Mechanisms of ANCA-Mediated Leukocyte-Endothelial Cell Interactions In Vivo

Abstract

Anti-myeloperoxidase (anti-MPO) antibodies have been implicated in the pathogenesis of small-vessel vasculitis, but the molecular mechanisms by which these antibodies contribute to disease are unknown. For determination of how anti-MPO antibodies affect inflammatory cell recruitment in small-vessel vasculitis, intravital microscopy was used to monitor leukocyte behavior in the accessible cremasteric microvessels under various experimental conditions. After local pretreatment of the cremaster muscle with cytokines (TNF-␣, IL-1␤, or keratinocyte-derived chemokine), administration of anti-MPO IgG to wild-type mice reduced leukocyte rolling in favor of augmented adhesion to and transmigration across the endothelium. This led to a decrease in the number of systemic circulating leukocytes and, similar to the early events in the development of vasculitic lesions, an increase in leukocyte recruitment to renal and pulmonary tissue. TNF-␣ led to the greatest recruitment of inflammatory cells, and IL-1␤ led to the least. When anti-CD18 was co-administered, anti-MPO IgG did not affect leukocyte rolling, adhesion, or transmigration; similarly, anti-MPO IgG did not produce these effects in Fc receptor ␥ chain Ϫ/Ϫ mice.This study provides direct in vivo evidence of enhanced leukocyte-endothelial cell interactions in the presence of anti-MPO IgG and highlights the critical roles of Fc␥ receptors and ␤ 2 integrins in mediating these interactions. In addition, it suggests that neutrophils primed by cytokines in the presence of anti-MPO IgG can have systemic effects and target specific vascular beds.

IgG Glycan Hydrolysis Attenuates ANCA-Mediated Glomerulonephritis

“…One day after disease induction, signs of acute inflammation are present, such as hematuria and glomerular neutrophil influx, whereas leukocyturia, albuminuria, and glomerular crescents are important disease characteristics on day 7. 9 Because the pathogenicity of anti-MPO antibodies in mice seems to be Fc␥R dependent, 11,25 we hypothesized that EndoS-mediated deglycosylation of the anti-MPO IgG Fc tail could reduce the pathogenic effects of the antibodies. Indeed, we found that EndoSmediated deglycosylation of anti-MPO IgG markedly diminished both early and late disease characteristics of this model.…”

Endothelium-Neutrophil Interactions in ANCA-Associated Diseases

“…44 The synergy between TNF-a, b2-integrins, and FcgR was confirmed in vivo in experimental anti-MPO-induced AAV. 6 Complement further amplifies the proinflammatory responses of adherent neutrophils in the presence of ANCA. Neutrophil-bound ANCAs trigger the complement classic pathway exclusively on adherent neutrophils, a condition allowing access of ANCA to their antigens in plasm 45 and in synergy with the alternative pathway activated on TNFstimulated cells.…”

“…Both physical trapping and immediate arrest involving adhesion molecules have been demonstrated in different models ( Figure 5). In particular, the trapping of neutrophils in microvessels ( Figure 5A) may explain the ANCA-associated accumulation of neutrophils in the glomerulus 6 ; it does not involve endothelial adhesion molecules and is reminiscent of selectinindependent neutrophil sequestrations observed in pulmonary capillaries. 72 Participation of platelets in neutrophil adhesion to the endothelium has been observed in experimental anti-GBM GN ( Figure 5B).…”

“…3 The original observation that small-vessel vasculitis, including granulomatous polyangiitis (GPA) and microscopic polyangiitis, was associated with antiproteinase 3 (PR3) 4 or antimyeloperoxidase (MPO) 5 ANCA, produced numerous studies that demonstrated the central role of neutrophils and their interaction with the endothelium in ANCA-associated vasculitis (AAV). [6][7][8] Endothelium-neutrophil interactions are essential to allow neutrophils to move toward inflammatory sites and regulate spatially and temporally neutrophil recruitment. Neutrophils contain intracellular pools of toxic proteins aimed to kill microbes and digest tissues.…”

Recent Aspects of Vasculitis and Future Direction

“…MPO-ANCAs reduce leukocytes rolling over the endothelium and augment adhesion and transmigration across the endothelium. Blocking Fcϒ receptors and β2 integrins can inhibit this process (72,73).…”