The role of alkyldihydroxyacetone phosphate synthase (ADS) on host immune response and virulence of leishmania major

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Salako, Enitan
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Introduction: Leishmaniasis is a spectral disease with clinical manifestations ranging from mild self-healing skin ulcers to chronic mucocutaneous lesions and severe and fatal systemic disease. While drugs are available for treating the disease, most are expensive or highly toxic, and there is emergence of drug-resistant strains. Interestingly, recovery from Leishmania infections leads to long-lasting protective immunity, suggesting that the disease can be prevented through vaccination. A key challenge is determining the antigens that could either be used as recombinant vaccine candidates or targeted for the generation of attenuated parasites to be used as a live-attenuated vaccine. Alkyl-dihydroxyacetone phosphate synthase (ADS) is the critical enzyme involved in the biosynthesis of glycerol-containing ether lipids, which is required for synthesizing glycosylphosphatidylinositol (GPI). GPI is important for anchoring lipophosphoglycan (LPG) and gp63, which are major virulence factors of the parasite, to the cell membrane. A deficiency of ADS synthesis leads to impaired synthesis of GPI-anchored molecules resulting in attenuated virulence. However, the impact of ADS deficiency on the immunopathogenesis of cutaneous leishmaniasis has not been studied. Methods: The growth kinetics of ADS deficient (ADS KO) L. major parasites in axenic culture were compared to wild-type (WT) and Add-back (ADS-AB) parasites in axenic culture. Also, bone marrow-derived macrophages were infected with WT, ADS KO and ADS-AB parasites. The infectivity and parasite proliferation were measured and compared at different times using cytospin preparation and Giemsa staining. Balb/c mice were infected intradermally with the other parasites at different time points; parasite burden, lesion size, and cell response in the ear were measured. Balb/c mice were also vaccinated with ADS KO parasites and were also re- II challenged with WT parasite; their DTH response, lesion size, parasite burden, and cytokine response were measured. Results: Our study shows that deficiency of ADS enzyme affects the growth kinetics of L. major in axenic culture. In addition, ADS KO parasites showed lower macrophage infectivity in vitro compared to their wild-type (WT) controls. Mice infected with ADS KO parasites had a significantly reduced lesion size and parasite burden compared to those infected with WT and ADS AB parasites. ADS KO-infected mice had reduced IFN-g, IL-4 and IL-10. Mice vaccinated with the ADS KO parasite had a significant DTH response, Parasite burden and lesion size. Conclusion: Deficiency of ADS in Leishmania major affects parasite growth rate in axenic culture, infection rate and proliferation in macrophages in-vitro. ADS-deficient parasites have impaired virulence in mice and induce protective immunity in re-challenged mice confirming the critical role of GPI-anchored molecules in parasite proliferation, infectivity and host immune response.
Leisihmania major, Alkyldihydroxyacetonephosphate synthase, Host immune response, T-cells response