Anti-neutrophil extracellular trap antibody in a patient with relapse of anti-neutrophil cytoplasmic antibody-associated vasculitis: a case report

Abstract

Background: Neutrophil extracellular traps (NETs) are web-like DNA decorated with antimicrobial proteins, such as myeloperoxidase (MPO), which are extruded from activated neutrophils. Although NETs are essential in innate immunity, an excessive formation of NETs has adverse effects, e.g., induction of anti-neutrophil cytoplasmic antibody (ANCA), to the hosts. Since ANCA can induce NET formation in the primed neutrophils, a positive feedback loop can be formed between NETs and ANCA, which is called "ANCA-NETs vicious cycle."

Case presentation: A 79-year-old Japanese woman developed hydralazine-induced pauci-immune necrotizing crescentic glomerulonephritis with MPO-ANCA. Although the illness improved after cessation of hydralazine, MPO-ANCA-associated vasculitis relapsed 16 months later. Remission was achieved 5 months after beginning of administration of prednisone. In order to determine the involvement of ANCA-NETs vicious cycle in this patient, we examined NET degradation and induction activities in sera obtained at the disease onset (Serum A; MPO-ANCA, 107 IU/ml), at relapse (Serum B; MPO-ANCA, 195 IU/ml), at 3 months after treatment (Serum C; MPO-ANCA, 4.5 IU/ml), and at remission (Serum D; MPO-ANCA, 2.4 IU/ml). NET degradation activity was low in the all sera. NET induction activity was high in Sera A, B, and C but not in D. Additionally, we demonstrated the presence of anti-NET antibody (ANETA) in Sera B and C but not in A or D.

Conclusions: The collective findings suggest NET induction potential of ANETA in the present patient and that the ANETA could contribute to the enhancement of NETs resulting in amplification of the ANCA-NETs vicious cycle.

Keywords: ANCA-NETs vicious cycle; ANCA-associated vasculitis (AAV); Anti-NET antibody (ANETA); Neutrophil extracellular traps (NETs).

Fig. 1

Renal biopsy findings and NET degradation and induction activities in sera. a Renal biopsy finding at the onset of disease. A total of 36 glomeruli, including 4 with global sclerosis, 17 with cellular crescent, 4 with segmental necrosis, and 11 intact glomeruli, were observed. A significant deposition of immunoglobulins (Ig) or complements was not evident (not shown). The representative glomerulus with cellular crescent formation is shown (Periodic acid methenamine silver with hematoxyline and eosin stain). Bar: 100 μm. b Renal biopsy finding at relapse of disease. A total of 18 glomeruli, including 6 with global sclerosis, 7 with cellular crescent, 1 with segmental necrosis, and 4 intact glomeruli, were observed. A significant deposition of Ig or complements was not evident (not shown). The representative glomerulus with cellular crescent formation is shown (Periodic acid Schiff stain, Bar: 100 μm). c NET degradation activity. Data are shown as the mean ± SD of sextuplicated results. **p < 0.01 in One-way ANOVA. Experiments were performed twice independently and we confirmed that the results were reproduced. d NET induction activity. Data are shown as the mean ± SD of sextuplicated results. *p < 0.05, **p < 0.01 in One-way ANOVA. Experiments were performed twice independently and we confirmed that the results were reproduced

Fig. 2

Detection of ANETA. Under the experimental condition, approximately 40% of neutrophils formed NETs (arrowheads in DAPI panels), whereas the others sustained the cell morphology (asterisks in DAPI panels). ANCA was detected in Sera A and B (asterisks in FITC panels) but not in Serum C or D. ANETA was detected in Sera B and C (arrowheads in FITC panels) but not in Serum A or D. Representative photomicrographs are shown