6533b7d7fe1ef96bd1267921

RESEARCH PRODUCT

Mixed Epidermal Cell Lymphocyte Reaction: HLA-DR+ Cells Exhibit a Greater Immunostimulatory Activity than CD1a+ Cells

subject

description

Induction and expression of immunity depends upon processing and presentation of antigens to T-cells by bone marrow derived HLA-DR+ antigen presenting cells (APC). In the induction of immunity to cutaneous antigens, the initial stages of this process begin within the skin itself, and both epidermis and dermis contain bone-marrow derived cells that have the capability of processing and presenting antigens. In normal epidermis, HLA-DR expression is believed to be confined to Langerhans cells with Birbeck granules and indeterminate cells without Birbeck granules. In diseased skin, particularly the inflammatory dermatoses, HLA-DR is commonly expressed by keratinocytes and has been related to the presence of intra-epidermal IFN-γ producing lymphocytes. Fresh and cultured Langerhans cells display disparate functional programs, based on their capacities to acitvate autologous and allogeneic T cells. Recent studies have revealed that the capacity of freshly prepared Langerhans cells to activate T cells is relatively poor. However, the antigen presenting capabilities can be considerably enhanced if the Langerhans cells are placed in culture in presence of GM-CSF, a cytokine produced by keratinocytes. On the other hand fresh Langerhans cells are at least tenfold more efficient at processing antigens than cultured cells.1 These issues are relevant to psoriasis, a cutaneous disease in which antigen-presenting cell functions of epidermal cells have found to be abnormal.2 We have studied the importance of epidermal Langerhans cells and other epidermal APC subsets for the stimulation of T-cells in patients with psoriasis and healthy individuals.