Frequencies of Vα24+ (invariant) NKT cells in patients with antibiotic-responsive or antibiotic-refractory arthritis. (a) Representative dot plots of peripheral blood (PB) from one patient showing the gating strategy used to determine the frequency of invariant natural killer T cells (iNKT) in patient samples. (b) Frequencies of iNKT cells in matched PB and synovial fluid (SF) samples from eight antibiotic-responsive (Resp) and fifteen antibiotic-refractory (Ref) patients, and for comparison four healthy control (HC) subjects. (c) Frequencies of iNKT cells in the SF of patients with antibiotic-refractory arthritis stratified by whether the sample was obtained early (≤3 months, N = 6) or late (>3 months, N = 9) after the start of antibiotics. Symbols indicate individual subjects, horizontal bars represent the median of each group and significant differences are denoted. Statistical analyses were performed by using the Mann-Whitney test.