Metabolic Syndrome in Psoriasis Is Associated With Upregulation of CXCL16 on Monocytes and a Dysbalance in Innate Lymphoid Cells.

Psoriasis is frequently associated with the metabolic syndrome and occurs more often in obese individuals. In order to understand innate immune mechanisms mediating this inflammatory pattern we investigated expression of the chemokine and lipid scavenger receptor CXCL16 in patients with psoriasis and associated comorbidities. CXCL16 expression was enhanced on all monocyte subsets in psoriatic patients compared with healthy controls and positively correlated with psoriasis activity and severity index, body mass index and the risk for cardiovascular disease indicated by PROCAM score. The intensity of CXCL16 expression on monocytes further correlated with their capability to phagocytose oxidized LDL indicating the possibility to transform into foam cells in atherosclerotic plaques. Patients with psoriasis and atherosclerosis or obesity displayed elevated numbers of innate lymphoid cells in blood with specific increase of the IFN-γ or IL-17 producing ILC1 and ILC3 subpopulations. The expression of the CXCL16 receptor, CXCR6, was increased in ILCs and co-expressed with CCR6 but not CCR7 indicating their migratory potential to psoriatic skin or adipose tissue that is characterized by strong CXCL16 and CCL20 expression. This hypothesis was supported by the finding that the percentage of CXCR6 expressing ILCs was alleviated in blood of psoriatic patients. Together these data link a strong expression of CXCL16 to metabolic syndrome in psoriasis and indicate a possible link to ILC activation and tissue distribution in obese psoriatic patients. These data contribute to the understanding of the complex interaction of innate immunity and metabolic state in psoriasis.

Toll-Like Receptor-Mediated Upregulation of CXCL16 in Psoriasis Orchestrates Neutrophil Activation.

Innate immune processes are central in the development of the chronic inflammatory skin disease psoriasis. Studying stimulation of keratinocytes, monocytes, and dendritic cells by type I interferons or ligation of Toll-like receptors 1/2, 2/6, or 7, but not 7/8, resulted in enhanced surface expression and secretion of CXC chemokine ligand (CXCL) 16. The corresponding CXC chemokine receptor 6 was expressed on neutrophils whose recruitment into skin is important, especially in early psoriatic disease. Using the recently developed technique real-time deformability cytometry demonstrated that CXCL16 and IL-8 decreased the stiffness and enhanced deformation of neutrophils facilitating transmigration through vessel wall. In addition, CXCL16 potently induced migration of neutrophils and enhanced the chemotactic effect of IL-8. The positive feedback loop was supported by IL-8 enhancing CXCL16 production of neutrophils. Blocking of CXCL16 expression by effective treatment of psoriasis patients with tumor necrosis factor-α blockers further supported the pathogenic role of this chemokine. In summary, the data link innate immune stimulation to CXCL16 upregulation and neutrophil infiltration into skin. CXCL16 could therefore represent a potent future target for treatment of psoriasis.

Reduction of inflammatory slan (6-sulfo LacNAc) dendritic cells in psoriatic skin of patients treated with etanercept.

Dermal dendritic cells (DCs) play a central role in the immunopathology of psoriasis. We previously identified slanDCs as pro-inflammatory TNF-α, IL-23- and IL-12-producing DCs in human blood and as prominent inflammatory dermal TNF-α secreting and CD11c-positive DC subset in psoriasis. Here, we ask for the effects of TNF-α-inhibition on inflammatory slanDCs in skin and blood of 10 patients with psoriasis during 24 weeks of treatment with etanercept. Treatment with etanercept reduced the frequency of dermal slanDCs but did not induce apoptosis as determined by lack of increased active caspase-3-expression. In parallel, we found increased frequencies of slanDCs in blood which expressed lower levels of HLA-DR. Stimulating slanDCs isolated from the blood of healthy donors in vitro induced a strong production of IL-1ß, IL-6, IL-23 and IL-12p70. This capacity was efficiently reduced in the presence of etanercept, thereby indicating that TNF-α is an autocrine stimulus for maturation and pro-inflammatory cytokine production of slanDCs. In vivo, we noticed that treatment with etanercept did reduce the number of dermal slanDCs in parallel to the overall expression of TNF-α and IL-23p19. However, successful treatment did not down-regulated the percentage of dermal slanDCs that stained positive for TNF-α and IL-23p19 indicating that remaining slanDCs kept their pro-inflammatory capacity. This study provides novel insights into the immune regulatory properties of etanercept at the level of inflammatory slanDCs in vivo in skin and blood as well as in vitro.