Myelin oligodendrocyte glycoprotein (MOG) is a key CNS-specific autoantigen for primary demyelination in multiple sclerosis. Although the disease-inducing role of MOG has been established, its precise function in the CNS remains obscure. MOG is a type I integral membrane protein possessing a single extracellular Ig variable domain (Ig-V) . The amino acid sequence of MOG is highly conserved among animal species (>90%), indicative of an important biological function. MOG is specifically expressed in the CNS on the outermost lamellae of the myelin sheath as well as the cell body and processes of oligodendrocytes. The developmentally late expression of MOG correlates with the later stages of myelinogenesis, suggesting that MOG has a role in the completion, compaction, and/or maintenance of myelin, further suggesting that MOG has an adhesive function within the CNS . Consistent with MOG's possible adhesive role in the CNS, a homodimeric form of MOG has not only been observed after isolation from the CNS but has additionally been observed in situ.