Toll-like receptor | EPFL Graph Search

Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single-pass membrane-spanning receptors usually expressed on sentinel cells such as macrophages and dendritic cells, that recognize structurally conserved molecules derived from microbes. Once these microbes have reached physical barriers such as the skin or intestinal tract mucosa, they are recognized by TLRs, which activate immune cell responses. The TLRs include TLR1, TLR2, TLR3, TLR4, TLR5, TLR6, TLR7, TLR8, TLR9, TLR10, TLR11, TLR12, and TLR13. Humans lack genes for TLR11, TLR12 and TLR13 and mice lack a functional gene for TLR10. TLR1, TLR2, TLR4, TLR5, TLR6, and TLR10 are located on the cell membrane, whereas TLR3, TLR7, TLR8, and TLR9 are located in intracellular vesicles (because they are sensors of nucleic acids). TLRs received their name from their similarity to the protein coded by the toll gene. Function The ability of the immune system to recognize mo

Analysis of a specific modular serine protease acting in the Drosophila Toll pathway

Valentin Sottas

In Drosophila, the Toll pathway plays an important role in the immune defense against Gram-positive bacteria and fungi. Molecular determinants coming from those pathogens are directly detected by pattern recognition receptors (PPRs) circulating in the hemolymph. It has been proposed that several serine protease cascades are activated by PRRs, leading to the activation of a cleaved form of the cytokine-like molecule Spätzle, the ligand of the Toll receptor. The results obtained during my master project demonstrate an essential role for ModSP, a modular serine protease acting in the activation of the Toll pathway upon Gram-positive and fungal infections. We demonstrate that ModSP integrates signals coming from GNBP3 and PGRP-SA recognition molecules and that ModSP sends this signal to Grass, a serine protease already known to activate SPE and thereby Spätzle. Further biochemical experiments show the interaction between ModSP and GNBP1 demonstrating an apical role of this serine protease in the proteolytic cascades leading to Toll pathway activation. We also find that ModSP is expressed in specific vesicles released from the fat bodies into the hemolymph. Also, preliminary studies suggest that ModSP does not participate in the melanization reaction, a secondary but important insect immune mechanism. Biochemical analysis done by some collaborators indicates that ModSP does not cleave Grass and that ModSP exhibits a high level of auto-proteolysis when this molecule is expressed. Our data reveal a conserved role of modular serine protease in the regulation of immune proteolytic cascade in insects

2009

A single modular serine protease integrates signals from pattern-recognition receptors upstream of the Drosophila Toll pathway

Bruno Lemaitre, Valentin Sottas

The Drosophila Toll receptor does not interact directly with microbial determinants, but is instead activated by a cleaved form of the cytokine-like molecule Spätzle. During the immune response, Spätzle is processed by complex cascades of serine proteases, which are activated by secreted pattern-recognition receptors. Here, we demonstrate the essential role of ModSP, a modular serine protease, in the activation of the Toll pathway by gram-positive bacteria and fungi. Our analysis shows that ModSP integrates signals originating from the circulating recognition molecules GNBP3 and PGRP-SA and connects them to the Grass-SPE-Spätzle extracellular pathway upstream of the Toll receptor. It also reveals the conserved role of modular serine proteases in the activation of insect immune reactions.

National Academy of Sciences2009

Role of Nimrod receptors in the Drosophila melanogaster cellular immune response

Claudia Melcarne

The use of modern molecular biology tools and simple but powerful tractable model organisms such as Drosophila has contributed significantly to our recent advances in the innate immunity field, notably phagocytosis. Since 2001, many phagocytic transmembrane receptors, potential opsonins, and in some cases their ligands, have been discovered. Among them, the Nimrod family, which contains key phagocytic receptors and potential opsonins, deserves special interest as accumulating genetic and biochemical evidence points to their critical role in phagocytosis of both bacteria and apoptotic cells. In this PhD thesis we provided a deeper characterization of two Nimrod transmembrane receptors, Eater and NimC1. In particular, by using single or combined mutations in eater and NimC1, we aimed to further elucidate i) the involvement of each receptor in bacterial phagocytosis and ii) the role of Eater in hemocytes sessility and adhesion. Both receptors have been shown to be specifically expressed in hemocytes, the insect blood cells, and to mediate Gram-positive but not Gram-negative bacteria phagocytosis. In this work we generated a novel NimC1 mutant and demonstrated that the single NimC1 deletion does not affect phagocytosis of bacteria. However, by using the compound NimC1;eater mutant we were able to show that these receptors contribute in a synergistic way to microbes engulfment, but that Eater can bypass the requirement for NimC1. Moreover, we discovered that NimC1, but not Eater, is required for phagocytosis of non-immunogenic particles, namely latex beads and yeast zymosan. Therefore, this work provides evidences of Eater and NimC1 being the main receptors for bacteria phagocytosis, and suggests that those proteins likely play distinct roles in microbial uptake, as tethering and docking receptors. The second part of this thesis re-addresses the role of Eater in hemocyte sessility and adhesion. A previous study showed that this phagocytic receptor is essential to mediate blood cell sessility to the animal integument during larval stages. However, a series of questions about Eater-mediated sessility remains still open. For example, is Eater mediating hemocyte adhesion also in adult flies? And yet, does Eater mediate hemocyte sessility by regulating the expression of cell adhesion genes, therefore functioning as a signalling receptor? By using eater1 mutant adult flies, we showed that, as in larval stages, Eater is required in adult hemocytes to confer adhesion and sessility. Interestingly, we uncovered a potential role of sessility in hemocyte survival during adulthood, since eater1 flies have a decreased number of blood cells. Preliminary transcriptomics analysis led us to hypothesise that this receptor might not work as a signalling molecule, but rather as an adhesion protein providing the initial hemocyte contact to its target surface. In line with Eaterâs role as an adhesion molecule, its over-expression in hemocytes leads to the formation of enlarged cells compared to control. To conclude, this thesis extended our knowledge on the Drosophila cellular immune response, by providing new insights on two Nimrod phagocytic receptors.

EPFL2020

Role of Nimrod receptors in the Drosophila melanogaster cellular immune response

Claudia Melcarne

EPFL2020