Abstract
The inability of sodium antimony gluconate (SAG)-unresponsive kala-azar patients to clear Leishmania donovani (LD) infection despite SAG therapy is partly due to an ill-defined immune-dysfunction. Since dendritic cells (DCs) typically initiate anti-leishmanial immunity, a role for DCs in aberrant LD clearance was investigated. Accordingly, regulation of SAG-induced activation of murine DCs following infection with LD isolates exhibiting two distinct phenotypes such as antimony-resistant (SbRLD) and antimony-sensitive (SbSLD) was compared in vitro. Unlike SbSLD, infection of DCs with SbRLD induced more IL-10 production and inhibited SAG-induced secretion of proinflammatory cytokines, up-regulation of co-stimulatory molecules and leishmanicidal effects. SbRLD inhibited these effects of SAG by blocking activation of PI3K/AKT and NF-κB pathways. In contrast, SbSLD failed to block activation of SAG (20 µg/ml)-induced PI3K/AKT pathway; which continued to stimulate NF-κB signaling, induce leishmanicidal effects and promote DC activation. Notably, prolonged incubation of DCs with SbSLD also inhibited SAG (20 µg/ml)-induced activation of PI3K/AKT and NF-κB pathways and leishmanicidal effects, which was restored by increasing the dose of SAG to 40 µg/ml. In contrast, SbRLD inhibited these SAG-induced events regardless of duration of DC exposure to SbRLD or dose of SAG. Interestingly, the inhibitory effects of isogenic SbSLD expressing ATP-binding cassette (ABC) transporter MRPA on SAG-induced leishmanicidal effects mimicked that of SbRLD to some extent, although antimony resistance in clinical LD isolates is known to be multifactorial. Furthermore, NF-κB was found to transcriptionally regulate expression of murine γglutamylcysteine synthetase heavy-chain (mγGCShc) gene, presumably an important regulator of antimony resistance. Importantly, SbRLD but not SbSLD blocked SAG-induced mγGCS expression in DCs by preventing NF-κB binding to the mγGCShc promoter. Our findings demonstrate that SbRLD but not SbSLD prevents SAG-induced DC activation by suppressing a PI3K-dependent NF-κB pathway and provide the evidence for differential host-pathogen interaction mediated by SbRLD and SbSLD.
Highlights
Kala-azar, caused by Leishmania donovani (LD), is regarded as the most severe form of leishmanial infection, which can be fatal in patients when left untreated
To determine the leishmanicidal effect of sodium antimony gluconate (SAG) on intracellular SbRLD culture supernatant (SbRLDs) and SbRLD (SbRLDs) and SbSLD (SbSLDs) in dendritic cells (DCs), bone marrow-derived DC (BMDC) and splenic DC (sDC) were infected with GFP expressing promastigotes of SbSLD strain 2001 (GFP2001) or SbRLD strain R5 (GFP-R5) for 3 hours, stimulated with SAG (20 mg/ml) for 24 hours, and the frequency of infected DCs measured via flow cytometry
The percentage of BMDCs or sDCs infected with GFP2001 (SbSLD) was reduced by 5 to 9-fold following SAG treatment (Figure 1B)
Summary
Kala-azar, caused by Leishmania donovani (LD), is regarded as the most severe form of leishmanial infection, which can be fatal in patients when left untreated. The second checkpoint involves a regulatory mechanism promoting reduced influx and/or enhanced efflux/sequestration of active drug that lowers its intracellular accumulation [2,3]. These two events are largely dependent on the intracellular level of thiol compounds such as glutathione (cglutamylcysteinylglycine, GSH) and parasite-specific trypanothione, which in turn are regulated by both host- and LDcglutamylcysteine synthetase, a rate-limiting enzyme in glutathione biosynthesis [2,3,4,5].
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.