CTLA-4 Gene Polymorphism at Position 49 in Exon 1 Reduces the Inhibitory Function of CTLA-4 and Contributes to the Pathogenesis of Graves’ Disease

Abstract

Activation of T cells requires at least two signals transduced by the Ag-specific TCR and a costimulatory ligand such as CD28. CTLA-4, expressed on activated T cells, binds to B7 present on APCs and functions as a negative regulator of T cell activation. Our laboratory previously reported the association of Graves’ disease (GD) with a specific CTLA-4 gene polymorphism. In theory, reduced expression or function of CTLA-4 might augment autoimmunity. In the present study, we categorized autoimmune thyroid disease patients and normal controls (NC) by genotyping a CTLA-4 exon 1 polymorphism and investigated the function of CTLA-4 in all subjects. PBMCs and DNA were prepared from GD (n = 45), Hashimoto’s thyroiditis (HT) (n = 18), and NC (n = 43). There were more GD patients with the G/G or A/G alleles (82.2% vs 65.1% in NC), and significantly fewer patients with the A/A allele (17.8% vs 34.9% in NC). In the presence of soluble blocking anti-human CTLA-4 mAb, T cell proliferation following incubation with allogeneic EBV-transformed B cells was augmented in a dose-dependent manner. Augmentation induced by CTLA-4 mAb was similar in GD and NC (GD, HT, NC = 156%, 164%, 175%, respectively). We related CTLA-4 polymorphism to mAb augmentation of T cell proliferation in each subgroup (GD, HT, NC). Although PBMC from individuals with the G/G alleles showed 132% augmentation, those with the A/A alleles showed 193% augmentation (p = 0.019). CTLA-4 polymorphism affects the inhibitory function of CTLA-4. The G allele is associated with reduced control of T cell proliferation and thus contributes to the pathogenesis of GD and presumably of other autoimmune diseases.

Analysis of the CTLA-4, CD28, and inducible costimulator (ICOS) genes in autoimmune thyroid disease

“…There was no difference in the expression of CTLA-4 and in the inhibitory function of CTLA-4 when T cells were transfected with CTLA-4 cDNA carrying the G or the A allele, suggesting that the A and G alleles of the CTLA-4 A/G 49 SNP did not directly influence its function. 47 Thus, our results and previous results showing decreased function and/or expression of CTLA-4 in individuals carrying the G allele [44][45][46] must reflect the effects of another CTLA-4 polymorphism that is in linkage disequilibrium with the A/G 49 SNP. Therefore, the A/G 49 SNP can be used as a surrogate marker until the causative polymorphism is identified.…”

“…Similarly, other investigators have examined the effects of the A and G alleles of the CTLA-4 A/G 49 SNP on the inhibitory function of CTLA-4. [44][45][46] The GG genotype was found to be associated with reduced inhibitory function of CTLA-4 on T-cell proliferation after stimulation with an allogeneic cell line, and with decreased CTLA-4 surface expression. [44][45][46] This could imply that the A and G alleles of the CTLA-4 leader sequence influenced its function and/or expression.…”

“…[44][45][46] The GG genotype was found to be associated with reduced inhibitory function of CTLA-4 on T-cell proliferation after stimulation with an allogeneic cell line, and with decreased CTLA-4 surface expression. [44][45][46] This could imply that the A and G alleles of the CTLA-4 leader sequence influenced its function and/or expression. However, a recent study showed that the G allele does not affect the function and/or expression of CTLA-4 directly, and another polymorphism in linkage disequilibrium may be responsible for the association with AITD.…”

The soluble CTLA-4 receptor and its role in autoimmune diseases: an update

“…Subsequently, the three known polymorphisms of the CTLA-4 gene were investigated for linkage and/or association in a large number of human autoimmune diseases. Of interest, some polymorphisms of the gene, such as those of exon 1 which alter CTLA-4 transcription, increase susceptibility to type 1 diabetes (T1D) and other autoimmune diseases [16][17][18][19].…”

The common variants of E-selectin gene in Graves’ disease

“…1,2 The search for genes that predispose such disease is complicated by their polygenic nature. Until recently, only the major histocompatibility complex (MHC) 3,4 and cytotoxic T-lymphocyte antigen-4 (CTLA-4) [5][6][7] have been consistently found associated with GD. With regard to the adhesion molecule, Kretowski A et al 8 had reported that intercellular adhesion molecule 1 (ICAM-1) gene polymorphisms were associated with GD.…”