[Current data on epidermal Langerhans cells]

The skin may be considered as well as a target and an initiator of self immune reactions. Two to 5% of the epidermal cells are Langerhans cells which are the only cells to specifically take, process and present the antigens to lymphocytes in order to induce an immune response. Such an ability and the location of the Langerhans cells enhance the role that they may play in antigenic stimulations or immuno-allergic situations. TNF alpha was shown to potentiate the effect of GM-CSF for the generation of Langerhans cells from their CD34-positive precursors found in the cord blood. Originated from the bone marrow, the Langerhans cells colonize skin and mucosa where they act as antigen presenting cells (APC) by taking, processing antigens, and migrating to lymph nodes in order to sensitize lymphocytes. Such a migration was shown, for the first in humans, in an induced irritant contact dermatitis. In vitro incubation of isolated Langerhans cells induces morphological, phenotypical and functional modifications which make Langerhans cells similar to interdigitating cells. Such an observation suggests that in vivo Langerhans cells could undergo a maturation when they migrate to lymph nodes. Many points remain to be explored in order to clarify the conditions which may stimulate or make langerhans migrate and play their immune function. For example, cellular interactions or positive/negative effects due to soluble mediators (cytokines, neuropeptides) may modulate their role as antigen presenting cells. In vitro model of T-cell sensitization confirmed their in vivo role of cutaneous surveillance in the recognition and elimination of exogenous antigens.(ABSTRACT TRUNCATED AT 250 WORDS)