The biology of langerhans cell and its role in cutaneous immune responses
2001
El-Hassan, A.M. (University of Khartoum, Khartoum (Sudan). Institute of Endemic Diseases)
Langerhans cell is a bone marrow derived- dendritic cell found primarily in the skin and some other epithelia. The cell is poorly phagocytic but is an excellent antigen presenter. It is recognised by its characteristic morphology, the presence of the distinctive birbeck granules and by a specific cell marker. In the epidermis langerhans cells from a network that allows them to efficiently pick up antigen for processing and presentation to T cells in regional lymph nodes. The cells are anchored to keratinocytes by the adhesion molecule cadherin. Their mobilization from the epidermis is effected by proinflammatory cytokines. In cutaneous leishmaniasis langerhans cells in the epidermis translocate from the epidermis, pick up leishmania parasites or antigen and migrate to lymph nodes. They primarily stimulate a Th1 response which is required for clearance of the parasite. Unlike cutaneous leishmaniasis, in post kala-azar dermal leishmaniasis (PKDL) Langerhans cells decrease in number, their HLA-DR expression is down-regulated and they express the co-stimulatory molecule B7-2 but not B7-1. It is suggested that these changes are attributible to the effects of UVB light on the skin where the PKDL lesions are most severe in the sun-exposed areas. Lnagerhans cells of the characteristics mentioned stimulate a Th2 response which is ineffective in eliminating the parasite
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