RNA interference reveals a role for TLR2 and TLR3 in the recognition of Leishmania donovani promastigotes by interferon–γ‐primed macrophages

Abstract

Leishmania donovani promastigotes evade the induction of a proinflammatory response during their invasion of naive macrophages. However, their entry into IFN-c-primed macrophages is accompanied by the secretion of nitric oxide (NO) and proinflammatory cytokines. In the present study, we addressed the hypothesis that priming with IFN-c induces the expression of a receptor that enables mouse macrophages to recognize L. donovani promastigotes. We observed that in IFN-c-primed macrophages, L. donovani promastigotes stimulated Interleukin-1 receptor-associated kinase-1 (IRAK-1) activity. We next showed that Toll-like receptor (TLR)3 is barely detectable in naive macrophages but is expressed in IFN-c-treated macrophages. Silencing of TLR3, TLR2, IRAK-1 and myeloid differentiation factor 88 (MyD88) expression by RNA interference revealed that both TLR are involved in the secretion of NO and TNF-a induced by L. donovani promastigotes. Using L. donovani mutants, we showed that TLR2-mediated responses are dependent on Galb1,4Mana-PO 4 -containing phosphoglycans, whereas TLR3-mediated responses are independent of these glycoconjugates. Furthermore, our data indicate a participation of TLR2 and TLR3 in the phagocytosis of L. donovani promastigotes and a role for TLR3 in the leishmanicidal activity of the IFN-c-primed macrophages. Collectively, our data are consistent with a model where recognition of L. donovani promastigotes depends on the macrophage activation status and requires the expression of TLR3.

Expression of TLR2 and TLR4 in lesions of patients with tegumentary american leishmaniasis

“…The cytokines promotes an up-regulation of the TLR2 to maintain a continuous inflammatory response by unknown mechanism 9 . Our results are similar to those obtained in experimental models of L. major in mice 4,6,8 . Lipophosphoglycan, a polymer of repeating Galβ1-4Manα-PO 4 units and a prominent Leishmania surface glycoconjugate 14 , activates both mouse macrophages and human NK cells through TLR2 4,6 .…”

“…In our study, TLR2 was expressed only by macrophage in the double immunostaining. Macrophage is the most important cell in the cutaneous leishmaniasis and several studies demonstrated that TLR2 is expressed at the surface of this cell 6,8,12,13 . The absence of TLR2 in other cells can be associated with the phase of the disease, because DC and NK cells decrease in this period of the leishmaniasis.…”

“…Recent studies revealed that TLR2 and TLR4 contribute to the recognition of Leishmania major and to the subsequent immune response 4,8,15 . Nevertheless, discrepancy in TLR signaling has been observed when in vitro and in vivo studies have been published 2,[10][11][12][13] .…”

Analysis of the expression of toll-like receptors 2 and 4 and cytokine production during experimental Leishmania chagasi infection

“…Additionally, IFN-γ stimulation of macrophages induced expression of TLR2 and 3 that participated in the recognition of L. donovani promastigotes. Additionally, the involvement of TLRs in nitric oxide (NO) induction and TNF-α production has been reported (Flandin et al 2006). Similarly, in in vivo experiments with mice, Kropf et al (2004) observed the involvement of TLR4 in the control of L. major infection through increased inducible NO synthase expression.…”

“…Toll-like receptors (TLRs) are essential PRRs that mediate the recognition of microbial structures and induce inflammatory and adaptive responses (Tuon et al 2008). Several studies have shown the recognition of Leishmania-derived molecules by different TLRs (Becker et al 2003, de Veer et al 2003, Flandin et al 2006. For instance, lipophosphoglycan (LPG) from Leishmania major stimulated macrophages to secrete cytokines such as IL-12 and TNF-α by binding to TLR2 (de Veer et al 2003).…”