Natural killer cells and dendritic cells: rendezvous in abused tissues

Human natural killer (NK) cells interact with dendritic cells (DCs) in inflamed peripheral tissues. NK cells induce DC maturation, but they also have cytolytic activity against immature DCs. So, NK cells regulate the progression of DC maturation by selecting the most appropriate antigen-presenting cells to undergo migration to secondary lymphoid compartments. The cell-surface NK-cell receptor that is responsible for DC recognition and killing is the NKp30 molecule, a member of the natural cytotoxicity receptor (NCR) family. In turn, DCs, which release interleukin-12 (IL-12) and IL-15 after antigen uptake, induce NK-cell activation. So, DCs can regulate NK-cell proliferation and lymphokine release in response to pathogens or tumours. NK cells that express CC-chemokine receptor 7 (CCR7) migrate to secondary lymphoid compartments, where they exert quality control (editing) of mature DCs. In patients with acute myeloid leukaemia (AML) who have received a bone-marrow transplant, alloreactive NK cells, derived from killer-cell immunoglobulin-like receptor (KIR)-mismatched donors, can kill leukaemic cells (graft-versus-leukaemia effect) and can prevent graft-versus-host reactions by killing DCs of the patient.