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

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).

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.

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.

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.