DO ANTINEUTROPHIL CYTOPLASMIC AUTOANTIBODIES CAUSE WEGENER’S GRANULOMATOSIS AND OTHER FORMS OF NECROTIZING VASCULITIS?

[Wegener's granulomatosis]

Wegener's granulomatosis is a necrotizing inflammation of small and medium size vessels with granuloma formation. It is a very heterogeneous disease in respect of severity and clinical manifestation. While it can be a rapidly progressive disease with fatal ending, there are forms limited only to one organ. Diagnosis is supported by the positivity of anti-neutrophil cytoplasmatic antibody and the presence of the typical histological findings. Unfortunately, these examinations cannot confirm clinical suspicion relatively frequently. In addition, there may be only symptoms related to one single organ for a long time at the beginning of the disease and, therefore, one have to be aware of the clinical signs and symptoms of the different organ systems. This may allow us to make an early diagnosis and start treatment in time.

C-ANCA-positive IgG fraction from patients with Wegener's granulomatosis induces lung vasculitis in rats

The aim of the present study was to analyse in rats the ability of C-ANCA-positive IgG fraction in triggering inflammatory response on pulmonary tissue. Wistar rats (n = 18) were injected via the the internal jugular vein with 20 mg of total C-ANCA-positive IgG fraction isolated from serum of three different Wegener's granulomatosis patients obtained before therapy. Similarly, control rats were treated with IgG fraction from two rheumatoid arthritis patients (n = 7), IgG from six normal human sera (n = 15) or saline (n = 18), respectively. Animals were sacrificed after 24h of injection for histological analysis of the lungs. Vasculitis and inflammatory infiltrate were consistently absent in rats injected with rheumatoid arthritis IgG or saline and in 14/15 of normal IgG treated animals. In contrast, marked vasculitis was observed in all 18 animals injected with C-ANCA-positive IgG fraction. The histological features were characterized by the presence of a perivascular pleomorphic cellular sheath, particularly around small vessels, endothelial adherence and diapedesis of polymorphonuclear leucocytes and presence of granuloma-like lesions. A dose-response relationship was observed between protein concentration of C-ANCA IgG sample and the intensity of the inflammatory response in the animals. In addition, IgG fraction with undetectable C-ANCA, obtained from one patient in remission after treatment, was not able to reproduce the pulmonary tissue alterations induced by its paired IgG that was positive for C-ANCA taken before therapy. The experimental model described herein may be useful to characterize more effectively the pathogenic mechanism of C-ANCA in Wegener's disease.

Antineutrophil Cytoplasmic Antibodies Preferentially Engage FcγRIIIb on Human Neutrophils

Antineutrophil cytoplasmic Abs (ANCA) are found in the circulation of many patients with systemic vasculitis. ANCA bind to ANCA target, such as proteinase 3 and myeloperoxidase, and activate neutrophils in an FcγR-dependent manner. Human neutrophils constitutively express FcγRIIa (CD32) and FcγRIIIb (CD16), and there is clear in vitro experimental evidence of ANCA-mediated engagement of FcγRIIa. However, direct experimental evidence of ANCA engagement of neutrophil FcγRIIIb has been obscured by technical problems related to activation-induced receptor shedding and activation-induced expression of receptor on the surface of neutrophils. In this study, by blocking receptor shedding and using appropriate reporter anti-FcγR mAb, we show that human cANCA and pANCA, and murine mAb with corresponding reactivities, can indeed engage FcγRIIIb. Furthermore, our data suggest that FcγRIIIb is preferentially engaged by ANCA relative to FcγRIIa presumably due to the nearly 10-fold excess of FcγRIIIb expression relative to FcγRIIa expression. These results clearly demonstrate that the Fc region of ANCA bound to an ANCA target on the neutrophil surface engage FcγRIIIb and indicate that FcγRIIIb and FcγRIIa may both be active participants in ANCA-induced neutrophil activation. However, given the low levels of ANCA target expression on neutrophils from patients with systemic vasculitis, FcγRIIIb is likely to play a critical role in initiating and perpetuating ANCA-induced neutrophil activation.

Koebner phenomenon in an ANCA-positive patient with pyoderma gangrenosum

A male with pyoderma gangrenosum is reported. The clinical and histological features were typical. The initial lesions resolved with characteristic cribriform scars. A few days after the complete recovery, he developed several necrotizing focal lesions localized to the scarred areas. A further histological examination revealed a granulation tissue rich in neutrophils and signs of necrotizing vasculitis. We found a high titer of circulating perinuclear antineutrophil antibodies (p-ANCA), which are a serological marker for various systemic diseases. An immunological circulating factor has been repeatedly suggested to be the "primum movens" of pyoderma gangrenosum. We discuss the unusual clinical presentation interpreted as a Koebner phenomenon and the possible role of immune factors in enhancing circulating-endothelial cell interactions in relation to the pathogenesis of pyoderma gangrenosum.

Pathogenesis of vasculitis syndromes

The pathogenesis of vasculitis is complex and involves a variety of mechanisms acting in concert to bring about necrotizing inflammation of blood vessel walls. In recent years, there has been considerable progress in dissecting the immunologic abnormalities present in specific vasculitis syndromes. The primary immunopathogenic events that initiate the process of vascular inflammation and blood vessel damage, however, are still largely unknown. Although the cause of most vasculitis syndromes remains a mystery, advances in molecular and cellular immunology have defined many of the effector mechanisms that mediate inflammatory vascular damage. In this regard, modulation of the inflammatory response by specific cytokine and adhesion molecule antagonists is now possible and may prove beneficial in the treatment of vasculitis.

Anti-endothelial cell IgG antibodies from patients with Wegener's granulomatosis bind to human endothelial cells in vitro and induce adhesion molecule expression and cytokine secretion

OBJECTIVE

To elucidate the role of anti-endothelial cell antibodies (AECA) in vascular inflammation in patients with Wegener's granulomatosis (WG).

METHODS

IgG fractions from 3 AECA-positive WG patients, IgG from 3 AECA-negative WG patients, and IgG from healthy donors were tested for their ability to: a) bind to endothelial cells and to display complement-dependent or antibody-dependent cellular cytotoxicity, b) modulate cell membrane expression of adhesion molecules, as evaluated by cytofluorometry and by immunoenzymatic assay, and c) induce the secretion of interleukin-1 beta (IL-1 beta), IL-6, IL-8, and monocyte chemotactic protein 1 (MCP-1).

RESULTS

We found that AECA IgG from WG patients do not display any significant cytotoxicity but are able to up-regulate the expression of E-selectin, intercellular adhesion molecule 1 and vascular cell adhesion molecule 1 and to induce the secretion of IL-1 beta, IL-6, IL-8, and MCP-1.

CONCLUSION

AECA in patients with WG could play a potential pathogenetic role by activating endothelial cells, and thus facilitating leukocyte recruitment and adhesion to endothelial surfaces, rather than by displaying a cytotoxic activity.

Leucocyte activation by anti-lactoferrin antibodies bound to vascular endothelium

Human polymorphonuclear neutrophil leucocytes (PMNL) prestimulated with the formylated tripeptide f-Met-Leu-Phe (fMLP) were activated to an immediate chemiluminescence (CL) response by polyclonal rabbit antibodies against human lactoferrin (Lf). This activation, indicating the formation of reactive oxygen species, was induced by intact IgG antibodies but could not be brought about by F(ab')2 fragments. Human Lf was also shown to adhere to the surface of cultured bovine aorta endothelial cells (BEC). When Lf-coated BEC grown on microcarrier beads were reacted with anti-Lf antibodies, an immediate CL response was achieved also with nonprimed PMNL. Here, too, the reaction required intact IgG antibodies. Also, patient sera containing anti-Lf autoantibodies of IgG class were shown to activate fMLP-treated PMNL. The same effect was obtained (in a dose-dependent manner) with the gammaglobulin fraction from anti-Lf-positive serum. Further, anti-Lf-antibody-positive patient sera incubated with Lf-coated BEC beads were also able to activate non-stimulated PMNL to a chemiluminescence response. The results are discussed in relation to possible mechanisms of cell/tissue damage induced by anti-neutrophil cytoplasmic antibodies (ANCA).

Characterization of biologically active antineutrophil cytoplasmic antibodies induced in mice. Pathogenetic role in experimental vasculitis

OBJECTIVE

To investigate the pathogenetic role of antineutrophil cytoplasmic antibodies (ANCA) in Wegener's granulomatosis (WG).

METHODS

BALB/c mice were immunized with human IgG ANCA from a patient with WG. Control mice were immunized with normal human IgG. Levels of mouse ANCA and other autoantibodies were determined. Mouse ANCA were tested for their ability to induce adhesion and respiratory burst of neutrophils. The mouse lungs and kidneys were examined for the development of vasculitis.

RESULTS

Mice immunized with human ANCA developed anti-human ANCA and anti-anti-human ANCA (mouse ANCA), while the controls did not develop these antibodies. Mouse ANCA were capable of inducing adhesion of neutrophils to fibronectin and activating the respiratory burst in neutrophils. Moreover, the mice that were immunized with human ANCA developed perivascular mononuclear cell infiltrates in the lungs, suggesting vasculitis.

CONCLUSION

The results suggest a pathogenic role of ANCA in WG, and may imply that activation of neutrophils is the initiating event in the development of vasculitis in WG.

The pathology of vasculitis involving the kidney

The kidneys are frequently affected by systemic vasculitides. This is not surprising given the numerous vessels within the renal parenchyma. The kidneys are most often involved by small vessel vasculitides, such as microscopic polyangiitis (microscopic polyarteritis), Wegener's granulomatosis, Henoch-Schönlein purpura, and cryoglobulinemic vasculitis. These vasculitides cause renal dysfunction predominantly by inducing glomerular inflammation with resultant nephritis and renal failure. Microscopic polyangiitis (microscopic polyarteritis) and Wegener's granulomatosis are associated with and may be caused by antineutrophil cytoplasmic autoantibodies. Henoch-Schönlein purpura is caused by immunoglobulin (Ig) A-dominant immune complex localization in small vessels. Cryoglobulinemic vasculitis is sometimes induced by hepatitis C infection. Necrotizing medium-sized vessel vasculitides, such as classic polyarteritis nodosa and Kawasaki's disease, are less frequent causes of renal disease. They cause infarction secondary to thrombosis of inflamed major extrarenal and intrarenal arteries, and may lead to life-threatening hemorrhage from rupture of aneurysms. Large vessel vasculitides, such as giant cell (temporal) arteritis and Takayasu arteritis, only rarely injure the kidneys, usually by ischemia secondary to vasculitic involvement of the renal arteries or abdominal aorta. This ischemia can cause renovascular hypertension.