CD47 blockade ameliorates autoimmune vasculitis via efferocytosis of neutrophil extracellular traps

Abstract

Neutrophil extracellular trap (NET) formation contributes to immune defense and is a distinct form of cell death. Excessive NET formation is found in patients with anti–neutrophil cytoplasmic antibody–associated (ANCA-associated) vasculitis (AAV), contributing to disease progression. The clearance of dead cells by macrophages, a process known as efferocytosis, is regulated by the CD47-mediated “don’t eat me” signal. Hence, we hypothesized that pathogenic NETs in AAV escape from efferocytosis via the CD47 signaling pathway, resulting in the development of necrotizing vasculitis. Immunostaining for CD47 in human renal tissues revealed high CD47 expression in crescentic glomerular lesions of patients with AAV. In ex vivo studies, ANCA-induced netting neutrophils increased the expression of CD47 with the reduction of efferocytosis. After efferocytosis, macrophages displayed proinflammatory phenotypes. The blockade of CD47 in spontaneous crescentic glomerulonephritis-forming/Kinjoh (SCG/Kj) mice ameliorated renal disease and reduced myeloperoxidase-ANCA (MPO-ANCA) titers with a reduction in NET formation. Thus, CD47 blockade would protect against developing glomerulonephritis in AAV via restored efferocytosis of ANCA-induced NETs.

Glioblastoma Phagocytic Cell Death: Balancing the Opportunities for Therapeutic Manipulation

“…CD47 is commonly found on healthy cells throughout the body, and therefore there is a theoretical risk of inducing off-target toxicities when treating with an anti-CD47 strategy. Approaches which allow for trapping of the therapeutic target in the CNS may have value [76,77]. SIRPα is diffusely expressed throughout the brain, so it is uncertain what this off-target binding would induce.…”

The involvement of NETs in ANCA-associated vasculitis

“…Meanwhile, under steady state, soluble NETs-DNA and netting neutrophils are processed by serum deoxyribonuclease (DNase) I ( 32 ) and phagocytic cells, respectively ( 33 , 34 ). However, patients with AAV have low activity of serum DNase I and netting neutrophils with phagocytosis-resistance ( 35 , 36 ), implying that unprocessed NETs might persistent in body and serves as autoantigens against ANCA, which contributes to the development of disease. In support of this hypothesis, propylthiouracil (PTU), a medication causing drug-induced AAV, induces DNase I-resistant NETs with the modification of MPO structure in ex vivo ( 37 ) and the administration of these PTU-treated NETs promotes the generation of MPO-ANCA in vivo ( 38 ).…”

“…The process of dead cell removal by macrophages, termed efferocytosis, is regulated by the CD47-mediated “don’t eat me” signal ( 83 ). Our laboratory has shown that kidney biopsy samples from patients with AAV and ex vivo ANCA-induced NETs show increased expression of CD47 ( 36 ). In vitro , ANCA-induced NETs with enhanced CD47 expression escape efferocytosis, and the blockade of CD47 with anti-CD47 antibody restored the efferocytosis of ANCA-induced NETs.…”

Efferocytosis by macrophages in physiological and pathological conditions: regulatory pathways and molecular mechanisms

“…These macromolecules function similar to a “QR code” in that macrophages and other efferocytes “scan” codes and decode information from dying cells to produce immunoreactions. Most studies highlight the repair and immunosuppression of efferocytosis; however, some studies have revealed pro-inflammatory outcomes after efferocytosis ( 18 , 19 ). Therefore, the precise regulation of these processes remains unknown (red box in Figure 2 ).…”