SERA FROM JRA PATIENTS CONTAIN ANTIBODIES AGAINST A DEFINED EPITOPE IN CHROMOSOMAL PROTEIN HMG-17

Autoantibodies against the nonhistone nucleosomal protein HMG-17 have been detected in a high percentage of ANA-positive patients with pauci articular-onset JRA(4). Here we report on the epitope mapping of the H MG-17 autoantigen with it set of overlapping and nested synthetic pept ides spanning the entire amino acid sequence of the human HMG-17 prote in. Competition ELISA experiments defined a proline and lysine rich oc tapeptide PKPEPKPK as the major epitope recognized by more than 70 % o f the HMG-17 positive JRA sera. Point mutations introduced in the auto immune peptide determined the amino acid residues important for autoan tibody recognition. Computer based sequence comparison shows close hom ology between the HMG-17 autoimmune epitope and certain infectious org anisms, supporting the possibility that molecular mimicry is an import ant factor in the etiology of JRA.