Association of IL-18 polymorphisms with rheumatoid arthritis and systemic lupus erythematosus in Asian populations: a meta-analysis

[Autoinflammatory diseases associated with IL-18]

Autoinflammatory diseases (AIDs) are conditions characterized by dysfunction of innate immunity, causing systemic inflammation and various clinical symptoms. The field of AIDs has expanded due to improved comprehension of pathophysiological mechanisms and advancements in genomics techniques. A new emerging category of AIDs is characterized by a significant increase in interleukin 18 (IL-18), a pro-inflammatory cytokine synthesized in macrophages and activated by caspase 1 via various inflammasomes. IL-18 plays a role in the regulation of innate and adaptive immunity. IL-18 is involved in various functions, such as the proliferation, survival, and differentiation of immune cells, tissue infiltration of immune cells, polarization of immune responses, and production of other pro-inflammatory cytokines. This review analyzes the literature on IL-18 regarding its functions and its implications in the diagnosis and treatment of AIDs. IL-18-associated AIDs comprise Still's disease and diseases associated with mutations in NLRC4, XIAP, CDC42, and PSTPIP1, as well as IL-18BP deficiencies. With the exception of PSTPIP1-associated diseases, these conditions all carry a risk of macrophagic activation syndrome. Measuring IL-18 levels in serum can aid in the diagnosis, prognosis, and monitoring of these diseases. Therapies targeting IL-18 and its signaling pathways are currently under investigation.

Interleukin-18 Gene Polymorphisms and Rheumatoid Arthritis Susceptibility: An Umbrella Review of Meta-Analyses

This study systematically analyzes the association between interleukin-18 (IL-18) gene polymorphisms and rheumatoid arthritis (RA) susceptibility. The electronic databases Ovid MEDLINE, Ovid Excerpta Medica Database, and Cochrane Library were searched to identify meta-analyses that included case-control studies reporting IL-18 gene polymorphisms and RA susceptibility. Data were reanalyzed using Review Manager Software 5.1, and Mantel-Haenszel random effects were applied for the five genetic models: allelic, recessive, dominant, homozygote, and heterozygote. The effect size of odds ratios (ORs) and their corresponding 95% confidence interval (CI) were calculated. A total of seven meta-analyses with poor quality were included. The IL-18 polymorphisms -607 A/C, -137 C/G, -920 T/C, and -105 C/A have been reported. With weak evidence, IL-18 -607 A/C polymorphisms were associated with a reduced risk of RA susceptibility using the allele model (OR = 0.76, 95% CI: 0.61 - 0.93, p=0.01), dominant model (OR = 0.67, 95% CI: 0.50 - 0.90, p=0.008), homozygote model (OR = 0.57, 95% CI: 0.35 - 0.91, p=0.02), and heterozygote model (OR = 0.71, 95% CI: 0.54 - 0.93, p=0.01) in the overall population. IL-18 gene polymorphisms and RA susceptibility are affected by ethnicity: With weak evidence, IL-18 -137 C/G polymorphisms were related to reduce RA susceptibility in the Asian population (allele model: OR = 0.59, 95% CI: 0.40 - 0.88, p=0.01; dominant model: OR = 0.57, 95% CI: 0.37 - 0.89, p=0.01; heterozygote model: OR = 0.60, 95% CI: 0.38 - 0.94, p=0.03). IL-18 -607 A/C gene polymorphisms are a protective factor for RA susceptibility in the overall population, and IL-18 -137 C/G gene polymorphisms are a protective factor for RA susceptibility in the Asian population. Further studies are needed to confirm these results owing to the limitations of the included studies.

Biological and clinical roles of IL-18 in inflammatory diseases

Several new discoveries have revived interest in the pathogenic potential and possible clinical roles of IL-18. IL-18 is an IL-1 family cytokine with potent ability to induce IFNγ production. However, basic investigations and now clinical observations suggest a more complex picture. Unique aspects of IL-18 biology at the levels of transcription, activation, secretion, neutralization, receptor distribution and signalling help to explain its pleiotropic roles in mucosal and systemic inflammation. Blood biomarker studies reveal a cytokine for which profound elevation, associated with detectable 'free IL-18', defines a group of autoinflammatory diseases in which IL-18 dysregulation can be a primary driving feature, the so-called 'IL-18opathies'. This impressive specificity might accelerate diagnoses and identify patients amenable to therapeutic IL-18 blockade. Pathogenically, human and animal studies identify a preferential activation of CD8+ T cells over other IL-18-responsive lymphocytes. IL-18 agonist treatments that leverage the site of production or subversion of endogenous IL-18 inhibition show promise in augmenting immune responses to cancer. Thus, the unique aspects of IL-18 biology are finally beginning to have clinical impact in precision diagnostics, disease monitoring and targeted treatment of inflammatory and malignant diseases.

Risk factors of systemic lupus erythematosus: an overview of systematic reviews and Mendelian randomization studies

BACKGROUND

The etiology of systemic lupus erythematosus is complex and incurable. A large number of systematic reviews have studied the risk factors of it. Mendelian randomization is an analytical method that uses genetic data as tool variables to evaluate the causal relationship between exposure and outcome.

OBJECTIVE

To review the systematic reviews and Mendelian randomization studies that focused on the risk factors of systemic lupus erythematosus and shed light on the development of treatments for its prevention and intervention.

METHODS

From inception to January 2022, we systematically searched MEDLINE (via PubMed) and Embase for related systematic reviews and Mendelian randomization studies. Extract relevant main data for studies that meet inclusion criteria. The quality of systematic reviews was assessed by using Assessment of Multiple Systematic Reviews 2 (AMSTAR-2). Finally, the risk factors are scored comprehensively according to the results' quantity, quality, and consistency.

RESULTS

Our study involved 64 systematic reviews and 12 Mendelian randomization studies. The results of systematic reviews showed that diseases (endometriosis, atopic dermatitis, allergic rhinitis), lifestyle (smoking, drinking, vaccination), and gene polymorphism influenced the incidence of systemic lupus erythematosus. The results of Mendelian randomization studies identified the role of disease (periodontitis, celiac disease), trace elements (selenium, iron), cytokines (growth differentiation factor 15), and gut microbiome in the pathogenesis of systemic lupus erythematosus.

CONCLUSION

We should pay attention to preventing and treating systemic lupus erythematosus in patients with endometriosis, celiac disease, and periodontitis. Take appropriate dietary supplements to increase serum iron and selenium levels to reduce the risk of systemic lupus erythematosus. There should be no excessive intervention in lifestyles such as smoking and drinking.

Therapeutic potential of targeting IL-1 family cytokines in chronic inflammatory skin diseases

The interleukin-1 (IL-1) family of cytokines is a central regulator of a myriad of immunological responses. It comprises several cytokines, including those belonging to the IL-1, IL-36 and IL-18 subfamilies, as well as IL-33. The IL-1 family primarily plays a role in orchestrating innate immune responses but also in adaptive immunity. Increased interest in the IL-1 family occurred following the discovery that dysregulation of IL-1 signalling underlies the pathogenesis of several monogenic auto-inflammatory diseases, characterized by sterile inflammation involving the skin and other organs. This also provided increased understanding of the role of innate immunity and the IL-1 family in polygenic auto-inflammatory skin conditions, such as neutrophilic dermatoses, as well as in some of the most common chronic inflammatory skin diseases, such as psoriasis or hidradenitis suppurativa. Several therapeutic agents have been developed to inhibit the IL-1 family members and their signalling pathways. These have shown therapeutic efficacy in several chronic inflammatory skin disorders. The aim of this review is to thoroughly describe the consequences of pathological dysregulation of IL-1, IL-33, IL-36, IL-18 pathways in dermatological conditions and to provide a forward-looking update on therapeutic strategies targeting signalling by IL-1 family cytokines.

Serum interleukin-18 and its relationship with subclinical atherosclerosis in systemic lupus erythematosus

BACKGROUND

Interleukin-18 (IL-18) is a pro-inflammatory and pro-atherogenic factor, and its blood level has shown a direct correlation with atherosclerosis. We aimed to evaluate the serum IL-18 level in patients with systemic lupus erythematosus (SLE) and its relationship with the intima-media thickness (IMT) of the carotid artery in these patients, as an indicator of atherosclerosis.

METHODS

In this cross-sectional study, 60 patients as the patient group and 30 healthy volunteers as the control group [matched sex, age, and body mass index (BMI)] were selected, and their disease status and general data were gathered using the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) form. A blood sample was also obtained from all participants to determine the serum level of IL-18 and other metrics, including high-sensitivity C-reactive protein (hs-CRP), cholesterol, triglyceride (TG), low-density lipoprotein (LDL), high-density lipoprotein (HDL), anti-double stranded deoxyribonucleic acid (anti-dsDNA), complement 3 (C3), and C4. The IMT of the carotid artery was calculated in both groups. We also evaluated the clinical cardiovascular manifestations.

RESULTS

The serum IL-18 levels in patients were significantly higher than in the control group (P ˂ 0.005). It had no significant correlation with disease activity (P = 0.10). The patients with SLE with high IL-18 serum levels (> 280 pg/ml) had higher SLEDAI-2K (P = 0.02) than the patients with a low level (< 280), where 280 was the median of the IL-18 levels. The serum IL-18 level had no significant correlation with the carotid artery IMT.

CONCLUSION

A high level of IL-18 reflects the disease activity, but it was not significantly correlated with subclinical atherosclerosis, denoted by the carotid artery IMT.

Role of the NLRP3 inflammasome in autoimmune diseases

NOD-like receptor family pyrin domain containing 3 (NLRP3) is an intracellular receptor that senses foreign pathogens and endogenous danger signals. It assembles with apoptosis-associated speck-like protein containing a CARD (ASC) and caspase-1 to form a multimeric protein called the NLRP3 inflammasome. Among its various functions, the NLRP3 inflammasome can induce the release of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 while also promoting gasdermin D (GSDMD)-mediated pyroptosis. Previous studies have established a vital role for the NLRP3 inflammasome in innate and adaptive immune system as well as its contribution to several autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Sjögren's syndrome (SS), systemic sclerosis (SSc), and ankylosing spondylitis (AS). In this review, we briefly introduce the biological features of the NLRP3 inflammasome and present the mechanisms underlying its activation and regulation. We also summarize recent studies that have reported on the roles of NLRP3 inflammasome in the immune system and several autoimmune diseases, with a focus on therapeutic and clinical applications.

Epigenetic and inflammatory events in experimental periodontitis following systemic microbial challenge

AIM

The purpose of this study was to determine inflammatory and epigenetic features following induction of oral and gut dysbiosis in experimental periodontitis in order to examine the interplay between oral and systemic infection.

MATERIALS AND METHODS

Periodontitis was induced in 6- to 8-week-old C57BL/6 mice by (a) Ligature placement (Lig group) (oral challenge); (b) P. gingivalis gavage (Pg group) (systemic challenge); and (c) the combination of the two models oral and systemic challenge (Pg + Lig). The duration of the experiment was 60 days, and the animals were then sacrificed for analyses. Alveolar bone loss was assessed, and a multiplex immunoassay was performed. Maxillae and gut tissues were immunostained for DNMT3b (de novo methylation marker), B and T lymphocyte attenuator (BTLA) and IL-18R1 (inflammation markers).

RESULTS

Pg and Pg + Lig groups exhibited higher bone loss when compared to Sham. BAFF, VEGF, RANKL, RANTES and IP-10 were significantly higher with Pg gavage. Likewise, DNMT3b was overexpressed in both gut and maxilla after the Pg administration. The same pattern was observed for BTLA and IL-18R1 in gut tissues.

CONCLUSIONS

The systemic microbial challenge either alone or in combination with local challenge leads to distinct patterns of inflammatory and epigenetic features when compared to simply locally induced experimental periodontitis.

Impact of functional IL-18 polymorphisms on genetic predisposition and diverse clinical manifestations of the disease in Indian SLE patients

Several studies have demonstrated associations between interleukin-18 polymorphisms and risk of systemic lupus erythematosus in different populations except one of Indian origin. We therefore investigated for the influence of interleukin-18 (-1297T/C, -607A/C, -137G/C; + 105A/C) polymorphisms on genetic susceptibility and clinical expression of the disease in Indian systemic lupus erythematosus patients. A total of 200 systemic lupus erythematosus patients and 201 controls were recruited. Genotyping of interleukin-18 polymorphisms were performed by polymerase chain reaction-restriction fragment length polymorphism. Serum interleukin-18 levels were measured by enzyme-linked immunosorbent assay. Interleukin-18 (-1297T/C; -137G/C) polymorphisms showed significant association with genetic susceptibility to the disease in our systemic lupus erythematosus cohort. Stratification analysis revealed -1297CC and -1297C associated with renal involvement (odds ratio = 3.4, correcting p value = 0.0207), (odds ratio = 2.0, correcting p value = 0.0054) respectively. Additionally, -1297C allele frequency was significantly increased in patients with anti-nucleosome antibody (odds ratio = 2.1, correcting p value = 0.0301). Haplotype analysis showed CC haplotype strongly associated with serositis (odds ratio = 9.1, correcting p values = 0.0009) and neurologic involvement (odds ratio = 9.3, correcting p value = 0.0018). We reported a 2.7-fold increase in serum interleukin-18 levels in patients (511.5 ± 242.3 pg/ml) compared to controls (189.4 ± 80.8 pg/ml) ( p < 0.0001). Furthermore, interleukin-18 levels were positively correlated with disease activity ( r = 0.548, p = 0.0001) and renal involvement in the patients with lupus nephritis ( r = 0.569, p < 0.0001). In summary, interleukin-18 polymorphisms elucidated in this study appear to confer genetic susceptibility to the disease and are associated with renal, serositis and neurologic involvement in Indian systemic lupus erythematosus patients.

Interleukin-18 in Health and Disease

Interleukin (IL)-18 was originally discovered as a factor that enhanced IFN-γ production from anti-CD3-stimulated Th1 cells, especially in the presence of IL-12. Upon stimulation with Ag plus IL-12, naïve T cells develop into IL-18 receptor (IL-18R) expressing Th1 cells, which increase IFN-γ production in response to IL-18 stimulation. Therefore, IL-12 is a commitment factor that induces the development of Th1 cells. In contrast, IL-18 is a proinflammatory cytokine that facilitates type 1 responses. However, IL-18 without IL-12 but with IL-2, stimulates NK cells, CD4⁺ NKT cells, and established Th1 cells, to produce IL-3, IL-9, and IL-13. Furthermore, together with IL-3, IL-18 stimulates mast cells and basophils to produce IL-4, IL-13, and chemical mediators such as histamine. Therefore, IL-18 is a cytokine that stimulates various cell types and has pleiotropic functions. IL-18 is a member of the IL-1 family of cytokines. IL-18 demonstrates a unique function by binding to a specific receptor expressed on various types of cells. In this review article, we will focus on the unique features of IL-18 in health and disease in experimental animals and humans.

Hepatitis B vaccine non response: A predictor of latent autoimmunity?

Unresponsiveness to Hepatitis B virus (HBV) vaccine has been associated with interleukins involved with Th1 functioning including Interleukin-8 (IL-18) and Interferon-γ (IFN-γ). IL-18 and IFN-γ have also been implicated in the onset of different types of immune-mediate inflammatory conditions such as Type 1 Diabetes (T1D), Celiac disease (CD), rheumatoid arthritis (RA), obesity and systemic lupus erythematosus (SLE). Taking into account that HBV vaccination is provided in the 1st year of life worldwide, I propose that all babies should be tested for anti-HBs response after completion of the vaccine series. And I suggest that children with undetectable anti-HBs titers after recommended immunization schedule as well as the additional booster doses should be followed up over time because they may be at risk of developing a number of autoimmune disorders. In this light, the non-responsiveness to HBV vaccine might be a predictor of latent autoimmunity. For that reason, research studies are needed in order to verify the existence of potential IL-18 and IFN-γ gene polymorphisms to utilize as biomarkers of latent autoimmunity. As a final point, administration of neutralizing antibodies against IFN-γ and/or IL-18 might represent a future target for immune-modulatory therapeutic approach to halt or even reverse autoimmune phenomena.

Deletion of IL-18 Expression Ameliorates Spontaneous Kidney Failure in MRLlpr Mice

The role of IL-18 in the pathogenesis of systemic lupus erythematosus is still not definitively solved. In this study, we generated MRL^lpr mice, which develop a disease resembling systemic lupus erythematosus, genetically devoid of IL-18 expression. These mice in comparison to IL-18-competent MRL^lpr mice show reduced signs of renal pathogenesis, while other parameters such as mean survival time, lymphadenopathy, constitutive interferon-γ production, and frequency of CD3⁺B220⁺ abnormal T cells were without differences. We conclude that in the systemic lupus erythematosus syndrom IL-18 is involved specifically in the renal pathogenesis.

MUTYH Gene Polymorphisms as Risk Factors for Rheumatoid Arthritis

OBJECTIVES

MUTYH glycosylase involved in DNA repair pathways may be associated with the risk of autoimmune diseases such as rheumatoid arthritis (RA). Therefore, the association between polymorphisms in the MUTYH gene and RA was evaluated.

METHODS

We recruited 192 RA patients and 192 healthy subjects in Taiwan. The 4 MUTYH polymorphisms (rs3219463, rs3219476, rs3219489, and rs3219493) were detected and haplotype analysis was performed using the Bayesian method. The genotype and allelic frequency distributions of the polymorphisms in both RA patients and healthy patients were compared by the chi-square test.

RESULTS

Comparison of the genotype/allele frequencies between individuals with RA and the control groups revealed significant differences in 2 MUTYH gene polymorphisms, rs3219463 and rs3219476. After we performed a haplotype-specific analysis, the haplotypes Ht6-GTGC and Ht8-GGCG had lower presenting rates in RA patients than in the control groups. Furthermore, the genotype frequency of rs3219463 G/  was significantly increased among patients with immunoglobulin M rheumatoid factors, whereas that of rs3219476 was not.

CONCLUSION

We demonstrated that the rs3219463 and rs3219476 polymorphisms in RA patients from a Taiwan Chinese population were associated with disease susceptibility. These data indicate that the MUTYH gene may play a role in the progression of RA.

Interleukins and interleukin receptors in rheumatoid arthritis: Research, diagnostics and clinical implications

Rheumatoid arthritis (RA) is an autoimmune disease, resulting in a chronic, systemic inflammatory disorder. It may affect many tissues and organs, but it primarily affects the flexible joints. In clinical practice patient care generates many questions about diagnosis, prognosis, and treatment. It is challenging for health care specialists to keep up to date with the medical literature. This review summarizes the pathogenesis, the polymorphisms of interleukin and interleukin genes and the standard available and possible future immunologic targets for RA treatment. The identification of disease-associated interleukin and interleukin receptor genes can provide precious insight into the genetic variations prior to disease onset in order to identify the pathways important for RA pathogenesis. The knowledge of the complex genetic background may prove useful for developing novel therapies and making personalized medicine based on the individual’s genetics.

Association of IL-18 promoter gene polymorphisms with rheumatoid arthritis: a meta-analysis

Interleukin-18(IL-18) plays a potential pathological role in rheumatoid arthritis (RA). The conclusions of the published reports on the relationship between single-nucleotide polymorphisms -607C/A (rs1946518) and -137G/C (rs187238) located in the IL-18 gene promoter and RA risk remain controversial. This meta-analysis was performed to evaluate the association between IL-18 gene promoter (-607A/C and -137C/G) polymorphisms and RA using (1) allele, (2) codominant, (3) dominant, and (4) recessive models. Literature search was conducted up to January, 2013, in PubMed, EMBASE, Spring-link, Web of Science, Wanfang (Chinese) and China National Knowledge Infrastructure (CNKI). A total of 10 studies from eight articles involving 2,662 cases and 2,168 controls for -607A/C polymorphism and 9 studies from six articles involving 1,331 cases and 1,468 controls for -137C/G polymorphism were considered in the meta-analysis. For the relationship of IL-18 -607A/C polymorphism with RA risk, significant association was observed in allele model (OR = 0.778, 95 % CI = 0.633-0.955) and dominant model (OR = 0.618, 95 % CI = 0.466-0.819). However, no significant association could be observed between -137C/G polymorphism and RA risk under all genetic models (allele model: OR = 0.940, 95 % CI = 0.777-1.138; codominant model: OR = 1.079, 95 % CI = 0.574-2.029; dominant model: OR = 0.913, 95 % CI = 0.779-1.069; recessive model: OR = 1.133, 95 % CI = 0.586-2.190). In the subgroup analysis by ethnicity, significant result was also found in Asian populations but not found in Caucasian populations for the relationship of IL-18 -607A/C polymorphism with RA risk; while no obvious association was found between IL-18 -137C/G polymorphism and RA risk. This meta-analysis indicates that IL-18 -607A/C polymorphism in promoter region may be associated with RA risk.

Significant association between TAP2 polymorphisms and rheumatoid arthritis: a meta-analysis

Background

Rheumatoid arthritis (RA) is a severe chronic immune mediated inflammatory disease that has been shown to be associated with human leukocyte antigen (HLA) loci. The transporter associated with antigen processing 2 (TAP2) has been identified to play an important role in the HLA-associated diseases and immune response. The goal of our meta-analysis was to summarize the contribution of TAP2 polymorphisms to the risk of RA.

Methods

Meta-analyses were performed between RA and 3 TAP2 coding polymorphisms that comprised TAP2-379Ile > Val (rs1800454), TAP2-565Ala > Thr (rs2228396) and TAP2-665Thr > Ala (rs241447). The meta-analyses were involved with 9 studies (24 individual studies) among 973 cases and 965 controls.

Results

Meta-analyses showed that TAP2-379Ile allele was significantly associated with an increased risk of RA (p = 0.0002, odds ratio (OR) = 1.44, 95% confidence interval (CI) = 1.18-1.74). This association was further shown only in the dominant model (p = 0.006, OR = 1.59, 95% CI = 1.14-2.22). Subgroup analyses by ethnicity revealed that the association of TAP2-379Ile was significant in Asians (p = 0.03, OR = 1.38, 95% CI = 1.04-1.83). In addition, another significant association of TAP2-565Thr allele with RA was observed in Europeans (p = 0.002, OR = 1.62, 95% CI = 1.20-2.20).

Conclusions

Our meta-analyses suggested that TAP2-379Ile allele was significantly associated with a 59% increased risk in the dominant effect model. Subgroup analyses by ethnicity showed that TAP2-379-Ile increased the risk of RA by 38% in Asians and TAP2-565Thr increased the risk of RA by 38% in Europeans.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2097080313124700

IL-18 gene polymorphisms in aphthous stomatitis vs. Behçet's disease in a cohort of Egyptian patients

OBJECTIVE

A clinical investigation of the potential correlation of two single-nucleotide polymorphisms at -137 (G/C) and -607 (C/A) in the promoter region of the IL-18 gene, with the susceptibility to aphthous stomatitis and Behçet's disease.

PATIENT AND METHODS

This study included 80 aphthous stomatitis patients and 80 patients with Behçet's disease. Eighty healthy subjects were enrolled as a control group. IL-18 single-nucleotide polymorphisms at -607 and -137 regions were analyzed using polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

The genotype and allele distributions of the two regions did not differ significantly between patients with aphthous stomatitis and controls. The genotype and allele distributions at -607 were significantly different between patients with Behçet's disease [CC (P = 0.044), C allele (P = 0.043), A allele (P = 0.043)], and controls. The frequency of the GG genotype at position -137 in patients with Behçet's disease was associated only with a higher rate of ocular manifestations (OR= 1.4, CI= 0.76-2.7, P = 0.031).

CONCLUSION

IL-18 gene polymorphisms were not associated with any susceptibility to aphthous stomatitis, while a positive association was found with patients with Behçet's disease regarding -607 promoter site. Moreover, patients with Behçet's disease carrying the GG genotype at position -137 had a higher risk of developing ocular manifestations.

Association between interleukin 18 polymorphisms and alopecia areata in Koreans

Interleukin 18 (interferon gamma-inducing factor) (IL18) is an important proinflammatory cytokine that belongs to the IL1 family. This study investigated whether IL18 single-nucleotide polymorphisms (SNPs) are associated with the susceptibility to alopecia areata (AA) in a Korean population. Two hundred thirty-three AA patients and 243 healthy control subjects were recruited. One promoter SNP (rs187238, -137G/C) and exonic SNP (rs549908, Ser35Ser) in IL18 were genotyped using direct sequencing. SNPStats, SPSS 18.0, and Haploview version 4.2 programs were used to evaluate genetic data. Multiple logistic regression models were used to determine odds ratios, 95% confidence intervals, and P values. Tested 2 SNPs (rs187238 and rs549908) were associated with the development of AA (rs187238, P=0.002 in a codominant model 1, P=0.0048 in a dominant model, P=0.02 in a log-additive model, P=0.023 in allele distribution; rs549908, P=0.003 in a codominant model 1, P=0.0052 in a dominant model, P=0.016 in a log-additive model, P=0.015 in allele distribution). Our data suggest that the IL18 may be a risk factor for AA susceptibility.

Genetics in rheumatoid arthritis beyond HLA genes: what meta-analyses have shown?

OBJECTIVE

Rheumatoid arthritis (RA) is a complex disorder with many genetic and environmental factors to account for disease susceptibility. Individual genetic association studies usually suffer from small sample size leading to biased results of polymorphisms association with RA liability. Therefore, meta-analyses seem to resolve this limitation, up to a point, increasing the power of statistical analyses. In this review, we summarize the current knowledge of non-HLA genetic factors contributing to RA predisposition based on meta-analyses.

METHODS

Using the key words: rheumatoid arthritis, meta-analysis, and polymorphism, we searched the PubMed database for the associated articles. Up to the middle of November 2012, seventy-nine articles fulfilled the criteria and highlighted the current findings on the genetic factors contributing to RA susceptibility.

RESULTS

The association with RA was confirmed for 32 gene polymorphisms, being population specific in some cases. However, meta-analyses did not confirm an association in case of 16 gene variants, previously studied in individual studies for their association with RA.

CONCLUSIONS

The use of bioinformatics tools and functional studies of the summarized implicated genes in RA pathogenesis could shed light on the molecular pathways related to the disorder, helping to the development of new drug targets for a better treatment of RA.

Interleukin-18 gene polymorphisms and rheumatoid arthritis: a meta-analysis

Interleukin-18 (IL-18) is a member of the IL-1 superfamily that enhances both innate and acquired immune responses. IL-18 is highly expressed in sera, synovial fluids and synovial tissues of patients with RA, and these IL-18 levels are correlated with RA disease activity, indicating an important role of IL-18 in the pathogenesis of RA. Several studies have examined the association of IL-18 gene polymorphisms with RA, but these studies have shown inconclusive and controversial results. To verify the association between IL-18 gene polymorphism and susceptibility to RA, we conducted a meta-analysis of all relevant reports cited in MEDLINE/PubMed before October 2012. A meta-analysis on the association between the IL-18 rs1946518 SNP and RA was performed for 2944 patients with RA and 2377 controls from 7 published studies and a meta-analysis on the association between the IL-18 rs187238 SNP and RA was performed for 1319 patients with RA and 1211 controls from 5 published studies. In addition, 2 studies involving 1873 RA patients and 1092 controls were considered in the meta-analysis of the association between the IL-18 rs360722 SNP and RA. No significant association was found between two IL-18 SNPs (rs1946518 and rs187238) and RA susceptibility in all subjects. In subgroup analysis stratified by ethnicity, there was still no significant association between these two IL-18 SNPs and RA susceptibility. However, the frequency of the T allele at rs360722 was found to be significantly lower in patients with RA compared with controls, although this finding was based on only 2 studies. The results of our meta-analysis suggest that IL-18 rs360722 SNP is only associated with RA susceptibility. However, due to only two studies included in our meta-analysis, large-scale well designed studies should be considered in future studies to confirm the exact role of IL-18 rs360722 SNP in RA susceptibility.