The significance of in-situ Ia antigen expression in the pathogenesis of autoimmune central nervous system disease.

Major histocompatibility class II antigen (Ia) expression is thought to play an important role in the pathogenesis of autoimmune central nervous system (CNS) disease. It has been suggested that Ia expression within the CNS might be sufficient to induce experimental allergic encephalomyelitis (EAE). The expression of Ia antigen in the CNS was studied during the natural course of both acute and chronic relapsing EAE. We found that Ia expression in the CNS starts at a relatively late stage in the course of EAE and persists after the disappearance of the clinical signs. In order to further evaluate the functional significance of Ia expression on glial cells we also studied the effect of intraventricular administration of interferon-gamma. This caused widespread Ia expression within the CNS but no signs of autoimmune CNS disease. Based on these results and data from the literature, the role of local Ia expression in the CNS is reconsidered. In certain circumstances Ia expression may contribute to suppressive rather than enhancing effects on the immune response.