Step 1: Understanding the Concept:
Mast cells (mastocytes) are resident cells of connective tissue that play a central role in inflammatory and immediate allergic reactions (Type I hypersensitivity).
Step 2: Detailed Explanation:
Let us analyze each statement individually:
(A) Mast cells are widely distributed throughout the body but are particularly abundant in loose (areolar) connective tissue, especially in the dermis of the skin and mucosal linings of the respiratory and digestive tracts, close to blood vessels. (True)
(B) Their cytoplasmic granules contain highly sulfated glycosaminoglycans (specifically heparin), which are highly acidic. When stained with basic dyes like toluidine blue, they exhibit metachromasia—the dye changes color from blue to purple/red due to the high density of negative charges on the heparin molecules. (True)
(C) The secretory granules of mast cells contain preformed mediators, including vasoactive amines (histamine), anticoagulants (heparin), and neutral proteases (such as tryptase and chymase). (True)
(D) The granules are highly basophilic because they bind readily to basic histochemical stains due to their acidic nature. (True)
Since all four statements (A, B, C, and D) are accurate descriptions of mast cell characteristics, the correct option is (C).
Step 3: Final Answer:
All statements are correct, so option (C) is the right choice.