Allergens

Abstract

Allergens are proteins or in rare cases, small molecular weight haptens that bind human proteins and induce IgE antibody production. The IgE binds surface FcϵR1 receptors on mast cells and basophils and stimulate release of histamine and other mediators when cross‐linked by allergen. These elicitors stimulate symptoms of allergy intended to expel parasitic worms and skin parasites including the scabies and possibly protection against toxic venoms. Allergen epitopes are segments of the proteins bound by MHCII and T helper cell receptors or by IgE from B cells. The T helper cells direct B cells to produce IgE rather than IgG. Circulating IgE circulates binds FcϵRI receptors on mast cells and basophils. Allergens bound by at least two IgE antibodies causes release of histamine and other mediators causing serum leakage, smooth muscle contraction and diverse symptoms: hives, angioedema, bronchoconstriction, asthma, diarrhoea, hypotension and anaphylaxis. Reactions occur rapidly after contact with allergen. This review discusses common allergens, allergen databases, and risks of allergy. Key Concepts Allergy is an adaptive immune response that requires previous immune education. Antigen‐presenting cells process and present peptides of proteins to T cells to determine specificity. Antigen specific T cells are important in switching B cells that are making IgM or IgD or in some cases, IgG to switch isotypes to make IgE antibodies. IgE antibodies bind FcϵRI receptors on mast cells and basophils. The mast cells and basophils make histamine, tryptase and leukotrienes that are released upon activation and trigger allergic symptoms. Some IgG antibodies or IgA that recognise the same epitope as the IgE can block IgE binding to allergens. Immunotherapy with the allergen may help develop tolerance and blocking antibodies that prevent allergic reactions. Diagnosis of allergy requires careful clinical history, plausibility of exposure and measurement of IgE specific binding as well as clinical reactivity.