Figure 1

Activation of NK cells by bacterial PAMPs. NK cells are activated within a network of accessory cells that sense bacterial PAMPs. Activation of accessory cells leads to the production of cytokines that contribute to the functional activation of NK cells, while sensing of PAMPs by NK cells themselves further enhances NK cell reactivity. All listed cytokines have been shown to amplify NK cell activity, either alone or in synergy. Negative signals can be directly delivered to NK cells (for example, IL-10 and TGF-β produced by Tregs, prostaglandins or glucocorticoids) or indirectly by downregulating the function of accessory cells. PGN, peptidoglycan; OmpA, outer-membrane protein A, MØ, macrophages; PMN, polymorphonuclear leukocytes (neutrophils); B, B lympocytes; MAST, mast cell; EPITH., epithelial cell; PGE₂, prostaglandin E₂; PGD₂, prostaglandin D₂.