Immunological aspects of allergy and anaphylaxis part 61

CONTACT DERMATITIS

Classical contact dermatitis is a Gell and Coombs type IV reaction, mediated by previously sensitized lymphocytes, which is exhibited by raised, very pruritic rash at the sight of the contact. Unlike allergic reactions of a type I, IgE-mediated contact dermatitis,  as a type IV reaction, involving-molecular-weight allergens (less  than 1 kDa). These contact allergens are haptens and need to link with proteins in the skin to become allergenic. These haptens may be readily absorbed into the skin, a reactions that renders them antigenic. If the skin is exposed to humidity or warmth, the penetration of the hapten is greater, and the chance of developing contact dermatitis is greater. As these haptens make their way into extravascular spaces, they combine with serum proteins or cell membranes  of antigen-presenting cells. The processed antigens is presented by Langerhans cells to T cells leading to a cascade of events that result in an influx of mononuclear cells into the dermis and epidermis, hence dermatitis.