Clinical and serological profiles of idiopathic and drug-induced autoimmune diseases can be very similar. We compared data from idiopathic and antithyroid drug (ATD)-induced antineutrophil cytoplasmic antibody (ANCA)-positive patients. From 1993 to 2003, 2474 patients were tested for ANCA in the Laboratory for Allergy and Clinical Immunology in Belgrade. Out of 2474 patients, 72 (2.9%) were anti-proteinase 3 (PR3)- or anti-myeloperoxidase (MPO)-positive and their clinical and serological data were analyzed. The first group consisted of ANCA-associated idiopathic systemic vasculitis (ISV) diagnosed in 56/72 patients: 29 Wegener's granulomatosis (WG), 23 microscopic polyangiitis (MPA) and four Churg-Strauss syndrome. The second group consisted of 16/72 patients who became ANCA-positive during ATD therapy (12 receiving propylthiouracil and four receiving methimazole). We determined ANCA and antinuclear (ANA) antibodies by indirect immunofluorescence; PR3-ANCA, MPO-ANCA, anticardiolipin (aCL) and antihistone antibodies (AHA) by ELISA; and cryoglobulins by precipitation. Complement components C3 and C4, alpha-1 antitrypsin (α1 AT) and C reactive protein (CR-P) were measured by nephelometry. Renal lesions were present in 3/16 (18.8%) ATD-treated patients and in 42/56 (75%) ISV patients (p <0.001). Skin lesions occurred in 10/16 (62.5%) ATD-treated patients and 14/56 (25%) ISV patients (p <0.01). ATD-treated patients more frequently had MPO-ANCA, ANA, AHA, aCL, cryoglobulins and low C4 (p <0.01). ISV patients more frequently had low α1 AT (p = 0.059) and high CR-P (p <0.001). Of 16 ATD-treated patients, four had drug-induced ANCA vasculitis (three MPA and one WG), while 12 had lupus-like disease (LLD). Of 56 ISV patients, 13 died and eight developed terminal renal failure (TRF). There was no lethality in the ATD-treated group, but 1/16 with methimazole-induced MPA developed pulmonary-renal syndrome with progression to TRF. ANCA-positive ISV had a more severe course in comparison with ATD-induced ANCA-positive diseases. Clinically and serologically ANCA-positive ATD-treated patients can be divided into two groups: the first consisting of patients with drug-induced WG or MPA which resemble ISV and the second consisting of patients with LLD. Different serological profiles could help in the differential diagnosis and adequate therapeutic approach to ANCA-positive ATD-treated patients with symptoms of systemic disease.

Decreased activity of serum desoxyribonuclease I (DNase I) in systemic lupus erythematosus (SLE) has been reported, but its role as a biomarker in SLE is still unelucidated. Seventy-seven SLE patients (aged 39.6 ± 13.1 years) were studied for serum DNase I activity, levels of antinuclear (ANA), anti-dsDNA [high-avidity ELISA, conventional ELISA and indirect immunofluorescence (IIF)], anti-nucleosome, anti-histone antibodies, complement components C3 and C4. SLE disease activity was evaluated by disease activity index (SLEDAI-2K). Thirty-five patients were serologically and clinically followed for 3-12 months (mean 5.6 ± 2.8). Thirty-seven healthy blood donors were the control group. DNase I activity in SLE patients was lower than in healthy controls (p<0.01). DNase I activity was in positive correlation with SLEDAI-2K (p<0.01), levels of ANA, anti-dsDNA, anti-nucleosome and anti-histone antibodies (p<0.01) and in negative correlation with C3 concentration (p<0.05). The highest correlation was found between DNase I activity and anti-dsDNA concentrations determined by high-avidity ELISA (r=0.624), followed by IIF (r=0.541) and conventional ELISA (r=0.405). In the follow-up study, DNase I activity also correlated with SLEDAI-2K (p<0.01). SLE patients with low DNase I activity more frequently had SLE-specific cutaneous lesions (p<0.05). Monitoring of DNase I activity simultaneously with SLEDAI-2K might be a useful tool in the follow-up of SLE. An increase of DNase I activity characterized relapse in most SLE patients, although it did not reach the levels of healthy individuals. A decrease of DNase I activity in SLE flare-ups might be a functional biomarker of a subset of patients with specific dysfunction of apoptotic chromatin degradation.