There is provided a peptide which is capable of binding to an MHC molecule in vitro and being presented to a T cell without antigen processing (i.e. an apitope) which peptide comprises a portion of the region 40-60 of myelin oligodendrocyte glycoprotein (MOG). In particular there is provided an apitope which is selected from the following myelin oligodendrocyte glycoprotein peptides: MOG 41-55, 43-57, 44-58 and 45-59. There is also provided the use of such a peptide in a pharmaceutical composition and a method to treat and/or prevent a disease using such a peptide.