Stimulation with 10 or 50 g/ml of SIR2RP1 resulted in a significant proliferative response, when compared with SIR2RP1-stimulated total spleen cell cultures, as confirmed by an increase in the stimulatory index (SI) (using 50 g/ml of SIR2RP1 and a 72-hr incubation period the SI reached 2102 and 4768 in isolated B cells versus 844 and 2061 in total spleen cell cultures of BALB/c and C57BL/6 mice, respectively) (Fig. of DCs. Nevertheless, immunization assays demonstrated that TLR2-deficient mice were able to mount a specific humoral response to SIR2RP1. Interestingly, further investigations showed that macrophages were activated by SIR2RP1 even in the absence of TLR2. Therefore, a different type of interplay between SIR2RP1 and the major antigen-presenting cells could explain the immune response observed in TLR2-deficient mice. Together, these results demonstrate that TLR2 signalling contributes to SIR2RP1 recognition by innate immune host cells. spp. (leishmaniasis), Toll receptors/Toll-like receptors Dibutyl phthalate Introduction Toll-like receptors (TLRs) are key components of effective innate immunity. They perform a vital role in mediating the innate recognition of pathogens and orchestrating the acquired immune response to bacteria, Dibutyl phthalate viruses and parasites. The family of TLRs is highly expressed in cells of the innate immune system, such as macrophages, dendritic cells (DCs), B cells and natural killer (NK) cells, and is responsible for recognizing conserved motifs, termed pathogen-associated molecular patterns (PAMPs), that are unique to invasive pathogens and not normally found in the host cells.1,2 All the members of the Toll family are transmembrane proteins containing an extracellular domain composed of leucine-rich repeats and a cytoplasmic domain homologous to the cytoplasmic region of the interleukin (IL)-1 receptor, known as the Toll/Interleukin-1 receptor (TIR) domain, which is required for downstream signalling.3 The identification of mammalian TLRs represented an important advance in our understanding of innate immunity to pathogenic micro-organisms. To date, 11 human and 13 mouse TLRs have been identified,4 and each TLR appears to respond to distinct PAMPs, leading to the activation of specific signalling pathways.5 TLR2 recognizes a myriad of unrelated molecules, including lipopeptides,6 peptidoglycans,7 outer membrane proteins,8 a protein belonging to the thiol-disulfide oxidoreductase family9 and porins from a broad spectrum of Gram-negative bacteria. 10C12 This diversity is a result of heterodimerization with TLR1 or TLR613 and/or accessory molecules, such as CD1414 and CD36.15 The activation of TLR2 by ligands triggers several intracellular signalling responses, including the activation of nuclear factor (NF)-B and the induction of pro- and anti-inflammatory cytokines.16 One of the most Dibutyl phthalate extensively studied pathways involves signalling through MyD88.17 In fact, MyD88 is involved in NF-B activation by every TLR with the exception of TLR3.18 Engagement of TLRs by PAMPs mediates downstream signalling that leads to up-regulation of both major histocompatibility complex (MHC) and costimulatory molecules, such as CD80 and CD86, which are involved in the optimal activation of na?ve T cells, strengthening the adaptive immune response.19 Although the majority of experimental studies have indicated an essential role for MyD88 signalization in resistance against several intracellular infections,20C26 the Dibutyl phthalate role of TLR2 is still controversial. A protective role for TLR2 has been described for several infections, such as infections with and CBLC phagocytosis,40 the absence of TLR2 did not modify the course of visceral leishmaniasis (VL) in either the spleen or the liver.41 Nevertheless, very few studies have so Dibutyl phthalate far explored the interaction of constituents with the family of Toll-like receptors. Lipophosphoglycan (LPG), a major surface promastigote phosphoglycan, can be considered as an exception, as it was demonstrated to behave as a TLR2 agonist activating mouse macrophage and human NK cells.22,42 This highlights the need for a thorough dissection of the parasite factors involved in TLR activation. In addition, TLR-based therapeutic or prophylactic strategies are currently measures used to fight infectious diseases. Indeed, TLRs have been implicated in the mechanism of adjuvanticity of many immunostimulants used in clinical or experimental vaccination. In this context, several bacterial proteins have recently been reported to mediate adjuvanticity by activating antigen-presenting cells (APCs) via TLR2. This has led to the assumption of multicomponent vaccines containing TLR2 agonists.43 Human leishmaniasis and experimental murine leishmaniasis have clearly demonstrated a central role for T lymphocytes in the immunological mechanisms of resistance against leishmaniasis. The contribution of B cells during the infectious process, either as APCs or as immunoglobulin-secreting cells, is more controversial. Some reports dissected the role of B cells and antibodies (Abs) in assisting cell-mediated responses during host defence against leishmaniasis. Although some reports failed to show evidence of a contribution of B cells to the development of polarized T-cell responses,44C46 others demonstrated a correlation between B-cell depletion and enhanced resistance to the disease.47,48 In.