Review Question - QID 100477

TH2 cells secrete IL-4 to promote B-cell class switching to IgE.

IL-4 is a cytokine produced by TH2 cells. It functions to induce differentiation of native helper T-cells and to promote B-cell class switching to IgE. Secreted IgE binds to local mast cells, and subsequent exposure to the allergen (e.g. pollen) leads to allergen binding to antibodies deposited on the mast cell surface. This leads to cross-linking of antibodies and the release of histamine, leukotrienes, and proteases, resulting in the hypersensitivity reaction that ensues.

Li 2002 provides an overview of percutaneous and intradermal skin tests and laboratory assays of specific IgE to be utilized in selected cases of allergy management. In general, laboratory assays are less sensitive than skin testing. Select patients with allergic rhinitis or asthma who are refractory to standard treatment may benefit from allergy testing.

Milgrom et al. demonstrate that anti-immunoglobulin E antibody may be useful in the treatment of asthma. They postulate that IgE-mediated mast cell activation contributes to chronic eosinophilia and airway remodeling. These changes may result in permanent loss in pulmonary function seen in chronic asthma.

Illustration A provides an overview of the cells and cytokines involved in the allergic response.

Incorrect answers:
Answer 1: TH1 cells secrete IFN-gamma, which is responsible for activating macrophages and stimulating the synthesis of IgG by B-cells.
Answer 3 and 5: TH17 cells secrete IL-17 and IL-22. The main function of these cytokines is to attract macrophages and neutrophils to the site of infection.
Answer 4: TGF-beta is secreted by many cells, including macrophages, and acts as an antiproliferative factor in normal epithelial cells.