The Langerhans cell is named after Paul Langerhans, a German physician and anatomist, who discovered the cells at 21 years old while he was a medical student. Because of their dendritic nature, he mistakenly identified the cells as part of the nervous system. Langerhans cells are dendritic cells of the skin and mucosa, and contain large granules called Birbeck granules. They are present in all layers of the epidermis, but are mostly found in the stratum spinosum. They are also found in the papillary dermis, particularly around blood vessels. They can be found in other tissues, such as lymph nodes, and in association with the condition Langerhans cell histiocytosis. In skin infections, the local Langerhans cells take up and process microbial antigens to become fully functional antigen-presenting cells. Generally, dendritic cells in tissue are active in the capture, uptake and processing of antigens. Once dendritic cells arrive in secondary lymphoid tissue, however, they lose these properties while gaining the capacity to interact with naive T-cells. In the rare disease Langerhans cell histiocytosis (LCH), an excess of cells similar to these cells are produced. However LCH cells stain positive to CD14 which is a monocyte marker and shows a different, hematopoietic origin for the disorder. LCH can cause damage to skin, bone and other organs. HIV
Langerhans cells may be initial cellular targets in the sexual transmission of HIV, and may be a target, reservoir, and vector of dissemination. Langerhans cells have been observed in foreskin, vaginal, and oral mucosa of humans; the lower concentrations in oral mucosa suggest that it is not a likely source of HIV infection relative to foreskin and vaginal mucosa. On March 4, 2007 the online Nature Medicine magazine published the research letter "Langerin is a natural barrier to HIV-1 transmission by Langerhans cells." One of the authors of the study, Teunis Geijtenbeek, said that "Langerin is...
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