Comparison of CD4+ T lymphocytes derived from peripheral blood and synovial fluid. A) Western blotting of unstimulated and stimulated CD4+ T cells for K2P5.1 and β-actin as loading control (left panel). Quantification of three independent Western blotting experiments (right panel). B) Exemplary flow cytometry stainings for the activation markers CD69 (left panel) and CD25 (right panel) are shown for cells derived from the peripheral blood (grey) and synovial fluid (black). C) K2P5.1 expression levels on CD4+ cells were compared by RT-PCR (left panel) and flow cytometry staining (middle panel). Black lines: RA; grey lines: reactive arthritis. One representative example for RA is depicted on the right side (white: isotyp, grey: peripheral blood, black: synovial fluid). D) Immunohistochemical staining of human synovial tissue sections for CD3 (left panel), TASK2 (middle panel) and overlay (right panel).