DRB1*0401-restricted human T cell clone specific for the major proinsulin73-90 epitope expresses a down-regulatory T helper 2 phenotype.
Recently, we have identified proinsulin (P-Ins)(73-90) as an immunodominant T cell epitope of HLA-DRB1*0401 (DR4) subjects with beta-islet cell autoimmunity and of HLA-DR4/CD4 double-transgenic mice immunized with human P-Ins. We have compared the fine specificities of one human CD4 T cell clone and two mouse T cell hybridoma clones recognizing this epitope, and, although these three clones all recognized the same core region (LALEGSLQK), there were major differences in how they interacted with the peptide (p)/HLA complex, reflecting the fact that human P-Ins is a foreign antigen in the mouse and an autoantigen in the type 1 diabetes patient. The human T cell clone was forkhead transcription factor 3 (Foxp3)-positive, a marker for regulatory T cell lineages, and secreted predominantly IL-5, IL-10, and low levels of IFNgamma in response to P-Ins(73-90). This finding is compatible with the previously detected regulatory cytokine pattern in subjects with beta-cell autoimmunity. However, added N- or C-terminal amino acids drastically changed HLA and tetramer binding capacity as well as T cell reactivity and the cytokine phenotype of the P-Ins(73-90)-specific human CD4 T cell clone, suggesting a potential for this P-Ins epitope as a target for therapeutic intervention in HLA-DR4-positive humans with beta-islet cell autoimmunity or recent-onset type 1 diabetes.