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 manif estations of chronic Chagas' disease. The pathogenesis seems to be associat ed with autonomic dysfunction. Here, we consider the muscarinic cholinocept or 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 megaco lon; group III, nonchagasic patients with megacolon; and group IV, normal h ealthy volunteers (control). Methods-Binding assay and immunoblot of cholinoceptors from human and rat c olon and enzyme immunoassay (ELISA) using a synthetic 24mer peptide corresp onding to the second extracellular loop of human M-2 muscarinic acetylcholi ne 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 M-2 mAChR, as they competed wit h binding of specific radioligand to mAChR and interacted with the second e xtracellular loop of human M-2 mAChR. Moreover, affinity purified anti-M-2 peptide IgG from group I, in common with monoclonal antihuman M, mAChR, rec ognised bands with a molecular weight corresponding to colon mAChR. This an tibody also displayed an agonist-like activity, increasing basal tone and d ecreasing cAMP accumulation. Both effects were blunted by AF-DX 116 and neu tralised by the synthetic peptide. Conclusions-In chagasic patients with megacolon there are antibodies that c an recognise and activate M-2 mAChR. The implications of these autoantibodi es in the pathogenesis of chagasic megacolon is discussed.