ANCA-associated vasculitis

History of Vasculitis

By Associate Professor Louise Smyth
Published November 2022

In Europe in 1973, in a study of neutrophil-specific antibodies by indirect immunofluorescence (IIF) in patients with rheumatoid arthritis and Felty’s syndrome, Allan Wiik detected antibodies demonstrating cytoplasmic granules of neutrophils that were present in a patient with crescentic glomerulonephritis.The first published series of Anti-Neutrophil Cytoplasmic Antibody (ANCA) in renal disease appeared, in a short report in the BMJ in 1982, from Melbourne’s St Vincent Hospital group – Davies, Moran, Niall and Ryan – who described the association of a serum factor (shown to be IgG) that demonstrated the cytoplasm of human neutrophils, by IIF, in eight patients with renal biopsy proven segmental necrotising glomerulonephritis with crescents, morphologically indistinguishable from microscopic polyarteritis nodosa. Viral infection was the suspected initiating event, and all cases resolved with treatment with only two reported recurrences (Davies, Moran, Niall, & Ryan, 1982).However, it would not be until 1985 that the diagnostic potential of testing for ANCA in Granulomatosis with Polyangiitis (Wegener’s) [GPA] was defined in a series of European papers by Niels Rasmussen, Fokke van der Woude and others (Rasmussen, Wiik, & Jayne, 2015). The immunofixation techniques used either alcohol or formalin fixed neutrophils, resulting in two different effects on the distribution of antigenic substances in neutrophils. Using ethanol-fixed substrate, some substances are dissolved and migrate to a perinuclear position and attach to the nucleus. The predominant antigen, behaving in this manner and thus producing a perinuclear (p-ANCA) pattern, is myeloperoxidase (MPO). This phenomenon means that when ANA is present, p-ANCA cannot be excluded. There are several other antigens present in neutrophil cytoplasm that behave in a similar manner: elastase, cathepsin G, azurocidin, lactoferrin, lysozyme, and bactericidal/permeability-increasing protein. Proteinase-3 (PR3) does not dissolve and remains within primary granules resulting in the classical c-ANCA (cytoplasmic) pattern. Antibody to LAMP-2 produces a similar pattern to PR-3, although some controversy exists regarding its clinical significance. The difference was codified and the standardisation of this method was agreed to for laboratory use at the first international workshop on ANCA in 1988 (Rasmussen, Wiik, & Jayne, 2015).

Table 1. Some ANCA associated disorders

Indirect Immunofluorescence, using ethanol-fixed substrate, remains the most frequent screening method for ANCAs, with follow up by specific, quantifiable tests for individual antibodies. In most (other than reference or research) laboratories this testing is limited to anti-PR3 and anti-MPO antibodies. Other ANCA are also seen in inflammatory bowel disease and liver diseases (predominantly in Ulcerative Colitis and Primary Sclerosing Cholangitis, respectively), in other systemic inflammatoryconditions, in infective diseases, in malignancies, and in adverse drug reactions (Table 1). ANCA that are perinuclear in distribution and negative for anti-MPO or anti-PR3 have been designated x-ANCA.

c-ANCA.https://commons.wikimedia.org/wiki/File:C_ANCA.jpg

p-ANCA.https://commons.wikimedia.org/wiki/File:P_ANCA.jpg#filelinks

The vasculitides

Vasculitis refers to inflammation within the wall of blood vessels. There may be inflammation in the surrounding adventitia. The International Chapel Hill Consensus Conference on the Nomenclature of Systemic Vasculitides 2012 (CHCC2012), revised its 1994 consensus that set names and constructed definitions for the most common forms of vasculitis; it forms the basis for the ACR/EULAR classification and diagnostic criteria for the vasculitides (Jennette et al., 2013). The Chapel Hill Nomenclaturedoes not include vasculitides of infectious origin. The vasculitides are divided by the size/type of the affected vessels and integrates aetiology, pathogenesis, pathology, demographics and clinical manifestations (Jennette et al., 2013). The major categories are:

• Large Vessel Vasculitis: Takayasu Arteritis, Giant Cell Arteritis
• Medium Vessel Vasculitis: Polyarteritis Nodosa, Kawasaki Disease
• Small Vessel Vasculitis    - ANCA-Associated Small Vessel Vasculitis: GPA, MPA, EGPA    - Immune Complex Small Vessel Vasculitis: Cryoglobulinaemic Vasculitis, IgA Vasculitis, Hypocomplementaemic Urticarial Vasculitis, Anti-GBM Disease
• Variable Vessel Vasculitis
• Single Organ Vasculitis
• Vasculitis Associated with Systemic Disorders
• Vasculitis Associated with Probable Aetiology.Adapted from Jennette et al.

The pathogenesis of some vasculitides is still poorly understood, but the discovery of the ANCAs has driven much of the revision (Table 2). In both GPA and MPA there is strong clinical and experimental evidence for pathogenicity of the antibodies (Weiner & Segelmark, 2016) and thus a rationale for immunosuppressive therapy.

Table 2. ANCA in Vasculitis

 GPA (granulomatosis with polyangiitis); formerly Wegener’s granulomatosis), MPA (microscopic polyangiitis); formerly microscopic polyarteritis nodosa, and EGPA (eosinophilic granulomatosis with polyangiitis); formerly Churg–Strauss syndrome. Data adapted from Weiner & Segelmark (2016) and Austin et al. (2022).

In February 2022, American College of Rheumatology/European Alliance of Associations for Rheumatology Classification Criteria for Granulomatosis with Polyangiitis, Microscopic Polyangiitis and Eosinophilic Granulomatosis with Polyangiitis were released, and are available on the website of the American College
of Rheumatology (https://www.rheumatology.org/Practice-Quality/Clinical-Support/Criteria#VasculitisClass).

Renal disease

Recent approaches to AAV are predicated upon the type of ANCA present as there is significant clinical overlap between the traditional diagnoses. Furthermore, while the majority of clinical phenotypes associate with either anti-PR3 or anti-MPO with some specificity, variable association occurs (Table 2). Additionally, ANCA may occur in anti-GBM Disease. ANCA, of either pattern or antigen association, also occur in idiopathic Rapidly Progressive Glomerulonephritis (RPGN), although late-stage crescentic disease may make classification more difficult.

In many cases quantitative results of, especially, the PR3 ANCA present corresponds with disease activity and can be used for disease monitoring and prognosis, in keeping with their role as a pathogenic antibody, especially in prediction of relapse. In renal disease, the outcome and likely antibody vary between younger and older patients, with corresponding differences in disease profile. While the risk of end-stage renal failure has been shown to be higher for PR3- positive disease and overall renal involvement to be greater in those who are MPO-positive, the Diagnostic and Classification Criteria for Primary Systemic Vasculitis (DCVAS) study showed that older patients (>65 years) are more likely to develop disease associated with MPOANCA, and succumb within 6 months (Austin et al., 2022). Anti-GBM Disease has been shown to have a poorer outcome when ANCA is present in addition to anti-GBM antibody.

Conclusion

ANCA are important diagnostic, prognostic and disease monitoring tools that are especially useful in the management of small vessel vasculitis in pauci-immune necrotising and crescentic glomerulonephritis. Several other specificities of ANCA than anti-PR3 and anti-MPO occur in a variety of clinical disorders and may provide useful information for clinicians, especially in the setting of Inflammatory Bowel Disease and related liver disease.