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Background: The clinical significance of pANCA by indirect immunofluorescence is well-established. However, their clinical utility is sometimes hindered by the fact that pANCA are also detected in various autoimmune diseases. Myeloperoxidase (MPO) is considered as the major autoantigen recognized by pANCA in ANCA-associated vasculitides (AAV) and predominantly in microscopic polyangiitis (MPA). However, information regarding the targets of pANCA in other autoimmune diseases is still elusive.
Objectives: To investigate the specific autoantigens recognized by pANCA in autoimmune diseases.
Methods: Sera from all patients that were found positive for pANCA in the diagnostic laboratories of the Department of Pathophysiology, School of Medicine, National and Kapodistrian University of Athens and the Department of Immunology and Histocompatibility, Evangelismos General Hospital, Athens, Greece during the last two years were studied. The pANCA+ sera were evaluated for reactivity with the major antigens that are recognized by pANCA [MPO, lactoferrin, neutrophil elastase, cathepsin G and bactericidal/permeability increasing protein (BPI)] by a commercially available multiplex ELISA (ANCA profile ELISA, Euroimmun, Lubeck, Germany).
Results: A total of 82 patients were included in the study. All patients had positive pANCA by indirect immunofluorescence with a title ranging from 1/160 to 1/640. According to respective classification criteria, 21 patients had systemic vasculitides (15 MPA, 1 granulomatosis with polyangiitis; GPA, 1 Behcet’s disease; BD, 1 aortitis, 2 Henoch-Schonlein purpura; HSP and 1 cryoglobulinemic vasculitis; CV), 29 had systemic lupus erythematosus (SLE), 6 antiphospholipid syndrome (APS), 8 Sjögren’s syndrome (SS), 2 rheumatoid arthritis (RA), 1 systemic scleroderma (SScl), 14 Hashimoto thyroiditis and 1 sarcoidosis. The specificities of pANCA in each entity are shown in the following table.
| Autoimmune Diseases | Antigens recognized by pANCA+ sera | |||||
| MPO | Elastase | Cathepsin G | BPI | Lactoferrin | ||
| Vasculitides | MPA | 66.7 (10/15) | 0 (0/15) | 0 (0/15) | 0 (0/15) | 0 (0/15) |
| GPA | 100 (1/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | |
| BD | 100 (1/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | |
| Aortitis | 0 (0/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | |
| HSP | 0 (0/2) | 0 (0/2) | 0 (0/2) | 0 (0/2) | 0 (0/2) | |
| CV | 0 (0/1) | 0 (0/1) | 0 (0/1) | 0(0/1) | 100 (1/1) | |
| SLE | 6.9 (2/29) | 0 (0/29) | 0 (0/29) | 0 (0/29) | 6.9 (2/29) | |
| APS | 16.6 (1/6) | 16.6 (1/6) | 0 (0/6) | 0 (0/6) | 0 (0/6) | |
| SS | 0 (0/8) | 12.5 (1/8) | 0 (0/8) | 12.5 (1/8) | 0 (0/8) | |
| RA | 50 (1/2) | 0 (0/2) | 0 (0/2) | 0 (0/2) | 0 (0/2) | |
| SScl | 100 (1/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | |
| Hashimoto | 0 (0/14) | 0 (0/14) | 0 (0/14) | 0 (0/14) | 0 (0/14) | |
| Sarcoidosis | 0 (0/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | 0 (0/1) | |
Conclusion: pANCA positive staining in AAVs is highly restricted to MPO specificity. On the contrary, pANCA staining pattern in other autoimmune diseases, involves unknown autoantigens that are under investigation in our laboratory.
Disclosure of Interests: None declared