ARHGAP25 and arthritic joint disease: In the present study, we show that 1) lacking ARHGAP25 mitigates the symptoms of serum-transfer arthritis in mice, 2) phagocyte infiltration into the inflamed ankle joint, but not the phagocyte effector functions, is reduced in ARHGAP25 knock-out animals, and 3) ARHGAP25 is expressed in fibroblast-like synoviocytes in an amount comparable to neutrophils.