Selective Expression of the Chemokine Receptor XCR1 on Cross-presenting Dendritic Cells Determines Cooperation with CD8 + T Cells

The expression of the chemokine receptor XCR1 and the function of its ligand XCL1 (otherwise referred to as ATAC, lymphotactin, or SCM-1) remained elusive to date. In the present report we demonstrated that XCR1 is exclusively expressed on murine CD8 + dendritic cells (DCs) and showed that XCL1 is a potent and highly specific chemoattractant for this DC subset. CD8 + T cells abundantly secreted XCL1 8–36 hr after antigen recognition on CD8 + DCs in vivo, in a period in which stable T cell-DC interactions are known to occur. Functionally, XCL1 increased the pool of antigen-specific CD8 + T cells and their capacity to secrete IFN-γ. Absence of XCL1 impaired the development of cytotoxicity to antigens cross-presented by CD8 + DCs. The XCL1-XCR1 axis thus emerges as an integral component in the development of efficient cytotoxic immunity in vivo.