CTLA-4 Isoforms, TaqMan SNP Genotyping, and Immunological Profile in Type 1 Diabetes Mellitus: A Cross Sectional Analytical Study
TL;DR
In this Saudi T1DM cohort, CTLA-4 SNP2 shows a high frequency of the mutant TT genotype, and absent CD152 surface expression is consistent with CTLA-4 internalisation biology in chronic disease.
Abstract
Background: Type 1 diabetes mellitus (T1DM) is a T-cell-mediated autoimmune disease characterised by progressive immune destruction of pancreatic β-cells. CTLA-4 (CD152) is a critical immune checkpoint molecule; its genetic variants, isoforms, and expression levels are implicated in autoimmune susceptibility. Despite growing evidence from other populations, simultaneous characterisation of CTLA-4 SNP genotype, surface expression, and associated cytokines in Saudi T1DM patients is lacking. Objectives: To determine CTLA-4 SNP genotype distributions by TaqMan allelic discrimination (assays 2315786-20 and 27834180-10), assess CD152 membrane expression by flow cytometry, quantify TGF-β1, IL-2, and sCTLA-4 serum levels, and evaluate their associations with clinical parameters in 115 established T1DM patients. Methods: Cross-Sectional Analytical Study of 114 T1DM patients. TaqMan genotyping was performed on genomic DNA. CD152 surface expression was assessed by flow cytometry (anti-CD45/CD152). Serum TGF-β1 was quantified by ELISA (R&D Systems DY240-05 with acid activation); IL-2 and sCTLA-4 by commercial ELISA. Clinical data were extracted from EPIC electronic health records. Results: 114 patients enrolled (66 male, 48 female; mean age 26.6 ± 8.8 yr; disease duration 14.3 ± 7.1 yr; HbA1c 8.35 ± 1.72%). SNP1 (assay 2315786- 20): 98.9% of valid samples showed heterozygous TC genotype. SNP2 (assay 27834180-10): mutant homozygous TT genotype was most prevalent (58.8%), followed by TC (40.0%). CD152 surface expression was undetected in all 115 samples. TGF-β1 was detectable (mean 122.2 ± 63.4 pg/mL); IL2 and sCTLA-4 were below minimum detection in nearly all samples. No significant genotype–phenotype associations were found (all p > 0.05). Conclusion: In this Saudi T1DM cohort, CTLA-4 SNP2 shows a high frequency of the mutant TT genotype. Absent CD152 surface expression is consistent with CTLA-4 internalisation biology in chronic disease. Future studies incorporating matched controls, stimulation-based flow cytometry, and expanded SNP panels are warranted.