6B6- binding protein: A novel antigenic protein of Trypanosoma cruzi with diagnostic potential

Abstract

Chagas disease (ChD), caused by the protozoan Trypanosoma cruzi, affects approximately between 6 and 7 million people around the world and remains a major public health concern throughout much of Latin America. During its chronic phase, the diagnosis relies on serological methods, being the most extensively used Indirect Hemagglutination Assay (IHA), Indirect Immunofluorescence Assay (IFA) and Enzyme-Linked ImmunoSorbent Assay (ELISA). Given that none of these assays render 100% specificity and sensitivity (gold standard method), the World Health Organization (WHO) recommends two tests in parallel with the use of a third one in case of discordances, for reaching a precise diagnosis of T. cruzi infection. In this context, the objective of our work is to establish the diagnostic utility of a T. cruzi protein, which was discovered as the target molecule to a single chain recombinant antibody (scFv 6B6), isolated from an antibody library made from B cell of patients with chronic Chagas heart disease. This 6B6 binding protein (6B6-BP), of 175-250 KDa, is found in the cytoplasm of the three morphological forms of the parasite belonging to different Discrete Typing Units (DTUs), but not in other trypanosomatids, like T. brucei and Leishmania spp, or in mammalian cells. After isolating 6B6-BP from T. cruzi lysate by immunoprecipitation, the reactivity of sera from patients with chronic ChD, with cutaneous leishmaniasis, and non-infected individuals was assessed by Western-Blot. Results showed that only sera from chronic ChD and one from a patient with mixed T. cruzi-Leishmania infection recognized 6B6-BP. Although its identity is under current investigation, our preliminary data positions 6B6-BP as a potential specific diagnostic marker for this disease. We expect that our research will contribute to overcome this issue, enabling the effective serologic discrimination of ChD from other trypanosomiasis.