B-cells influence T-cell reactivity by facilitating antigen presentation, but the role of autoantibody-secreting B-cells in regulating T-cell responses in Type 1 diabetes is poorly defined. The aims of this study were to characterise epitopes on the IA-2 autoantigen for three monoclonal antibodies from diabetic patients by amino acid substitutions of selected residues of IA-2, establish contributions of these epitopes to binding of serum antibodies in Type 1 diabetes and relate B- and T-cell responses to overlapping determinants on IA-2. The monoclonal antibodies recognised overlapping epitopes, with residues within the 831-860 region of IA-2 contributing to binding; substitution of Glu836 inhibited binding of all three antibodies. Monoclonal antibody Fab fragments and substitution of residues within the 831-836 region blocked serum antibody binding to an IA-2 643-937 construct. IL-10-secreting T-cells responding to peptides within the 831-860 region were detected by cytokine-specific ELISPOT in diabetic patients and responses to 841-860 peptide were associated with antibodies to the region of IA-2 recognised by the monoclonal antibodies. The study identifies a region of IA-2 frequently recognised by antibodies in Type 1 diabetes and demonstrates that these responses are associated with T-cells secreting IL-10 in response to a neighbouring determinant.