications while these were absent in microparticles from healthy individuals (126). Microparticles from SLE patients activate pDCs and myeloid DCs that results in the induction of proinflammatory cytokines and type I IFN and also primes neutrophils for neutrophil extracellular trap (NET) formation (126). Based on this evidence, increased apoptosis-induced histone modifications in SLE may have immunostimulatory roles and contribute to the pathogenesis of LN…”

Regulation of chronic inflammatory and immune processes by extracellular vesicles

“…For example, EVs present in synovial fluid of patients with RA not only contain citrullinated autoantigens, but also can be found in complexes with anti-citrullinated peptide antibodies (68). Similarly, plasma EVs from systemic lupus erythematous (SLE) were shown to not only contain self antigens (69,70), but also to interact with IgG, IgM, and complement proteins. However, it was not clear whether these interactions represent true immune complexes (71)(72)(73).…”

Endothelial microparticles: Pathogenic or passive players in endothelial dysfunction in autoimmune rheumatic diseases?

“…This microparticle subpopulation, when isolated from the plasma of SLE patients, increases the expression of co-stimulatory surface molecules and production of pro-inflammatory cytokines IL-6, TNF-α and IFN-α by blood-derived plasmacytoid dendritic cells (pDCs) and myeloid dendritic cells (mDCs), as well as priming blood-derived neutrophils for NETosis. These results underline the important role of apoptotic endothelial microparticles in driving the autoimmune response in SLE patients [49]. This novel activation pathway may be implicated in various additional inflammatory disorders suggesting endothelial microparticles could be an important immunomodulatory therapeutic target [50].…”