T-CELL INFILTRATION AND EXPRESSION OF MHC CLASS-II ANTIGEN BY MACROPHAGES AND MICROGLIA IN A HETEROGENEOUS GROUP IN LEUKOENCEPHALOPATHY

We report here on T-cell infiltration and diffuse expression of the ma jor histocompatibility complex (MHC) class II antigen in a heterogeneo us group of macrophages and microglia in leukoencephalopathy (LE). Mic roglia reacting positively for HLA-DR were five times more numerous in LE than those in non-LE cases and were distributed densely in the deg enerated white matter but sparsely in the subcortical arcuate fibers. CD4- and CD8-positive lymphocytes were 9 and 15 times more plentiful, respectively, in LE cases; they aggregated in the expanded Virchow-Rob in spaces and frequently infiltrated the neural parenchyma. An intimat e association of T cells with macrophages, and the expression of leuko cyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1), accessory molecules in antigen presentation, were observed in each cell in the region of macrophage clusters. These res ults indicate that expression of MHC antigen is accompanied by cell ad hesion molecules and by infiltration of T cells in a heterogeneous gro up in leukoencephalopathy and suggests their immunocompetence, althoug h it may be secondary to destruction of myelin.