Differential up-regulation of HLA-DM, invariant chain, and CD83 on myeloid and plasmacytoid dendritic cells from peripheral blood

Two main dendritic cell (DC) subsets have been described in peripheral blood, the myeloid subset or DC1 that is characterized by the presence of CD11c and the plasmacytoid subset or DC2 negative for this marker. The two subsets may perform different functions and have been defined as immunogenic (the myeloid subset) or tolerogenic (the plasmacytoid subset). The expression of human leukocyte antigen (HLA)-DM molecules, which act as peptide editors in the antigen presentation process, was studied in freshly isolated plasmacytoid and myeloid DCs from peripheral blood. The expression of the invariant chain (Ii), the major histocompatibility complex class II (MHC-II) : class II-associated Ii peptide (CLIP) complex, and CD83 was also investigated. The results showed that intracellular expression of HLA-DM and the Ii was significantly higher in the plasmacytoid than in the myeloid DC subset. In contrast, a higher fraction of cell expressing MHC-II : CLIP complex was found in the myeloid than in the plasmacytoid DC subpopulation. CD83 was not detected in any of these two subsets. Following culture of these cells with interleukin-3 (IL-3), tumor necrosis factor-alpha (TNFalpha) and/or heat shock protein-70 (HSP-70), the expression of intracellular HLA-DM was up-regulated in the myeloid DCs to levels similar to those found in the plasmacytoid DCs, whilst the Ii was down-regulated in the plasmacytoid subset to similar levels to those expressed in the myeloid DCs. In addition, CD83 was up-regulated in the myeloid (CD11c+) but not in the plasmacytoid (CD11c-) DCs. The expression pattern of these antigen-processing molecules could be related to the immaturity and function attributed to these DC subsets.