Anti-myeloperoxidase antibodies and associated diseases

Antineutrophil cytoplasmic autoantibodies: how should the biologist manage them?

Antineutrophil cytoplasmic antibodies (ANCA) are directed against enzymes found in the granules of the polymorphonuclear (PMN) leukocytes. They are detected by indirect immunofluorescence microscopy assays on human ethanol fixed neutrophils. Three different fluorescence patterns can be distinguished: a cytoplasmic pattern (cANCA), a perinuclear pattern (pANCA), and an atypical pattern (aANCA). The use of other fixatives, e.g., formalin and methanol, allows differentiation between the pANCA and the antinuclear antibodies. ANCA specificity is determined by solid phase assays (ELISA, immunodot, and multiplex assay). ANCA with high titres and defined specificities (antiproteinase 3 [PR 3] or antimyeloperoxidase [MPO]) are proven to be good serological markers of active primary systemic vasculitis: c/PR 3-ANCA for Wegener's granulomatosis and p/MPO-ANCA for microscopic polyangiitis. The former have higher sensitivity and specificity for Wegener's granulomatosis than the latter for microscopic polyangiitis. ANCA with low titres and unknown specificity have been detected in a wide range of inflammatory and infectious diseases leading to a critical reappraisal of the diagnostic significance of ANCA testing. Physicians must keep in mind the possible occurrence of infectious diseases like subacute endocarditis that could be dramatically worsened by irrelevant immunosuppressive therapy. ANCA findings in certain manifestations, such as the pulmonary-renal syndrome in which massive pulmonary hemorrhage can quickly be life-threatening, warrant ANCA testing as an emergency test for patient care.

[Antineutrophil cytoplasmic antibodies in cystic fibrosis. Frequency and significance]

Some immune system abnormalities have been reported in cystic fibrosis, particularly the presence of antineutrophil cytoplasmic antibodies (ANCAs). The purpose of this study was to determine the frequency of these antibodies in a population of patients with cystic fibrosis and to assess their relationship with the disease progression.

POPULATION AND METHODS

This retrospective study looked for the presence of these antibodies in sera from 64 patients (30 boys and 34 girls) aged one to 29 years. All patients were followed up within the Cystic Fibrosis Center of the University Hospital of Angers. The serum samples were collected in 2001 during the yearly check-up to evaluate disease status.

RESULTS

Seven of the 64 patients presented the antibodies. Univariate analysis showed that these patients were significantly older and more often chronically infected with Pseudomonas aeruginosa than the other patients. They also scored significantly more poorly on pulmonary radiography and showed significantly higher IgG and CRP. Multivariate analysis revealed that the two following independent factors were associated with the presence of ANCAs: chronic P. aeruginosa infection and high IgG level.

CONCLUSION

This work confirms the abnormally high frequency of antineutrophil cytoplasmic antibodies in patients with cystic fibrosis. These antibodies were observed in the sickest patients with severe infection status. They reflect the impact of inflammatory processes in the pathogenesis of the disease. Detection of these antibodies might be an indication for intensified treatment of bronchial infections.

Wegener's granulomatosis

Clinical manifestations of Wegener's granulomatosis are nonspecific and indistinguishable from a variety of neoplastic, infectious, and inflammatory diseases. Ophthalmic disease is the presenting feature in nearly one sixth of patients with Wegener's granulomatosis and will ultimately develop in a majority. The discovery of antineutrophil cytoplasmic antibodies, particularly antiproteinase-3, has changed the clinical approach to evaluating patients suspected of having Wegener's granulomatosis. These antibodies are distinguished from other related autoantibodies because they produce a coarse granular pattern of cytoplasmic staining on indirect immunofluorescence with ethanol-fixed neutrophils. Treatment of Wegener's granulomatosis with oral cyclophosphamide and corticosteroids has decreased morbidity and improved survival, but side effects from long-term immunosuppressive therapy are common and sometimes serious. The effectiveness of trimethoprim-sulfamethoxazole in decreasing the number and severity of recurrences of Wegener's granulomatosis is being investigated. It remains to be determined if wide use of trimethoprim-sulfamethoxazole in limited Wegener's granulomatosis could further improve the quality of life for some patients.