The mast cells of the multiple sclerosis brain

Abstract Traditional staining methods, plus indirect immunoperoxidase techniques for IgE and mast cell tryptase (MC Tr ) were used to study the mast cells (MCs) of multiple sclerosis (MS) and normal brains. The MCs varied in number in MS amongst perivascular inflammatory cells as well as free in the parenchyma, especially inside and around ‘chronic active’ plaques. Since MCs do not migrate, and rarely divide in maturity, they must have developed locally. Staining for IgE was moderately strong on and within MCs, and weak within some plasma cells. MC Tr reacted strongly both within CNS and outside it. Being a strong neutral proteinase, MC Tr , plus IgE, could conceivably have played some role in the pathogenesis of the MS plaques.