Expression of the CD1a molecule in B- and T-lymphoproliferative skin conditions.

The skin immune system is characterized by the presence of two types of CD1a expressing cells: langerhans cells and dermal dendritic cells, which are professional antigen processing and presenting cells. It is well established that several dermatoses are associated with T-cell mediated immune responses. In these pathological skin conditions, T-cells are activated by professional antigen presenting cells and dendritic cells are the most potent antigen presenting cells for both T-helper cells and T-cytotoxic cells. Therefore, it is plausible that dendritic cells are crucially involved in the pathogenesis of lymphoproliferative skin conditions characterized by the presence of a T-cell infiltrate. In this study, we examined the frequency and distribution of CD1a expressing cells and CD3+ cells in both the dermal and epidermal compartment in a wide range of lymphoproliferative dermatoses with a T-lymphoid infiltrate. In the skin conditions investigated, the CD1a molecule was highly expressed in mycosis fungoides, T-cutaneous lymphoid hyperplasia, lymphomatoid papulosis and parapsoriasis, whereas few CD1a-positive cells were observed in cutaneous B-cell lymphomas. Our study demonstrates a distinct pattern of CD1a staining in the infiltrates of cutaneous lympho-proliferative disorders which may reflect different immunoregulatory events involving T-lymphocytes and CD1a-positive dermal and epidermal dendritic cells.