Fig. 6.

Natural cytotoxicity is not measurable in active (non-remission) granulomatosis with polyangiitis (GPA). Freshly isolated, thawed peripheral blood mononuclear cells (PBMCs) from 11 healthy controls (HC) and patients with GPA from cohort II (in remission = 11 and non-remission = 7 patients; total = 18) were cultured overnight in medium. After washing PBMCs (effector cells) and ⁵¹Cr-labeled K562 (target) cells were co-cultured for 4 hours without further stimulation. The highest effector (PBMC)/target (E:T) ratio was 25:1, only viable PBMCs were counted. Percent specific lysis was determined by measuring ⁵¹Cr in the supernatant. The sensitivity threshold of this assay lies at about 5–10 % specific lysis. a No natural cytotoxicity was detectable in PBMCs from 7/18 patients (left), whereas typical cytotoxicity curves were measured in PBMCs from the remaining 11/18 patients and all HC (right). b Analysis of the GPA activity states in patients revealed that PBMCs without natural cytotoxic response were all from patients in the non-remission group, except for the two patients with the lowest natural killer (NK)/target ratios within the remission group (0.96 and 1.1, respectively). Two patients from the non-remission group exhibited measurable minor natural cytotoxicity; both were clinically categorized as having "grumbling disease". c Statistical analysis at the highest E (viable PBMC):T ratio (25:1); Kruskal-Wallis test, p = 0.0016; Dunn's post hoc test was significant where indicated in the graph. d NK/target ratios of the highest E:T were calculated based on the percentages of NK cells in PBMCs and blotted against the percentage of lysed target cells (% specific lysis); linear equation, r ², Spearman's r and statistical significance of the correlation as indicated in the graphs