CTLA-4 gene exon-1 +49 A/G polymorphism: lack of association with autoimmune disease in patients with common variable immune deficiency

What did we learn from CTLA-4 insufficiency on the human immune system?

Cytotoxic-T-lymphocyte-antigen-4 (CTLA-4) is a negative immune regulator constitutively expressed on regulatory T (Treg) cells and upregulated on activated T cells. CTLA-4 inhibits T cell activation by various suppressive functions including competition with CD28, regulation of the inhibitory function of Treg cells, such as transendocytosis, and the control of adhesion and motility. Intrinsic CTLA-4 signaling has been controversially discussed, but so far no distinct signaling pathway has been identified. The CTLA-4-mediated Treg suppression plays an important role in the maintenance of peripheral tolerance and the prevention of autoimmune diseases. Human CTLA-4 insufficiency is caused by heterozygous germline mutations in CTLA4 and characterized by a complex immune dysregulation syndrome. Clinical studies on CTLA4 mutation carriers showed a reduced penetrance and variable expressivity, suggesting modifying factor(s). One hundred and forty-eight CTLA4 mutation carriers have been reported; patients showed hypogammaglobulinemia, recurrent infectious diseases, various autoimmune diseases, and lymphocytic infiltration into multiple organs. The CTLA-4 expression level in Treg cells was reduced, while the frequency of Treg cells was increased in CTLA-4-insufficient patients. The transendocytosis assay is a specific functional test for the assessment of newly identified CTLA4 gene variants. Immunoglobulin substitution, corticosteroids, immunosuppressive therapy, and targeted therapy such as with CTLA-4 fusion proteins and mechanistic target of rapamycin (mTOR) inhibitors were applied; patients with life-threatening, treatment-resistant symptoms underwent hematopoietic stem cell transplantation. The fact that in humans CTLA-4 insufficiency causes severe disease taught us that the amount of CTLA-4 molecules present in/on T cells matters for immune homeostasis. However, whether the pathology-causing activated T lymphocytes in CTLA-4-insufficient patients are antigen-specific is an unsolved question. CTLA-4, in addition, has a role in autoimmune diseases and cancer. Anti-CTLA-4 drugs are employed as checkpoint inhibitors to target various forms of cancer. Thus, clinical research on human CTLA-4 insufficiency might provide us a deeper understanding of the mechanism(s) of the CTLA-4 molecule and immune dysregulation disorders.

CTLA-4 +49 G/A Polymorphism Confers Autoimmune Disease Risk: An Updated Meta-Analysis

BACKGROUND

Cytotoxic T lymphocyte antigen-4 (CTLA-4) plays a pivotal role in immune homeostasis. Dysregulated expression of CTLA-4 leads to many autoimmune diseases, including rheumatoid arthritis, systemic lupus erythematosus, and type 1 diabetes (T1D). There has been a controversial association between the CTLA-4 +49 G/A SNP (rs231775) and autoimmune diseases. Therefore, this meta-analysis was performed to assess the link between rs231775 and autoimmune disease risk.

MATERIALS AND METHODS

We retrieved the available studies from PUBMED and EMBASE through February, 2016 and then performed meta-analyses that included all populations, as well as by ethnicity.

RESULTS

After evaluating data from 4732 patients and 6270 healthy controls that included both Caucasian and Asian ethnicities, we found that rs231775 is strongly associated with autoimmune disease incidence in a homozygote comparison (GG vs. AA, 95% confidence interval [95% CI] 1.382-2.401), in a heterozygote comparison (AG vs. AA, 95% CI 1.151-1.611), in an allelic model (T allele vs. G allele, 95% CI 1.109-1.441), in a dominant model (GG/AG vs. AA, 95% CI 1.220-1.787), and in a recessive model (GG vs. AA/AG, 95% CI 1.128-1.661). The OR (odds ratio) from all models suggested a very significant association between rs231775 and autoimmune diseases.

CONCLUSION

Our present study indicates that CTLA-4 +49 G/A (rs231775) is associated with the susceptibility of autoimmune disease. Hence, rs231775 might be utilized as a diagnostic biomarker in both Asian and Caucasian populations.

Association of CTLA-4 gene polymorphisms -318C/T and +49A/G and Hashimoto's thyroidits in Zahedan, Iran

Hashimoto's thyroiditis (HT) is a chronic inflammation of the thyroid gland and is known as the most common autoimmune disease. Development of autoimmune destruction of thyroid cells is a multi-step process involving convergence of genetic and environmental factors. Cytotoxic T-lymphocyte antigen-4 (CTLA-4) has an important role in homeostasis and negative regulation of immune responses, and is therefore considered to be a key element in the development of autoimmune diseases. The present study evaluated the association of the CTLA-4 gene polymorphisms 318C/T (rs5742909) and +49A/G (rs231775) with HT in an Iranian population (including 82 patients with HT and 104 healthy controls who were referred for routine premarital blood screenings). Genotyping was performed using the tetra-primer amplification refractory mutation system polymerase chain reaction technique. No significant differences were observed in genotype and allele frequencies in the single nucleotide polymorphisms (SNPs) between cases and controls. In the cases as well as in the controls, the TT genotype in the -318C/T polymorphism was absent and the predominant genotype was CC, while the predominant genotype for the +49A/G SNP was AA. As only few studies in this field have assessed Iranian and even Middle Eastern populations, additional studies with a higher number of samples are recommended to further assess the impact of -318C/T (rs5742909) and +49A/G (rs231775) polymorphisms of CTLA-4 on HT.

Influence of molecular genetics in Vogt-Koyanagi-Harada disease

Vogt-Koyanagi-Harada (VKH) disease is a systemic autoimmune disorder against melanocytes. Recent studies have identified multiple genetic factors that might be associated with the pathogenesis of VKH disease. We performed an electronic database search of PubMed, MEDLINE, and EMBASE, and all relevant papers published up to 13 June 2014 were reviewed. A total of 1,031 publications including articles relevant to the genetics of VKH disease and the references of these articles were reviewed. The review identified a number of genetic factors which might be involved in the pathogenesis of VKH disease, some of which may alter the clinical course of VKH disease. Genes which might be involved in the pathogenesis of VKH disease included genes expressing HLA, complement factor H, interleukins, cytotoxic T-lymphocyte antigen 4 (CTLA-4), killer cell immunoglobulin-like receptors (KIR), programmed cell death 1 (PDCD1), protein tyrosine phosphatase non-receptor 22 (PTPN22), osteopontin, tumor necrosis factor alpha-induced protein 3 (TNFAIP3), macrophage migration inhibitory factor (MIF), and other immune response genes. Further studies to explore the correlation among different genotypes and phenotypes of VKH disease will be useful to shed light on the pathogenesis of uveitis in VKH disease and may facilitate the development of new treatment modalities of uveitis in VKH disease.

CTLA4 and CD86 gene polymorphisms and susceptibility to chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) may be related to chronic inflammation and immune-mediated conditions, and its pathogenesis involves T-cell activation and proliferation. Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and costimulatory molecules (CD80/CD86) genes are important mediators of T-cell activation in the immune response. The aim of this study was to investigate whether +2379G/C (rs17281995) and +1057G/A (rs1129055) in CD86 and -318C/T (rs5742909) and +49A/G (rs231775) in CTLA-4 genes single nucleotide polymorphisms (SNPs) are associated with COPD in a Chinese population. The four polymorphisms were identified in 396 COPD patients and 400 controls using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The frequency of the T allele of the -318C/T in CTLA-4 and the A allele of the +1057G/A in CD86 polymorphisms showed significant association with COPD when compared with controls (T allele: p < 0.0001; A allele: p = 0.009). Comparison of genotype frequencies showed that -318CT, +1057GA, and +1057AA genotype was overrepresented in the COPD group, respectively (-318CT: 50.8% vs 28.5%, p < 0.0001; +1057GA: 58.6% vs 54.2%, p = 0.002; +1057AA: 30.1% vs 25.8%, p = 0.002). However, we failed to find any association between the four SNPs and COPD when cases were classified by smoking status or clinical stages (p > 0.05). The results indicate that the polymorphisms of CTLA-4 (-318C/T) and CD86 (+1057G/A) may be important genetic factor associated with risk or protection for COPD in Chinese population.

Update in understanding common variable immunodeficiency disorders (CVIDs) and the management of patients with these conditions

The common variable immunodeficiency disorders are a mixed group of heterogeneous conditions linked by lack of immunoglobulin production and primary antibody failure. This variability results in difficulty in making coherent sense of either immunopathogenesis or the role of various genetic abnormalities reported in the literature. The recent attempt to collate the varied complications in these conditions and to define particular clinical phenotypes has improved our understanding of these diseases. Once refined and confirmed by other studies, these definitions will facilitate improved accuracy of prognosis and better management of clinical complication. They may also provide a method of analysing outcomes as related to new immunopathological and genetic findings.

Antibody deficiency diseases

Primary immunodeficiency diseases are rare disorders characterized by quantitative or qualitative defects in cells or components in the immune system, resulting in a high degree of susceptibility to various types of infections. During differentiation, stem cells undergo a series of discrete steps, governed by a large number of different genes. Mutations/deletions in these genes will result in a block in differentiation of the affected cell lineage(s), leading to immunodeficiency. To date, more than 150 different types of disorders have been described. In this review, we will focus on novel findings in antibody deficiency syndromes.

Association of the CTLA-4 gene with Vogt-Koyanagi-Harada syndrome

Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), a critical negative regulator of the T cell response, has been shown to be associated with a variety of autoimmune diseases. In this study, we investigated the association of CTLA-4 gene polymorphisms (- 1661A/G; - 318C/T; + 49G/A, and CT60) with Vogt-Koyanagi-Harada (VKH) syndrome in Chinese Han patients and normal controls. The results showed that the frequency of the G allele at the + 49 site was significantly higher in VKH patients than that observed in healthy controls (71.6% versus 62.8%, P = 0.0046, Pc = 0.037). Three haplotypes were identified from the four SNPs. The frequency of haplotype - 1661A:- 318C:+ 49G:CT60G, the most prevalent haplotype both in patients and controls, was significantly higher in patients than that in controls (70.1% versus 60.0%, P= 0.0013, n= 16, Pc = 0.021). These results suggest that CTLA-4 genetic polymorphisms are associated with the susceptibility to VKH syndrome.