MHC-II EXPRESSION IN THE CNS AFTER LONG-TERM DEMYELINATION

The ability of chronically demyelinated central nervous system (CNS) t issue to express major histocompatibility complex (MHC) class II molec ules has been measured in mouse spinal cord cultures exposed for 1 and 3 weeks to demyelinating anti-white matter (WM) serum. From previous studies, it was known that after 3 weeks of demyelination in vitro, su ch cultures are incapable of remyelination. In the present report, MHC II levels were evaluated by immunocytochemistry and by Western and No rthern blots. The results have shown that after both 1 and 3 weeks of exposure to myelinotoxic anti-WM serum, the cultures retained the abil ity to express MHC II and this could be further upregulated by incubat ion with interferon gamma (IFN gamma). Control groups showed increased expression of MHC II with age. By immunocytochemistry, all groups of cultures expressed high levels of MHC II and all groups showed upregul ation after IFN gamma treatment. Anti-WM-treated cultures demonstrated slightly higher levels of MHC II than controls. Morphologically, the MHC II expression was associated with the surface of astrocytes. Semiq uantitative analysis by Western blotting confirmed the increase in cla ss II MHC expression in the long-term treated cultures after IFN gamma exposure, revealing no differences between anti-WM-treated and comple ment-treated cultures. This was also supported by Northern blotting wh ich showed similar mRNA levels in both groups. These findings suggest that long-term demyelinated CNS tissue still possesses the ability to interact with CD4+ T cells, observations of significance to the expans ion of the chronic multiple sclerosis lesion.