The Src and Abl family kinases activate the Spleen Tyrosine Kinase to maximize phagocytosis and Leishmania infection

Leishmania spp. are obligate intracellular parasites that must be internalized by phagocytic cells to evade immune responses and cause disease. The uptake of both Leishmania promastigotes (insect-stage parasites) and amastigotes (proliferative stage parasites in humans and mice) by phagocytes is thought to be mainly host cell-driven, not parasite-driven. Our previous work indicates that host Src and Abl family kinases facilitate Leishmania entry into macrophages and pathogenesis in murine cutaneous leishmaniasis. Here we demonstrate that host spleen tyrosine kinase (SYK) is required for efficient uptake of Leishmania promastigotes and amastigotes. A Src family kinase-Abl family kinase-SYK signaling cascade induces Leishmania amastigote internalization. Finally, lesion size and parasite burden during Leishmania infection is significantly decreased in mice lacking SYK in monocytes or by treatment with the SYK inhibitor entospletinib. In summary, SYK is required for maximal Leishmania uptake by macrophages and disease in mice. Our results suggest potential for treating leishmaniasis using host cell-directed agents. SUMMARY STATEMENT Activation of Spleen Tyrosine Kinase by Src and Abl family kinases is required for maximal Leishmania uptake by macrophages and disease in a mouse model of cutaneous leishmaniasis. ### Competing Interest Statement The authors have declared no competing interest. * BMDM : bone marrow-derived macrophages C3bi : terminal component of complement CR3 : complement receptor 3 FcR : Fc receptor h : hour IgG : immunoglobulin G LPS : lipopolysaccharide Mϕ : macrophage m : minutes SE : standard error p- : phosphorylated SFK : Src family kinases SYK : spleen tyrosine kinase