B-cell developmental stages in time-matched samples from the peripheral blood (PB) and synovium. (a) Original scatter plots of flow cytometric analyses on PB (top row) and synovial B cells (bottom row) in three different patients. CD27 staining is depicted on the horizontal axis, and IgD surface staining is depicted on the vertical axis. Quadrants are set according to the results in unstained cells for compensation of autofluorescence. Patient 1 (left column) had persistent arthritis 4 months after rituximab (RTX) and a PB B-cell count of 4/μL. Patient 2 (middle column) had arthritis relapse 10 months after RTX and a PB CD19+ B-cell count of 27/μL. Patient 3 (right column) had arthritis relapse 9 months after RTX and a PB CD19+ B-cell count of 71/μL. (b) Cumulative data on the frequency of B-cell subsets in six pairs of samples, including patients depicted in (a), indicate preferential accumulation of CD27+IgD- switched memory B cells in the synovium (P = 0.028). FITC, fluorescein isothiocyanate; PE, phycoerythrin.