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Complement receptor Mac-1 is an adaptor for NB1 (CD177)-mediated PR3-ANCA neutrophil activation.

ABSTRACT: The glycosylphosphatidylinositol (GPI)-anchored neutrophil-specific receptor NB1 (CD177) presents the autoantigen proteinase 3 (PR3) on the membrane of a neutrophil subset. PR3-ANCA-activated neutrophils participate in small-vessel vasculitis. Since NB1 lacks an intracellular domain, we characterized components of the NB1 signaling complex that are pivotal for neutrophil activation. PR3-ANCA resulted in degranulation and superoxide production in the mNB1(pos)/PR3(high) neutrophils, but not in the mNB1(neg)/PR3(low) subset, whereas MPO-ANCA and fMLP caused similar responses. The NB1 signaling complex that was precipitated from plasma membranes contained the transmembrane receptor Mac-1 (CD11b/CD18) as shown by MS/MS analysis and immunoblotting. NB1 co-precipitation was less for CD11a and not detectable for CD11c. NB1 showed direct protein-protein interactions with both CD11b and CD11a by surface plasmon resonance analysis (SPR). However, when these integrins were presented as heterodimeric transmembrane proteins on transfected cells, only CD11b/CD18 (Mac-1)-transfected cells adhered to immobilized NB1 protein. This adhesion was inhibited by mAb against NB1, CD11b, and CD18. NB1, PR3, and Mac-1 were located within lipid rafts. In addition, confocal microscopy showed the strongest NB1 co-localization with CD11b and CD18 on the neutrophil. Stimulation with NB1-activating mAb triggered degranulation and superoxide production in mNB1(pos)/mPR3(high) neutrophils, and this effect was reduced using blocking antibodies to CD11b. CD11b blockade also inhibited PR3-ANCA-induced neutrophil activation, even when β2-integrin ligand-dependent signals were omitted. We establish the pivotal role of the NB1-Mac-1 receptor interaction for PR3-ANCA-mediated neutrophil activation.

SUBMITTER: Jerke U

PROVIDER: S-EPMC3044964 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundMyeloperoxidase released after neutrophil and monocyte activation can generate reactive oxygen species, leading to host tissue damage. Extracellular glomerular myeloperoxidase deposition, seen in ANCA-associated vasculitis, may enhance crescentic GN through antigen-specific T and B cell activation. Myeloperoxidase-deficient animals have attenuated GN early on, but augmented T cell responses. We investigated the effect of myeloperoxidase inhibition, using the myeloperoxidase inhibitor AZM198, to understand its potential role in treating crescentic GN.MethodsWe evaluated renal biopsy samples from patients with various forms of crescentic GN for myeloperoxidase and neutrophils, measured serum myeloperoxidase concentration in patients with ANCA-associated vasculitis and controls, and assessed neutrophil extracellular trap formation, reactive oxygen species production, and neutrophil degranulation in ANCA-stimulated neutrophils in the absence and presence of AZM198. We also tested the effect of AZM198 on ANCA-stimulated neutrophil-mediated endothelial cell damage in vitro, as well as on crescentic GN severity and antigen-specific T cell reactivity in the murine model of nephrotoxic nephritis.ResultsAll biopsy specimens with crescentic GN had extracellular glomerular myeloperoxidase deposition that correlated significantly with eGFR and crescent formation. In vitro, AZM198 led to a significant reduction in neutrophil extracellular trap formation, reactive oxygen species production, and released human neutrophil peptide levels, and attenuated neutrophil-mediated endothelial cell damage. In vivo, delayed AZM198 treatment significantly reduced proteinuria, glomerular thrombosis, serum creatinine, and glomerular macrophage infiltration, without increasing adaptive T cell responses.ConclusionsMyeloperoxidase inhibition reduced neutrophil degranulation and neutrophil-mediated endothelial cell damage in patients with ANCA-associated vasculitis. In preclinical crescentic GN, delayed myeloperoxidase inhibition suppressed kidney damage without augmenting adaptive immune responses, suggesting it might offer a novel adjunctive therapeutic approach in crescentic GN.

Project description:BackgroundThe primary challenge of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) patient care is the early detection of relapses to prevent organ damage and increase survival. Potential biomarkers for relapses are ANCA and B cells, but their predictive value is a matter of debate. Therefore this study investigated how ANCA and B-cell status related to relapses in AAV patients treated with rituximab (RTX) as remission induction (RI).MethodsThis single-centre cohort study identified 110 ANCA-positive AAV patients treated with RTX between 2006 and 2018. Serial ANCA, CD19+ B-cell status and relapses were assessed >2 years.ResultsPatients (31/110) relapsed within 2 years after RTX RI treatment. Patients who achieved and maintained PR3-ANCA negativity (n = 29) had few relapses (3%), while persistent proteinase 3 (PR3)-ANCA positivity (n = 49) and reappearance of PR3-ANCAs (n = 10) associated significantly with more relapses (37%, P = 0.002 and 50%, P = 0.002). Patients with incomplete B-cell depletion (n = 11) had significantly more relapses (54%) as compared with patients with B-cell depletion [n = 76 (26%), P = 0.02]. Also, patients with repopulation of B cells (n = 58) had significantly more relapses (41%) as compared with patients without B-cell repopulation [n = 27 (15%), P = 0.03]. Overall, the absence of PR3- or myeloperoxidase (MPO)-ANCA positivity was highly predictive for remaining relapse-free. In PR3-ANCA-positive patients, 96% of the relapses occurred with persistent or reappearance of PR3-ANCAs and 81% with B-cell repopulation. In MPO-ANCA-positive patients, all relapses were restricted to patients with persistent MPO-ANCAs and B-cell repopulation.ConclusionsUpon RI treatment with RTX in AAV patients, ANCA and B-cell status were predictive of the majority of relapses and specifically their absence strongly predicted a relapse-free status. Therefore the implementation of ANCA and B-cell monitoring could guide therapeutic decision-making to prevent relapses in AAV patients treated with RTX.

Project description:BACKGROUND & AIMS:The macrophage scavenger receptor 1 (Msr1, also called SRA) is a pattern recognition receptor primarily expressed on myeloid cells, which plays an important role in the maintenance of immune homeostasis. Since MSR1 expression was upregulated in the livers of patients with fulminant hepatitis (FH), we investigated the functional mechanism of Msr1 in FH pathogenesis. METHODS:Msr1-deficient (Msr1-/-) mice and their wild-type (WT) littermates were infected with mouse hepatitis virus strain-A59 (MHV-A59) to induce FH, and the levels of tissue damage, serum alanine aminotransferase, inflammatory cytokines and complement component 5a (C5a) were measured and compared. Liver injury was studied after MHV infection with or without neutrophil depletion. RESULTS:Our results showed that Msr1-/- mice were resistant to MHV-induced hepatitis. Treatment with the C5a receptor antagonist (C5aRa) diminished the differences in inflammatory responses and liver injury between MHV-infected wild-type and Msr1-/- mice, suggesting that C5a-induced pro-inflammatory response plays a critical role in the Msr1-mediated regulation of FH pathogenesis. We demonstrated that Msr1 efficiently enhanced transforming growth factor-activated kinase-1 phosphorylation in neutrophils upon MHV-A59 stimulation, thereby promoting the activation of the extracellular signal-regulated kinase pathway and subsequent NETosis formation. Moreover, we provided evidence that blockage of Msr1 attenuated the liver damage caused by MHV-A59 infection. CONCLUSIONS:Msr1 promotes the pathogenesis of virus-induced FH by enhancing induction of neutrophil NETosis and subsequent complement activation. Targeting Msr1 may be employed as a new immunotherapeutic strategy for FH. LAY SUMMARY:Virus-induced fulminant hepatitis (FH) is a disease with a high mortality worldwide. Enhanced levels of macrophage scavenger receptor 1 (Msr1) in the liver of patients with FH and of murine experimental FH indicated Msr1 plays a role in the pathogenesis of FH. Herein, we demonstrate that mice deficient in Msr1 are resistant to FH induced by MHV-A59, and the Msr1 inhibitor fucoidan suppresses the progression of FH in mice. Our study suggests that use of drugs inhibiting MSR1 function could be beneficial to patients with FH.

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Complement receptor Mac-1 is an adaptor for NB1 (CD177)-mediated PR3-ANCA neutrophil activation.

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