Subsequently, the identified PDC-E2 residue was modified by replacing lipoic acid with a series of similar but distinct synthetic structures. Following this modification, PDC-E2-specific autoantibodies from patients with PBC reacted with higher affinity to the modified epitopes than to the native PDC-E2 peptide. The structure inducing maximal affinity was demonstrated to be derived from 2-nonynoic acid, a compound widely used in cosmetics [116] .