Question

In what state is histamine present in mast cells and basophils?

Options

• Free dissolved state

• Protein-conjugated state only

• Bound state

• Chemically inactivated state

Answer 1

Histamine is present in a bound state in mast cells in tissues and in basophils in the blood. This binding keeps histamine inactive until the cells are triggered by allergen exposure. Upon activation, mast cells and basophils undergo degranulation, releasing the bound histamine into the extracellular space where it becomes free and can bind to histamine receptors to produce allergic symptoms.