Subsets of NK cells secrete distinct cytokine profiles. Conventional NK cells, consisting of CD56bright and CD56dim 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.
