In the presence of dexamethasone, gamma interferon induces rat oligodendrocytes to express major histocompatibility complex class II molecules.

Cells that express major histocompatibility complex (MHC) class II molecules can interact directly with CD4 T lymphocytes and either activate immune reactions or become the targets of T-cell-mediated cytotoxic attack. Using rat optic nerve cultures combined with immunocytochemistry and in situ hybridization, we have shown that oligodendrocytes, the major myelin-forming cells of the central nervous system and the main casualty of the immune attacks associated with multiple sclerosis and experimental allergic encephalomyelitis, can be readily induced to express MHC class II mRNA and surface antigens in vitro by exposure to gamma interferon, provided the glucocorticoid dexamethasone is included in the culture medium. Oligodendrocytes exposed to gamma interferon without dexamethasone fail to express MHC class II molecules, which may account for the failure of previous attempts to induce expression in these cells. In the experiments reported here MHC class II expression can be demonstrated both on galactocerebroside-positive cells and on mature oligodendrocytes that express proteolipid protein. These findings expand possibilities for understanding immune-related oligodendrocyte killing and demyelination in human and experimental demyelinating diseases.