Evidence for antigen driven selection in two monoclonal auto-antibodies derived from nonobese diabetic mice.

The nonobese diabetic (NOD) mouse is a model of human type I diabetes. This diabetes is due to massive infiltration of the pancreatic beta cell of islets by autoreactive T cells (insulitis) followed by the destruction of insulin-producing cells. Circulating autoantibodies are also detected, notably against glutamic acid decarboxylase, peripherin and insulin. Two monoclonal autoantibodies directed against insulin and peripherin were obtained by fusing NOD spleen and myeloma cells. We report here the nucleotide sequence of the genes encoding for the V regions of these two antibodies. Somatic mutations were identified by comparing the light chain nucleotide sequence of one of these autoantibodies with its germline counterpart precursor established from NOD mice after PCR gene amplification. The other one displays N additions on both sides of the D region. These results strongly suggest that both autoantibodies have undergone diversification, either N additions or somatic mutations, and therefore present structural features of antibodies derived from animals immunized against exogenous antigens.