Interleukin-33 alleviates psoriatic inflammation by suppressing the T helper type 17 immune response

Abstract

Psoriasis is a chronic inflammatory skin disease with unclear pathogenesis. Interleukin-33 (IL-33) is highly expressed in patients with psoriasis, but its role in psoriasis is unknown. The aim of this study was to investigate the possible role of IL-33 in the pathogenesis and treatment of psoriasis. IL-33 expression was determined using enzyme-linked immunosorbent assay, real-time fluorescent quantitative polymerase chain reaction and immunohistochemical staining. CD4⁺ T cells were sorted using magnetic beads and treated with or without IL-33. Imiquimod (IMQ) was used to induce psoriatic inflammation in mice. The frequency of immune cells was determined using flow cytometry. The cytokine level in mouse skin was measured using cytometric bead array. Our results showed that IL-33 was highly expressed in the lesional skin and serum of patients with moderate-to-severe plaque psoriasis. IL-33 inhibited the expression of IL-17 in CD4⁺ T cells of psoriasis patients. Subcutaneous injection of IL-33 alleviated the IMQ-induced psoriatic inflammation in mice, reduced tumor necrosis factor-α and IL-23 expression, and decreased the proportion of T helper type 17 (Th17) cells in the skin-draining lymph nodes in the mice. Our results suggest that IL-33 plays a protective role in the pathogenesis of psoriasis by suppressing Th17 cell differentiation and function. The potential therapeutic effect of IL-33 in treating psoriasis warrants further investigation.

Keywords: T helper type 17 cells; interleukin-17; interleukin-33; psoriasis.

Figure 1

Interleukin‐33 (IL‐33) expression is markedly increased in individuals with moderate‐to‐severe psoriasis. (a) mRNA expression of IL‐33 in the skin of normal people (n = 16) and lesional skin of psoriasis patients (n = 16). (b) mRNA expression of IL‐17A in the skin of normal people (n = 6) and lesional skin of psoriasis patients (n = 6). (c) The correlation of the mRNA expression of IL‐33 and IL‐17A in the skin (n = 12). (d,e) Immunohistochemical staining of IL‐33 in the epidermis (d) and dermis (e) of skin of normal people (n = 10) and lesional skin of psoriasis patients (n = 10). (f) Serum level of IL‐33 of normal people (n = 15) and psoriasis patients (n = 25). (g) mRNA expression of IL‐33 and IL‐17A in the lesional of psoriasis patients before and after anti‐tumor necrosis factor‐α (TNF‐α) therapy (n = 5). (h) Serum level of IL‐33 of psoriasis patients before and after anti‐TNF‐α therapy (n = 10). Data show mean + SEM or mean ± SEM. P‐values were determined by unpaired Student’s t‐test. Correlation of the mRNA expression of IL‐33 and IL‐17A was determined by Pearson coefficient. **P < 0·01, ***P < 0·001 and ****P < 0·0001

Figure 2

Interleukin‐33 (IL‐33) suppresses T helper type 17 (Th17) cells in individuals with moderate‐to‐severe psoriasis. (a,b) The proportion of IL‐17A⁺ IFN‐γ ^–, IL‐17A⁺ IFN‐γ ⁺ and IL‐17A^– IFN‐γ ⁺ cells and the geometric mean fluorescence intensity (gMFI) of IL‐17A and interferon‐γ (IFN‐γ) in CD4⁺ T cells from psoriasis patients (n = 17) treated with or without IL‐33 (50 ng/ml) for 72 hr. (c) The supernatant level of IL‐4 in CD4⁺ T cells from psoriasis patients (n = 10) treated with or without IL‐33 (50 ng/ml) for 72 hr. (d) The proportion of IL‐10⁺ and IFN‐γ ⁺ cells in Th17 (CD4⁺ and IL‐17A⁺) cells from psoriasis patients (n = 10) treated with or without IL‐33 (50 ng/ml) for 72 hr. (e) The proportion of regulatory T (Treg) (CD25⁺ and Foxp3⁺) cells in CD4⁺ T cells from psoriasis patients (n = 10) treated with or without IL‐33 (50 ng/ml) for 72 hr. (f) The proportion of invariant natural killer T (iNKT) (CD3⁺ and αGalCer‐CD1d⁺) cells in the peripheral blood mononuclear cells (PBMCs) from psoriasis patients (n = 10) treated with αGalCer and with or without IL‐33 (50 ng/ml) for 72 hr. Data show mean + SEM. P‐values were determined by paired Student’s t‐test. ns, no significance, *P < 0·05, **P < 0·01, ***P < 0.001 and ****P < 0.0001

Figure 3

Subcutaneous injection of interleukin‐33 (IL‐33) alleviates imiquimod (IMQ) ‐induced murine psoriatic inflammation. (a) Schematic representation of the plan with the injection of PBS or IL‐33 on mice treated with IMQ. (b) Representative photos of the lesional skin of mice from each group. (c) The disease severity scoring of the mice from each group based on scaling, erythema, and skin thickness from day 1 to day 7. (d) Representative hematoxylin & eosin staining of skin sections of mice from each group on day 7 (bar = 200 um). (e) Epidermal thickness and infiltrating inflammatory cells of the skin sections of mice from each group on day 7. Each group contains six mice and all experiments were repeated at least twice. Data show mean + SEM. P‐values were determined by one‐way analysis of variane with Bonferroni multiple‐comparisons t‐test. *P < 0·05, **P < 0·01 and ***P < 0·001

Figure 4

Interleukin‐33 (IL‐33) altered the expression of inflammatory cytokines and T‐cell subpopulations of skin‐draining lymph nodes in imiquimod (IMQ) ‐treated mice. (a) The protein level of tumor necrosis factor‐α (TNF‐α), IL‐23, IL‐10 and interferon‐γ (IFN‐γ) of the skin of mice from each group. (b) The serum level of TNF‐α and IFN‐γ of the mice from each group. (c,d) The proportion of T‐cell subpopulations in the skin‐draining lymph nodes of mice from each group. (e) Immunohistochemical staining of CD3 in the skin of mice from each group. (f) Immunohistochemical staining of Ki67 in the skin of mice from each group. Each group contains six mice and all experiments were repeated at least twice. Data show mean + SEM. P‐values were determined by one‐way analysis of variance with Bonferroni multiple‐comparisons t‐test. *P < 0·05, **P < 0·01, ***P < 0·001 and ****P < 0·0001

Figure 5

Summary of interleukin‐33 (IL‐33) actions in psoriatic inflammation. IL‐17‐producing T cells [T helper type 17 (Th17), IL‐17‐producing γδT (γδT17) and IL‐17‐producing CD8⁺ T (Tc17) cells] produce and secrete large amounts of IL‐17A under the inflammatory microenvironment of psoriasis. Then IL‐17A acts on keratinocytes to promote the IL‐33 expression. On the one hand, the increased IL‐33 from keratinocytes or other cells in the dermis, such as fibroblasts, can promote the proliferation of keratinocytes to aggravate the psoriatic inflammation, but on the other hand, inhibit the differentiation and function of Th17 cells to remit the psoriatic inflammation