CHARACTERIZATION AND DISTRIBUTION OF PHAGOCYTIC MACROPHAGES IN MULTIPLE-SCLEROSIS PLAQUES

Populations of phagocytic cells in multiple sclerosis (MS) plaques wer e examined by quantitative immunocytochemical analysis of macrophage m arkers and myelin degradation products in serial cryostat sections fro m 10 cases of MS. Around lesions with ongoing demyelination expression of the Class II antigen HLA-DQ appeared to be a marker of microglial activation. Alpha 1-antichymotrypsin+ monocytes and myelin-laden macro phages expressing the later differentiation markers Ber-MAC3 and RFD7 were predominantly perivascular in location. On the basis of the distr ibution of oil red 0 (ORO)+ phagocytes and myelin loss, plaques were d ivided into groups representing different stages in lesion development . In early lesions (group 1), there was no apparent myelin loss around ORO+ macrophages although these cells contained material stained with antibodies against myelin basic protein (MBP) epitopes and neoepitope s. However, patchy myelin loss was detectable around the phagocytic ma crophages uniformly distributed throughout group 2 plaques. ORO+ macro phages containing MBP peptides were confined to the hypercellular bord er of group 4 lesions, in which the demyelinating process may be recur rent.