Dermatological Modeling for Inflammatory and Autoimmune Diseases of the Skin
Contact dermatitis is inflammation of the skin resulting from direct contact with a foreign substance. There are two main types of contact dermatitis: irritant and allergic. Irritant contact dermatitis occurs when the skin comes in contact with a harsh or dangerous substance usually resulting from structural damage to the skin (loss of oils, moisture, and increased permeability). Allergic contact dermatitis, which is also known as contact hypersensitivity, indicates an overreaction of the body's immune system to a normally harmless substance. Irritant contact dermatitis may occur on first exposure to the substance, while contact hypersensitivity requires that a previous sensitization to the substance has occurred. Unlike atopic eczema, in contact dermatitis this sensitization almost exclusively occurs via the skin. Clinically, allergic contact dermatitis is a common cause of occupational allergic dermatitis and may be caused by a wide variety of substances such as heavy metals (i.e. nickel), a variety of petrochemicals (many of which are used in dyes and paints) or plant-derived compounds. The rash associated with poison oak/ivy exposure is also an example of allergic contact hypersensitivity (urushiol-induced contact dermatitis).
In contact hypersensitivity, the sensitizing agent is usually a small molecule which alone would be insufficient to generate an immune response. However, during the sensitization phase of allergic contact dermatitis, these small molecules become highly immunogenic by binding to proteins within the skin, effectively acting as a hapten. These proteins are then picked up by Langerhans cells of the skin which subsequently present haptenated peptides to T cells in the draining lymph nodes. Re-exposure to the sensitizing agent following sensitzation results in expansion of these T cells and infiltration into the skin where they induce the recruitment of additional cells and ultimately resulting in the dermatitis.
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