Final answer:
Upon irritation, mast cells release chemicals including histamine and proteases. Chymases are a type of protease released by mast cells that break down proteins into peptides.
Step-by-step explanation:
When a mast cell reacts to an irritation, it releases a variety of chemicals that are involved in the body's immune response. These include histamine, which is responsible for many of the symptoms observed in allergic reactions, such as itching, swelling, and redness. Mast cells also release proteases, which are enzymes that break down proteins. Examples of proteases released include chymases, which break down proteins into peptides; therefore, the answer to the question is (d) Chymases.