Evaluation of Cysteine Protease C of Leishmania donovani in comparison with Glycoprotein 63 and Elongation Factor-1α for diagnosis of human visceral leishmaniasis and for post-treatment follow-up response

Visceral leishmaniasis (VL) is a threat in many developing countries. Plenty of efforts have been put to eliminate this disease, for which serodiagnosis remains the mainstay for VL control programs. New and improved antigens as diagnostic candidates are required since available antigens fail to demonstrate optimum performance in endemic areas equally. Moreover, the diagnosis is dependent on invasive serum sampling. In the current study, we cloned and expressed Leishmania donovani cysteine protease C (CPC) and evaluated its diagnostic and test of cure possibilities by detecting the antibody levels in human serum and urine through ELISA and immunoblot assays. Two immunodominant antigens, recombinant glycoprotein 63 (GP63) and elongation factor 1α (EF1α), identified earlier by our group were also assessed employing human serum and urine samples. Out of these three antigens in ELISA, CPC demonstrated the highest sensitivities being 98.15% and 96% positive in serum and urine of VL patients, respectively. Moreover, CPC depicted 100% specificity with serum and urine of nonendemic healthy controls as compared to GP63 and EF1α. Urine samples were found to be more specific than serum for distinguishing endemic healthy controls and other diseases for all the three antigens. In all cases CPC gave the most promising results. Unlike serum, urine tests demonstrated a significant decrease in antibody levels for CPC, GP63 and EF1α after six months of treatment. The diagnostic and test of cure performances of CPC in the immunoblot assay was found to be better than GP63 and EF1α. In conclusion, CPC, followed by GP63 and EF1α, may be utilized as candidates for diagnosis of VL and to assess treatment response.