Significance We identified a previously undescribed disease mechanism for psoriasis (Ps) and psoriasis arthritis (PsA)-like disease by developing a new mouse model having characteristic features similar to those of Ps and PsA in human patients. Mannan-induced activation of tissue macrophages triggers IL-17A secretion from γδ T cells, causing Ps-like inflammation. Such inflammation was significantly increased under a reduced oxidative environment. Increased frequency of monocytes/macrophages, depletion experiments, and the disease suppressor function of macrophage-derived reactive oxygen species clearly argue in favor of a role for monocytes/macrophages in this disease model, which is in accordance with the findings in patients with the psoriatic form of skin lesions and arthritis. This novel PsA model could be immensely useful to test new therapeutics for patients with Ps and PsA.

Psoriasis, a chronic autoimmune-related skin disease, involves both immune and non-immune cells like T cells and keratinocytes. This study investigates the regulatory role of T cells-keratinocyte interactions during psoriasis on immune factors production. Cytokines and chemokines were evaluated by multiplex and ELISA assays in an in vitro model of co-culture of keratinocytes with T lymphocytes. Keratinocytes were from psoriatic skin lesions or healthy skin. T lymphocytes were from healthy volunteers. Psoriatic keratinocytes (PKs) alone generated concentrations of tumor necrosis factor (TNF)-a, interleukin (IL)-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-1b, IL-8, monocyte chemotactic protein (MCP)-1, interferon-g-induced protein 10 kDa (IP-10) and vascular endothelial growth factor (VEGF) higher than those produced by healthy keratinocytes (HKs). In contrast, IL-1a and IL-Ra production was reduced in PKs. Normal T cells, which had no effect on HKs, increased the production of TNF-a, IL-6, GM-CSF, IL-8, MCP-1 and IP-10 by PKs, but did not influence PK production of IL-1b, IL-1a, IL-Ra and VEGF. The most striking effects were obtained with PK-and IL-2-stimulated T lymphocytes: most of the above cytokines and chemokines were greatly upregulated, except IL-1b and VEGF that were decreased or unchanged, respectively. In addition, fractalkine was overproduced in this latter condition only. Our results indicate (1) a functional interaction between keratinocytes and T lymphocytes that requires a direct cellular contact, and (2) a reciprocal influence that depends on cytokine and chemokine types. In conclusion, lesional keratinocytes from psoriasis vulgaris alter functions of normal T lymphocytes that conversely modulate these keratinocytes.

Inducible nitric oxide from skin macrophages promotes IL-17 release and psoriatic arthritis by innate lymphoid cells.

Chronic active arthritis can be driven innately by macrophages without the involvement of T and B cells in the adaptive immune system.

Psoriatic plaques result from an abnormal proliferation of keratinocytes associated with the local presence of T lymphocytes and neutrophils. The exact role of neutrophils in psoriatic lesions remains unclear. The present investigation was aimed at deciphering the capacity of psoriatic keratinocytes to alter in vitro functions of neutrophils. Blood neutrophils from healthy donors were incubated with psoriatic (PK) or healthy keratinocytes (HK) with and without IL-2-activated healthy T lymphocytes. The study was focussed on neutrophil capacity of adherence, viability and superoxide anion production. PK or HK with or without T lymphocytes similarly augmented neutrophil viability after 48 h of co-incubation. PK or HK did not directly activate the superoxide production by neutrophils. However, they both primed neutrophils for an increased fMLF-induced production of superoxide, an effect enhanced by the presence of T lymphocytes. PK were 1.5-fold more efficient than HK to augment this superoxide production. PK cultured with T lymphocytes induced the adhesion of neutrophils 4.7 times more efficiently than HK. The adherence of neutrophils was mediated through ICAM-1, LFA-1 and Mac-1, independently of bioactive lipids. The effects of PK and HK on neutrophil viability and priming were independent of direct cellular contact. In conclusion, keratinocytes can impact neutrophils by increasing their lifespan, and by priming them to overproduce superoxide. PK are more efficient than HK in priming neutrophils, an effect enhanced by T lymphocytes. These results indicate that neutrophils could contribute to psoriasis pathogenesis partly through their pathological interactions with PK.