Activated CD8+ T lymphocytes induce differentiation of monocytes to dendritic cells and restore the stimulatory capacity of interleukin 10-treated antigen-presenting cells.

We analyzed the role of CD8+ T cells on dendritic cells (DCs). Incubation of monocytes with activated but not resting CD8+ T cells induced their differentiation into DCs with a CD1a+ and CD14- phenotype. Activated CD8+ lymphocytes induced down-regulation of CD14 expression in interleukin (IL)-10-treated macrophages and resulted in the expression of DC-related CD1a and up-regulation of mRNA transcripts for RelB, IL-12p40, MCP-2, MIP-1alpha, and ELC. These DCs were potent stimulatory cells in mixed lymphocyte reaction and induced primary CTL responses. This interaction was independent of a direct cell-to-cell contact. Monoclonal antibodies against IFN-gamma completely abolished the CD1a induction on IL-10-treated antigen-presenting cells. These results demonstrate that CD8+ cells can provide stimulatory signals to antigen-presenting cells to induce their differentiation in DC and to increase their immunostimulatory capacity.