4 IGG ANTIISLET HUMAN MONOCLONAL-ANTIBODIES ISOLATED FROM A TYPE-1 DIABETES PATIENT RECOGNIZE DISTINCT EPITOPES OF GLUTAMIC-ACID DECARBOXYLASE-65 AND ARE SOMATICALLY MUTATED

The selective destruction by an autoimmune process of the beta cells i n the pancreas is the hallmark of the type 1 insulin-dependent diabete s mellitus. What triggers islet cell-specific autoreactive T and B cel ls, however, remains unclear. Identification of the targets of the ant i-islet cell autoantibodies frequently found in insulin-dependent diab etes mellitus patients and analysis of their sequences should provide some insights into the nature of this disease. We have combined EBV tr ansformation with CD40 activation of peripheral B cells from one patie nt with insulin-dependent diabetes mellitus to isolate four B cell clo nes that secrete islet cell-specific autoantibodies. These four human monoclonal autoantibodies are of the IgG1 isotype, and they each recog nize a different epitope of the glutamic acid decarboxylase enzyme. An alysis of their variable gene sequences shows that, while clonally unr elated, three of the four human monoclonal autoantibodies use a member of the V(H)4 family, and two have rearranged the same lambda light ch ain variable gene. The IgG1 isotype of the four autoantibodies as well as the presence of somatic mutations in both heavy and light drain ge nes provide concrete evidence for their derivation by a T cell-depende nt immune response.