Fig. 2

Natural killer (NK) cell proportions negatively correlate with granulomatosis with polyangiitis (GPA) activity and are increased in inactive GPA. Peripheral blood mononuclear cells from patients and healthy controls (HCs) were isolated using Ficoll-Paque density gradient medium and analyzed by flow cytometry. a Gating strategy. Peripheral blood lymphocytes (PBLs) were determined using forward and sideward scatter (FSC and SSC, respectively). Cell viability was confirmed by negative 7-aminoactinomycin (7-AAD) staining in each experiment. NK cells were determined by costaining of CD3 (negative) and CD56 (positive). b Scatterplot showing the relationship between NK cell proportions and Birmingham Vasculitis Activity Score (BVAS). Note that in one case, two patients are represented by a single dot; both had a BVAS of 3 and NK cell proportions of 15.6 % and 15.8 %, respectively (n = 28). Spearman’s correlation coefficient (r) and statistical significance were as indicated on the figure. c and d Box-and-whisker plots. Whiskers represent 10th–90th percentile range, statistical significance is as indicated. Left graph in (c) depicts NK cell proportions of PBLs from HCs (n = 29), patients with active GPA (n = 11), patients with inactive GPA (n = 17), and patients with inactive systemic inflammatory control diseases (CD; n = 12). Right graph in (c) illustrates NK cell counts in PBLs from patients with active GPA (n = 6), patients with inactive GPA (n = 5), and patients with inactive CD (n = 12). Statistical significance was determined by Kruskal-Wallis test (p = 0.0002 for relative and p = 0.014 for absolute NK cell numbers) and Dunn’s multiple comparison posttests (asterisks) as shown in the graphs. d T-cell proportions of patients with active (n = 11), inactive (n = 17) GPA and of HCs. Statistical analysis using the Kruskal-Wallis test revealed that CD56⁻ but not CD56⁺ T-cell proportions were significantly different (p = 0.04). Dunn’s multiple comparison posttests were positive where indicated by asterisks. e Receiver operating characteristic curve showing sensitivity and specificity of different NK cell proportions to distinguish inactive from active GPA. NK cells >18.5 % of PBLs determined GPA inactivity with a specificity of 100 % and a sensitivity of 71 %. AUC area under the curve