Multiple sclerosis: oligodendrocytes in active lesions do not express class II major histocompatibility complex molecules.

The expression of major histocompatibility complex (MHC) molecules by oligodendrocytes has been proposed as evidence for their involvement in the multiple sclerosis (MS) lesion although the literature on the subject is controversial and based largely upon observations in vitro. With a modified immunocytochemical procedure on 1 micron epoxy sections, the present study has examined the expression of class II MHC molecules (Ia) on cells within actively demyelinating lesions in a central nervous system biopsy from a case of acute MS. White Ia was readily demonstrable on microglial cells and astrocytes, it was never detected on adjacent surviving oligodendrocytes. Unexpectedly, in parallel sections, the oligodendrocytes stained positively for myelin-associated glycoprotein, a marker for immature oligodendrocytes. The unequivocal lack of Ia expression by oligodendrocytes in MS makes it unlikely that they serve as immunomodulators in lesion pathogenesis.