Essential role of Rip2 in the modulation of innate and adaptive immunity triggered by Nod1 and Nod2 ligands

Abstract

Muramyl peptides are the building blocks of bacterial peptidoglycan, and their biological functions in mammals have been extensively studied. In particular, muramyl peptides trigger inflammation, contribute to host defense against microbial infections, and modulate the adaptive immune response to antigens. These bacterial molecules are detected by nucleotide oligomerization domain 1 (Nod1) and Nod2, and recent evidence suggests that muramyl dipeptide also activates NLRP3 and NLRP1 inflammasomes. Here, we investigated the role of Rip2, the adaptor for Nod1-and Nod2-dependent signaling, in multiple aspects of the host response to muramyl peptides in vivo, such as inflammatory cytokine secretion, activation and recruitment of macrophages and neutrophils to the site of injection, systemic activation of myeloid, T and B cells in the spleen, adjuvanticity and capacity to polarize the adaptive response to ovalbumin. Our results demonstrate that Rip2 was crucial for all the biological functions studied. We also identified CD11c int CD11b 1 inflammatory dendritic cells as a major myeloid cell population responding to Nod stimulation in vivo. Together, our results highlight the importance of Rip2 for Nod-dependent induction of innate and adaptive immunity.Keywords: CD11c int CD11b 1 inflammatory DC . Nod 1/2 . Rip2Supporting Information available online IntroductionThe innate immune system plays a crucial role in host defense against invading pathogens, and relies on pattern recognition molecules (PRMs), which detect conserved microbial-and danger-associated molecular patterns (MAMPs or DAMPs). The best-studied PRMs are the Toll-like receptors (TLRs), which localize either at the cell surface or within endosomes. More recently, intracellular cytosolic PRMs, such as the nucleotide oligomerization domain (Nod)-like receptors (NLRs) and the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), have been identified. Nod1 and Nod2 are NLR proteins that trigger nuclear factorkB (NF-kB) signaling in response to bacterial peptidoglycan. Specifically, Nod1 recognizes muramyl peptides containing meso-DAP (diaminopimelic acid) found in the peptidoglycan of most Gram-negative bacteria and certain Gram-positive bacteria [1,2], whereas Nod2 recognizes muramyl dipeptide (MDP) produced in all bacteria [3,4]. Upon peptidoglycan detection, Nod1 and Nod2 recruit and associate with the adaptor protein à These authors have contributed equally to this study. [11,12]. Moreover, Nod1 and Nod2 induce the production of nitric oxide, a molecule that is known to be directly microbicidal [13][14][15]. Activation of Nod1 and Nod2 by live bacteria triggers proinflammatory responses, leading to the induction of cytokine and chemokines [16,17]. Using Nod-deficient mice, several in vivo studies have demonstrated a key role for Nod1 and Nod2 in host defense against pathogens such as H. pylori, L. monocytogenes, and Staphylococcus aureus [12,18,19].In addition to contributing to innate immunity, Nod1 and Nod2 have been implicated in the induction o...

Role of nucleotide-binding oligomerization domain 1 (NOD1) and its variants in human cytomegalovirus control in vitro and in vivo

“…RIPK2's role in NOD-dependent induction of innate and adaptive immunity has been reported previously (15). For some intracellular bacteria, collaboration between NOD1 and NOD2, rather than individual activation of each receptor, is important in host response (16).…”

Nucleotide oligomerization domain-containing proteins instruct T cell helper type 2 immunity through stromal activation

“…Flow cytometry was performed as described previously (47). FlowJo software was used for the analysis of the results.…”

RIP kinases: key decision makers in cell death and innate immunity

“…[166][167][168] Notably, RIP2 is required to mediate all of the in vivo host responses to MDP. 169 The ubiquitination of RIP2 is a critical step in mediating activation of these NOD2 pathways, especially activation of NFkB, 164,165 and a number of E3 ubiquitin ligases, including TRAF6, 164 cIAP and XIAP proteins [170][171][172] and ITCH 173 have been proposed to catalyse ubiquitination of RIP2. However, other studies have questioned the importance of many of these E3 ligases in the context of ubiquitinating RIP2 and activating NFkB.…”