Figure 2.

Subsets of NK cells secrete distinct cytokine profiles. Conventional NK cells, consisting of CD56^bright and CD56^dim subsets, are found in the general blood circulation. They are responsive to cytokines, with IL-2, IL-12, IL-15, and IL-18 being viewed as most important. These cytokines, some of which may act alone while others are only effective in as part of a milieu, activate effector functions such as secretion of cytokines including IFN-γ and TNF-α and degranulation of cytotoxic granules. In contrast, NK22 cells are a recently described subset of NK cells that are primarily resident in mucosal sites within the body. They differentiate towards the NK22 phenotype in response to IL-23 stimulation. NK22 cells secrete IL-22 cytokine (but not IL-17). IL-22 is known to be pathogenic in psoriasis.