IgE levels are often increased in patients with allergic disease.

IgE levels are often increased in patients with allergic disease. IgE binds to the membranes of mast cells and basophils, and if specific antigen is present to react with the IgE molecule, degranulation of these cells occurs, releasing histamines, and other substances into the blood or tissues.

Which of the following immunoglobulin classes is chiefly responsible for the degranulation of mast cells and basophils: