C3d Elicits Neutrophil Degranulation and Decreases Endothelial Cell Migration, with Implications for Patients with Alpha-1 Antitrypsin Deficiency

Abstract

Alpha-1 antitrypsin (AAT) deficiency (AATD) is characterized by increased risk for emphysema, chronic obstructive pulmonary disease (COPD), vasculitis, and wound-healing impairment. Neutrophils play a central role in the pathogenesis of AATD. Dysregulated complement activation in AATD results in increased plasma levels of C3d. The current study investigated the impact of C3d on circulating neutrophils. Blood was collected from AATD (n = 88) or non-AATD COPD patients (n = 10) and healthy controls (HC) (n = 40). Neutrophils were challenged with C3d, and degranulation was assessed by Western blotting, ELISA, or fluorescence resonance energy transfer (FRET) substrate assays. Ex vivo, C3d levels were increased in plasma (p < 0.0001) and on neutrophil plasma membranes (p = 0.038) in AATD compared to HC. C3d binding to CR3 receptors triggered primary (p = 0.01), secondary (p = 0.004), and tertiary (p = 0.018) granule release and increased CXCL8 secretion (p = 0.02). Ex vivo plasma levels of bactericidal-permeability-increasing-protein (p = 0.02), myeloperoxidase (p < 0.0001), and lactoferrin (p < 0.0001) were significantly increased in AATD patients. In endothelial cell scratch wound assays, C3d significantly decreased cell migration (p < 0.0001), an effect potentiated by neutrophil degranulated proteins (p < 0.0001). In summary, AATD patients had increased C3d in plasma and on neutrophil membranes and, together with neutrophil-released granule enzymes, reduced endothelial cell migration and wound healing, with potential implications for AATD-related vasculitis.

Neutrophils, Fast and Strong

“…Neutrophils are actively involved in inflammatory processes in Alpha-1 antitrypsin (AAT) deficiency (AATD). Dysregulation of neutrophil degranulation has been found to be an important feature in the pathogenesis of AATD [10]; this study supports approaches to the therapeutic use of AAT augmentation therapy to balance the neutrophil response.…”

Links Between Vitamin D-Binding Protein, Alpha-1 Antitrypsin and Neutrophil Proteins in Meconium

“…As observed by other authors [2,8], VDBP binding to the activated sites on neutrophils is an important stage in their role in the immune system as chemotactic activity of complement (C) peptides C5a and C5a des arg is enhanced [10,13]. AAT has a key role in the innate immune response, possesses an anti-inflammatory capacity, inhibits VDBP shedding from neutrophils and its serving as a chemotactic co-factor for C5a [12,14,15]. Calprotectin released from activated neutrophils increases its concentration mainly in inflammatory processes and may be a sensitive indicator of local inflammation [3,16].…”

“…It is a serine protease inhibitor, which inhibits a range of proteases derived from degranulated neutrophils including neutrophil elastase. AAT inhibits VDBP shedding from neutrophils [12,14,15]. Calprotectin (36.5 kDa), a heterodimeric (S100A8/A9) calcium-and zinc-binding protein which makes up 5 % of the total protein and 60% of the cytosolic protein of neutrophils.…”

A Review of Alpha-1 Antitrypsin Binding Partners for Immune Regulation and Potential Therapeutic Application

“…Treatment of patients with AATD involves AAT augmentation therapy, which can aid in modulating this uncontrolled complement cascade by disrupting C3 activation and significantly reducing C3d plasma levels when compared with those not on therapy [ 16 ]. Moreover, C3d binding to CR3 neutrophil receptors triggered granule release, increased cytokine secretion, and reduced endothelial cell migration and wound healing, with potential implications for AATD-related vasculitis [ 156 ].…”