Nod2 sensing of lysozyme-digested peptidoglycan promotes macrophage recruitment and clearance of S. pneumoniae colonization in mice

Abstract

Streptococcus pneumoniae colonizes the mucosal surface of the human upper respiratory tract. A colonization event is gradually cleared through phagocytosis by monocytes/macrophages that are recruited to the airway lumen. Here, we sought to define the bacterial and host factors that promote monocyte/macrophage influx and S. pneumoniae clearance using intranasal bacterial challenge in mice. We found that the recruitment of monocytes/macrophages required their expression of the chemokine receptor CCR2 and correlated with expression of the CCR2 ligand CCL2. Production of CCL2 and monocyte/macrophage recruitment were deficient in mice lacking digestion of peptidoglycan by lysozyme (LysM) and cytosolic sensing of the products of digestion by Nod2. Ex vivo macrophages produced CCL2 following bacterial uptake, digestion by LysM, and sensing of peptidoglycan by Nod2. Sensing of digested peptidoglycan by Nod2 also required the pore-forming toxin pneumolysin. The generation of an adaptive immune response, as measured by anti-pneumococcal antibody titers, was also LysM-and Nod2-dependent. Together, our data suggest that bacterial uptake by professional phagocytes is followed by LysM-mediated digestion of S. pneumoniae-derived peptidoglycan, sensing of the resulting products by Nod2, release of the chemokine CCL2, and CCR2-dependent recruitment of the additional monocytes/macrophages required for the clearance of an S. pneumoniae colonization event.

Streptococcus pneumoniaeStimulates a STING- and IFN Regulatory Factor 3-Dependent Type I IFN Production in Macrophages, which Regulates RANTES Production in Macrophages, Cocultured Alveolar Epithelial Cells, and Mouse Lungs

“…In contrast to this positive regulation of RANTES by type I IFNs, two recent studies showed that type I IFNs negatively regulate KC and CCL2 production in an influenza/S. pneumoniae coinfection model (57,58). Collectively, type I IFNs appear to regulate differentially various proinflammatory mediators during infections in the lung, possibly depending on the magnitude of production and on the infection conditions.…”

Synergistic stimulation of type I interferons during influenza virus coinfection promotes Streptococcus pneumoniae colonization in mice

“…In contrast, the inhibitory effect of poly-ICLC and IFN-β was not seen in macrophages from Ifnar -/-mice. We had previously shown that the CCL2 response to S. pneumoniae was NF-κB-dependent and required sensing of peptidoglycan by Nod2 (17). To examine directly the inhibitory effect of poly-ICLC and IFN-β on Nod2 signaling, we used HEK293T cells transfected with a Nod2-expressing plasmid or empty vector control and NF-κB reporter plasmid.…”

“…The decline in the bacterial load requires the influx of monocytes/macrophages into the airway lumen (15). Recruitment of these cells correlates with the expression of the chemokine CCL2 and is deficient in mice lacking its receptor, CCR2, which is also required for early clearance (15,17). Recognition of pneumococci by pattern recognition receptors TLR2 and Nod2 - which sense lipid-modified constituents and muramyl dipeptide-containing (MDP-containing) peptidoglycan fragments, respectively - contributes to the production of CCL2, the influx of macrophages, and bacterial clearance.…”

The C-type lectin receptor Mincle binds to Streptococcus pneumoniae but plays a limited role in the anti-pneumococcal innate immune response

“…For example, the Toll-like receptor (TLR) members TLR2 and TLR9 detect pneumococcal cell wall components and CpG-rich DNA, respectively [9][10][11]. Among NOD-like receptors (NLRs), NOD2 recognizes pneumococcal peptidoglycan and NLRP3 is activated by PLY [12][13][14][15]. Moreover, AIM2 as well as another STING-dependent cytosolic DNA sensor detect pneumococcal nucleic acid in the host cell cytosol [7,12].…”