Inflammatory Dendritic Cells, Regulated by IL-4 Receptor Alpha Signaling, Control Replication, and Dissemination of Leishmania major in Mice.

Ramona Hurdayal,Natalie Eva Nieuwenhuizen,Rethabile Khutlang,Frank Brombacher

doi:10.3389/fcimb.2019.00479

Abstract

Leishmaniasis is a vector-borne disease caused by Leishmania parasites. Macrophages are considered the primary parasite host cell, but dendritic cells (DCs) play a critical role in initiating adaptive immunity and controlling Leishmania infection. Accordingly, our previous study in CD11ccreIL-4Rα−/lox mice, which have impaired IL-4 receptor alpha (IL-4Rα) expression on CD11c+ cells including DCs, confirmed a protective role for IL-4/IL-13-responsive DCs in replication and dissemination of parasites during cutaneous leishmaniasis. However, it was unclear which DC subset/s was executing this function. To investigate this, we infected CD11ccreIL-4Rα−/lox and control mice with L. major GFP+ parasites and identified subsets of infected DCs by flow cytometry. Three days after infection, CD11b+ DCs and CD103+ DCs were the main infected DC subsets in the footpad and draining lymph node, respectively and by 4 weeks post-infection, Ly6C+ and Ly6C− CD11b+ DCs were the main infected DC populations in both the lymph nodes and footpads. Interestingly, Ly6C+CD11b+ inflammatory monocyte-derived DCs but not Ly6C−CD11b+ DCs hosted parasites in the spleen. Importantly, intracellular parasitism was significantly higher in IL-4Rα-deficient DCs. In terms of DC effector function, we found no change in the expression of pattern-recognition receptors (TLR4 and TLR9) nor in expression of the co-stimulatory marker, CD80, but MHCII expression was lower in CD11ccreIL-4Rα−/lox mice at later time-points compared to the controls. Interestingly, in CD11ccreIL-4Rα−/lox mice, which have reduced Th1 responses, CD11b+ DCs had impaired iNOS production, suggesting that DC IL-4Rα expression and NO production is important for controlling parasite numbers and preventing dissemination. Expression of the alternative activation marker arginase was unchanged in CD11b+ DCs in CD11creIL-4Rα−/lox mice compared to littermate controls, but RELM-α was upregulated, suggesting IL-4Rα-independent alternative activation. In summary, L. major parasites may use Ly6C+CD11b+ inflammatory DCs derived from monocytes recruited to infection as “Trojan horses” to migrate to secondary lymphoid organs and peripheral sites, and DC IL-4Rα expression is important for controlling infection.

Highlights

Leishmaniasis is a vector-borne parasitic infection caused by Leishmania species, obligate intracellular protozoans that are transmitted by the bite of infected female Phlebotominae sandflies
Confocal imaging of FACS-sorted B cells demonstrated Green-fluorescent protein (GFP)+ parasites adhering to the outside of the cells and not intracellularly (Figure 1D) confirming that lymphocyte populations do not support replication of intracellular Leishmania
Since TLR4 and TLR9 are reportedly required for mounting an effective T helper 1 (Th1) response (Faria et al, 2012) and hypersusceptible CD11ccreIL-4Rα−/lox mice showed a shift toward Th2 responses in L. major infection (Hurdayal et al, 2013), we evaluated expression of these receptors on CD11b+ Dendritic cells (DCs) by gating CD11c+CD11b+MHCII+ populations and analyzing mean fluorescence intensity of histograms of expression levels (Supplementary Figure S2 and Figure 4)

Summary

Introduction

Leishmaniasis is a vector-borne parasitic infection caused by Leishmania species, obligate intracellular protozoans that are transmitted by the bite of infected female Phlebotominae sandflies. There are over 20 Leishmania species, and over 90 sandfly species known to transmit the parasites (Burza et al, 2018; WHO, 2019). Mucocutaneous leishmaniasis leads to destruction of the mucous membranes of the nose, mouth, and throat, while visceral leishmaniasis involves dissemination of the parasites to organs, such as the spleen, liver, and bonemarrow, and is usually fatal if left untreated (Burza et al, 2018). While vector control remains an important component in controlling disease transmission, other efforts have focused on the design of novel drugs or vaccines against Leishmania species (Handman, 2001)

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