Detailed analysis of early immunopathologic events during lesion formation in acute experimental autoimmune encephalomyelitis.

To investigate early immunopathologic events, SJL/J mice were challenged for acute experimental autoimmune encephalomyelitis (EAE) and sampled between 12 hr and 14 days postinoculation (PI). Complete Freund's adjuvant (CFA)-inoculated mice served as controls. T cells, T cell subsets, Class II major histocompatibility (MHC) antigen (Ia)-positive and immunoglobulin (Ig)-positive cells, albumin and Ig deposits, and myelin antigens were localized in frozen sections of central nervous system (CNS) and non-CNS tissue (heart, liver, kidney) by immunocytochemical techniques. In both experimental groups, a few Ia-positive endothelial cells and low-grade diffuse infiltration by T cells, T cell subsets, and Ia+ and Ig+ cells were seen from 12 hr PI onward in CNS and non-CNS tissue. Only in acute EAE but not in CFA-challenged mice were these early changes followed at 10 days PI by extensive inflammation which was restricted to the CNS and was accompanied by Ia-positive astrocytes. Thus, in acute EAE, immunopathologic changes appear to develop in two stages. During the early low-grade generalized phase, recirculation of lymphocytes is moderately enhanced while during the late phase, extensive immunopathology is focused upon the target organ, the CNS.