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Pathology - Allergic Contact Dermatitis
There are numerous crucial features to this classic, delayed, cell-mediated (Type IV) hypersensitivity reaction. This process requires prior exposure to the sensitizer, most often poison ivy or poison oak in the United States. Upon exposure, the plant antigen is picked up by Langerhans cells, which migrate to lymph nodes and transmit the processed antigen via major histocompatibility complex (MHC) class II molecules to CD4 + T lymphocytes. These T cells develop into T-helper type 1 lymphocytes, which proliferate and enter the blood circulation. With re-exposure by presentation of the same particular antigen, the sensitized T lymphocytes produce cytokines, most notably interferon-gamma (IFN-γ), which mediates the local inflammatory response involving activated macrophages, natural killer cells, and CD8 + T cells. The clinical skin manifestations typically present 48 to 72 hours after contact, which is diagnostic of the delayed hypersensitivity reactions. Metals such as nickel and chromium are also capable of generating contact dermatitis and can typically present as a pruritic rash around the neck or wrist due to jewelry.
There are numerous crucial features to this classic, delayed, cell-mediated (Type IV) hypersensitivity reaction. This process requires prior exposure to the sensitizer, most often poison ivy or poison oak in the United States. Upon exposure, the plant antigen is picked up by Langerhans cells, which migrate to lymph nodes and transmit the processed antigen via major histocompatibility complex (MHC) class II molecules to CD4 + T lymphocytes. These T cells develop into T-helper type 1 lymphocytes, which proliferate and enter the blood circulation. With re-exposure by presentation of the same particular antigen, the sensitized T lymphocytes produce cytokines, most notably interferon-gamma (IFN-γ), which mediates the local inflammatory response involving activated macrophages, natural killer cells, and CD8 + T cells. The clinical skin manifestations typically present 48 to 72 hours after contact, which is diagnostic of the delayed hypersensitivity reactions. Metals such as nickel and chromium are also capable of generating contact dermatitis and can typically present as a pruritic rash around the neck or wrist due to jewelry.
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