The involvement of dendritic cells in the cutaneous lesions associated with tuberculoid and lepromatous leprosy.

Full thickness skin biopsies were examined from 12 untreated leprosy patients and included five borderline tuberculoid (BT leprosy), five borderline lepromatous (BL leprosy) and two subpolar lepromatous leprosy cases. The non-lymphoid mononuclear cells present in the dermal infiltrates were analysed with immunohistological techniques using monoclonal antibodies (MoAb) which in normal tissues identify subpopulations of macrophage-like cells in tissue sections; RFD2 (recognizing all and monocytes/macrophages), RFD1 (recognizing interdigitating cells), NA1/34 (recognizing Langerhans cells) and RFD7 (recognizing only mature tissue macrophages). It was observed that using these MoAb no single cell type was unique to a particular state of the disease but that major differences in the proportions of these non-lymphoid mononuclear cells existed between BT leprosy and BL and LL leprosy. In BL leprosy lesions RFD2+ macrophages were the major cell type although a significant number (15-30%) of RFD1+ macrophage-like cells were also present. In contrast, in the dermal infiltrates of BT leprosy, RFD1+ cells were the predominant cell type (45-55%). The distribution of NA1/34+ Langerhans cells and the expression of Class II major histocompatibility (MHC) antigens was characteristically different in BT, BL and LL leprosy. The relationship between the presence and phenotype of cells considered to be involved in antigen presentation is discussed in relationship to the different clinical states in leprosy.