Effectiveness of oral vitamin D supplementation in lessening disease severity among patients with psoriasis: A systematic review and meta-analysis of randomized controlled trials

The association between serum 25-hydroxyvitamin D levels and psoriasis in a large population-based cohort: a cross-sectional analysis of The Tromsø Study 2015-16

BACKGROUND

Case-control studies indicate an association between lower serum 25-hydroxyvitamin D [25(OH)D] levels and psoriasis. Data from larger population-based cohorts including mild cases are sparse.

OBJECTIVES

To investigate the association between 25(OH)D and psoriasis in a large population-based cohort, and assess possible effect modification by overweight.

METHODS

Data from the Tromsø Study 2015-16 (Tromsø7), which included 19 520 participants from the general population aged 40-79 years, were subjected to a cross-sectional analysis. We assessed the shapes of the relationships between 25(OH)D and psoriasis using fractional polynomials. Odds ratios (ORs) for lifetime and active psoriasis were estimated using logistic regression. Adjusted models included month of blood sampling, body mass index (BMI), age and sex. Two-way and additive interaction between BMI and 25(OH)D were explored.

RESULTS

From a total of 19 520 participants [10 203 women (52.3%); mean age 56.3 years (SD 10.4); mean 25[OH]D, 63.4 nmol L-1 (SD 21.9)], 2088 (10.7%) reported lifetime psoriasis and 1179 (6.0%) reported active psoriasis the past 12 months. There was no association between 25(OH)D and lifetime psoriasis [OR per 10 nmol L-1 increase in 25(OH)D 1.02, 95% confidence interval (CI) 0.99-1.04]. The relationship between 25(OH)D and active psoriasis was suggested to be nonlinear, but the model was not significant (P = 0.098). There was evidence for a superadditive effect (i.e. larger than the sum of the factors) of BMI > 27.5 kg m-2 and 25(OH)D < 25 nmol L-1 on the odds for active psoriasis (OR 1.92, 95% CI 1.18-3.12), but not for lifetime psoriasis (OR 1.41, 95% CI 0.93-2.15). There was no evidence for two-way interaction between BMI and 25(OH)D.

CONCLUSIONS

This large population-based study found no significant relationship between 25(OH)D and psoriasis. The analysis may have been underpowered to detect a threshold effect in the lower 25(OH)D spectrum. Interaction analysis indicates that high BMI and vitamin D deficiency combined increase the odds of active psoriasis more than the sum of these factors, with an estimated 92% higher odds for active psoriasis in participants with BMI > 27.5 kg m-2 and 25(OH)D < 25 nmol L-1. Providing advice to prevent vitamin D deficiency may be considered in the follow-up of overweight patients with psoriasis.

Efficacy and safety of vitamin D supplementation on psoriasis: A systematic review and meta-analysis

OBJECTIVES

Our aim was to analyze the results of published randomized controlled trials (RCTs) on vitamin D supplementation for psoriasis in order to explore its effectiveness and safety.

PATIENTS AND METHODS

As of July 7 2023, we conducted a systematic literature search in PubMed, Cochrane, Embase, and Web of Science Core Collection databases. The study outcomes included change values in Psoriasis Area and Severity Index (PASI) (at 3 months, 6 months, and end of follow-up)/Dermatology Life Quality Index (DLQI)/Psoriasis disability index (PDI)/C-reactive protein (CRP), and adverse events.

RESULTS

333 patients from 4 studies were evaluated. Pooled analyses showed no significant effect of DLQI/PDI/CRP change value (P > 0.05) or PASI change value (3 months, end of follow-up; P > 0.05). Sensitivity analyses and statistical tests did not support the results of the PASI change values (6 months, P = 0.05). However, the results of subgroup analyses should not be ignored(supplementation with vitamin D2 or Asia would be more effective; P = 0.03). There were no serious adverse effects, and only a few individuals experienced nausea.

CONCLUSIONS

The efficacy and safety of vitamin D supplementation in the treatment of psoriasis remains unremarkable. The search for a new prognostic index that combines clinical and laboratory factors is needed to compensate for the shortcomings of existing measures and provide stronger evidence of validity.

Vitamin D: immune function, inflammation, infections and auto-immunity

Vitamin D plays an active role beyond mineral metabolism and skeletal health, including regulation of the immune system. Vitamin D deficiency is widely prevalent, and observational studies link low vitamin D status to a risk of infections and auto-immune disorders. Reports indicate an inverse relationship between vitamin D status and such conditions. This review details vitamin D signalling interactions with the immune system and provides experimental and clinical evidence evaluating vitamin D status, vitamin D supplementation and host susceptibility to infections, inflammation and auto-immunity. The published literature including related reviews, systematic reviews, meta-analyses, randomised controlled trials (RCTs), observational studies and basic science reports have been synthesised. Meta-analyses of observational studies have demonstrated a link between low vitamin D status and risk of acute respiratory infections, COVID-19 disorders, multiple sclerosis, type 1 diabetes (T1DM), inflammatory bowel disease (IBD), systemic lupus erythematosus and other auto-immune disorders. Observational studies suggest that vitamin D supplementation may protect against several infectious and auto-immune conditions. Meta-analyses of RCTs had mixed results, demonstrating a small protective role for vitamin D supplementation against acute respiratory infections, especially in those with vitamin D deficiency and children, and providing modest benefits for the management of T1DM and IBD. Vitamin D status is inversely associated with the incidence of several infectious and auto-immune conditions. Supplementation is recommended for those with vitamin D deficiency or at high risk of deficiency, and it might provide additional benefit in acute respiratory infections and certain auto-immune conditions.

Metabolic Disorders and Psoriasis: Exploring the Role of Nutritional Interventions

(1) Background: Psoriasis is a chronic autoimmune disease with a close relationship with metabolic diseases such as obesity, diabetes, and dyslipidemia. The aim of this review was to identify the relationship between psoriasis, metabolic diseases, and dietetic therapies. According to recent findings, there is a strong association between psoriasis and obesity as well as vitamin D and micronutrient deficiencies. (2) Methods: This review was conducted via PubMed, aiming to search for studies involving psoriasis linked with metabolic disorders or with nutritional treatments. (3) Results: Our review shows that a healthy lifestyle can positively influence the course of the disease. The maintaining of a proper body weight together with physical activity and good nutritional choices are associated with an improvement in psoriasis severity. A Mediterranean diet rich in fiber, vitamins, and polyphenols may indeed be a strategy for controlling psoriasis symptoms. The effectiveness of this diet lies not only in its anti-inflammatory power, but also in its ability to favorably influence the intestinal microbiota and counteract dysbiosis, which is a risk factor for many autoimmune diseases. (4) Conclusions: In synergy with standard therapy, the adoption of an appropriate diet can be recommended to improve the clinical expression of psoriasis and reduce the incidence of comorbidities.

Psoriasis and Vitamin D: A Systematic Review and Meta-Analysis

Psoriasis is a chronic immune-dysregulated inflammatory disease and hypovitaminosis D is considered a risk factor. We conducted an online database search to review and meta-analyze the relationship between vitamin D, other bone metabolism parameters, and psoriasis. The efficacy of oral vitamin D supplementation in improving Psoriasis Area and Severity Index (PASI) was also evaluated. Non-original articles, case reports, and animal studies were excluded. Bias risk was assessed according to the Cochrane Collaboration's tool and the Newcastle-Ottawa scale in randomized controlled trials (RCTs) and case-control studies, respectively. Unstandardized mean differences were used for data synthesis. Twenty-three studies reported serum 25 hydroxyvitamin D (25(OH)D) levels in 1876 psoriasis patients and 7532 controls. Psoriasis patients had significantly lower 25(OH)D levels than controls (21.0 ± 8.3 vs. 27.3 ± 9.8, p < 0.00001). Conversely, 450 psoriasis patients had lower levels of parathormone than 417 controls (38.7 ± 12.8 vs. 43.7 ± 16.5, p = 0.015). Four RCTs examined the effect of oral vitamin D supplementation on psoriasis for 173 patients and 160 patients were treated with placebo. No significant differences were found in PASI after 3, 6, and 12 months of supplementation. It is shown that 25(OH)D serum levels are significantly lower in psoriasis, but, although the granularity of RCT methodology may have influenced the pooled analysis, vitamin D supplementation did not seem to improve clinical manifestations.

Effect of Vitamin D Supplementation on Psoriasis Severity in Patients With Lower-Range Serum 25-Hydroxyvitamin D Levels: A Randomized Clinical Trial

Importance

Topical vitamin D analogues are routine treatment for psoriasis, but the effect of oral supplementation has not been established.

Objective

To examine the effect of vitamin D supplementation on psoriasis severity throughout the winter.

Design, Setting, and Participants

This randomized, double-blind placebo-controlled clinical trial with 2 parallel groups was performed through 2 winter seasons (2017 to 2018 and 2018 to 2019). Randomization was computer generated. All participants, health care clinicians, and outcome assessors were masked to group assignment. Each participant was followed for 4 months. The presented analyses were conducted in May 2022. The trial was conducted at the clinical research unit of the University Hospital of North Norway (Tromsø; Norway). Adults from the general population in Tromsø with active plaque psoriasis and 25-hydroxyvitamin D (25[OH]D) levels of less than 24 ng/mL (to convert to nmol/L, multiply by 2.496) were included.

Intervention

Vitamin D (cholecalciferol, 100 000 IU, loading dose, followed by 20 000 IU/week) or placebo for 4 months.

Main outcomes and Measures

Psoriasis Area Severity Index (PASI) (primary outcome), Physician Global Assessment, self-administered PASI, and Dermatology Life Quality Index scores (secondary outcomes).

Results

A total of 122 participants (46 women [37.7%]; mean [SD] age, 53.6 [10.0] years; mean [SD] PASI score, 3.1 [2.0]; mean [SD] serum 25(OH)D, 14.9 [3.9] ng/mL) were included. Of these, 60 (49.2%) were randomized to the vitamin D group and 62 (50.8%) to the placebo group. A total of 120 participants (59 vitamin D [49.2%]/61 placebo [51.8%]) completed the study. By completion, mean (SD) 25(OH)D levels were 29.7 (5.2) ng/mL (vitamin D) and 12.0 (3.8) ng/mL (placebo). There was no significant difference in change in PASI score between the groups (adjusted difference, 0.11; 95% CI, -0.23 to 0.45). There was no significant difference in change in Physician Global Assessment score (adjusted odds ratio, 0.66; 95% CI, 0.27-1.63), self-administered PASI (adjusted difference, -0.60; 95% CI, -1.76 to 0.55) or Dermatology Life Quality Index (adjusted difference, -0.86; 95% CI, -1.9 to 0.19) between the groups. No adverse effects of the intervention were registered.

Conclusion and Relevance

The results of this randomized clinical trial showed that vitamin D supplementation did not affect psoriasis severity. Low baseline severity scores may explain the lack of measurable effect. Levels of 25(OH)D in the intervention group increased to a less-than-expected degree based on previous experimental data from the same source population, and this may have affected the results.

Trial Registration

ClinicalTrials.gov Identifier: NCT03334136.

Vitamin D and Autoimmune Rheumatic Diseases

Vitamin D is a steroid hormone with potent immune-modulating properties. It has been shown to stimulate innate immunity and induce immune tolerance. Extensive research efforts have shown that vitamin D deficiency may be related to the development of autoimmune diseases. Vitamin D deficiency has been observed in patients with rheumatoid arthritis (RA) and has been shown to be inversely related to disease activity. Moreover, vitamin D deficiency may be implicated in the pathogenesis of the disease. Vitamin D deficiency has also been observed in patients with systemic lupus erythematosus (SLE). It has been found to be inversely related to disease activity and renal involvement. In addition, vitamin D receptor polymorphisms have been studied in SLE. Vitamin D levels have been studied in patients with Sjogren's syndrome, and vitamin D deficiency may be related to neuropathy and the development of lymphoma in the context of Sjogren's syndrome. Vitamin D deficiency has been observed in ankylosing spondylitis, psoriatic arthritis (PsA), and idiopathic inflammatory myopathies. Vitamin D deficiency has also been observed in systemic sclerosis. Vitamin D deficiency may be implicated in the pathogenesis of autoimmunity, and it may be administered to prevent autoimmune disease and reduce pain in the context of autoimmune rheumatic disorders.

Mineral Metabolism in Children: Interrelation between Vitamin D and FGF23

Fibroblast growth factor 23 (FGF23) was identified at the turn of the century as the long-sought circulating phosphatonin in human pathology. Since then, several clinical and experimental studies have investigated the metabolism of FGF23 and revealed its relevant pathogenic role in various diseases. Most of these studies have been performed in adult individuals. However, the mineral metabolism of the child is, to a large extent, different from that of the adult because, in addition to bone remodeling, the child undergoes a specific process of endochondral ossification responsible for adequate mineralization of long bones’ metaphysis and growth in height. Vitamin D metabolism is known to be deeply involved in these processes. FGF23 might have an influence on bones’ growth as well as on the high and age-dependent serum phosphate concentrations found in infancy and childhood. However, the interaction between FGF23 and vitamin D in children is largely unknown. Thus, this review focuses on the following aspects of FGF23 metabolism in the pediatric age: circulating concentrations’ reference values, as well as those of other major variables involved in mineral homeostasis, and the relationship with vitamin D metabolism in the neonatal period, in vitamin D deficiency, in chronic kidney disease (CKD) and in hypophosphatemic disorders.

Vitamin D May Be Connected with Health-Related Quality of Life in Psoriasis Patients Treated with Biologics

Suboptimal states of vitamin D may play a role in psoriasis evolution, but the interconnections have been studied over the past years with controversial results. Although a peerless therapy among moderate to severe types of psoriasis, the therapeutic effectiveness of biological therapy may vary unforeseeably between patients and leads to biologics switch. We conducted a pilot study in patients diagnosed with psoriasis and treated with biologics, the purpose of which was to explore the prevalence of suboptimal states of vitamin D, especially in the group of patients characterized by the failure of previous biologics, and to investigate the associations between vitamin D levels and psoriasis, regarding aspects such the severity of the disease and quality of life. Their current result of latent tuberculosis infection (LTBI) was also considered concerning a feasible relationship with vitamin D levels. From July to December 2021, 45 patients corresponding to our inclusion criteria were assessed. Variables such as Psoriasis Area and Severity Index (PASI) score and the Dermatology Life Quality Index (DLQI) score, as well as vitamin D serum concentrations and their LTBI result, were recorded for them. Lower serum concentrations of vitamin D were not more common in patients characterized by failure to previous biologics (p = 0.443), but we concluded a weak correlation between the DLQI score and vitamin D (rho = -0.345, p-value = 0.020), although a statistically insignificant result was obtained between vitamin D and the PASI score (rho = -0.280, p-value = 0.062), and with the LTBI result (rho = -0.053, p-value = 0.728). These results establish a connection between higher levels of vitamin D and a better outcome of psoriasis from the perspective of the patient's quality of life, with no significant association with psoriasis severity and no significant prevalence of suboptimal states among patients that failed previous biologics compared to those with a continuously good response.

Vitamin D Signaling in Psoriasis: Pathogenesis and Therapy

Psoriasis is a systemic, chronic, immune-mediated disease that affects approximately 2–3% of the world’s population. The etiology and pathophysiology of psoriasis are still unknown, but the activation of the adaptive immune system with the main role of T-cells is key in psoriasis pathogenesis. The modulation of the local neuroendocrine system with the downregulation of pro-inflammatory and the upregulation of anti-inflammatory messengers represent a promising adjuvant treatment in psoriasis therapies. Vitamin D receptors and vitamin D-mediated signaling pathways function in the skin and are essential in maintaining the skin homeostasis. The active forms of vitamin D act as powerful immunomodulators of clinical response in psoriatic patients and represent the effective and safe adjuvant treatments for psoriasis, even when high doses of vitamin D are administered. The phototherapy of psoriasis, especially UVB-based, changes the serum level of 25(OH)D, but the correlation of 25(OH)D changes and psoriasis improvement need more clinical trials, since contradictory data have been published. Vitamin D derivatives can improve the efficacy of psoriasis phototherapy without inducing adverse side effects. The anti-psoriatic treatment could include non-calcemic CYP11A1-derived vitamin D hydroxyderivatives that would act on the VDR or as inverse agonists on RORs or activate alternative nuclear receptors including AhR and LXRs. In conclusion, vitamin D signaling can play an important role in the natural history of psoriasis. Selective targeting of proper nuclear receptors could represent potential treatment options in psoriasis.

Dietary Intervention and Supplements in the Management of Psoriasis: Current Perspectives

Nutrition is a complex topic encompassing diet and a variety of supplements including vitamins, fish oil, herbal products, and probiotics. Patients with psoriasis display high interest in understanding the potential impact of nutritional modifications on their psoriasis. In this review, we examine the evidence for nutritional interventions in psoriasis and summarize important concepts. We found that certain diets, such as low-calorie diets for obese patients, gluten-free diets for patients with comorbid celiac disease, and the Mediterranean diet, may have benefits for psoriasis patients. Supplements in general do not show strong evidence of benefit, though more studies are required given the heterogeneity of these trials. Finally, the gut microbiome has drawn considerable interest in recent years, with specific probiotics showing promising results for psoriasis patients and warranting further exploration.

Vitamin D-Binding Protein and the Free Hormone Hypothesis for Vitamin D in Bio-Naïve Patients with Psoriasis

High levels of vitamin D-binding protein (DBP) have been reported in patients with psoriasis and the possibility of DBP as a marker of inflammation has been discussed. Furthermore, high DBP levels might negatively affect free 25(OH)D concentrations. According to the free hormone hypothesis, only the free fraction of a steroid hormone is capable of exerting biological action. Thus, free 25(OH)D level could be a better biomarker of vitamin D status than total 25(OH)D level. The objectives of this study were to identify the strongest determinants for DBP levels and to test the free hormone hypothesis for vitamin D in psoriasis. Additionally, we also aimed to investigate correlations between directly measured free 25(OH)D levels in serum and psoriasis disease severity compared to total 25(OH)D levels. This was a retrospective cross-sectional study including 40 bio-naïve patients with mild to severe plaque psoriasis. Psoriasis disease severity was evaluated using high sensitivity C-reactive protein (hsCRP), Psoriasis Area Severity Index (PASI) and visual analogue scale (VAS). Vitamin D metabolites including directly measured free 25(OH)D and serum DBP levels were measured. DBP levels were higher in patients with self-reported arthropathy than those without irrespective of confounding factors like sex, age and body weight. Total and free 25(OH)D levels correlated well (ρ = 0.77, p < 0.0001) and both were inversely correlated to intact parathyroid hormone (iPTH) (ρ = −0.33, p = 0.038 for total 25(OH)D and ρ = −0.40, p = 0.010 for free 25(OH)D). Only total 25(OH)D correlated to serum calcium levels (ρ = 0.32, p = 0.047). No correlations between any of the vitamin D metabolites and psoriasis disease severity were observed. In conclusion, DBP might be a new inflammatory biomarker in psoriasis, especially in psoriatic arthritis. Total 25(OH)D was a reliable measure for vitamin D status in this psoriasis cohort. However, evaluation of free 25(OH)D in patients with psoriatic disease and multiple co-morbidities and/or ongoing biologic treatment should be considered.

The Brain-Skin Axis in Psoriasis-Psychological, Psychiatric, Hormonal, and Dermatological Aspects

Psoriasis is a chronic inflammatory skin disease with systemic manifestation, in which psychological factors play an important role. The etiology of psoriasis is complex and multifactorial, including genetic background and environmental factors such as emotional or physical stress. Psychological stress may also play a role in exacerbation of psoriasis, by dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis, sympathetic–adrenal–medullary axis, peripheral nervous system, and immune system. Skin cells also express various neuropeptides and hormones in response to stress, including the fully functional analog of the HPA axis. The deterioration of psoriatic lesions is accompanied by increased production of inflammatory mediators, which could contribute to the imbalance of neurotransmitters and the development of symptoms of depression and anxiety. Therefore, deregulation of the crosstalk between endocrine, paracrine, and autocrine stress signaling pathways contributes to clinical manifestations of psoriasis, which requires multidisciplinary approaches.

Evidence of a Causal Relationship Between Vitamin D Status and Risk of Psoriasis From the UK Biobank Study

Background

Plenty of observational studies suggested that vitamin D concentrations were associated with psoriasis, but the causality of this relationship was elusive.

Objective

To investigate the causal relationship between vitamin D and psoriasis.

Methods

Cox proportional hazard model was used to investigate the association between vitamin D status and psoriasis in a prospective cohort study from UK Biobank. Single nucleotide polymorphisms (SNPs) that are strongly associated with circulating 25OHD were constructed as instrumental variables in Mendelian randomization (MR) to determine the causality between vitamin D and psoriasis.

Results

During a median follow-up of 10.99 years, we identified 2,856 participants with incident psoriasis. The prospective cohort study demonstrated individuals with 25OHD deficiency (< 25 nmol/L) at baseline were associated with approximately 20% increased risk of incident psoriasis in different categories of sex, age, and body mass index (BMI) after adjusting for covariates. The largest effect size was observed in the obese group (BMI > 30 kg/m²), as 25OHD deficiency presented with 30% additional risk of incident psoriasis compared to those with 25OHD > 50 nmol/L (HR = 0.701; 95% CI: 0.583-0.843; p < 0.001). Additionally, 69 independent SNPs associated with circulating 25OHD level were selected for the MR analysis, and the result suggested that genetically predicted one standard deviation (SD) increment in log-transformed 25OHD was associated with 24% decreased risk of psoriasis (OR = 0.76; 95% CI: 0.60-0.98, p = 0.020).

Limitations

The association of 25OHD and severity of psoriasis could not be estimated in the current study.

Conclusion

The combined prospective and MR analysis additionally provided evidence that the epidemiologically and genetically determined level of 25OHD conferred an increased risk of psoriasis.

Vitamin D and Rheumatic Diseases: A Review of Clinical Evidence

Vitamin D plays an important role in maintaining a healthy mineralized skeleton. It is also considered an immunomodulatory agent that regulates innate and adaptive immune systems. The aim of this narrative review is to provide general concepts of vitamin D for the skeletal and immune health, and to summarize the mechanistic, epidemiological, and clinical evidence on the relationship between vitamin D and rheumatic diseases. Multiple observational studies have demonstrated the association between a low level of serum 25-hydroxyvitamin D [25(OH)D] and the presence and severity of several rheumatic diseases, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), spondyloarthropathies, and osteoarthritis (OA). Nevertheless, the specific benefits of vitamin D supplements for the treatment and prevention of rheumatic diseases are less accepted as the results from randomized clinical trials are inconsistent, although some conceivable benefits of vitamin D for the improvement of disease activity of RA, SLE, and OA have been demonstrated in meta-analyses. It is also possible that some individuals might benefit from vitamin D differently than others, as inter-individual difference in responsiveness to vitamin D supplementation has been observed in genomic studies. Although the optimal level of serum 25(OH)D is still debatable, it is advisable it is advisable that patients with rheumatic diseases should maintain a serum 25(OH)D level of at least 30 ng/mL (75 nmol/L) to prevent osteomalacia, secondary osteoporosis, and fracture, and possibly 40–60 ng/mL (100–150 nmol/L) to achieve maximal benefit from vitamin D for immune health and overall health.

The Defect in Regulatory T Cells in Psoriasis and Therapeutic Approaches

Psoriasis is a chronic inflammatory skin disease characterized by accelerated tumor necrosis factor-α/interleukin (IL)-23/IL-17 axis. Patients with psoriasis manifest functional defects in CD4⁺CD25⁺ forkhead box protein 3 (Foxp3)⁺ regulatory T cells (Tregs), which suppress the excess immune response and mediate homeostasis. Defects in Tregs contribute to the pathogenesis of psoriasis and may attribute to enhanced inhibition and/or impaired stimulation of Tregs. IL-23 induces the conversion of Tregs into type 17 helper T (Th17) cells. IL-17A reduces transforming growth factor (TGF)-β1 production, Foxp3 expression, and suppresses Treg activity. Short-chain fatty acids (SCFAs), butyrate, propionate, and acetate are microbiota-derived fermentation products that promote Treg development and function by inducing Foxp3 expression or inducing dendritic cells or intestinal epithelial cells to produce retinoic acids or TGF-β1, respectively. The gut microbiome of patients with psoriasis revealed reduced SCFA-producing bacteria, Bacteroidetes, and Faecallibacterium, which may contribute to the defect in Tregs. Therapeutic agents currently used, viz., anti-IL-23p19 or anti-IL-17A antibodies, retinoids, vitamin D3, dimethyl fumarate, narrow-band ultraviolet B, or those under development for psoriasis, viz., signal transducer and activator of transcription 3 inhibitors, butyrate, histone deacetylase inhibitors, and probiotics/prebiotics restore the defected Tregs. Thus, restoration of Tregs is a promising therapeutic target for psoriasis.