Although control neutrophils stained with anti-CD69 mAb yielded very low fluorescence, just above that of unstained cells (%CD69+ cells: 1.3 ± 0.5; MFI: 1.0 ± 0.3), CD69 was significantly expressed on neutrophils from RA patients at baseline (%CD69+ cells: 22.8 ± 5.4; MFI: 7.6 ± 1.4; P < 0.001 versus controls; Fig. 4). Here, CD69 is linked to rheumatoid arthritis.