The potential for oligodendrocyte proliferation during demyelinating disease

The potential for oligodendrocytes to proliferate in response to central nervous system injury was examined. We used intracerebral infection of Theiler's murine encephalomyelitis virus, a model for multiple sclerosis, which results in chronic demyelinating disease of SJL/J mice. Proliferating cells in spinal cord sections of adult mice were identified using simultaneous immunohistochemistry and in situ autoradiography ([3H]-thymidine incorporation). Seven different cell-specific markers were used to characterize proliferating cells as oligodendrocytes (myelin basic protein, proteolipid protein, galactocerebroside, CNPase), astrocytes (glial fibrillary acidic protein), microglia/macrophages (Griffonia simplicifolia isolectin B4) or T-lymphocytes (CD3). The average number of proliferating cells per area of spinal cord white matter was 11/mm2 in normal young adult mice compared to 61/mm2 in chronically infected mice. Most proliferating cells in normal spinal cord were not identified with these markers and were presumed to be progenitor glial cells. However, in spinal cord white matter of mice infected with Theiler's virus for approximately 4 months, 88% of proliferating cells were identified. Approximately one-third of all proliferating cells were in the oligodendrocyte lineage and expressed markers observed late in myelin differentiation. In demyelinated areas as compared to normal white matter, there was an 80- to 211-fold increase in the number of proliferating oligodendrocytes expressing myelin basic protein or proteolipid protein, respectively. The remainder of the proliferating cells in areas of demyelination were astrocytes, microglial cells and T-cells. These experiments support the hypothesis that factors within a demyelinating lesion promote the proliferation and differentiation of cells within the oligodendroglial lineage.