ABSTRACT
Langerhans cells (LC) are members of a wide family of bone marrow derived, immunoactive dendritic cells (DC). LC reside in the epidermis where they are regarded as sentinels of the adaptive immune system with responsibility for surveying changes in the microenvi ronment and forming a trap for external antigen. In response to local antigen (including con tact allergen) and/or skin trauma, LC are mobilized, induced to leave the skin and migrate via afferent lymphatics to draining lymph nodes. During this journey LC are subject to a func tional maturation such that they differentiate from what are essentially antigen recognition and processing cells in the skin, to mature immunocompetent D C that are able to present antigen effectively to responsive T lymphocytes. The migration of LC from the skin is a very complex process. Coordinated interactions are required between cytokines and chemokines that to gether orchestrate the changes in LC necessary for successful trafficking from the skin to re gional lymph nodes. If LC migration is compromised then skin sensitization fails to develop, or is sub-optimal. Here we examine in detail the molecular and cellular events that initiate and regulate LC migration during the induction phase of skin sensitization.
