Final answer:
The major storage site for histamine in the body is the mast cells. These cells release histamine during inflammatory and allergic responses. Antihistamines block the effect of released histamine, alleviating symptoms.
Step-by-step explanation:
The major site of storage of histamine within the body is the mast cells (A). Mast cells, found in connective tissue, are packed with granules containing histamine and heparin. When these cells are irritated or damaged, they release histamine, which is a key mediator in inflammatory responses, causing symptoms such as vasodilation, increased blood flow, itching, swelling, and redness typically associated with allergic reactions. Basophils, also involved in allergic responses, have a similar function but are less numerous in the body and do not primarily store histamine. Platelets and eosinophils are not the major storage sites for histamine.Regarding hypersensitivity reactions, mast cells are involved in type I hypersensitivities, where they release inflammatory molecules including histamines. In type II hypersensitivities, the main mediators are antibodies that can cause cell lysis or cytotoxicity when they react against specific antigens on cell surfaces. Antihistamines work by preventing histamines that have been released by mast cells from stimulating body tissues, thereby reducing symptoms.