Cruzipain induces autoantibodies against cardiac muscarinic acetylcholine receptors. Functional and pathological implications.

The goal of this study was to investigate whether cruzipain, a Trypanosoma cruzi immunodominant antigen, was able to induce antibodies reactive to the cardiac M(2) muscarinic acetylcholine receptor (M(2) mAChR). Immunization with cruzipain that was devoid of enzyme activity triggered IgG antibodies against cardiac M(2) mAChR. By radioligand competition assay we proved that the anti-cruzipain IgG fraction, purified from serum, inhibited binding of the specific M(2) mAChR radioligand [(3)H]quinuclidinyl benzilate. We also demonstrated that anti-cruzipain IgG reacted against the second extracellular loop of the M(2) mAChR. The corresponding affinity-purified serum anti-M(2)e2 IgG (reacting against a synthetic peptide corresponding to this loop in humans) displayed agonist-like activity associated with specific M(2) mAChR activation - increase of cGMP, inositol phosphate accumulation and nitric oxide synthase activity - triggering a decrease in myocardial contractility. Moreover, the same IgG fraction decreased heart frequency, related to inhibition of adenylate cyclase activity. These results imply that cruzipain plays a role in the production of antibodies against M(2) mAChR, which have been related to the pathogenesis of dysautonomic syndrome described in Chagas' disease.