Fig.  3

NK cells in tumor immunosurveillance. This figure shows the potential role of NK cells in tumor immunosurveillance. NK cells initially recognize tumor cells through stress or danger signals. Activated NK cells directly kill target tumor cells through at least four mechanisms: cytoplasmic granule release, death receptor-induced apoptosis, effector molecule production, or ADCC. In addition, NK cells interact as regulatory cells with dendritic cells to improve their antigen uptake and presentation and promote the generation of antigen-specific CTL responses. Also, activated NK cells induce CD8⁺ T cells to become CTLs by producing cytokines such as IFN-γ. Activated NK cells also promote CD4⁺ T cells to differentiate toward Th1 responses and promote CTL differentiation. Cytokines produced by NK cells may also regulate the production of anti-tumor antibodies by B cells. Abs, antibodies; ADCC, antibody-dependent cellular cytotoxicity; CTL, cytotoxic T lymphocyte; DC, dendritic cell; IFN, interferon; NK, natural killer