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Presence of antibodies against the third intracellular loop of the m2 muscarinic receptor in the sera of chronic chagasic patients

FERNANDA COUTINHO RETONDARO^*, PATRICIA C. DOS SANTOS COSTA, ROBERTO COURY PEDROSA and ELEONORA KURTENBACH^*1

^* Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas,
Hospital Universitário Clementino Fraga Filho, Universidade Federal do Rio de Janeiro, Centro de Ciências da Saúde, Cidade Universitária, 21941–900, Rio de Janeiro, Brazil

¹Correspondence: Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Centro de Ciências da Saúde, Cidade Universitária, 21941–900, RJ, Brazil. E-mail: kurten{at}bioqmed.ufrj.br

Patients in the chronic phase of Chagas' disease suffer from a slowly evolving inflammatory cardiomyopathy that can lead to severe cardiac dilatation, congestive heart failure, and death. This process appears to be caused by autoimmune recognition of heart tissue by a mononuclear cell infiltrate decades after infection with the parasite Trypanosoma cruzi. Recent evidence suggests that there are circulating antibodies in chronic chagasic patients that alter the physiological behavior of the heart on binding to G-protein-coupled cardiovascular receptors, including ß1-adrenergic and m2 muscarinic receptors. A 42 kDa fusion protein was constructed that contains the central part of the third intracellular loop (i3; Arg₂₆₇-Arg₃₈₁) of the human m2 muscarinic receptor, linked to glutathione S-transferase. This fusion protein was overexpressed in Escherichia coli and subsequently purified by affinity chromatography. Based on Western blots, the i3 loop is specifically recognized by the sera of chronic chagasic patients who have reached advanced stages of cardiac failure (according to the Los Andes classification). Analysis of the prevalence and distribution of these antibodies shows a strong association between seropositive patients and moderate (group II) to severe (group III) heart dysfunction.—Retondaro, F. C., dos Santos Costa, P. C., Pedrosa, R. C., Kurtenbach, E. Presence of antibodies against the third intracellular loop of the m2 muscarinic receptor in the sera of chronic chagasic patients.

Key Words: Trypanosoma cruzi • autoimmune disease • chagasic cardiomyopathy • G-protein-coupled receptors

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