The role of TLR9 on Leishmania amazonensis infection and its influence on intranasal LaAg vaccine efficacy

Abstract

Leishmania (L . ) amazonensis is one of the etiological agents of cutaneous leishmaniasis (CL) in Brazil. Currently, there is no vaccine approved for human use against leishmaniasis, although several vaccine preparations are in experimental stages. One of them is Leishvacin, or LaAg, a first-generation vaccine composed of total L . amazonensis antigens that has consistently shown an increase of mouse resistance against CL when administered intranasally (i.n.). Since Toll-like receptor 9 (TLR9) is highly expressed in the nasal mucosa and LaAg is composed of TLR9-binding DNA CpG motifs, in this study we proposed to investigate the role of TLR9 in both L . amazonensis infection and in LaAg vaccine efficacy in C57BL/6 (WT) mice and TLR9 -/- mice. First, we evaluated, the infection of macrophages by L . amazonensis in vitro , showing no significant difference between macrophages from WT and TLR9 -/- mice in terms of both infection percentage and total number of intracellular amastigotes, as well as NO production. In addition, neutrophils from WT and TLR9 -/- mice had similar capacity to produce neutrophil extracellular traps (NETs) in response to L . amazonensis . L . amazonensis did not activate dendritic cells from WT and TLR9 -/- mice, analysed by MHCII and CD86 expression. However, in vivo , TLR9 -/- mice were slightly more susceptible to L . amazonensis infection than WT mice, presenting a larger lesion and an increased parasite load at the peak of infection and in the chronic phase. The increased TLR9 -/- mice susceptibility was accompanied by an increased IgG and IgG1 production; a decrease of IFN-γ in infected tissue, but not IL-4 and IL-10; and a decreased number of IFN-γ producing CD8 + T cells, but not CD4 + T cells in the lesion-draining lymph nodes. Also, TLR9 -/- mice could not control parasite growth following i.n. LaAg vaccination unlike the WT mice. This protection failure was associated with a reduction of the hypersensitivity response induced by immunization. The TLR9 -/- vaccinated mice failed to respond to antigen stimulation and to produce IFN-γ by lymph node cells. Together, these results suggest that TLR9 contributes to C57BL/6 mouse resistance against L . amazonensis , and that the TLR9-binding LaAg comprising CpG motifs may be important for intranasal vaccine efficacy against CL.

Paradoxical immune response in leishmaniasis: The role of toll‐like receptors in disease progression

“…Susceptibility is marked with larger lesion and increased parasite burden during chronic stage infection due to decreased IFNγ production in infected tissue as well as increased IgG production. 99 Taken together, the result of this study suggests that TLR9 contributes to C57BL/6 mice resistance to L. amazonensis infection. However, TLR9 signalling can promote progression of cutaneous lesions as well as promote intracellular survival of L. amazonensis by inducing the expression of CD200, a ligand known for suppressing pro-inflammatory cytokines production by macrophages.…”

The role of Toll-like receptor 9 in a murine model of Cryptococcus gattii infection

“…Many studies have shown the importance of TLR9, a receptor of the TLR family, in fungal infections, mainly in models of infection by Aspergillus fumigatus 28 , Candida albicans 29 and Cryptococcus neoformans 30,31 . TLR9 is found in endosomal vesicles and capable of recognizing fractions of non-methylated DNA, which are common in viruses, prokaryotes and some protozoa, such as those of the genus Leishmania 32,33 . TLR9 is located in endoplasmic reticulum and is translocated to the lysosome and Golgi complex after direct interaction with CpG motifs present in single-stranded DNA (ssDNA).…”

The Paradox of a Phagosomal Lifestyle: How Innate Host Cell-Leishmania amazonensis Interactions Lead to a Progressive Chronic Disease

“…In this context, TLR4, which can also be activated by LPG, is associated with both NO and TNF production following in-vitro macrophage infection ( 104 , 105 ). The role played by TLR9 is controversial, L.a. amastigotes can release DNA on micro-vesicles, activating endosomal TLR9, which required both Myd88 and TRIF to induce CD200, which blocks iNOS expression, resulting in a transient higher resistance in TLR9 -/- mice compared to Wt mice, in early but not chronic phases of the disease ( 106 , 107 ). Lastly, the expression of TLR2, TLR4 and TLR9 is different during different clinical manifestations of L.a. infection in humans.…”