Expression of B and T lymphocyte attenuator, retinoid-related orphan receptor gamma-isoform-t and interleukin 7 in psoriasis vulgaris

Cytokines in psoriasis: From pathogenesis to targeted therapy

Psoriasis is a multifactorial disease that affects 0.84% of the global population and it can be associated with disabling comorbidities. As patients present with thick scaly lesions, psoriasis was long believed to be a disorder of keratinocytes. Psoriasis is now understood to be the outcome of the interaction between immunological and environmental factors in individuals with genetic predisposition. While it was initially thought to be solely mediated by cytokines of type-1 immunity, namely interferon-γ, interleukin-2, and interleukin-12 because it responds very well to cyclosporine, a reversible IL-2 inhibitor; the discovery of Th-17 cells advanced the understanding of the disease and helped the development of biological therapy. This article aims to provide a comprehensive review of the role of cytokines in psoriasis, highlighting areas of controversy and identifying the connection between cytokine imbalance and disease manifestations. It also presents the approved targeted treatments for psoriasis and those currently under investigation.

The Role of Co-Signaling Molecules in Psoriasis and Their Implications for Targeted Treatment

Psoriasis is a chronic, systemic immune-mediated inflammatory disease manifesting in the skin, joint or both. Co-signaling molecules are essential for determining the magnitude of the T cell response to the antigen. According to the function of co-signaling molecules, they can be divided into co-stimulatory molecules and co-inhibitory molecules. The role of co-signaling molecules in psoriasis is recognized, mainly including the co-stimulatory molecules CD28, CD40, OX40, CD27, DR3, LFA-1, and LFA-3 and the co-inhibitory molecules CTLA-4, PD-1, and TIM-3. They impact the pathological process of psoriasis by modulating the immune strength of T cells, regulating the production of cytokines or the differentiation of Tregs. In recent years, immunotherapies targeting co-signaling molecules have made significant progress and shown broad application prospects in psoriasis. This review aims to outline the possible role of co-signaling molecules in the pathogenesis of psoriasis and their potential application for the treatment of psoriasis.

Infliximab modifies regulatory T cells and co-inhibitory receptor expression on circulating T cells in psoriasis

BACKGROUND

Psoriasis is a T cell-mediated autoimmune skin disease. Accumulating evidence has demonstrated that co-inhibitory receptors (CIRs) play a vital role in regulating T cell-mediated immune response, especially in neoplasm and autoimmunity. However, the immuno-function of CIRs in the development of psoriasis remains unclear.

OBJECTIVE

We investigated the expression of CIRs on the circulating T lymphocytes of psoriasis patients before and after anti-tumor necrosis factor-α (TNF-α) therapy.

METHODS

We enrolled 17 patients with moderate-to-severe plaque psoriasis, 17 patients with mild plaque psoriasis, and 18 healthy controls in this study. Fourteen of the moderate-to-severe psoriasis patients were treated with infliximab, a monoclonal antibody against TNF-α. Peripheral blood was collected, and peripheral blood mononuclear cells were extracted. The proportion of T cell subsets along with their expression of CIRs, namely T cell immunoreceptor with Ig and ITIM domains (TIGIT), lymphocyte activating gene 3 (LAG-3), cytotoxic T-lymphocyte associated protein 4 (CTLA-4), B and T lymphocyte-associated protein (BTLA), endothelial protein C receptor (PROCR), podoplanin (PDPN), programmed cell death 1 (PD-1), and T cell immunoglobulin mucin family containing molecule 3 (TIM-3), were determined by flow cytometric assay.

RESULTS

The moderate-to-severe plaque psoriasis patients had less circulating Tregs, which increased after infliximab treatment. They also had decreased TIGIT, LAG-3 but increased PDPN expression on peripheral CD4⁺ T cells. Infliximab enhanced TIGIT, LAG-3, CTLA-4 but reduced PROCR expression on circulating CD4⁺ T cells. Remarkably, both the frequency of circulating Tregs and the expression level of TIGIT on CD4⁺ T cells at baseline (pre-treatment) negatively correlated with the extent of PASI score reduction benefited from infliximab therapy.

CONCLUSION

Anti-TNF-α therapy increased the frequency of Tregs and TIGIT, LAG-3, CTLA-4 expression but reduced PROCR expression on circulating CD4⁺ T cells in psoriasis patients. The baseline proportion of Tregs and the expression level of TIGIT on circulating CD4⁺ T cells might serve as predictive markers for the degree of disease remission benefited from infliximab treatment.

Gamma Delta T Cells and Their Pathogenic Role in Psoriasis

γδT cells are an unconventional population of T lymphocytes that play an indispensable role in host defense, immune surveillance, and homeostasis of the immune system. They display unique developmental, distributional, and functional patterns and rapidly respond to various insults and contribute to diverse diseases. Although γδT cells make up only a small portion of the total T cell pool, emerging evidence suggest that aberrantly activated γδT cells may play a role in the pathogenesis of psoriasis. Dermal γδT cells are the major IL-17-producing cells in the skin that respond to IL-23 stimulation. Furthermore, γδT cells exhibit memory-cell-like characteristics that mediate repeated episodes of psoriatic inflammation. This review discusses the differentiation, development, distribution, and biological function of γδT cells and the mechanisms by which they contribute to psoriasis. Potential therapeutic approaches targeting these cells in psoriasis have also been detailed.

Opposing roles of endothelial and leukocyte-expressed IL-7Rα in the regulation of psoriasis-like skin inflammation

The interleukin 7 receptor alpha chain (IL-7Rα) is predominately expressed by lymphocytes, and activation by its ligand IL-7 supports the development and maintenance of T cells and boosts T-cell mediated immunity. We recently reported that lymphatic endothelial cells (LECs) in dermal lymphatics also express IL-7 and its receptor chains (IL-7Rα and CD132) and that IL-7 supports lymphatic drainage. This suggested that activation of IL-7Rα signaling in lymphatics could exert inflammation-resolving activity, by promoting the clearance of excess tissue fluid. Here we investigated how the potentially opposing effects of IL-7Rα signaling in immune cells and in the lymphatic vasculature would affect the development and progression of psoriasis-like skin inflammation. We found that during acute and chronic skin inflammation mice with an endothelial-specific deletion of IL-7Rα (IL-7Rα^ΔEC mice) developed more edema compared to control mice, as a consequence of impaired lymphatic drainage. However, systemic treatment of wild-type mice with IL-7 exacerbated edema and immune cell infiltration in spite of increasing lymphatic drainage, whereas treatment with IL-7Rα blocking antibody ameliorated inflammatory symptoms. These data identify IL-7Rα signaling as a new pathway in psoriasis-like skin inflammation and show that its pro-inflammatory effects on the immune compartment override its anti-inflammatory, drainage-enhancing effects on the endothelium.