A circulating IgG in Chagas' disease which binds to beta-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 beta-adrenoceptor agonist increasing the contractile tension and frequency of isolated rat atria, as occurs with IgG purified from chagasic serum. In this paper we demonstrated that IgG present in chagasic patients sera could bind to the beta-adrenoceptors of the heart and stimulate contractile activity of myocardium. The positive inotropic and chronotropic effect could be blocked by the specific beta 1-adrenoceptor antagonist but not by the beta 2-adrenoceptor antagonist. Chagasic IgG inhibited the binding of (-) 3H-DHA to beta-adrenoceptors of purified rat myocardial membranes behaving as non-competitive inhibitors. The reactivity of chagasic serum or IgG with beta 1-adrenoceptor was lost after absorptions with turkey red blood cells. In contrast, guinea-pig red blood cells were unable to remove the beta 1 reactivity of chagasic serum or chagasic IgG. This supports the specificity of beta 1-adrenoceptors of the chagasic IgG and the independence of beta 1-adrenoceptor reactivity in relation to the EVI system. Clinical specificity of the beta 1-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.