Figure 2.

NK and NKT cells in psoriatic skin. NK and NKT cells are innate immune cells that have cytokine-producing and cytotoxic functions. They both reside in the dermis. The NK cells can be divided into two groups, namely cNK and trNK cells, based on the receptors CD49a and DX5. Unlike NK cells, NKT cells also express an antigen-specific TCR that recognizes glycolipid through CD1 presentation by antigen-presenting cells. In psoriatic skin lesions, NK and NKT cells are rare. However, CD1d expression is reported to be elevated in keratinocytes in inflamed skin. In addition, NK and NKT cells have decreased degranulation ability, but display increased IFNγ production. High IFNγ production can contribute to an increase in keratinocyte-derived chemokines such as CXCL10 and CCL5, and the elevated expression of MHCI, both of which increase cell recruitment and presentation of autoantigens. In addition, NK and NKT cells produce TNFα that activate keratinocytes in an IL-24/Stat3-dependent manner as well as indirectly enhance dermal IL-17⁺T cell activation by facilitating dendritic cells to produce IL-1 and IL-23.