Molecular expression cloning techniques revealed that patients with the severest clinical form of Chagas disease, chronic Chagas heart disease, presented a strong humoral response against the cloned C-terminal portion of a Trypanosoma cruzi ribosomal P protein. Parasite P antigens identification led to characterize the ribosomal P protein system in T. cruzi. Their exposed location on the ribosome, and the "amplification" of their parasite specific, serine free C-terminal domain, generate a strong parasite specific anti-P response, that in certain cases may induce anti-P autoimmunity.