Antineutrophil cytoplasmic autoantibodies (ANCA) and their target antigens in Chinese patients with lupus nephritis

Background. ANCA have been found in patients with systemic lupus erythematosus (SLE); however, the prevalence of ANCA and their target antigens is still not certain. This study is to investigate the prevalence of ANCA and their target antigens in Chinese patients with lupus nephritis. Methods. Ninety-five serum samples were collected from 95 renal-biopsy-proven lupus nephritis patients. Indirect immunofluorescence using ethanol-fixed leukocytes as substrate and ELISA using six highly purified known ANCA antigens as solid-phase ligands were performed. The specific ANCA antigens included proteinase 3, myeloperoxidase, bactericidal/permeability-increasing protein, human leukocyte elastase, cathepsin G, and lactoferrin. The prevalence of ANCA in patients with (n = 65) and without (n = 30) active renal pathological lesions was also compared to reveal whether ANCA correlates with disease activity. Results. (i) None of the sera recognized proteinase 3, myeloperoxidase, and human leukocyte elastase, and only one serum recognized bactericidal/permeability-increasing protein. The striking finding was that 59/95 (62.1%) sera recognized cathepsin G and the titres of some sera reached 1/3200. Eight of 95 sera (8.4%) recognized lactoferrin. (ii) The percentage of anticathepsin G antibody positive samples in patients with active renal lesions was significantly higher than in patients without active lesions (73.4 vs 36.7%, P < 0.0001), whereas, anti-lactoferrin antibodies had no correlation with active renal lesions. (iii) By indirect immunofluorescence, only 22% of the 95 sera were ANCA positive. Conclusions. Our results suggest that the majority of lupus nephritis patients have ANCA and that the major target antigens is cathepsin G. Anti-cathepsin G antibodies seem to be correlated with renal disease activity.