Myelin Protein Expression Is Increased in Lymph Nodes of Mice with Relapsing Experimental Autoimmune Encephalomyelitis

Myelin proteins had been thought to be sequestered behind the blood-brain barrier. Recently, however, myelin proteins have been found to be expressed in lymphoid tissues. The myelin basic protein (MBP) gene is embedded within a larger transcription unit called the golli-MBP gene. This larger gene encodes both the "classic" MBPs as well as the structurally related golli-MBPs. In this study, golli-MBP expression in lymph nodes was examined in four different models of relapsing experimental autoimmune encephalomyelitis (rEAE). Disease in these rEAE models was induced by the adoptive transfer of T lymphocytes specific for 18.5-kDa MBP, MBP peptide 83-102, or PLP peptide 139-151 in the SJL/J mouse and the adoptive transfer of T lymphocytes specific for MBP peptide Ac1-9 in the (SJL/J x PL/J)F₁ mouse. In all four models, expression of golli-MBP BG21 mRNA was increased two- to fivefold in lymph nodes of mice 45 to 60 days post-transfer. Immunohistochemical analysis indicated that expression occurred principally in macrophages within lymph nodes. Endogenous golli-MBP epitopes within lymph node cells stimulated "classic" MBP 1-44-specific T lymphocytes, and this stimulatory ability resided within the adherent lymph node cell population. An increase in myelin protein expression within lymph nodes during rEAE has implications with regard to intra- and intermolecular epitope spreading. This is the first report describing an increase in target autoantigen expression within lymphoid tissue during an autoimmune disease.