Mast cell

Mast cells are spherical to oval-shaped with a centrally-located, spherical nucleus. Their cytoplasm is filled with numerous granules that contain heparin, histamine and protease enzymes that function in the inflammatory response.  Shown here are connective tissue mast cells that are located in a loose connective tissue.  Toluidine blue  1000x

Mast cell granules exhibit metachromasia, due to their proteoglycan content. Metachromatic staining results when cellular structures with abundant polyanions, e.g., sulfate groups, are stained with a basic dye, such as toluidine blue. Dye molecules bind in close proximity and form aggregates having different absorptive properties from the single dye molecule, thus producing a different color.  Note how the color of the granules is purple in contrast to the non-metachromatic blue staining of the other tissue elements.

Blood vessels, an adipocyte and collagen fibers are also visible in the loose connective tissue.

Blood vessels, an adipocyte and collagen fibers are also visible in the loose connective tissue.

Blood vessels, an adipocyte and collagen fibers are also visible in the loose connective tissue.