The frequency of GM-CSF–producing T helper cells was significantly enriched in SF mononuclear cells compared to PB mononuclear cells from the patients with JIA (24.1% of CD4+ T cells versus 2.9%) and closely correlated with the erythrocyte sedimentation rate (r2 = 0.91, P < 0.001). Here, CD4 is linked to juvenile idiopathic arthritis.