A structurally available encephalitogenic epitope of myelin oligodendrocyte glycoprotein specifically induces a diversified pathogenic autoimmune response.

Multiple sclerosis is an inflammatory disease of the CNS that involves immune reactivity against myelin oligodendrocyte glycoprotein (MOG), a type I transmembrane protein located at the outer surface of CNS myelin. The epitope MOG92-106 is a DR4-restricted Th cell epitope and a target for demyelinating autoantibodies. In this study, we show that the immune response elicited by immunization with this epitope is qualitatively different from immune responses induced by the well-defined epitopes myelin basic protein (MBP) 84-96 and proteolipid protein (PLP) 139-151. Mice with MOG92-106-, but not with MBP84-96- or PLP139-151-induced experimental autoimmune encephalomyelitis developed extensive B cell reactivity against secondary myelin Ags. These secondary Abs were directed against a set of encephalitogenic peptide Ags derived from MBP and PLP as well as a broad range of epitopes spanning the complete MBP sequence. The observed diversification of the B cell reactivity represents a simultaneous spread toward a broad range of antigenic epitopes and differs markedly from T cell epitope spreading that follows a sequential cascade. The Abs were of the isotypes IgG1 and IgG2b, indicating that endogenously recruited B cells receive help from activated T cells. In sharp contrast, B cell reactivity in MBP84-96- and PLP139-151-induced experimental autoimmune encephalomyelitis was directed against the disease-inducing Ag only. These data provide direct evidence that the nature of the endogenously acquired immune reactivity during organ-specific autoimmunity critically depends on the disease-inducing Ag. They further demonstrate that the epitope MOG92-106 has the specific capacity to induce a widespread autoimmune response.