DETECTION OF MHC CLASS-II ANTIGENS ON MACROPHAGES AND MICROGLIA, BUT NOT ON ASTROCYTES AND ENDOTHELIA IN ACTIVE MULTIPLE-SCLEROSIS LESIONS

Tissue sections of brains from patients with multiple sclerosis (MS) a nd from control individuals were immunostained with MHC class II and g lial or vascular endothelial cell antibodies and analyzed by confocal microscopy. MHC class II was abundant in and around actively demyelina ting MS lesions and was detected on microglia, phagocytic macrophages, and perivascular macrophages. Astrocytes and vascular endothelial cel ls were MHC class II-negative. Changes in the size and shape of MHC cl ass II-positive cells associated with MS lesions suggest that microgli a transform into phagocytic macrophages, and that they are actively in volved in demyelination. Many MHC class II-positive perivascular macro phages within MS lesions contained abundant intracellular MHC class II immunoreactivity; these cells may be involved in antigen presentation and in T cell activation.