Comparison of cell-mediated immunity due to Leishmania infantum promastigotes and axenic amastigotes

Introduction: Leishmania infantum is the causative agent of visceral leishmaniasis (VL). Cell-mediated immunity (CMI) is required to control leishmaniases. Therefore, simple tests that can evaluate the cellular immunity of the target populations can help to understand the immune status of the human subjects, their immunity to the re-infection and the evaluation of the effectiveness of the potential vaccines. Here, we compared antigens based on single clones of L. infantum promastigotes and axenic amastigotes by in vitro and in vivo tests. Methods: Using serial dilutions, L. infantum promastigotes were selected as single clones (PSC) or were grown under axenic conditions with succinate-tris to prepare amastigote-like single clones (ASC). Antigens prepared from PSC and ASC were then compared with typical Leishmania major and L. infantum amastigotes by SDS-PAGE, Western-blotting and proliferation tests as well as an in vivo delayed-type hypersensitivity test on guinea pigs. Results Both PSC and ASC exhibited a distinctive ~50-kDa band could be detected by Western-blotting. The proliferation tests results indicated that both PSC and ASC could cause higher lymphocyte proliferation compared to typical L. infantum and L. major promastigotes; however the differences were not significant. Moreover, both PSC and ASC had an ability to induce comparable DTH and hence CMI. Conclusion: Similar proliferation or delayed-type hypersensitivity could be caused with antigens based on PSC, ASC or the typical promastigotes and any of these reagents could potentially be used for in vivo detection of CMI in VL epidemiological or vaccine studies.