IFN regulatory factor (IRF)-2 is one of the potential susceptibility genes for psoriasis, but how this gene influences psoriasis pathogenesis is unclear.
There are three common pathways leading to psoriasis: (1) Th17 cells secrete IL-17, which is stimulated by IL-23; (2) Th1 cells secrete IL-21, TNF-[Formula: see text] and IFN-[Formula: see text], with the help of Th17 cells; (3) Th22 cells secrete IL-22 under the stimulation of Th17 cells.
IFN-<i>γ</i> and IL-22 are deeply involved in the pathogenesis of psoriasis, as they boost the expression of inflammatory genes and alter proliferative and differentiative programs in keratinocytes.
In contrast, other antimicrobial peptides expressed in psoriatic skin including elafin, hBD1, and psoriasin (S100A7) did not show similar activities. hBD2, hBD3, and lysozyme were detected in psoriatic skin lesions in the vicinity of pDCs and found to cooperate with LL37 to induce high levels of IFN production by pDCs, suggesting their concerted role in the pathogenesis of psoriasis.
Functionally, Wnt5a lowers the concentration of IFN required to induce target genes, and increases the magnitude of IFN target gene induction, suggesting a molecular mechanism underlying IFN hypersensitivity in psoriasis.
Our results (1) establish a direct molecular link between type 1 IFN signaling and PPARdelta, (2) define a functional role for PPARdelta in human T cells, and (3) suggest that the induction of PPARdelta by type 1 IFN contributes to the persistence of activated T cells in psoriasis skin lesions.