IN-VITRO STIMULATION WITH GLUTAMIC-ACID DECARBOXYLASE (GAD65) LEADS TO AN OLIGOCLONAL RESPONSE OF PERIPHERAL T-CELLS IN AN IDDM PATIENT

The enzyme glutamic acid decarboxylase (GAD65) is a major autoantigen in insulin-dependent diabetes mellitus (IDDM). To study T-cell reactiv ity towards GAD, peripheral blood leucocytes from seven patients with IDDM and five control subjects were stimulated in vitro with recombina nt GAD. All diabetics studied were heterozygous for diabetes-associate d HLA alleles, i.e. HLA-DRB103,*04-DQB1*0302,*0201. A single IDDM sub ject (no. GAD65.05) revealed a strong response against GAD65. After st imulation, his T-cell receptor beta (TCRBV) usage was found to be olig oclonal. The sequence analysis: of the putative peptide binding region of the T-cell receptor (CDR3 region) of 37 GAD-reactive T-cell clones revealed no common CDR3 motif. The stimulation of GAD-reactive T-cell s could be inhibited with anti-class II monoclonal antibodies, indicat ing a class II restricted T-cell response. In addition, GAD65-responsi ve T-cells revealed a Th1 cytokine response pattern. The author's data suggest that GAD-reactive T-cells of Th1 phenotype can be obtained af ter in vitro stimulation of peripheral blood leucocytes from an HLA-DR B103/*04 heterozygous IDDM patient. The lack of a common CDR3 motif s uggests the absence of an immunodominant T-cell epitope in that patien t, or may indicate receptor repertoire spreading of peripheral T-lymph ocytes.