Clinical and pathophysiological significance of anti-neutrophil cytoplasmic autoantibodies in vasculitis syndromes

Neutrophil extracellular traps in neuropathy with anti-neutrophil cytoplasmic autoantibody-associated microscopic polyangiitis

To clarify the roles of neutrophils in anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitic neuropathy, we studied neutrophil extracellular traps (NETs) in peripheral nerve vasculitis. Stored nerve samples from 17 patients with microscopic polyangiitis (MPA) were immunohistochemically analyzed using antibodies for citrullinated histone H3 (citH3) and various neutrophil enzymes. We defined merged citH3 and extracellularly released myeloperoxidase (MPO) as NET formation. We also compared NET formation between MPO-ANCA-positive/negative MPA and rheumatoid arthritis (RA)-associated vasculitic neuropathy. NETs were identified mostly in vasculitic small arterioles of 6 of 12 MPO-ANCA-positive MPA patients, and their frequency was higher (p < 0.05) than in ANCA-negative patients. NETs were not found in vasculitic neuropathy with RA or patients with chronic inflammatory demyelinating polyradiculoneuropathy. NETs were also observed in the peripheral nervous system of MPA patients as well as in the lung and kidney. These results suggest that NETs may be involved in the pathogenesis of MPA neuropathy.

[Microscopic polyangiitis associated with antineutrophil cytoplasmic antibodies: clinical features]

AIM

To study the clinical features of early- and extended-stage microscopic polyangiitis (MPA) and its outcomes on the basis of a long-term follow-up in a rheumatologist's practice.

SUBJECTS AND METHODS

The clinical features of early- and extended-stage MPA were studied in detail and the premorbid background and possible precipitating factors were analyzed in 70 patients with MPA and the proven hyperproduction of antineutrophil cytoplasmic antibodies (anti-proteinase-3 (anti-PR3) antibodies in 55% and anti-myeloperoxidase (anti-MPO) antibodies in 45%) who had been followed up for more than a year.

RESULTS

There is evidence for the nosological unity of the two immunological types of MPA associated with anti-PR-3 or anti-MPO antibodies. MPA has been demonstrated to be an aggressive, polysyndromic disease prone to recurrences (52%), the typical manifestation of which is glomerulonephritis (94%) that is rapidly progressive in every four cases and accompanied by hemorrhagic alveolitis (69%) and involvement of other organs. ENT organs and lungs have been noted to be commonly involved in early-stage MPA, which was observed in 61% of the patients in the premorbid period, and to become the first manifestation of MPA (63%) concurrent with body temperature rises (64%), arthralgia or arthritis (41%). Respiratory tract involvement in MPA may be asymptomatic. Anti-PR-3-associated MPA may manifest itself more aggressively and in the first 2 years it is characterized by a poorer prognosis than of anti-MPO-associated MPA (survival rates, 82 and 94%, respectively; p = 0.04). With time, the differences were levelled off; recurrences in the patients with anti-PR-3 and anti-MPO develop equally frequently and proceed showing the similar clinical picture; the survival curves converge by age 3. Anti-MPO-associated MPA is characterized by the highest rate of lung involvement in the clinical phase of the disease (61%) and by a propensity to develop hemorrhagic alveolitis, diffuse interstitial (22%) or circumscribed pulmonary fibrosis in the outcome. CONCLUSION. The findings emphasize how important to diagnose MPA early and to prescribe long-term active treatment using the entire current arsenal of medications as soon as possible until severe injury to organs and systems develops. To specify regularities in the development of MPA may be of value for the better diagnosis of the disease and the further elaboration of optimal treatment policy.