L-(+)-Ergothioneine is a naturally-occurring amino acid derived from histidine via hercynine. Ergothioneine is a stable antioxidant that scavenges and detoxifies free radicals and oxidants, increases intracellular thiol levels, controls nuclear factor-κB activation, and inhibits inflammatory gene expression. In addition, it inhibits the peroxynitrite-dependent nitration of nitrotyrosine, blocks oxidative DNA damage and cell death, and prevents the formation of xanthine and hypoxanthine. Ergothioneine is transported by the organic cation/carnitine transporter 1, which has been linked with autoimmune diseases, including rheumatoid arthritis and Crohn's disease.