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

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 th…