Cloning, characterization, and serodiagnostic evaluation of Leishmania infantum tandem repeat proteins

Visceral leishmaniasis (VL) is a form of leishmaniasis, which is caused by infection with the protozoan parasite Leishmania, and is often fatal unless it is treated. Rapid and accurate diagnosis of VL is important for effective treatment. Here we report the cloning of previously undescribed tandem repeat (TR) proteins of Leishmania infantum and an evaluation of VL patient antibody responses to the corresponding proteins. By screening an L. infantum expression library with sera from human VL patients or infected hamsters, we identified 43 genes encoding B-cell antigens. Surprisingly, 19 of the 43 genes (44%) were TR proteins, and that percentage was significantly higher than that for genes picked randomly from the database. We then expressed the TR regions of LinJ16.1750, LinJ22.1590, and LinJ33.2870 and the entire LinJ28.2310 protein. These recombinant proteins were all recognized by Sudanese VL patient sera in an enzyme-linked immunosorbent assay. Recombinant LinJ16.1750 (rLinJ16.1750) showed the best performance among these antigens in terms of both sensitivity and specificity. Serological evaluation revealed that 97% (34 of 35) of Sudanese VL patients had significantly elevated antibody levels to rLinJ16.1750. Furthermore, when eight of the patient sera which had low reactivities to rK39 were tested with the novel recombinant antigens, some of the sera showed stronger antibody responses to these antigens than to rK39. Our results suggest that TR regions from the novel L. infantum proteins identified in this study are immunodominant B-cell epitopes and may represent good candidates for serodiagnosis of VL.