Recombinant antibodies against Trypanosoma cruzi modulate cardiac rhythm and retina

SMULSKI CR; LABOVSKY V; LONGHI SA; SIMONETTI L; LEVIN MJ

Rio de Janeiro, Brasil

Congreso; 13th International Congress of Immunology; 2007

IUIS, ALAI, SBI

Human antibodies from patients with Chagas heart disease and monoclonal antibodies (mAb) against the carboxy-terminal end (B cell epitope R13) of the ribosomal P2ß protein of Trypanosoma cruzi (TcP2ß) have been found to cross-react and stimulate the ß1 adrenergic receptor (ß1-AR). To study the structural basis of this cross-reactivity the variable regions of the anti-R13 mAb 17.2 were cloned, sequenced and used to express two different single-chain Fv fragments (scFv) in E. coli (C5 (VH-VL short linker) and B7 (VH-VL long linker)). Both were characterized for their physicochemical and immunochemical properties. The scFv C5 was a dimer and bound to TcP2ß with an affinity of Kd=8 nM, whereas scFv B7 was monomeric and had less affinity than scFv C5 for TcP2ß, Kd=46 nM. Interestingly, while scFv C5 induced an increase in cAMP levels in CHO-K cells transfected with the human ß1-AR, scFv B7 had no intrinsic effect on these cells, but blocked isoproterenol induced stimulation. The agonist-like activity of scFv C5 and the antagonist activity of scFv B7 were both confirmed in vitro on neonatal rat cardiomyocytes, and in vivo on heart beating frequency after their passive transfer to mice. Bio-distribution experiments confirmed high scFv C5 concentration in heart concomitantly with tachycardia and revealed binding to eyes, including functional effect on retina. This may be explained by the presence of ß1-AR in the retinal pigmented epithelium. These results suggest a relevant role of antibodies against the carboxy-terminal end of T. cruzi ribosomal proteins in the pathogenesis of Chagas disease.