The cellular origin of lysosomal enzymes in the plaque in multiple sclerosis. II. A histochemical study with combined demonstration of myelin and acid phosphatase.

Existing techniques have been adapted and it has been possible to demonstrate acid phosphatase (APP) and myelin, lipid or astrocytic fibres in the same histological section. In normal controls APP was demonstrated in neurons, astrocytes, ependyma including choroid plexus epithelium and in pericytes, but not in oligodendrocytes. In multiple sclerosis (MS), APP positive cells were found in the plaque, plaque edge and macroscopically normal white matter. Contrary to some previous reports, not only macrophages, but also astrocytes in the MS plaque were found to be APP positive, although the distribution of enzyme in these cells was predominantly diffuse, unlike the particulate distribution in normal astrocytes and other APP positive cells: the significance of this finding is discussed. It is concluded that astrocytes and macrophages are the main source of the elevated levels of APP found biochemically in MS and that in old plaques astrocytes make the major contribution.