Allergy

There are four types of hypersensitivity diseases. Allergy is the type I characterized by high level of IgE antibodies arising from hypersensitive reaction to allergens such as pollen or food. IgE antibodies are produced from antibody-secreting plasma cells that are differentiated from B cells upon activation by allergens. The produced antibodies may bind to the Fc receptors on mast cells, which will trigger allergic reactions when the allergens interact with the bound antibodies.

The activation of B cells for the production of IgE requires two separate signals: (1) the cytokines IL-4 or IL-13 interacting with receptors on the B-cell surface, and (2) interaction between CD40 ligand on the helper T cell surface and CD40 on the B-cell surface (Figure). There are two types of helper T cells: T_H1 and T_H2. T_H2 is a better initiator for antibody response because it can produce IL-4 and IL-13. Thus, differentiation from native helper T cells into either T_H1 or T_H2 also plays an important role in the production of IgE. Exposure to IL-4 favors the differentiation into T_H2 whereas T_H1 is favored in the presence of macrophage-derived cytokines such as IL-12, IL-18 and IFN-g.

Book sections
(Immunobiology by C. A. Janeway, 2001 Edition)

The production of IgE

B-cell activation by armed helper T cells

Associated Genes

CSF2
Encodes GM-CSF (colony stimulating factor) which controls the production, differentiation, and function of granulocytes and macrophages. Granulocytes include eosinophils and basophils which are involved in late-phase allergic reactions (more info).

FCER1A
Encodes an Fc fragment of IgE receptor, which plays a central role in allergic disease.

HLA-DQA1, -DQB1, -DRB1
Encodes a subunit of major histocompatibility complex.

IL13
Encodes interleukin 13.

IL4
Encodes interleukin 4.

IL5
Encodes interleukin 5.

STAT6
Encodes STAT6 which plays the central role in mediating signals from IL4 and IL13.

Review articles:

New insights into atopic dermatitis - J. Clin. Invest., 2004.