Leprosy is considered a long-term infectious disease caused by M. leprae. It can affect mostly nerves, skin, respiratory tract, and eyes causing their damage. The symptoms of leprosy may appear within a year, but for some people, symptoms may take 20 years or more to occur.1

Leprosy remains a major health problem in some countries2 including Egypt which is still one of the 22 countries of global priority.3

Leprosy is classified into two polar types; tuberculoid Leprosy (TL) and lepromatous Leprosy (LL), plus three types in between; borderline Tuberculoid (BT), borderline Borderline (BB), and borderline Lepromatous (BL). TL is characterized by the presence of a few bacilli, paucibacillary (PB), and vigorous cell mediate immunity. However, in LL, numerous bacilli, multibacillary (MB), and inefficient cell mediate immunity were found.4

In TL, there are a high proportion of CD4+ T-cells with increasing type 1 cytokines. On the other hand, LL shows a predominance of CD8+ T-cells plus type 2 cytokines. The aforementioned data demonstrate the immunopathological interactions between type 2 and type 1 cytokine and activated macrophage products (monokines) in leprosy.5

However, a certain T-cell subset was shown to produce cytokines that could not be classified conferring to the Th1-Th2 scheme. Interleukin (IL)-17 was among these cytokines and T-cells producing IL-17 were named Th17 cells.6

IL-17A is a protein that in humans is encoded by the IL-17A gene. It is a pro-inflammatory cytokine.7 Originally IL-17A was supposed to be exclusively produced by T-cells, but it is also secreted by many cells including dendritic Cells (DC), macrophages, natural Killer (NK), and γδ-T cells.8

IL-17A acts on structural cells such as epithelial cells, fibroblasts, and keratinocytes in various tissues including skin. These cells express IL-17 receptors and produce many cytokines required for inflammation such as granulocyte Colony-Stimulating Factor (GCSF) and IL-6 as well as chemokines to attract neutrophils and macrophages to the inflamed tissues. These inflammatory cells (neutrophils and macrophages) can both clear the infection and initiate pathogenic inflammation.6

Additionally, the binding of IL-17A to IL-17 receptor causes important conformational changes that enable the binding of signaling adaptors, such as TRAFs proteins. The binding of these signaling adaptors triggers activation of several signaling pathways, including nuclear Factor Kappa B (NF-κB), pathways of mitogen-activated protein kinase.9

Activation of these pathways leads to the production of many inflammatory cytokines like IL-1β and tumor Necrosis Factor-Alpha (TNF-α) and chemokines, which attract macrophages as well as antimicrobial products such as mucins and defensins. Through its inflammatory effects, these products help in the elimination of many foreign pathogens.10

It was demonstrated that IL-17A protects the human body against several bacterial and fungal infections caused by invading pathogens.9

The aim of the present study was to shed light on the hypothesized role of interleukin-17A in leprosy pathogenesis, through analysis of IL-17A (rs2275913) gene polymorphism plus its serum levels in leprosy patients, and to correlate the detected results with different clinical aspects of leprosy in the investigated patients.

The current study was a case-control study. It was conducted on 60 patients having various types of leprosy and 29 age and sex-matched healthy volunteers with no past or family history of leprosy (control group). Leprosy patients and control group were collected from Dermatology and Leprosy Clinic, Menoufia Teaching, and university Hospitals. The laboratory part of the study was done at the Microbiology and Immunology Department, Faculty of Medicine, Menoufia University.

This study was approved by the Ethical Committee of Human Rights in Research at Menoufia University. Informed written consent was signed by each participant after informing them about the study.

Patients from both sexes that had been confirmed as leprosy by clinical aspects of their lesions, previous positive SSS, and/ or histopathology evaluation were included.

Subject with any of the following conditions was excluded from this study: 1- systemic diseases (e.g., diabetes mellitus, cirrhosis, systemic infection, renal failure, collagen disease, or malignancy); 2- endocrinopathies (such as Cushing’s syndrome, and hyper-and hypothyroidism); 3- anti-inflammatory drugs or hormonal medicines, such as steroids. 4- pregnancy and lactation.

A sheet was performed for all patients, including name, age, gender, residence, occupation, and history of leprosy state. To assess socioeconomic Level (SEL), the authors used a scale including 7 domains (education and cultural domain, occupation domain, family possessions domain, family domain, home sanitation domain, economic domain, and health care domain). Each participant was asked about occupations, an account income, and educational levels. SEL total score is 84. A high SEL was indicated as at least 70% (59–84), a medium level as 40% to less than 70% (34–58), and a low level as less than 40% (less than 34).11

The dermatological examination was done including a complete clinical assessment of skin lesions to determine the distribution, number, and consequently its clinical variants. In addition, a neurologic examination of possible affected nerves was performed. The studied leprosy patients have categorized in relation to the Madrid (1953) criteria to tuberculoid leprosy, borderline leprosy, and lepromatous leprosy.12

Under the complete aseptic condition, 5mL of blood was withdrawn from every subject and divided into two parts. The first part (2mL) was kept in a plain tube, left at 37°C for 30min to clot, and after that centrifuged at 4000r.p.m for 10min. The serum obtained was put into aliquots and kept in −80°C till the time of analysis for determination of IL-17A serum level by ELISA kits (Neo Bioscience Technology Co., Ltd, Shenzhen, People’s Republic of China) according to the manufacturer’s instructions.

The second part (3mL) was transferred into an EDTA vacutainer tube immediately and stored for DNA extraction. DNA extraction was done using Gene JET™ Whole Blood Genomic DNA Purification Mini Kit (THERMO SCIENTIFIC, EU/Lithuania), following the manufacturer's instructions. SNP to IL17A -197G\A (rs2275913) genotyping was achieved by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP). Primers sequences for IL17A -197G\A were 5′-AACAAGTAAGAATGAAAAGAGGACATGGT-3′(sense) and 5′- CCCCCAATGAGGTCATAGAAGAATC-3′(anti-sense).

Amplification of PCR was done in a volume of 30μL mixture containing 100ng genomic DNA, 1.0 μM of each primer, 200 μM of each dNTP, 2.0mM of MgCl2, 3μL 10×PCR buffer, and 1.5 U Taq DNA polymerase (Invitrogen Life Technologies, Grand Island, NY, USA). Restriction enzymes XagI (THERMO SCIENTIFIC, EU/Lithuania) were used to distinguish IL17A -197G\A (rs2275913) (102,68, 34 bp) genotypes. PCR product and enzyme were well mixed and incubated at 37°C for 1.5h. The pattern of the digestion products migration on 3% agarose gel allowed the identification of the IL17A -197G\A genotypes. Genotyping was performed blindly and most equally in number of cases and controls. G genotype (68+34 bp), A genotype (102 bp), and AG genotype (102, 68, 34 bp) were identified.13

In various pathogenic conditions, IL-17A can clear the infection and initiate an inflammatory reaction that could be mediated through the NF-κB pathway,9 production of many inflammatory cytokines such as TNF-α, IL-1β,10 G-CSF, and IL-6 as well as chemotaxis of macrophages and neutrophils to the inflamed tissues.6

In agreement with these data, the authors demonstrated that the circulating IL-17A levels were of significantly higher mean values in leprosy patients than controls and in TL than LL. This high level may represent the body's defense mechanism against leprae bacilli infection.

In line with the present result, Sakdiah et al.14 studied 40 Indonesian patients with leprosy versus 40 controls. They showed that IL-17 serum levels in leprosy patients were higher than in controls. Also, Santos et al.15 investigated 51 Brazilian leprosy patients and 23 controls. The authors revealed that IL‐17A concentrations were elevated in TL patients than in LL and controls. Additionally, they demonstrated more CD4+ IL-17A+cells in skin lesions from TL than those from LL patients. Santos and his co-workers reported a significant association between Th17 cells with the effective inflammatory response present in the PB forms.15

In this study, the authors found a significantly high serum level of IL-17A in female than male patients. Tsuboi et al.16 studied 409 patients (200 males, 208 females) in Japan and found elevated IL-17A serum levels among females having depression. Therefore, the authors could speculate that the increased IL-17A serum levels in female patients may possibly be explained by that these females could be suffering from psychiatric disorders including depression resulting from their disease state. Moreover, females are more susceptible to developing many inflammatory and autoimmune disorders than males, and increased IL-17 serum levels may participate in these disorders even before appearing in their clinical picture.

Although M. leprae can infect many people, few become sick, which can be attributed, in part, to the influence of genetic inheritance on the immune response. Many SNPs are taught to be linked with the production of cytokines and chemokines have been implicated with clinical forms of leprosy and reactional episodes.17,18

In the existing study, the authors found a statistically non-significant difference between leprosy patients and the control group regarding IL-17 (rs2275913A/G) genotypes and allele distribution. However, a comparison between leprosy subgroups (LL, TL, and BL) revealed that IL-17 (rs2275913A/G) GG genotype in addition to the G allele was associated significantly with LL.

In line with the present result, Aquino et al.19 studied 150 Brazilian patients with leprosy and 150 household contacts. They found that genotype frequencies had non-significant differences in the overall leprosy patients and controls.19 Also, Escamilla-Tilch et al.20 investigated 75 Mexican Mestizo leprosy patients versus 69 controls. Sixty-two patients were classified as LL, 2 as TL, 2 as BL, and 9 as dimorphic. They found no association between IL-17A (rs2275913A/G) gene SNPs and leprosy.20 Therefore, the present study confirmed the evidence of a lack of relationship between IL-17A (rs2275913A/G) gene polymorphism and leprosy susceptibility.

Regarding leprosy subgroups, although the authors reported a significant link between IL-17A (rs2275913A/G) G allele and GG genotype with LL, Escamilla-Tilch et al.20 did not find this association. This difference could be explained on the bases of environmental and socioeconomic factors that may influence the development of different pathologies. Moreover, Escamilla-Tilch and his collages investigated only 4 cases (2 as TL and 2 as BL) versus 62 having LL, and this sample size may be not suitable for statistical assessment.20

In this study, the authors noticed that a higher percentage of grade 2 disability and positive SSS were associated significantly with IL-17A (rs2275913A/G) GG genotype confirming the current demonstrated a higher predominance of GG genotype in the study’s LL patients.

Among the studied IL-17(rs2275913A/G) genotypes, AG genotype carriers demonstrated the highest IL-17 serum levels. This could be clarified by the predominance of AG genotype in the current studied TL cases, which is characterized by good immunity and high cell mediate the immune response.

However, Aquino et al.19 showed that IL-17A (rs2275913) AA genotype was related to high levels of IL-17A in the serum. This difference could be attributed to racial and genetic factors. Aquino et al.19 studied a mixed population from southern Brazil, however, the authors investigated the Egyptian population who belong to the African race. According to Pedia for IL-17A (rs2275913) snipe, IL-17A (rs2275913) A allele was found only in 1.8%–21.1% in African peoples. In agreement with Pedia snipe data, the authors found IL-17A (rs2275913) A allele was lower than G allele (29.2% and 70.8% respectively), and AA genotype was the lowest genotype (10/60, 16.7%) in leprosy patient group. Recently, Mazurek-Mochol et al.21 reported that the A allele was associated with increased production of IL-17. Therefore, decreased IL-17A (rs2275913) A allele and AA genotype in the present studied cases could also explain that difference.

IL-17A may have an active role in leprosy pathogenesis. Although IL-17A (rs2275913A/G) polymorphisms have a non-significant role in the genetic susceptibility to the development of leprosy, IL-17A (rs2275913A/G) GG genotype, as well as G allele, were of significant value in and linked to the progression to LL in the Egyptian population.

None declared.

All authors should have made substantial contributions to all of the following:

Azza Gaber Antar Farag: Critical literature review; Study conception and planning.

Azza Zagloul Labeeb: Data collection, analysis, and interpretation.

Amany Nagy Abdalla Gerges: Data collection.

Mustafa Elsayed Elshaib: Statistical analysis.

None declared.