Inflammatory cells, microglia and MHC class II antigen-positive cells in the spinal cord of Lewis rats with acute and chronic relapsing experimental autoimmune encephalomyelitis.

Chronic relapsing experimental autoimmune encephalomyelitis (CR-EAE) was induced in Lewis rats by inoculation with guinea pig spinal cord and adjuvants and treatment with low dose cyclosporin A (CsA). Acute EAE was induced by the same method without CsA treatment. Immunocytochemistry and flow cytometry were used to assess inflammatory cells and MHC class II (Ia) antigen expression in the central nervous system of these rats. The inflammatory infiltrate was composed mainly of CD4+ T cells and macrophages, and alpha beta T cells constituted about 65% of the CD2+ T cells. After recovery from acute EAE and during the first remission of CR-EAE, the number of T cells was significantly less than in the preceding episodes. The number of T cells was higher in the second episode of CR-EAE than in the first remission. Throughout the course of CR-EAE, the majority of the CD2+ T cells were CD45RC-. The ratio of IL-2R+ cells to CD2+ cells ranged from 10.5 to 24.0%. The ratio of CD4+ T cells to B cells was lower in the later episodes of CR-EAE than in the first episode. Ia antigen was expressed on infiltrating round cells at all stages of CR-EAE and on microglial cells (identified by dendritic morphology) with increasing intensity throughout the course of CR-EAE. With flow cytometry, the number of Ia+ cells obtained from the spinal cord rose throughout the course of CR-EAE. The number of FSClowOX1low cells, which we consider represent microglia, also increased during the course of CR-EAE.