Several reports have recently raised the possible significance of the presence of autoantibodies against the β 1 -adrenoceptor in patients with idiopathic dilated cardiomyopathy. An investigation was thus initiated to study the immune response against this receptor at the T-cell and the B-cell level. Using membranes of E coli transfected with the human β 1 -adrenoceptor gene as immunogen, T-helper cells of the immunized mice were stimulated with synthetic peptides derived from the receptor and predicted to be immunogenic to assess the T-cell immunodominant regions of the receptor. Three peptides derived from the second transmembrane region, from the second extracellular loop and from the C-terminal domain were shown to be stimulatory. Synthetic peptides, derived from two domains of the receptor which could be potential targets for autoantibodies, yielded an antibody response after immunization with the free peptides. The peptide derived from the N-terminal region yielded antibodies which recognized the receptor in immunoblot and by immunoprecipitation but they had no functional effect on the receptor. The peptide derived from the second extracellular loop yielded antibodies which recognized the receptor in immunoblot and by immunoprecipitation of the free receptor and which had a pharmacological effect on the receptor. The second extracellular loop thus contains T- and B-cell epitopes which could be involved in the autoimmune process.
