|Year : 2022 | Volume
| Issue : 3 | Page : 197-203
A case control study on the role of interleukin 17 in the pathogenesis of vitiligo
Priyanka Karagaiah, Leelavathy Budamakuntla
Department of Dermatology, Bangalore Medical College and Research Centre, Bangalore, Karnataka, India
|Date of Submission||07-Jan-2021|
|Date of Decision||16-Aug-2021|
|Date of Acceptance||28-Oct-2021|
|Date of Web Publication||30-Nov-2022|
Dr. Priyanka Karagaiah
Department of Dermatology, Bangalore Medical College and Research Centre, No 3082, 1st A Main, Vbhbcs Layout, Girinagar 4th Phase, BSK 3rd Stage, Bangalore 560085, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Interleukin 17 (IL-17) has recently been implicated in the pathogenesis of vitiligo by many studies but it is unclear whether it has any definitive role in causing depigmentation. IL-17 inhibitors have already been used in other inflammatory disorders with good results and may prove to be a valuable therapeutic modality in vitiligo. Thus, this study aims at adding to the existing data on the role of IL-17 in the pathogenesis of vitiligo. Objectives: (1) To determine the correlation between IL-17 and the extent of body surface area involvement. (2) To determine the correlation between IL-17 and the severity of disease activity. (3) To determine the correlation between IL-17 and serum vitamin D levels. Methodology: Thirty-two clinically diagnosed patients with vitiligo and 26 age- and sex-matched controls who fulfill the inclusion criteria were enrolled in the study. After obtaining a detailed history, a complete dermatologic examination was performed and vitiligo area severity index (VASI) and vitiligo disease activity score (VIDA) were assigned. The baseline serum IL-17 level was measured using Raybiotech serum IL-17 enzyme-linked immunosorbent assay kit. Serum vitamin D was measured for all cases and controls. Results: In our study, the mean VASI score of all the patients was 6.32 ± 10.14 and the mean VIDA score was 1.97 ± 0.999. The mean serum IL-17 levels were 155.72 ± 79.412 pg/mL in patients with vitiligo compared to 102.73 ± 56.478 pg/mL of the controls, with a mean difference of 52.99 pg/mL and the difference was statistically significant (P = 0.008). Although, there is no significant correlation between the serum IL-17 levels with the VASI score, our study noticed slightly higher levels of IL-17 in generalized vitiligo and lowest levels were noticed in localized vitiligo. Limitations: Our study was limited by the small sample size of 32. Conclusion: Although, serum IL-17 levels were significantly higher in the patient group than the controls, there was no correlation with the disease extent or activity. Thus, it is difficult to establish a causal role of serum IL-17 in vitiligo.
Keywords: Cytokine, IL-17, vitiligo
|How to cite this article:|
Karagaiah P, Budamakuntla L. A case control study on the role of interleukin 17 in the pathogenesis of vitiligo. Pigment Int 2022;9:197-203
| Introduction|| |
Vitiligo is an autoimmune disease that results in progressive loss of functional melanocytes, presenting as milky white circumscribed depigmented macules and patches. The etiology of vitiligo is multifactorial with both genetic and nongenetic factors contributing to the causation of the disease. Several cytokines are increased in patients with vitiligo compared to healthy controls. Most studies have been conducted on tumor necrosis factor-α (TNF-α) and transforming growth factor-β. Several independent studies have revealed consistently elevated interleukin 17 (IL-17) levels in patients with vitiligo compared to healthy controls and its association with the affected body surface area (BSA).
IL-17 has a synergistic action on inflammatory mediators such as IL-1, IL-6, and TNF-α and by itself is capable of secreting IL-6 and TNF-α. A low-grade inflammation orchestrated by the cytokines activate macrophages and cytotoxic CD8 T lymphocytes prompting melanocyte apoptosis via Fas-Fas ligand or perforin–granzyme pathways. The melanocyte damage thus created may expose the melanocyte-specific self-antigens activating autoimmune T cells against it, thereby, further aggravating the process. Therefore, it could be hypothesized that overexpression of T-helper 17 (Th17) cells would lead to the perpetuation of vitiligo by facilitating an unchecked inflammatory cascade.
This study aims at determining the role of IL-17 in the pathogenesis of vitiligo by measuring the serum IL-17 levels in patients with vitiligo and comparing it with age- and sex-matched controls.
Aims and objectives
The objectives of the study are as follows:
- To determine the correlation between IL-17 and the extent of BSA involvement.
- To determine the correlation between IL-17 and the severity of disease activity.
- To determine the correlation between IL-17 and serum vitamin D levels.
| Materials and Methods|| |
A case–control study was conducted in our dermatology outpatient department from November 2017 to May 2019 after obtaining institutional ethics committee clearance (PGs/170/2017-18). In this study, we had enrolled 32 cases aged above 18 years and of either gender, clinically presenting with vitiligo as defined by the presence of milky‐white sharply demarcated macules or patches and 26 age- and sex-matched healthy controls after obtaining written informed consent.
Patients with concomitant psoriasis, atopic dermatitis, alopecia areata, lichen planus, lupus, Behcet disease, chronic suppurative infections and known cases of rheumatoid arthritis, ankylozing spondylitis, inflammatory bowel disease, patients treated with systemic corticosteroids or other immunosuppressive therapy, or narrowband UV-B in the preceding 1 month of blood collection and patients with any past or current history of smoking, alcohol, and drug usage were excluded from the study.
A complete dermatologic examination was performed and the vitiligo area severity index (VASI) was calculated by using the single palmar surface area method as per the scoring system guidelines and the vitiligo disease activity (VIDA) score was assigned based on the duration of active disease. About a 5-mL venous blood sample was drawn from both cases and controls and serum was separated by centrifuging the sample at 3000 rpm for 10 minutes. The serum thus separated was stored in cryovials at –80°C cryopreservation. The baseline serum IL-17 level was measured using Raybiotech serum IL-17 enzyme-linked immunosorbent assay (ELISA) kit (Raybiotech Inc., USA). ELISA for serum IL-17 was performed as per standard protocols and manufacturer’s guidelines. The values were recorded at a wavelength of 450 nm and a standard curve was plotted on a linear graph. The values were then calculated from the standard curve. Results were expressed in picograms per milliliter as mean ± standard deviation. About 5 mL of blood was collected separately for measuring serum vitamin D for all the cases and controls.
SPSS software was used to analyze the data. Mean and standard deviation were used to calculate the numerical data. Mann–Whitney test was used to compare the serum IL-17 levels between cases and controls. Spearman correlation was used to analyze the correlation between VASI and VIDA scores with serum IL-17 levels. The results were considered to be statistically significant if P-value was <0.005.
| Results|| |
The results of the study comparing the demographics of the patients with the controls, and the serum IL-17 levels are summarized in [Table 1].
|Table 1 Results of the study comparing the demographics of the patients with the controls|
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The majority of patients (18, 56.3%) had onset of disease before 30 years of age. Eight (25%) patients had onset of disease between 30 and 50 years and 6 (18.8%) patients had disease onset after 50 years of age.
The mean duration of disease was 4.67 ± 5.33 years. Twelve (37.5%) patients had been affected by the disease for more than 5 years and 11 (34.4%) patients had been affected for less than a year. Nine (28.1%) patients had a disease duration ranging between 2 and 5 years. In our study, 11 (34.4%) patients were affected with generalized vitiligo followed by 8 (25%) and 7 (21.9%) patients with acral and localized vitiligo, respectively. The frequency of distribution was least in mucosal vitiligo with two (6.2%) patients followed by acrofacial vitiligo with four (12.5%) patients. Thirteen patients had not received any form of treatment previously for vitiligo. Although none of the patients had received any form of treatment 1 month prior to the collection of samples, 19 patients had received some forms of treatment prior to that.
The mean serum IL-17 levels were 155.72 ± 79.412 pg/mL in patients with vitiligo compared to 102.73 ± 56.478 pg/mL of the controls, with a mean difference of 52.99 pg/mL and the difference was statistically significant (P = 0.008). The mean serum vitamin D levels in cases were 19.70 ± 7.83 mg/dL versus 20.83 ± 7.81 mg/dL in controls and the difference was statistically insignificant (P = 1.000). However, there was no correlation between serum IL-17 and VASI (P = 0.45) and VIDA scores (P = 0.32). In addition, there was no correlation of serum vitamin D levels with VASI (P = 0.09) or VIDA score (P = 0.86) and IL-17 levels (P = 0.91).
| Discussion|| |
The etiopathogenesis of vitiligo is multifaceted with a complex interaction between the genetic and nongenetic factors. Autoimmunity plays a pivotal role in the apoptosis and destruction of melanocytes, especially by the autoreactive T-cell lineage acting against the melanocyte self-antigens. Cytokine variance in the epidermal and systemic milieu and the resulting imbalance between pro- and anti-inflammatory cytokines have been vital in the disease causation. Among them, the role of interferon-γ (IFN–γ) and TNF-α has been well established.
IL-17 is a major effector cytokine released by the Th17 subset of T cells in the face of an exaggerated immune response. It has been implicated in the occurrence of many autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, psoriasis, etc. It has a stimulatory effect on the production of other proinflammatory cytokines such as IL-1, IL-6, and TNF-α, which may perpetuate the disease course and progression in vitiligo.
The mean serum IL-17 levels in the patients were 155.72 ± 79.412 pg/mL compared to 102.73 ± 56.478 pg/mL in the controls, with a mean difference of 52.99 pg/mL which was statistically significant (P = 0.008).
This result was comparable to the study conducted by Khan et al., where 45 cases and controls were assessed for serum IL-17 levels and cases showed a significantly elevated IL-17 level, 474.75 ± 118.7 pg/mL compared to 66.75 ± 16.4 pg/mL in the healthy controls with a P-value of 0.001.
Habeb and colleagues reported significantly higher serum IL-17 in vitiligo subjects with a mean value of 353 ± 110 pg/mL, compared to age- and sex-matched controls, as detected by reverse transcription polymerase chain reaction (RT-PCR; P < 0.01).
Zhou et al. conducted a cross-sectional study including 45 patients with active nonsegmental vitiligo (NSV) and 45 age-, sex-, and race-matched healthy controls, where they quantified peripheral blood Th17 cells. The peripheral Th17 cells were more in cases compared to controls (P = 0.001).
Studies conducted by van den Boorn et al. and Wang et al. also demonstrated consistently higher IL-17 mRNA expression in leading-edge biopsies of vitiliginous lesions compared to nonlesions via quantitative real-time PCR (qRT-PCR)., These results were consistent with the results of our study.
Sushama et al. conducted a similar study in India where IL-17 was significantly raised in generalized vitiligo (P = 0.00) and was positively correlated with BSA.
Correlation between serum IL-17 and VASI/VIDA score
Our study demonstrated no significant correlation between the serum IL-17 levels and VASI score [Figure 1] or VIDA score [Figure 2].
|Figure 1 Correlation of serum interleukin 17 with VASI score. VASI, vitiligo area severity index.|
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|Figure 2 Correlation of serum interleukin 17 with VIDA score. VIDA, vitiligo disease activity score.|
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Similarly, a study by Habeb et al. demonstrated no significant correlation between IL-17 levels and extent of body surface involvement or disease activity. Similar results were obtained by Esmaeili et al., but the only drawback was a small sample size of 15.
But many studies in the past have demonstrated a significant correlation between serum IL-17 and both disease duration and extent of body area involvement of vitiligo. Study conducted by Bassiouny and Shaker also showed significant positive correlations between serum IL-17 and both disease duration (r = 0.42, P = 0.02) and extent of body area involvement of vitiligo (r = 0.65, P = 0.001). Lesional expression of IL-17 mRNA in NSV has been reported to be up to seven-fold higher, with perilesional expression three-fold higher compared to nonlesional control skin.
In a study conducted by Basak et al. with 40 patients with vitiligo, positive correlation was found between IL-17 and BSA involved (r = 0.329, P = 0.038), and it was negatively correlated with age at disease onset (r = ‒0.397, P = 0.011).
Zhou et al. demonstrated positive correlation between peripheral Th17 cells and affected BSA (r = 0.0615, P < 0.001). They also found that serum IL-17 levels were higher in patients with NSV than controls (P < 0.001).
Elela et al. conducted a study including 84 nonsegmental patients with vitiligo and 80 controls. IL-17A levels were measured using both ELISA and qRT-PCR and a positive correlation was found with both VASI and VIDA [Table 2].
Hegazy et al. found that after 12 weeks of narrow band (NB-UVB) treatment, IL-17 expression decreased by 33% in lesional and 50% in perilesional skin (P < 0.05 for both). This was accompanied by significant reductions in VASI (P < 0.001). Moreover, there was a significant positive correlation of VASI score with systemic IL-17 levels at baseline and posttreatment. Part of NB-UVB therapy efficacy may be facilitated through reduction in IL-17 expression.
Kotobuki et al. conducted a study on the effects of exogenous IL-17 on melanocytes and suggested that IL-17 contributes to local depigmentation in autoimmune vitiligo via its antagonism of factors related to melanocyte function, reduction in melanogenesis, and dramatic induction of other Th17 type cytokines from dermal fibroblasts and keratinocytes.
But in a recent study by Speeckaert et al., IL-17 inhibitor Secukinumab 300 mg was administered to eight patients with active vitiligo for 7 months and followed up for 2 months posttreatment. Signs of further progression were reported in seven out of eight patients and one patient reported limited depigmentation. CXCL9, CXCL10, sCD25, sCD27, and B cell activating factor (BAFF) which are the biomarkers of vitiligo revealed no significant alterations over time. sCD25, a biomarker of active vitiligo, was inversely correlated with baseline Th17 cells, which was a paradox. There was a negative correlation between the percentage of Th17 cells with the percentage of Th1 cells and was positively associated with Th2, Th9, and Th22 lymphocytes. These findings do not comply with the previous reports where the Th17 pathway was correlated with active disease. In contrast, Th17.1 lymphocytes were positively correlated with Th1 cells (P < 0.001).
In a further study with a larger cohort of active NSV, authors noticed that there was a shift in Th1/Th17.1/Th17 balance toward Th1 differentiation instead of the Th17 pathway. Th17 represents an intermediate phenotype with the characteristics of both Th1 and Th17. High circulating IL‐17 levels in patients with active NSV reported previously were most likely due to increased percentages of Th17.1 lymphocytes. In a skewed Th1 environment, Th17.1 cells are capable of polarizing toward Th1 phenotype and produce both IL‐17 and IFN‐γ. Thus, concluded that IL-17 may not actually have a role in pathogenesis as it may be a bystander in the Th1/Th17.1/Th17 shift, and inhibition of IL-17 may have no role in treating active vitiligo. The only drawback of the study was the inclusion of patients with limited BSA involvement. This may have implications on the observed results as Th17 cells were linked with disease extent. This may possibly explain the lack of any correlation between serum IL-17 levels and the VASI or VIDA score, despite significantly elevated IL-17 levels in cases compared to controls in our study.
Vitamin D and IL-17 in vitiligo
Vitamin D plays an important role in the differentiation of melanocyte precursors and also maintains Ca2+ homeostasis required for tyrosinase activation in the melanocytes. Vitamin D ligands are also known to prevent melanocyte apoptosis by the production of sphingosine-1-phosphate.
Vitamin D exerts immunomodulatory action on both innate and acquired immune mechanisms and inhibits the formation of proinflammatory cytokines such as TNF-α, IFN-γ, IL-6, IL-8, etc., which also play a causative role in the pathogenesis of vitiligo. It is also known to have an inhibitory effect on Th17 cells and act by suppressing the production of downstream cytokines such as IL-17 by induction of CHOP (C/EBP homologous protein) molecules.
Several studies have reported the presence of reduced vitamin D levels in patients with vitiligo in comparison with the control population., However, no such observations were made in our study. There was no correlation of serum vitamin D levels with IL-17 levels. Similar results were demonstrated by a study by Aly et al.
However, the effect of vitamin D on IL-17 or causation of vitiligo cannot be completely ruled out given the complex relationship between vitamin D and immunomodulation.
Our study was limited by the small sample size of 32 and mRNA expression from the lesions was not measured.
| Conclusion|| |
Although serum IL-17 levels were significantly higher in the patient group than the controls, there was no correlation with the disease extent or activity. However, slightly higher levels of IL-17 were found in generalized and mucosal vitiligo, and the lowest levels were noticed in localized vitiligo. In addition, there was no correlation with serum vitamin D level. Thus, it is difficult to establish a causal role of serum IL-17 in vitiligo as it may be an intermediary cytokine produced in a skewed Th1 environment.
Thus, large multicentric studies involving genetic and molecular analysis to substantiate the possible role of IL-17 pathway in the pathogenesis of vitiligo are required.
What is new in the study?
This is one of the few studies determining the role of IL-17 in vitiligo, also only study assessing the correlation of IL-17 with disease characteristics using standardized scoring systems such as VASI and VIDA. It is also the first study from southern part of India. We have also included vitamin D assessment to look for any possible associations with IL-17 pathway. In this regard, our study is of significance in the Indian peninsula.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]