A circulating IgG in Chagas' disease which binds to β-adrenoceptors of myocardium and modulates their activity.

It has been shown that sera from chagasic patients with positive EVI serology could act in co-operation with complement or normal human lymphocytes as a partial β-adrenoceptor agonist increasing the contractile tension and frequency of isolated rat atria, as occurs with IgG purified from chagasic serum. In this paper we demonstrate that IgG present in chagasic patients sera could bind to the β-adrenoceptors of the heart and stimulate contractile activity of myocardium. The positive inotropic and chronotropic effect could be blocked by the specific β₁-adrenoceptor antagonist but not by the β₂-adrenoceptor antagonist. Chagasic IgG inhibited the binding of (-) ⊃3H-DHA to β-adrenoceptors of purified rat myocardial membranes behaving as non-competitive inhibitors. The reactivity of chagasic serum or IgG with β₁-adrenoceptor was lost after absorptions with turkey red blood cells. In contrast, guinea-pig red blood cells were unable lo remove the β₁ reactivity of chagasic serum or chagasic IgG. This supports the specificity of β₁-adrenoceptors of the chagasic IgG and the independence of β₁-adrenoceptor reactivity in relation to the EVI system. Clinical specificity of the β₁-adrenoceptor reactivity seems rather high in Chagas' disease since it was lacking in 14 individuals with other cardiopathies, such as ischaemic and rheumatic heart disease, even after heart surgery. [ABSTRACT FROM AUTHOR]