IL18 and viral infectious disease: In summary, NK cells are triggered by viral infections through the activation of receptors (KIRS, NKps,DNAM-1,NKG2) that recognize viral products or peptide-loaded MHC molecules, or by recognizing stress-induced ligands, TLR stimulation, and cytokines (IFNs, IL-12, IL-15 and IL-18) that either directly activate NK cells for cell-mediated cytotoxicity or enhance activating receptor-mediated NK cell activation (Brandstadter and Yang, 2011).