To compare the activation states of JIA and CF neutrophils, we performed ELISA assays for S100 A8/A9 complexes (also known as myeloid-related proteins [MRP] 8/14), potent pro-inflammatory proteins that are sensitive indicators of neutrophil activation38 in plasma of children with untreated JIA (n = 31), children with CF (n = 8), and healthy controls (n = 20). The gene discussed is IGKV1D-22; the disease is cystic fibrosis.