Psoriasis is a type I interferon-driven T cell -mediated disease characterized by the recruitment of plasmacytoid dendritic cells (pDC) into the skin. The molecules involved in pDC accumulation in psoriasis lesions are unknown. Chemerin is the only infl ammatory chemotactic factor that is directly active on human blood pDC in vitro. The aim of this study was to evaluate the role of the chemerin/ChemR23 axis in the recruitment of pDC in psoriasis skin. Prepsoriatic skin adjacent to active lesions and early lesions were characterized by a strong expression of chemerin in the dermis and by the presence of CD15 + neutrophils and CD123 + /BDCA-2 + /ChemR23 + pDC. Conversely, skin from chronic plaques showed low chemerin expression, segregation of neutrophils to epidermal microabscesses, and few pDC in the dermis. Chemerin expression was localized mainly in fi broblasts, mast cells, and endothelial cells. Fibroblasts cultured from skin of psoriatic lesions expressed higher levels of chemerin messenger RNA and protein than fi broblasts from uninvolved psoriatic skin or healthy donors and promoted pDC migration in vitro in a chemerin-dependent manner. Therefore, chemerin expression specifi cally marks the early phases of evolving skin psoriatic lesions and is temporally strictly associated with pDC. These results support a role for the chemerin/ChemR23 axis in the early phases of psoriasis development.

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Psoriasis is an immune-mediated skin disease characterized by lymphocytic infiltration and altered keratinocyte differentiation. Using immunohistochemical techniques we found that the cellular infiltrate in acute psoriatic plaques includes 5-8% CD3 -CD56 + natural killer (NK) cells, mostly localized in the mid and papillary dermis. NK lymphocytes isolated from punch biopsy specimens of psoriatic plaques showed a CD56 bright CD16 -CD158b -phenotype, failed to express the skin homing cutaneous lymphocyte-associated antigen and released abundant IFN-c upon stimulation. Supernatants from psoriatic NK cells induced MHC class II and ICAM-1 expression and release of CXCL10 and CCL5 by cultured psoriatic keratinocytes. Skin NK cells expressed high levels of the chemokines receptors CXCR3 and CCR5, intermediate amounts of CXCR1, CCR6 and CCR8, and low levels of CCR1, CCR2, CCR4, CCR7 and CX3CR1. In addition, they promptly migrated in vitro toward CXCL10, CCL5, supernatants of IFN-c-activated psoriatic keratinocytes and, to a lower extent, CCL20 and CCL4. In contrast, they failed to migrate toward CXCL8, CCL1, CCL2, CCL3, CCL17, CCL19 and CX3CL1. Taken together, our results implicate NK lymphocytes as newly identified protagonists in the pathogenesis of psoriasis. Their distinctive homing properties should be taken into account in the design of specific therapy aimed at blocking pathogenic cell accumulation in the skin.

Human β-defensins (HBDs) are a major class of antimicrobial peptides that play an important role in the innate immune response, however, the induction and regulation of these antimicrobial peptides is not well understood. We demonstrate here that stimulation of keratinocytes with TNF-α/IFN-γ induces HBD-2 and HBD-3 by activating STAT-1 and NF-κB signaling. We further demonstrate that IL-4 and IL-13 activate STAT-6 and induce the suppressors of cytokine signaling (SOCS)-1 and -3. This interferes with STAT-1 and NF-κB signaling, thereby inhibiting TNF-α/IFN-γ-mediated induction of HBD-2 and HBD-3. These data suggest that targeting the STAT-1-signaling pathway or suppressor of cytokine signaling expression enhances β-defensin expression and represents a new therapeutic strategy for reduction of infection in human diseases associated with β-defensin deficiency.