Association of leukocyte immunoglobulin-like receptor A3 (LILRA3) with neutrophil activation and its susceptibility in adult-onset Still's disease.

OBJECTIVES Adult-onset Still's disease (AOSD) is a severe auto-inflammatory disease. Neutrophil activation with enhanced neutrophil extracellular trap (NET) formation is involved in the pathogenesis of AOSD. Functional leukocyte immunoglobulin-like receptor A3 (LILRA3) has been reported to be associated with many autoimmune diseases. We aimed to investigate the association of LILRA3 with susceptibility and neutrophil activation in AOSD. METHODS The LILRA3 deletion polymorphism and its tagging SNP rs103294 were genotyped in 164 AOSD patients and 305 healthy controls (HCs). Impact of LILRA3 on clinical features and mRNA expression was evaluated. Plasma LILRA3 level was detected using ELISA and its correlation with disease activity and circulation NET-DNA level was investigated. LILRA3-induced NETs were determined using PicoGreen dsDNA dye and immunofluorescence in human neutrophils and neutrophil-like differentiated NB4 cell line transfected with LILRB2 siRNA. RESULTS We identified that functional LILRA3 was a risk factor in AOSD (11.0% vs. 5.6%, p=0.034, OR=2.089; 95% CI 1.030 to 4.291), and associated with leukocytosis (p=0.039) and neutrophilia (p=0.027). Functional LILRA3 mRNA expression was higher in LILRA3+/+ patients' PBMC (p<0.0001) and neutrophils (p<0.001). Plasma LILRA3 level was elevated in AOSD (p<0.0001) and correlated with disease activity indicators and circulation NET-DNA complexes. Finally, enhanced NET formation was identified in neutrophils from HCs and inactive AOSD patients with LILRA3 stimulation, and impaired in LILRB2 gene knocked down NB4 cells. CONCLUSIONS Our study provides the first evidence that functional LILRA3 is a novel genetic risk factor for AOSD, and functional LILRA3 may play a pathogenic role by inducing NETs formation.