Comparison of a recombinant endonuclease III protein and its synthetic peptides in ELISA for the diagnosis of tegumentary leishmaniasis using human serum and urine samples: A preliminary study

Background The laboratory diagnosis of ‌‌tegumentary leishmaniasis (TL) remains challenging, mainly because of the variable sensitivity and specificity of tests used. Moreover, biological samples are typically collected through invasive procedures. In this pilot study, the recombinant Leishmania endonuclease III (rENDO) protein and two specific B-cell epitopes predicted from its amino acid sequence were evaluated as diagnostic antigens for TL, by using paired serum and urine samples from patients. Methodology/Principal findings rENDO protein, two synthetic peptides and a Soluble Leishmania Antigen (SLA) extract as comparator, were used to develop an ELISA that was tested with a controlled panel of paired urine and serum samples from 175 patients. Results showed that the serum-based ELISA reported sensitivity of 100% for rENDO, Peptide 1, and Peptide 2, and of 85.0% for SLA. Specificity values were of 100%, 100% and 96.6% for the protein and peptides, and 67.3% for SLA, respectively. For the urine-based ELISA, sensitivity was also of 100% for rENDO, Peptide 1, and Peptide 2, and of 90.6% for SLA. Specificity values were 100%, 100% and 96.5%, for the protein and peptides, and 91.5% for SLA, respectively. The antibody response was compared with a commercial kit, and results showed a kappa index higher than 0.90 for rENDO using both serum and urine samples, whereas the kit showed values below 0.80. Additionally, a one-point longitudinal study for antibody response monitoring in treated ML patients revealed a drop in rENDO-specific IgG levels of nearly 50% after six months. Conclusions Preliminary data suggest that the ELISA using rENDO and its derived peptides demonstrated good sensitivity and specificity for identifying TL cases, and the rENDO-based assay could potentially have a role in monitoring the treatment of TL patients.