Decreased β₂-adrenergic receptor density on peripheral blood mononuclear cells in myasthenia gravis

β₂-adrenergic receptors (β₂AR) are present on both lymphocytes and skeletal muscle cells. Antibodies and T cells that react with these receptors are present in patients with myasthenia gravis (MG). Immune reactivity against the β₂AR may thus modify both the immune and the muscle functions in MG. In this study, we analysed the density and affinity of β₂AR on peripheral blood mononuclear cells using a radioligand binding assay. The density (B(max)) of the receptor on cells from patients with MG was significantly lower than that on cells from patients with other neurological disorders and healthy individuals. The affinity (Kd) of the receptor and the concentration of the second messenger, cAMP, in the cells did nor differ between the groups. Serum antibodies against β₂AR were demonstrated in 22% of 27 MG patients vs. 0% of 26 healthy controls. Incubation of cells with serum or purified IgG containing antibodies against the β₂AR resulted in a decline in ligand binding of the receptor in samples from three out of five patients. Thus, this study suggests that a downregulation of the β₂AR may occur in MG. This downregulation might be of importance in the pathogenesis of the disease and its symptoms.