Evaluation of the immune response in visceral leishmaniasis

Detection of parasites in culture or by microscopy is still necessary to make diagnosis of visceral leishmaniasis (VL). Serological methods still need assessment, as they are quick but not very sensitive, especially in immunosuppressed subjects. This paper compares the results obtained with three serological methods (indirect immunofluorescence test (IFAT), direct agglutination test (DAT), and enzyme-linked immunosorbent assay (ELISA) and the specific cell-mediated immune response, evaluated as proliferation and IFN-gamma production by peripheral blood lymphocytes (PBL) following stimulation with heat-killed L. infantum promastigotes. PBL and sera were obtained from 10 healthy donors, 3 VL patients in acute phase, and 3 patients recovering after two glucantim treatment courses. No false positive results were observed with the serological methods. IFAT can be considered the most sensitive and best suited for follow-up, as it allowed a good discrimination between the acute and remission phase. DAT did not discriminate between healthy donors and remission-phase patients, whereas ELISA is unsuited for follow-up, as it did not show any significant difference between remission- and acute-phase patients. Assessment of the cellular response is not recommended for making a diagnosis, because false positive results are frequent. However, a strong cellular response in a patient stands for a successful treatment. IFN-gamma titration is preferable to the proliferation test, because it gives earlier results and does not require the use of radioactive isotopes.