Plasma Mast Cells

Abstract

DURING a histopathological examination of three hundred canine mastocytomata fixed in formalin, cells were repeatedly observed which presented characteristics of both plasma cells and mast cells¹. These cells were intermediate in size between mast cells and plasma cells and presented eccentric nuclei, paranuclear clear areas and a large amount of clumped nuclear chromatin, all of which are characteristic of plasma cells rather than mast cells (Figs. 1 and 2). Unlike normal plasma cells, however, these intermediate forms contained cytoplasmic granules which stained metachromatically with 0.1 per cent aqueous toluidine blue (Figs. 2 and 3) and thus possessed the single, most outstanding, characteristic of mast cells. Various stages were observed ranging from typically appearing plasma cells with a few metachromatic cytoplasmic granules (Fig. 3) to cells more nearly approximating mature mast cells but revealing such plasma cell features as paranuclear clear areas, eccentric nuclei and clumped nuclear chromatin (Fig. 2).