Interaction of human chagasic IgG with human colon muscarinic acetylcholine receptor: molecular and functional evidence.

BACKGROUND AND AIMS Gastrointestinal disorders is one of the clinical manifestations of chronic Chagas' disease. The pathogenesis seems to be associated with autonomic dysfunction. Here, we consider the muscarinic cholinoceptor mediated alteration in distal colon function in chagasic megacolon. PATIENTS Patients were divided into four groups: group I, chronic chagasic patients with megacolon; group II, chronic chagasic patients without megacolon; group III, non-chagasic patients with megacolon; and group IV, normal healthy volunteers (control). METHODS Binding assay and immunoblot of cholinoceptors from human and rat colon and enzyme immunoassay (ELISA) using a synthetic 24mer peptide corresponding to the second extracellular loop of human M2 muscarinic acetylcholine receptors (mAChR) were used to detect the presence of serum antibodies. The effect of antibodies on basal tone and 3',5'-cyclic monophosphate (cAMP) production of human and rat distal colon strips were also tested. RESULTS Group I but not the other groups had circulating antibodies capable of interacting with human colon activating M2 mAChR, as they competed with binding of specific radioligand to mAChR and interacted with the second extracellular loop of human M2 mAChR. Moreover, affinity purified anti-M2 peptide IgG from group I, in common with monoclonal antihuman M2 mAChR, recognised bands with a molecular weight corresponding to colon mAChR. This antibody also displayed an agonist-like activity, increasing basal tone and decreasing cAMP accumulation. Both effects were blunted by AF-DX 116 and neutralised by the synthetic peptide. CONCLUSIONS In chagasic patients with megacolon there are antibodies that can recognise and activate M2 mAChR. The implications of these autoantibodies in the pathogenesis of chagasic megacolon is discussed.