The cellular origin of lysosomal enzymes in the plaque in multiple sclerosis: a combined histological and biochemical study.

Using a combined biochemical and histological approach certain conclusions can be drawn as to the origin of the increase in lysosomal enzymes in white matter from MS brains. Firstly, there is a gradient of lysosomal enzyme activity, plaque greater than periplaque greater than macroscopically normal white matter, which appears to be independent of the stage of evolution of the plaque. The most consistent change in cellular composition within and around all plaques is a marked astrocytosis. It thus appears that the increases in lysosomal enzymes can be mainly attributed to reactive astrocytes; macrophages and the cells of the perivascular infiltrate making only a limited contribution. Secondly, only one of the enzymes tested was significantly elevated in histologically normal white matter, i.e. n-acetyl-beta-D-glucosaminidase. Since this enzyme appears to be a particularly sensitive marker for astrocytes this may be indicative of proliferation of astrocytes in so-called normal white matter.