ANCA induces β2integrin and CXC chemokine-dependent neutrophil-endothelial cell interactions that mimic those of highly cytokine-activated endothelium

Update on the use of biologics in primary systemic vasculitides

The introduction of biologic therapies, which selectively target components of the immune system, has revolutionized the treatment of rheumatoid arthritis. Anti-TNF-alpha therapy (infliximab, etanercept and adalimumab) and B-cell-depleting agents, such as rituximab, are the most widely used agents. Increased experience of the use of biologic drugs in other immune-mediated inflammatory diseases has led to the application of biologic therapies in the treatment of primary systemic vasculitis. Conversely, the success of biological agents has improved understanding of the immunopathogenesis of vascular inflammation. The need for biologic agents arises from the failure of the current standard of care to maintain remission while limiting drug toxicity. Evidence for the efficacy of biologic agents does not match that of conventional immunosuppressants yet, but it is building rapidly. This paper reviews the current evidence for the standard of care of patients with vasculitis and the role of biologic therapy in primary systemic vasculitis. In this review, we examine the rationale for using biologics based on the pathophysiology of primary systemic vasculitis. The risks and benefits of the use of biologics are discussed, together with future directions and predictions of these emerging therapies.

Antineutrophil Cytoplasm Antibody–Stimulated Neutrophil Adhesion Depends on Diacylglycerol Kinase–Catalyzed Phosphatidic Acid Formation

Patients with certain forms of systematic vasculitis, such as Wegener's granulomatosis, have circulating antineutrophil cytoplasmic antibodies (ANCA). These inappropriately stimulate circulating neutrophils adhere to and thereby obstruct small vessels. This, together with ANCA-induced degranulation and an oxidative burst, leads to local tissue damage. The signaling pathways that are activated by ANCA IgG are distinct from those that are involved in normal neutrophil activation. This study shows that diacylglycerol kinase is selectively activated by ANCA and that the generated phosphatidic acid is responsible for promoting neutrophil adhesion, in part through integrin activation. The data presented point to diacylglycerol kinase alpha as a novel but selective target for the development of drugs to treat this potentially fatal disorder.

Chimeric antibodies to proteinase 3 of IgG1 and IgG3 subclasses induce different magnitudes of functional responses in neutrophils

BACKGROUND

Antineutrophil cytoplasmic antibodies (ANCA) are associated with small-vessel vasculitis and have been implicated in its pathogenesis. The subclass distribution of ANCA IgG deviates from normal patterns, and it has been suggested that the IgG3 subclass may have pathogenic potential over the IgG1 subclass and may be more likely to be associated with active disease and renal involvement.

OBJECTIVE

To deal with potential pathogenicity, chimeric antibodies were constructed of IgG1 and three subclasses with human IgG1 or three constant regions and a murine-derived variable region that binds an epitope within the ANCA antigen proteinase 3 (PR3) that is recognised by human autoantibodies.

METHODS

The antibodies were characterised for binding to PR3, including affinity and avidity, before being used as tools to explore their ability to activate human neutrophils for superoxide release, cytokine release, degranulation and ability to induce neutrophil adhesion under flow.

RESULTS

Both subclass antibodies elicited similar neutrophil responses for superoxide release, degranulation and interleukin (IL) 8 production, although quantitative responses showed that the IgG1 subclass favoured degranulation and the IgG3 subclass favoured IL8 production. Both antibodies were able to convert neutrophils from selectin-dependent rolling adhesion to integrin-dependent stationary adhesion in a flow assay.

CONCLUSIONS

These findings indicate that humanised antibodies directed against a single epitope of PR3 can recapitulate the effects of polyclonal human ANCA, which recognises multiple PR3 epitopes. Further, PR3-ANCA of both IgG1 and IgG3 subclasses can activate neutrophils, although the more potent IL8 response by IgG3 PR3-ANCA may encourage further neutrophil recruitment and amplify injury.

Antineutrophil cytoplasmic antibodies

Much like other autoantibodies (eg, anti-double stranded DNA in systemic lupus erythematosus or antiglomerular basement membrane antibodies in Goodpasture's syndrome), antineutrophil cytoplasmic antibodies (ANCA) have provided doctors with a useful serological test to assist in diagnosis of small-vessel vasculitides, including Wegener's granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome, and their localised forms (eg, pauci-immune necrotising and crescentic glomerulonephritis). 85-95% of patients with Wegener's granulomatosis, microscopic polyangiitis, and pauci-immune necrotising and crescentic glomerulonephritis have serum ANCA. ANCA directed to either proteinase 3 or myeloperoxidase are clinically relevant, yet the relevance of other ANCA remains unknown. Besides their diagnostic potential, ANCA might be valuable in disease monitoring. In addition, data seem to confirm the long-disputed pathogenic role of these antibodies. Present treatments for ANCA-associated vasculitis are not free from side-effects and as many as 50% of patients relapse within 5 years. Accurate understanding of the key pathogenic points of ANCA-associated vasculitis can undoubtedly provide a more rational therapeutic approach.

Anti-Neutrophil Cytoplasmic Antibodies and Effector CD4+Cells Play Nonredundant Roles in Anti-Myeloperoxidase Crescentic Glomerulonephritis

Most humans with microscopic polyarteritis and anti-myeloperoxidase (anti-MPO), anti-neutrophil cytoplasmic antibodies (ANCA) develop "pauci-immune" crescentic glomerulonephritis. For dissection of the roles of ANCA and cell-mediated effectors in microscopic polyarteritis, experimental autoimmune anti-MPO glomerulonephritis was induced by immunizing C57BL/6 mice with human MPO. Autoimmunity to mouse MPO (ANCA and CD4+ cell reactivity) was induced. Challenge with anti-glomerular basement membrane globulin resulted in accumulation of neutrophils, CD4+ cells and macrophages, and significant numbers of crescentic glomeruli compared with similarly challenged control-immunized mice. MPO-deficient (Mpo(-/-)) mice immunized with MPO developed similar immune responses to MPO but failed to recruit effector cells to glomeruli or develop significant crescent formation, suggesting that MPO is acting as a planted glomerular autoantigen. Effector CD4+ cell depletion in this model attenuated crescentic glomerulonephritis and effector cell influx without altering ANCA titers. However, B cell-deficient mice, with no ANCA, still developed severe crescentic glomerulonephritis with accumulation of effector cells. Intravital microscopy studies demonstrated that passive transfer of sera from MPO-immunized Mpo(-/-) mice to LPS-primed mice rapidly induced glomerular neutrophil accumulation and release of MPO. These studies provide in vivo evidence in a relevant vascular bed for both humoral and cellular anti-MPO responses as key inducers of injury. ANCA induces glomerular neutrophil infiltration and MPO deposition. Subsequently, anti-MPO CD4+ cells recognize MPO as a planted glomerular antigen and act with macrophages to amplify severe glomerular injury.

Anti-neutrophil cytoplasm-associated glomerulonephritis

Wegener's granulomatosis, microscopic polyangiitis, and renal limited vasculitis are associated with circulating anti-neutrophil cytoplasm antibodies and are an important cause of rapidly progressive glomerulonephritis. This review gives an account of recent advances in the understanding of the pathogenesis underlying these conditions and how these may lead to future treatments. Consideration is given to recent clinical trials in the management of anti-neutrophil cytoplasm antibodies (ANCA)-associated vasculitides.

Pathogenesis of vascular inflammation by anti-neutrophil cytoplasmic antibodies

The reports of a newborn who developed glomerulonephritis and pulmonary hemorrhage after transplacental transfer of anti-neutrophil cytoplasmic antibody (ANCA) IgG with specificity for myeloperoxidase (MPO) is compelling clinical evidence that ANCA are pathogenic. In vitro studies indicate that ANCA activate cytokine-primed neutrophils and monocytes through both direct Fab'2 binding and Fc receptor engagement. Neutrophils that have been activated by ANCA release oxygen radicals, lytic enzymes, and inflammatory cytokines and adhere to and kill endothelial cells. A murine model caused by passive administration of mouse anti-mouse MPO IgG provides convincing evidence that ANCA IgG alone in the absence of antigen-specific T cells can cause necrotizing glomerulonephritis and vasculitis. This pathogenic process is enhanced by synergistic inflammatory factors, probably through priming of neutrophils. Immunization of rats with human MPO induces antibodies that cross-react with rat MPO and cause glomerulonephritis and vasculitis. These ANCA act in concert with chemokines to cause adherence of leukocytes to the walls of small vessels with subsequent injury. To date, animal models of disease that is induced by anti-proteinase 3 are less robust. Clinical and experimental data suggest but do not prove that the ANCA autoimmune response is initiated by an immune response to an antisense peptide of the ANCA antigen or its mimic that may be introduced into the body by an infectious pathogen. This antibody response elicits anti-idiotypic antibodies that cross-react with ANCA antigens. The pathogenesis of ANCA disease is multifactorial, with genetic and environmental factors influencing onset of the autoimmune response, the mediation of acute injury, and the induction of the chronic response to injury.

Chemokine- and adhesion-dependent survival of neutrophils after transmigration through cytokine-stimulated endothelium

We examined the fate of neutrophils following transmigration through an endothelial monolayer cultured on "Transwell" membrane filters. Treatment of human umbilical vein endothelial cells (HUVEC) with increasing doses of tumor necrosis factor-alpha increased the efficiency of transmigration and markedly reduced apoptosis among the transmigrated neutrophils in a dose-dependent manner. Apoptosis was also inhibited after transmigration of neutrophils through HUVEC stimulated with interleukin (IL)-1beta but not so effectively after chemotaxis through unstimulated HUVEC driven by IL-8 added below the filter. Inhibition of beta2-integrin binding after transmigration or coating the lower chamber with a nonadhesive polymer (polyhydroxyl-ethyl-methacrylate) abrogated neutrophil survival. Although integrin engagement during migration itself was not essential to inhibit apoptosis, activation of neutrophils through CXC chemokine receptors was necessary. Quite brief exposure to the HUVEC (30-120 min) was effective in reducing subsequent apoptosis, although if coincubation with the HUVEC were prolonged, neutrophil apoptosis was reduced further. Neutralization of granulocyte macrophage-colony stimulating factor inhibited this additional effect. Thus, a complex interplay between migration- and activation-dependent signals and adhesive interaction in tissue may combine to effectively prolong the survival of neutrophils recruited during inflammation.

Translating basic science into patient therapy for ANCA-associated small vessel vasculitis

ANCA (anti-neutrophil cytoplasm antibody)-associated small vessel vasculitis is an inflammatory condition associated with the production of autoantibodies to neutrophil cytoplasmic components. The disorder results in destruction of the microvasculature, infiltration of neutrophils into tissues, which is followed later by mononuclear cells, leading to injury and the formation of granulomatous lesions. Initiators for the disease are undetermined but a pro-inflammatory environment is required. Other influencing factors may include environmental triggers, genetic propensity or infectious agents. The primary cellular event in the condition involves the neutrophils, which are likely to be responsible for the majority of tissue injury. Binding of the autoantibody to neutrophils initiates cell activation via a complex intracellular signalling cascade, culminating in the release of pro-inflammatory mediators, proteolytic enzymes and reactive oxygen species. Adhesion of neutrophils to endothelial cells is observed in vitro and more investigations in this area may explain the focussing of the disease to certain vessels/tissues. Current treatment regimens have substantial toxicity. Although newer developments are an improvement there is still a pressing need for more targeted therapies, which could be provided by extrapolating information emerging from basic scientific research.