T cell recognition of human pre-proinsulin peptides depends on the polymorphism at HLA DQ locus: A study using HLA DQ8 and DQ6 transgenic mice

HLA DQ8 (DQ A1*0301/DQB1*0302) molecule is implicated in the susceptibility to insulin dependent diabetes mellitus whereas, HLA DQ6 (DQA1*0103/DQB1*0601) molecule may have a protective effect. In this study we used mice transgenic to HLA DQ8 and HLA-DQ6 to elucidate the T cell determinants on a putative islet cell target antigen, insulin. These mice do not express endogenous mouse class II heterodimers on cell surface. Using overlapping synthetic peptides spanning the complete sequence of human pre- proinsulin, we identified the sequences recognized by T cells in DQ8 transgenic mice and compared these to those in DQ6 transgenic mice. We observed a differential pattern of recognition of epitopes on human pre- proinsulin (HPI) polypeptide presented by the HLA DQ8 allele as compared to HLA DQ6. The sequences 1-24 and 44-63 were immunodominant in DQ8 transgenic mice while DQ6 transgenic mice primarily recognized sequences 14-33 and 74- 93 of HPI. We found that the immune response generated in HLA DQ8 transgenic mice against HPI 1-24 cross-reacted to the mouse pre-proinsulin sequence 1- 24. The T cell response were specifically inhibited using anti-CD4 and anti- DQ8 monoclonal antibodies. This cross-recognition of self sequences raises the possibility of modulation of experimental diabetes using this peptide.