HLA‐DR3 mediated CD4 T cell response against GAD65 in type 1 diabetes patients

AIM: We planned this study to identify diabetogenic glutamic acid decarboxylase (GAD65) peptides possibly responsible for human leucocyte antigen (HLA)‐DR3/DQ2‐mediated activation of GAD65‐specific CD4 T cells in type 1 diabetes (T1D). METHODS: Top 30 GAD65 peptides, found to strongly bind in silico with HLA‐DR3/DQ2 molecules, were selected and grouped into four pools. The peptides were used to stimulate CD4 T cells of study subjects in 16‐h peripheral blood mononuclear cell culture. CD4 T cells' stimulation in terms of interferon‐gamma (IFN‐γ), interleukin (IL)‐17, tumor necrosis factor‐alpha (TNF‐α), and IL‐10 expression was analyzed using flow cytometry. RESULTS: Although all four GAD65 peptide pools (PP1‐4) resulted in significantly higher expression of IFN‐γ by CD4 T cells (p = .003, p < .0001, p = .026, and p = .002, respectively), only pool 2 showed significant increase in IL‐17 expression (p < .0001) in T1D patients vs healthy controls. Interpeptide group comparison for immunogenicity revealed significantly higher IFN‐γ and IL‐17 expressions and significantly lower IL‐10 expression for PP2 compared to other groups (p < .0001, p = .02, and p = .04, respectively) in patients but not in controls. Further, group 2 peptides resulted in significant increase in CD4 T cells' expression of IFN‐γ and IL‐17 (p = .002 for both) and significant decrease in IL‐10 (p = .04) in HLA‐DRB1*03‐DQA1*05‐DQB1*02+ patients vs HLA‐DRB1*03‐DQA1*05‐DQB1*02+ controls. The CD4 T cells' expression of IL‐17 was significantly higher (p = .03) in recently diagnosed vs long‐standing HLA‐DRB1*03‐DQA1*05‐DQB1*02+ T1D patients. CONCLUSION: GAD65 peptides, particularly those belonging to PP2, induced CD4 T cells to express IFN‐γ and IL‐17 cytokines in T1D patients, suggesting that group 2 peptides possibly presented by HLA‐DR3 molecule to CD4 T cells shift immune balance toward inflammatory phenotype in patients.