Live attenuated Leishmania donovani Centrin knock out parasites generate non-inferior protective immune response in aged mice against Visceral Leishmaniasis

Abstract

Abstract Visceral Leishmaniasis (VL) causes significant mortality. Age appears to be critical in determining the clinical outcome of VL and there is no effective vaccine available against VL for any age group. Previously, we showed that gene deleted live attenuated L. donovani parasites (LdCen−/−) induced a strong protective immune response in young mice. In this study we analyzed LdCen−/− mediated modulation of immune response in aged mice (18 months) and compared to young (2 months) mice. Analysis of innate response in dendritic cells (DCs) from both young and aged mice upon infection with LdCen−/− parasites, showed significant enhancement of innate effector responses, which consequently augmented CD4+ Th1 cell effector function compared to LdWT infected DCs in vitro. Similarly, parasitized splenic DCs from LdCen−/− infected young and aged mice revealed induction of proinflammatory cytokines and down regulation of anti-inflammatory cytokine genes compared to LdWT infected mice. Furthermore, immunization with LdCen−/− induced higher IgG2a antibodies, lymphoproliferative response and stimulated splenocytes for heightened leishmanicidal activity in young and aged mice. Additionally, upon virulent L. donovani challenge, LdCen−/− immunized mice from both age groups displayed multifunctional Th1-type CD4 and cytotoxic CD8 T cells leading to significantly reduced parasite burden in the spleen and liver compared to naïve mice. Although, there was no difference in the LdCen−/− induced innate response in DCs between aged and young, the adaptive response in terms of T cell and B cell activation in aged was reduced, which correlated with LdCen−/− induced significant but diminished protective response in aged compared to young mice against VL.