We, subsequently, subjected 10 JIA patients’ sera to affinity chromatography on a rabbit anti-human IgM column eluting with 1 M ammonia and 0.1 M glycine–HCl buffer, pH 3.0, and 15 patients to 4% PEG precipitation followed by acid dissociation of the precipitate. This evidence concerns the gene CD40LG and juvenile idiopathic arthritis.