Multiple sclerosis protein complex, molecular model. The proteins forming this complex are a T-cell receptor (TCR), a peptide antigen (myelin basic protein, MBP), and a major histocompatibility complex (MHC) molecule. The interaction between these proteins is being studied as part of research into multiple sclerosis. Multiple sclerosis is an autoimmune condition, in which the immune system attacks the myelin sheath that insulates nerve cells, impairing their ability to relay signals efficiently.