Co-ordinated Role of TLR3, RIG-I and MDA5 in the Innate Response to Rhinovirus in Bronchial Epithelium

The relative roles of the endosomal TLR3/7/8 versus the intracellular RNA helicases RIG-I and MDA5 in viral infection is much debated. We investigated the roles of each pattern recognition receptor in rhinovirus infection using primary bronchial epithelial cells. TLR3 was constitutively expressed; however, RIG-I and MDA5 were inducible by 8–12 h following rhinovirus infection. Bronchial epithelial tissue from normal volunteers challenged with rhinovirus in vivo exhibited low levels of RIG-I and MDA5 that were increased at day 4 post infection. Inhibition of TLR3, RIG-I and MDA5 by siRNA reduced innate cytokine mRNA, and increased rhinovirus replication. Inhibition of TLR3 and TRIF using siRNA reduced rhinovirus induced RNA helicases. Furthermore, IFNAR1 deficient mice exhibited RIG-I and MDA5 induction early during RV1B infection in an interferon independent manner. Hence anti-viral defense within bronchial epithelium requires co-ordinated recognition of rhinovirus infection, initially via TLR3/TRIF and later via inducible RNA helicases

Increased expression of Toll-like receptor 3 in intrahepatic biliary epithelial cells at sites of ductular reaction in diseased livers

Background Toll-like receptors (TLRs) may play active roles in both innate and adaptive immune responses in human intrahepatic biliary epithelial cells (HIBECs). The role of TLR3 expressed by HIBECs, however, remains unclear. Methods We determined the in vivo expression of TLRs in biopsy specimens derived from diseased livers immunohistochemically using a panel of monoclonal antibodies against human TLRs. We then examined the response of cultured HIBECs to a TLR3 ligand, polyinosinic–polycytidylic acid (polyI:C). Using siRNAs specific for Toll-IL-1R homology domain-containing adaptor molecule 1 (TICAM-1) and mitochondrial antiviral signaling protein (MAVS), we studied signaling pathways inducing IFN-β expression. Results The expression of TLR3 was markedly increased in biliary epithelial cells at sites of ductular reaction in diseased livers, including primary biliary cirrhosis (PBC), autoimmune hepatitis (AIH), and chronic viral hepatitis (CH) as compared to nondiseased livers. Although cultured HIBECs constitutively expressed TLR3 at both the protein and mRNA levels in vitro, the addition of polyI:C to culture media induced only minimal increases in IFN-β mRNA. In contrast, transfection of HIBECs with polyI:C induced a marked increase in mRNAs encoding a variety of chemokines/cytokines, including IFN-β, IL-6, and TNF-α. The induction of IFN-β mRNA was efficiently inhibited by an siRNA against MAVS but not against TICAM-1, indicating that the main signaling pathway for IFN-β induction following polyI:C transfection is via retinoic acid-inducible gene I (RIG-I)/melanoma differentiation-associated gene 5 (MDA5) in HIBECs. Conclusions TLR3 expression by biliary epithelial cells increased at sites of ductular reaction in diseased livers; further study will be necessary to characterize it’s in vivo physiological role

TLR4 activation mediates kidney ischemia/reperfusion injury

Ischemia/reperfusion injury (IRI) may activate innate immunity through the engagement of TLRs by endogenous ligands. TLR4 expressed within the kidney is a potential mediator of innate activation and inflammation. Using a mouse model of kidney IRI, we demonstrated a significant increase in TLR4 expression by tubular epithelial cells (TECs) and infiltrating leukocytes within the kidney following ischemia. TLR4 signaling through the MyD88-dependent pathway was required for the full development of kidney IRI, as both TLR4–/– and MyD88–/– mice were protected against kidney dysfunction, tubular damage, neutrophil and macrophage accumulation, and expression of proinflammatory cytokines and chemokines. In vitro, WT kidney TECs produced proinflammatory cytokines and chemokines and underwent apoptosis after ischemia. These effects were attenuated in TLR4–/– and MyD88–/– TECs. In addition, we demonstrated upregulation of the endogenous ligands high-mobility group box 1 (HMGB1), hyaluronan, and biglycan, providing circumstantial evidence that one or more of these ligands may be the source of TLR4 activation. To determine the relative contribution of TLR4 expression by parenchymal cells or leukocytes to kidney damage during IRI, we generated chimeric mice. TLR4–/– mice engrafted with WT hematopoietic cells had significantly lower serum creatinine and less tubular damage than WT mice reconstituted with TLR4–/– BM, suggesting that TLR4 signaling in intrinsic kidney cells plays the dominant role in mediating kidney damage