The TLR2/NOD2/RICK signaling axis regulates stimulus-specific IL-10 production

Recognition and response to gram-positive bacteria by macrophages and dendritic cells is mediated in part through TLR2. We found that that Streptococcus pneumoniae cell wall fragments, containing primarily peptidoglycan and teichoic acids, induced prodigious secretion of IL-10 from macrophages and dendritic cells and was dependent on TLR2 and NOD2, a cytoplasmic CARD-NACHT-LRR protein encoded by Card15. IL-10 secretion in response to cell walls was also dependent on RICK/RIP2, a kinase associated with NOD2, and MYD88 but independent of the ERK/p38 pathway. The reduction of IL-10 secretion by cell wall-activated NOD2-deficient myeloid–derived cells translated into downstream effects on IL-10 target gene expression and elevations in subsets of pro-inflammatory cytokine expression normally restrained by autocrine/paracrine effects of IL-10. Since NOD2 is linked to aberrant immune responses in Crohn’s Disease patients bearing mutations in CARD15, the temporal and quantitative effects of the TLR2/NOD/RICK pathway on IL-10 secretion may affect homeostatic control of immune responses to gram-positive bacteria. Keywords: immune response simulated pathogen response KO mice were treated with a cel wall extract and evaluated for immune response 1 hr and 4 hrs after treatment