Fc epsilon RI on human epidermal Langerhans cells: An old receptor with new structure and functions

Structural and functional analysis of the high-affinity receptor for IgE (Fc epsilon RI) on Langerhans cells (LCs) has highlighted new aspects of the biology of this structure when expressed on antigen-presenting cells. In contrast to effector cells of anaphylaxis i.e. basophils and mast cells, where Fc epsilon RI is a tetrameric structure constitutively expressed at high levels, this receptor on LCs lacks the classical beta-chain and its expression varies depending on the donor and the inflammatory environment of the cells in the skin. Although the signalling pathway seems to be similar to that of basophils or mast cells, only LCs from individuals with atopic dermatitis are fully activated by receptor ligation while LCs from normal individuals fail to exhibit calcium mobilization. LCs from normal and atopic individuals use Fc epsilon RI to maximise antigen uptake via specific IgE and subsequent presentation to T cells and may be responsible for driving the T cell response in either Th1, Th1 or Th2 type.