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Characteristics of cytokine gene polymorphisms in children with different phenotypes of bronchial asthma
- Authors: Prosekova E.V.1, Dolgopolov M.S.1, Sabynych V.A.1, Zhdanova O.L.2, Turyanskaya A.I.1
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Affiliations:
- Pacific State Medical University
- Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences
- Issue: Vol 19, No 1 (2022)
- Pages: 80-90
- Section: Original studies
- Submitted: 02.12.2021
- Accepted: 04.02.2022
- Published: 06.04.2022
- URL: https://rusalljournal.ru/raj/article/view/1504
- DOI: https://doi.org/10.36691/RJA1504
- ID: 1504
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Abstract
BACKGROUND: Bronchial asthma is a chronic inflammatory disease of the airways, the development of which is based on genetic predictors associated with the differentiation and functioning of T-helper (Th) cells. Polymorphisms in the genes of cytokines involved in the regulation of the direction of the Th cell-mediated immune response are risk factors for the development of the disease and the realization of various phenotypes of bronchial asthma.
AIM: To study of the structure and frequency of occurrence of single nucleotide polymorphisms of cytokine genes with an assessment of the risk of various phenotypes of bronchial asthma in children.
MATERIALS AND METHODS: In this case–control study, 250 children were examined, including 150 children with a verified diagnosis of bronchial asthma (including 75 children with virus-induced and 75 children with allergen-induced disease phenotypes) and 100 sexually comparable healthy peers. The children underwent a comprehensive general clinical and allergological examination, genotyping, structure analysis, frequency of occurrence of cytokine gene polymorphisms, and calculation of the odds ratio of the risk of developing different bronchial asthma phenotypes. DNA samples isolated from peripheral venous blood were used as material for molecular genetic analysis. The following mutation points were selected: IFN-γ (T-874A), IL-4 (C-589T), IL-6 (C-174G), IL-17A (G-197A), and TNF-α (G-308A).
When processing digital data, we used the methods of descriptive, parametric, and nonparametric statistics of the Statistica 10 program, comparison of unrelated groups by qualitative characteristics, and assessment of the correspondence of the distributions of genotypes to the expected values at the Hardy–Weinberg equilibrium. The frequency distributions of genotypes and alleles in two subpopulations were analyzed using the chi-square test (χ2).
RESULTS: A comparative analysis of the frequencies of alleles and genotypes of cytokines of various Th profiles with the definition of features in allergen-induced and virus-induced phenotypes of the disease revealed the predominance of homozygous genotypes IFN-γ (A-874A), IL-4 (T-589T), IL-6 (G-174G), IL-17A (A-197A), and TNF-α (A-308A) in children with bronchial asthma, and in healthy peers, IFN-γ (T-874T), IL-4 (C-589C), IL-6 (C-174C), IL-17A (G-197G), and TNF-α G-308G were prevalent. Heterozygous genotypes IL-4 (C-589T), IL-6 (G-174C), IL-17A (G-197A), and TNF-α (G-308A) were found in children with bronchial asthma more often than in healthy peers, with the exception of the IFN-γ genotype (T-874A). In children with the virus-induced bronchial asthma phenotype, the presence of the IL-4 (C-589T) mutant allele was found in 30.67% of cases with an odds ratio of 19.3 (95% CI, 11.23–33.31). When carrying the mutant A-genotype IFN-γ (T-874A), the odds ratio of the risk of developing the disease reflected a high degree of probability of the virus-induced bronchial asthma phenotype (OR, 5.11; 95% CI, 3.18–8.23). Carriage of homozygous genotypes IL-6 (G-174G) and IL-17A (A-197A) determined an increased risk of developing allergen-induced bronchial asthma (OR, 2.71; 95% CI, 1.73–4.18, and OR, 0.51; 95% CI, 0.32–0.71, respectively). Among children with bronchial asthma, a statistically significant increase was noted in the incidence of the functionally unfavorable genotype A308A of the TNF-α gene, and the odds ratio reflects a 2.6-fold increase in the risk of developing a virus-induced bronchial asthma phenotype (χ2=18.66; p=0.017; OR, 2.60; 95% CI, 1.67–4.01).
CONCLUSIONS: As a result of the study, significant differences were determined in the structure and frequency of occurrence of cytokine gene polymorphisms in children with allergen and virus-induced bronchial asthma, depending on the realized phenotype of the disease. Carriage of mutant alleles IFN-γ (A-874A), IL-4 (T-589T), IL-6 (G-174G), IL-17A (A-197A), and TNF-α (A-308A) can be characterized as genetic predictors of bronchial asthma, for the implementation of the virus-induced phenotype, and the odds ratio is higher in the presence of mutant alleles IFN-γ (A-874A), IL-4 (T-589T), and TNF-α (A-308A), for the allergen-induced phenotype of the disease — IL-6 (G-174G) and IL-17A (A-197A).
Full Text
BACKGROUND
Bronchial asthma is a chronic heterogeneous disease with numerous mechanisms involved in the development and regulation of inflammation, including genetic factors. Mutations in cytokine genes and cytokine regulation of immune response pathways, development, and activation of inflammation in the airways all play a role in the immunopathogenesis of bronchial asthma. The clinical polymorphism and heterogeneity of the condition are determined by a variety of etiological and pathogenetic factors. The implementation of the genetic predisposition for bronchial asthma development occurs in interaction with environmental factors and results in the formation of the disease pathological phenotype. The occurrence and structure of genotype polymorphisms can vary significantly depending on ethnicity and regional factors, influencing the levels of cytokines and immunoglobulin E in blood serum [1–5].
Several researchers have noted that genetic predictors are involved in the regulation of bronchial asthma phenotypic realization and that disease control is a gene-mediated process that is dependent on the allelic variant of the disease immunopathogenesis mediator genes. Modern publications focus primarily on the study of cytokine genes of the immune response Th2 profile in bronchial asthma, with only a few studies of the structure, occurrence, and significance of cytokine gene polymorphisms of Th1 and Th17 profiles [6–12].
Knowledge of genetic markers will allow for the prediction of phenotypic features of the bronchial asthma course [2, 3, 4, 9–12]. The study and analysis of bronchial asthma genetic predictors that determine pathogenetic disorders and realization of the biological phenotypes of the disease are relevant and allow to assess disease risk and personalize prevention and therapy programs, which defined the purpose and objectives of this study.
The aim was to characterize the occurrence of single nucleotide polymorphisms in cytokine genes and assess the risks of developing various phenotypes of bronchial asthma in children.
MATERIALS AND METHODS
Study design
An observational, single-center, prospective, randomized, parallel-group, controlled study was performed.
Eligibility criteria
The study included children with a confirmed diagnosis of virus-induced and allergen-induced bronchial asthma, with an isolated course or in combination with allergic rhinitis. The diagnosis and phenotype were verified in accordance with the national program “Bronchial asthma in children. Treatment strategy and prevention” and international consensus documents on bronchial asthma in children (Global Strategy for Asthma Management and Prevention; PRACTALL) [5].
Inclusion criteria include children aged 3 to 11 years, a confirmed diagnosis of bronchial asthma, and written parental consent.
Exclusion criteria include a history of severe somatic diseases; the presence of allergic skin disease, such as atopic dermatitis; as well as autoimmune and other chronic inflammatory diseases.
The control group included healthy peers with the first health group, no history of allergic disease or family history of allergy, and complaints at the time of examination; exclusion criteria were allergic diseases and evidence of a history of food/drug intolerance or realization of an allergic disease during the observation period from 2015 to 2020.
Experimental setting
Clinical and laboratory research was conducted at the clinical bases of Vladivostok Clinical Diagnostic Center (Vladivostok) and the laboratory of the Department of Clinical Laboratory Diagnostics, General and Clinical Immunology of the FSBEI HE “Pacific State Medical University” of the Ministry of Healthcare of the Russian Federation (Vladivostok).
Study duration
The study was conducted with annual ambulatory examinations from 2015 to 2020.
Description of medical intervention
In all children, blood was drawn from the cubital vein in accordance with the rules for conducting the preanalytical stage of laboratory studies.
Primary outcome of the study
All children underwent a thorough clinical and allergological examination, as well as genotyping, structural analysis, frequency of occurrence of cytokine gene polymorphisms, and estimation of the odds ratio of developing various disease phenotypes. In DNA samples isolated from peripheral venous blood, the following mutation points were determined: IFN-γ (T-874A), IL-4 (С-589Т), IL-6 (C-174G), IL-17A (G-197A), and TNF-α (G-308A).
Subgroup analysis
In the observation group of 150 children with a confirmed diagnosis of bronchial asthma, two subgroups were distinguished based on the disease phenotype, with 75 children having a diagnosed virus-induced phenotype and 75 children having an allergen-induced phenotype, matched by sex and age. The control group consisted of 100 healthy peers who were matched by sex.
Outcome registration methods
DNA samples were isolated using the organic solvent chloroform with Genomic DNA Purification Kits (Thermo Fisher Scientific, Waltham, USA). Typing of single nucleotide genes polymorphisms of the studied cytokines was carried out by the polymerase chain reaction method with melting of reaction products in the presence of adjacent oligonucleotides with genotyping of polymorphisms. For amplification, we used detecting amplifier in thermal cycle (model Re Bis-M111 (OOO Bis-N, Novosibirsk)) and standard sets of primers from Scientific and Production Company Litekh-SNP (Moscow). Electrophoresis in 3% agarose gel with ethidium bromide addition was used to visualize amplification products under ultraviolet light. Detection was conducted in agarose gel stained with ethidium bromide using horizontal electrophoresis. Photofixation was carried out using the VersaDoc Model 4000 gel documentation system (Bio-Rad, USA).
Ethical review
This study followed the ethical principles stated by the Declaration of Helsinki of the World Medical Association and the Rules of Clinical Practice in the Russian Federation; study design was approved by the Interdisciplinary Ethics Committee of the FSBEI HE Pacific State Medical University of the Ministry of Healthcare of the Russian Federation; informed voluntary consents were signed by parents. The decision to conduct the study was approved by the Interdisciplinary Ethics Committee of the FSBEI HE Pacific State Medical University of the Ministry of Healthcare of the Russian Federation, protocol No. 8 dated April 27, 2015.
Statistical analysis
When processing digital data, methods of comparing unrelated groups by qualitative traits and conformance evaluation of genotype frequency distribution to expected values under Hardy–Weinberg equilibrium were used, while the chi-square test (χ2) was used to compare the distributions of genotype and allele frequencies in two subpopulations. Statistica 10, a statistical analysis system (StatSoft Inc., USA), was used to analyze the results.
The study employed standard statistical criteria: calculation of the odds ratio (OR), confidence interval (CI), and confidence factor of index and differences (p) with a critical significance level of p <0.05. The scope of the research performed made it possible to evaluate the results with a reliability of 95%–99%.
RESULTS
Objects (participants) of the study
The study included 250 children, 150 of whom had a confirmed diagnosis of bronchial asthma and 100 healthy peers who were matched by sex.
Primary outcome of the study
The study of the structure, comparison of the frequency distribution of the alleles, cytokine genotypes of various T-helper profiles in healthy children and in children with bronchial asthma was conducted, followed by an analysis of polymorphism features in the realization of allergen-induced and virus-induced disease phenotypes.
An assessment of the prevalence of cytokine genes polymorphisms in children with bronchial asthma revealed the predominance of homozygous genotypes: IFN-γ (A-874A), IL-4 (T-589T), IL-6 (G-174G), IL-17A (A-197A ), and TNF-α (A-308A). Homozygous genotypes IFN-γ (T-874T), IL-4 (C-589C), IL-6 (C-174C), IL-17A (G-197G), and TNF-α (G-308G) were more frequently detected in healthy peers. In terms of genotype structure, heterozygous variants of IL-4 (C-589T), IL-6 (G-174C), IL-17A (G-197A), and TNF-α (G-308A) were more common in children with bronchial asthma compared to healthy peers, and the IFN-γ (T-874A) genotype was found in a higher percentage of cases in the population of healthy children (Table 1).
Table 1. Structure and occurrence of cytokine gene polymorphisms in children with bronchial asthma and healthy peers
Cytokine | Polymorphism | Genotypes | Healthy children n=100 (%) | Children with bronchial asthma n=150 (%) |
Interferon gamma (IFN-γ) | 874 Т/А | ТТ | 32 (32.00) | 13 (8.67) |
ТА | 56 (56.00) | 63 (42.00) | ||
АА | 12 (12.00) | 74 (49.33) | ||
Allele frequency | Т | 120 (60.00) | 89 (29.67) | |
А | 80 (40.00) | 211 (70.33) | ||
Interleukin-4 (IL-4) | 589 C/T | СС | 75 (75.00) | 20 (13.33) |
СТ | 20 (20.00) | 93 (62.00) | ||
ТТ | 5 (5.00) | 37 (24.67) | ||
Allele frequency | С | 170 (85.00) | 133 (44.33) | |
Т | 30 (15.00) | 167 (55.67) | ||
Interleukin-6 (IL-6) | 174 G/C | GG | 7 (7.00) | 39 (26.00) |
CG | 55 (55.00) | 84 (56.00) | ||
CC | 38 (38.00) | 27 (18.00) | ||
Allele frequency | G | 69 (34.50) | 162 (54.00) | |
C | 131 (65.50) | 138 (46.00) | ||
Interleukin-17А (IL-17А) | 197 G/A | GG | 34 (34.00) | 15 (10.00) |
GА | 56 (56.00) | 85 (56.67) | ||
АА | 10 (10.00) | 50 (33.33) | ||
Allele frequency | G | 124 (62.00) | 115 (38.33) | |
А | 76 (38.00) | 185 (61.67) | ||
Tumor necrosis factor alpha (TNF-α) | 308 G/A | GG | 40 (40.00) | 25 (16.67) |
GА | 40 (40.00) | 70 (46.67) | ||
АА | 20 (20.00) | 55 (36.66) | ||
Allele frequency | G | 120 (60.00) | 120 (40.00) | |
А | 80 (40.00) | 180 (60.00) |
In the distribution of IFN-γ (T-874A) genotypes among children with a virus-induced bronchial asthma phenotype, a statistically significant increase in the frequency of occurrence of the A874A allele (61.33 vs. 12.00%, respectively) was observed in comparison with healthy peers. When carrying a functionally unfavorable allele A of the IFN-γ gene A874A polymorphism, the OR value was 5.11, indicating a significant increase in the risk of developing a virus-induced disease phenotype. The heterozygous T874A genotype was found in 32.00% of children with virus-induced bronchial asthma and 56.00% of healthy peers (Table 2).
Table 2. Frequency distributions of IFN-γ alleles and genotypes for 874T/A polymorphism in children with virus-induced bronchial asthma phenotype
Polymorphism | Genotypes | Children with virus-induced bronchial asthma phenotype n=75 (%) | Healthy children (control) n=100 (%) |
IFN-γ (T-874A) | ТТ | 5 (6.67) | 32 (32.00) |
ТА | 24 (32.00) | 56 (56.00) | |
АА | 46 (61.33) | 12 (12.00) | |
Allele frequency | Т | 34 (22.67) | 120 (60.00) |
А | 116 (77.33) | 80 (40.00) | |
OR (CI 95%) | 5.11 (3.18–8.23) | ||
χ2 test | 28.48; р=0.001 | ||
Note: OR ― odds ratio; CI ― confidence interval.
In children with the allergen-induced phenotype of bronchial asthma, the carriage of the IFN-γ A874A mutant allele was less common than in children with the virus-mediated phenotype of the disease (37.33 vs. 61.33% of cases, respectively). The presence of the single nucleotide polymorphism IFN-γ A874A increases the risk of developing allergen-induced bronchial asthma phenotype by 2.59 times (χ2=18.66; p=0.013; OR=2.59; CI 95% 1.67–4) and virus-induced phenotype by 5.11 times (Table 2).
In a study of IL-4 (C-589T) polymorphism in the group with the virus-induced bronchial asthma phenotype, the frequency of homozygous allele IL-4 T874T occurrence was 30.67% versus 5.00% in healthy peers, while the frequency of heterozygous genotype occurrence was 53.33 and 20.00%, respectively. The presence of a functionally unfavorable T allele of the T874T IL-4 gene polymorphism increased the risk of developing and manifesting a virus-induced disease phenotype (χ2=56.97; p=0.001; OR=19.30; CI 95% 11.23–33.31). In children with the allergen-induced disease phenotype, the carriage of the mutant allele was less common than in children with the virus-mediated phenotype but significantly more frequent than in the group of healthy peers, increasing the risk of developing bronchial asthma (Table 3).
Table 3. Frequency distribution of IL-4 alleles and genotypes (589C/T polymorphism) in children with allergen-induced bronchial asthma phenotype
Polymorphism | Genotypes | Children with allergen-induced bronchial asthma phenotype n=75 (%) | Healthy children (control) n=100 (%) |
IL-4 (С-589Т) | СС | 8 (10.67) | 75 (75.00) |
СТ | 53 (70.67) | 20 (20.00) | |
ТТ | 14 (18.66) | 5 (5.00) | |
Allele frequency | С | 69 (46.00) | 170 (85.00) |
Т | 81 (54.00) | 30 (15.00) | |
OR (CI 95%) | 7.172 (4.31–11.92) | ||
χ2 test | 15.21; р=0.01 | ||
Note: OR ― odds ratio; CI ― confidence interval.
In children with virus-induced bronchial asthma phenotype, the occurrence of the IL-6 gene G174G mutant genotype is higher than in healthy peers (24.00 vs. 7.00%, respectively) (OR=1.49 at χ2=3.35; p=0.224 CI 95% 0.96–2.29). The heterozygous G174C allele in this group of children was identified in 53.00% of cases, and in children with the allergen-induced disease phenotype, the carriage of this allele and the homozygous G174G was identified more frequently with a high OR (Table 4).
Table 4. Carriage of IL-6 gene polymorphism in children with allergen-induced bronchial asthma phenotype
Polymorphism | Genotypes | Children with allergen-induced bronchial asthma phenotype n=75 (%) | Control group n=100 (%) |
IL-6 (C-174G) | GG | 24 (32.00) | 7 (7.00) |
CG | 44 (58.67) | 60 (60.00) | |
CC | 7 (9.33) | 33 (33.00) | |
Allele frequency | G | 92 (46.00) | 74 (37.00) |
C | 58 (54.00) | 126 (63.00) | |
OR (CI 95%) | 2.71 (1.73–4.18) | ||
χ2 test | 20.34; р=0.015 | ||
Note: OR ― odds ratio; CI ― confidence interval.
When analyzing the structure and occurrence of IL-17A (G-197A) single nucleotide polymorphisms in children with allergen-induced phenotype of bronchial asthma, a high proportion of the A197A genotype (40.00%) and a singular occurrence of the G197G allele at CI 95% 0.32–0.71 for the OR were identified (Table 5). In children with the virus-induced bronchial asthma phenotype, the presence of the mutant allele A was found in 26.70% of cases with an OR of 0.27 (CI 95% 0.19–0.37) and χ2=12.02 (p=0, 39).
Table 5. 197G/A polymorphism of the IL-17A gene in children with allergen-induced bronchial asthma
Polymorphism | Genotypes | Children with allergen-induced bronchial asthma phenotype n=75 (%) | Control group n=100 (%) |
IL-17A (G-197A) | GG | 5 (6.70) | 34 (34.00) |
GА | 40 (53.30) | 56 (56.00) | |
АА | 30 (40.00) | 10 (10.00) | |
Allele frequency | G | 50 (33.00) | 124 (62.00) |
А | 100 (67.00) | 76 (38.00) | |
OR (CI 95%) | 0.51 (0.32–0.71) | ||
χ2 test | 28.22; р=0.031 | ||
Note: OR ― odds ratio; CI ― confidence interval.
The prevalence of TNF-α (G-308A) polymorphism and the distribution of genotype frequency in children with various bronchial asthma phenotypes differed from that of healthy peers for the A allele — 63.30 versus 40.00% and 36.70 versus 60.00%. The sampling revealed a statistically significant increase in the incidence of the functionally unfavorable A308A genotype, as well as a 2.6-fold increase in the risk of developing a virus-induced phenotype of bronchial asthma (χ2=18.66; p=0.017; OR=2.60; CI 95% 1.67–4.01).
The distribution of the heterozygous A308G genotype of the TNF-α gene in samples of children with various bronchial asthma phenotypes differed slightly, accounting for 46.60 and 46.70% of cases in the groups of children with allergen-induced and virus-induced phenotype, respectively, and 40.00% in the group of healthy peers (Table 6).
Table 6. Frequency distribution of alleles and genotypes for the 308G/A polymorphism of the TNF-α gene with the realization of the allergen-induced disease phenotype
Polymorphism | Genotypes | Children with allergen-induced bronchial asthma phenotype n=75 (%) | Control group n=100 (%) |
TNF-α (G-308A) | GG | 15 (20.00) | 40 (40.00) |
GА | 35 (46.60) | 40 (40.00) | |
АА | 25 (33.40) | 20 (20.00) | |
Allele frequency | G | 65 (43.30) | 120 (60.00) |
А | 85 (56.70) | 80 (40.00) | |
OR (CI 95%) | 1.96 (1.27–3.01) | ||
χ2 test | 9.55; р=0.05 | ||
Note: OR ― odds ratio; CI ― confidence interval.
Thus, according to the findings, carriage of the mutant A genotype can be used to predict the relative risk of developing bronchial asthma in children.
Adverse events
No adverse events were reported during the course of the study.
DISCUSSION
Summary of the primary outcome of the study
Among the genetic risk factors for the development and realization of bronchial asthma phenotypic variants in children, cytokine genes, which are involved in both the regulation of the direction of immune response and the immunopathogenesis of the disease, play an important role. Variations in the level of expression and production of cytokines that regulate the differentiation of T-lymphocyte populations are determined by the structure of polymorphisms in the coding or promoter parts of genes [7–9, 11, 12].
Cytokines are important regulators of the development and progression of the chronic inflammatory process as well as immunopathogenesis of respiratory tract structural disorders in bronchial asthma [1, 3, 5–7]. Interferon gamma (IFN-γ) regulates immune response and differentiation of Th1 lymphocytes, whereas IL-4 is involved in the differentiation of Th2 lymphocytes and the development of allergic inflammation. The development of allergic inflammation is associated with the predominance of Th2 type immune response and aberrant production of the corresponding spectrum of cytokines. At the same time, data on the role of other subpopulations of T-helpers and their cytokines in the development of bronchial asthma are described in literature [1, 3, 4, 7, 10, 13]. Tumor necrosis factor (TNF), which is secreted by neutrophils and alveolar macrophages and initiates the secretion of IL-1, IL-6, and IL-8, plays a significant role in the implementation of the type of inflammatory process in the airways in bronchial asthma. Data on the causal significance of TNF-α in the chronicity of atopic inflammation, control of the infiltration degree of bronchial wall by neutrophils, and regulation of the expression of eosinophil adhesion molecules in the focus of inflammation have been published [6, 10].
The literature contains conflicting data about the role of cytokines and genetic factors in the pathogenesis of bronchial asthma [3, 8, 13–15]. Data on genetic predictors of the bronchial asthma phenotype realization in children are important for personifying prevention and therapy programs.
Discussion of the primary outcome of the study
In this case-control study single nucleotide substitutions in cytokines genes in various profiles of T-lymphocytes-helpers were studied. When assessing the prevalence of cytokine gene polymorphism in children with allergen-induced and virus-induced bronchial asthma phenotypes, a sample of 100 healthy Caucasian children living in the city of Vladivostok was used as a population control.
In children with bronchial asthma, there was а statistically significant increase in the frequency of occurrence of the IFN-γ A874A allele, an association of the A allele of IFN-γ gene with an increased risk of developing the disease, and the fact that the carriage of the functional unfavorable polymorphism A874A of the IFN-γ gene increases the risk of development and realization of virus-induced bronchial asthma phenotype by 5.11 times.
There was a statistically significant increase in the occurrence of the homozygous T589T allele in children with virus-induced phenotype of bronchial asthma, as well as an increased risk of developing this phenotype of the disease when carrying a functionally unfavorable allele T of the T589T polymorphism of the IL-4 gene. The results of the study of the frequency of the mutant T allele of IL-4 (C-589T) allowed to characterize the carriage of this homozygote as a genetic predictor of the risk of bronchial asthma with a higher degree of probability of the virus-induced phenotype realization.
In the scientific literature, conflicting data from studies of the relationship between IL-4 gene polymorphism and the risk of developing asthma are presented. In a meta-analysis of the association of IL-4 (C-589T) (rs224350) polymorphism of IL-4 gene with predisposition to bronchial asthma, A. Kousha et al. (2020) [8] found that this polymorphism increases the risk of asthma in all genetic models, including dominant (OR=1, 22), recessive (OR=1.17), allelic (OR=1.21), and TT vs.in comparison with CC model (OR=1.34), with the exception of CT vs. TT model (OR =1.13). Additional analysis of subgroups by age showed that IL-4 gene polymorphism (C-589T) was significantly associated with the risk of asthma in children and adults, as well as a substantial association in subgroups by ethnicity [8]. T.Y. Shumna et al. (2019) [15] determined that the C589C genotype of the IL-4 gene is linked to bronchial asthma (OR=4.31; 95% CI 1.63–11.36; p=0.002) and allergic rhinitis (OR=4.421; 95 % CI 1.04–7.81, p=0.04).
Our study of the association between the development of bronchial asthma and the distribution of alleles of the polymorphic variant of IL-6 (G-174C) found that the G174G genotype increases the risk of developing the virus-induced phenotype of bronchial asthma by 1.93 times with an OR of 1.49 and, with the allergen-induced phenotype, allele G increases the risk of developing this phenotype by 2.71 times. Y.L. Liu et al. (2016) [13] confirmed the importance of IL-6 signaling in dendritic cells for the uptake of allergens and the initiation of Th2/Th17-mediated inflammation in airways in the development of allergic bronchial asthma in animal models.
E. Babusikova et al. (2017) [7], studying the predictive significance of IL-6 (G-174C) gene polymorphisms for bronchial asthma among Slovak children, found GG, GC, and CC genotypes in 37.90; 45.80, and 16.30% of those with the disease and 20.00, 50.80, and 29.20% of healthy peers, respectively, concluding that the dominant GG genotype is a risk factor for asthma (OR=3.4; 95% CI 2.045–5.638; p <0.001). In our study, in contrast to the data presented above, the occurrence of heterozygous genotype G174C of IL-6 gene among children with bronchial asthma and healthy children practically did not differ.
The frequency of allele distribution in groups with allergen-induced and virus-induced phenotypes differs statistically significantly from those in the control group of healthy peers, according to an analysis of the distribution structure of IL-17A (G-197A) genotypes. Among children with allergen-induced phenotype of bronchial asthma, there is a high proportion of the AA genotype and a low proportion of the GG allele; it was also estimated that the carriage of the mutant allele A increases the risk of developing bronchial asthma by 2.62 times. Among children with virus-induced phenotype and healthy children, the mutant allele A was found in 26.70 and 10.00% of cases, respectively. The research done by A.M. Ammar et al. (2020) [9] focused on the association of single nucleotide polymorphisms of IL-17A (G-197A) (rs2275913) and the development of sensitization to house dust mites and discovered that the occurrence of heterozygous genotype and the frequency of carriage of the A allele are higher among patients with bronchial asthma (p < 0.01), whereas the carriage of the G allele was more prevalent in the control group.
After analyzing TNF-α (G-308A) genotype, we discovered an exclusive relationship between the homozygous A308A genotype and the risk of developing bronchial asthma. The prevalence of mutant A and wild G alleles in patients with allergen-induced phenotype of bronchial asthma and the control group of children was 56.70 and 40.00% and 43.30 and 60.00%, respectively, and according to the OR of carrying a functional unfavorable allele A G308A polymorphism of TNF-α gene causes a 1.96-fold risk of developing bronchial asthma and the realization of virus-induced phenotype of the disease. I.C. Bocsan et al. (2020) [6], studying the correlation of polymorphisms of IL-6, IL-10, TNF-α genes and risks of developing bronchial asthma and allergic rhinitis, registered the dominance of the G allele carriage in both subgroups with IL-6 (G-174C) polymorphism, and A308A genotype of TNF-α gene was found only in patients with bronchial asthma.
Study limitations
During the planning and execution of the study, the sample size for achieving the required statistical power of the results was not calculated, but the sample obtained during the study can be considered sufficiently representative, allowing extrapolating the results and their interpretation to the general population of similar patients outside of the study.
CONCLUSION
The study provides data on the importance of functional polymorphisms of cytokine genes as predictors associated with the risk of developing various asthma phenotypes in children.
Significant differences in the structure and occurrence of cytokine gene polymorphisms in children with allergen-induced and virus-induced bronchial asthma were determined depending on the manifested disease phenotype. The carriage of mutant IFN-γ (A-874A), IL-4 (T-589T), IL-6 (G-174G), IL-17A (A-197A), and TNF-α (A-308A) alleles have been identified as genetic predictors of bronchial asthma development: the OR is higher in the presence of IFN-γ (A-874A), IL-4 (T-589T), and TNF-α (A-308A) mutant alleles for the realization of virus-induced phenotype and in the presence of IL-6 (G-174G), IL-17A (A-197A) for allergen-induced phenotype of the disease.
ADDITIONAL INFORMATION
Funding source. This study was not supported by any external sources of funding.
Competing interests. The authors declare that they have no competing interests.
Authors’ contribution. E.V. Prosekova ― created concept and designed the study, editing; M.S. Dolgopolov, A.I. Turyanskaya ― collection and processing of material; M.S. Dolgopolov, O.L. Zhdanova ― analyzed data; E.V. Prosekova, V.A. Sabynych, M.S. Dolgopolov ― wrote the manuscript with input from all authors. All authors made a substantial contribution to the conception of the work, acquisition, analysis, interpretation of data for the work, drafting and revising the work, final approval of the version to be published and agree to be accountable for all aspects of the work.
About the authors
Elena V. Prosekova
Pacific State Medical University
Author for correspondence.
Email: pros.ev@mail.ru
ORCID iD: 0000-0001-6632-9800
SPIN-code: 3547-6974
Scopus Author ID: 6507148681
ResearcherId: A-5843-2016
MD, Doctor of Medical Sciences, Full Professor, Head of Department of Clinical Laboratory Diagnostics and General and Clinical Immunology
Russian Federation, 2, Ostryakova Prospekt, Vladivostok, 690002
Maxim S. Dolgopolov
Pacific State Medical University
Email: gades.med@mail.ru
ORCID iD: 0000-0003-4657-6868
SPIN-code: 9152-6008
Teaching Assistant of Department of Clinical Laboratory Diagnostics and General and Clinical Immunology
Russian Federation, 2, Ostryakova Prospekt, Vladivostok, 690002Vitaly A. Sabynych
Pacific State Medical University
Email: irjnjdj@mail.ru
ORCID iD: 0000-0003-3874-6433
SPIN-code: 9347-1831
MD, Candidate of Medical Sciences, Associate Professor of Department of Clinical Laboratory Diagnostics and General and Clinical Immunology
Russian Federation, 2, Ostryakova Prospekt, Vladivostok, 690002Oksana L. Zhdanova
Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences
Email: axanka@iacp.dvo.ru
ORCID iD: 0000-0002-3090-986X
SPIN-code: 6668-3246
Doctor of Physical and Mathematical Sciences, senior research associate
Russian Federation, VladivostokAlina I. Turyanskaya
Pacific State Medical University
Email: alinakld@mail.ru
ORCID iD: 0000-0001-6993-9575
SPIN-code: 7090-3410
MD, Candidate of Medical Sciences, Teaching Assistant of Department of Clinical Laboratory Diagnostics and General and Clinical Immunolog
Russian Federation, 2, Ostryakova Prospekt, Vladivostok, 690002References
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