This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (December 2008)

A hapten is a small molecule that can elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself. (In general, only large molecules, infectious agents, or insoluble foreign matter can elicit an immune response in the body.) Once the body has generated antibodies to a hapten-carrier adduct, the small-molecule hapten may also be able to bind to the antibody, but it will usually not initiate an immune response; usually only the hapten-carrier adduct can do this. Sometimes the small-molecule hapten can even block immune response to the hapten-carrier adduct by preventing the adduct from binding to the antibody.

The concept of haptens emerged from the work of Karl Landsteiner^{[1] [2]} who also pioneered the use of synthetic haptens to study immunochemical phenomena.^[3]

Contents 1 Examples of haptens 2 References 3 See also 4 External links

[edit] Examples of haptens

A well-known example of a hapten is urushiol, which is the toxin found in poison ivy. When absorbed through the skin from a poison ivy plant, urushiol undergoes oxidation in the skin cells to generate the actual hapten, a reactive molecule called a quinone, which then reacts with skin proteins to form hapten adducts. Usually, the first exposure only causes sensitization, in which there is a proliferation of effector T-cells. After a second exposure later, the proliferated T cells can become activated, generating an immune reaction, producing the typical blisters of poison ivy exposure.

Some haptens can induce autoimmune disease. An example is hydralazine, a blood pressure-lowering drug that occasionally can produce drug-induced lupus erythematosus in certain individuals. This also appears to be the mechanism by which the anaesthetic gas halothane can cause a life-threatening hepatitis, as well as the mechanism by which penicillin-class drugs causes autoimmune hemolytic anemia.

Other haptens that are commonly used in molecular biology applications include fluorescein, biotin, digoxigenin, and dinitrophenol.

[edit] References

[edit] See also

• Toxin
• Antigen

[edit] External links

• MeSH Haptens

v • d • e Immune system / Immunology Systems Adaptive vs. Innate · Humoral vs. Cellular · Complement (Anaphylatoxins) · Intrinsic Lymphoid Antigens Antigen (Superantigen, Allergen) · Hapten Epitope (Linear, Conformational) Antibodies Antibody (Monoclonal antibodies, Polyclonal antibodies, Autoantibody) · Polyclonal B cell response · Allotype · Isotype · Idiotype Immune complex Immunity vs. tolerance action: Immunity · Autoimmunity · Alloimmunity · Allergy · Inflammation · Cross-reactivity inaction: Tolerance (Central, Peripheral, Clonal anergy, Clonal deletion, Tolerance in pregnancy) · Immunodeficiency Immunogenetics Somatic hypermutation · V(D)J recombination · Junctional diversity  · Immunoglobulin class switching · MHC/HLA Immune cells/ White blood cells Lymphoid: T cell · B cell · NK cell Myeloid: Mast cell · Basophil · Eosinophil · Phagocytes (Neutrophil, Macrophage/Reticuloendothelial system) Professional APCs: Dendritic cell · Macrophage · B cell Substances Cytokines · Opsonin · Cytolysin Lymphopoiesis Lymphoblast · Prolymphocyte · Thymocyte Other Diagnostic immunology · Plant disease resistance ErbB2/PI3K signaling pathways Vascular Endothelial Growth Factor A  · NOV-002  · NOV-205 lymphocyte navs: cells/physio, immunodeficiency/immunoproliferative immunoglobulin/neoplasia, proc