Frequencies of various immune cell subsets in patients with antibiotic-responsive or antibiotic-refractory Lyme arthritis. (a) Representative dot plots of peripheral blood (PB) from one patient showing the gating strategy for the various lymphocyte populations. (b and c) Enumeration of various immune cell subsets of 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. (d) Frequencies of cells in the SF of patients with antibiotic-refractory arthritis were categorized based upon whether the sample was obtained early (≤3 months, N = 6) or late (>3 months, N = 9) after the start of antibiotics. The graph on the left shows the percentages of CD56bright and CD56dim natural killer (NK) cells in refractory patients whose samples were collected early in the course of their arthritis (≤3 months) compared with those from responsive patients. The graph on the right compares the frequencies of CD56bright and CD56dim NK cells in refractory patients whose samples were obtained >3 months 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.