Eosinophils and mast cell homogeneity of the guinea pig eyelid skin, conjunctiva, and ileum

Mast cell heterogeneity has been described on the basis of differential staining reactions, light microscopic morphology, anatomic location, degranulation after polyamines, biochemical contents, growth requirements, and reactions to lymphokines. We have demonstrated typical "connective-tissue mast cells" by using anatomic criteria, histological staining reactions, electron microscopy, and reaction to compound 48/80 in the guinea pig conjunctiva, eyelid skin, and ileum. A second, much larger population of cells in the ileal mucosa and the conjunctiva, and rarely in the eyelid skin stained reddish-blue with acid toluidine blue in tissue fixed in ethanol-acetate-lead subacetate (BLA) and with alkaline Giemsa in formaldehyde-fixed tissue, did not stain with ethanolic or acid toluidine blue in formaldehyde-fixed tissue or with alkaline Giemsa in BLA-fixed tissue, and did not degranulate after 48/80 treatment. These are features of the rat intestinal "mucosal mast cells"; however, ultrastructural and light microscopic studies with the orcein Giemsa stain demonstrated these cells in the guinea pig to be eosinophils. Tissue culture, biochemical, and immunological studies indicate the existence of a second type of mast cell (bone-marrow-derived mast cell), ultrastructurally almost indistinguishable from the connective tissue mast cell. Our studies demonstrate only one mast cell type in the guinea pig and support the contention that other forms of mast cells are immature forms or variants of the connective-tissue mast cell.