Masahiro Onji

An essential role for the N-terminal fragment of Toll-like receptor 9 in DNA sensing

Toll-like receptor 9 (TLR9) is an innate immune sensor for microbial DNA that erroneously responds to self DNA in autoimmune disease. To prevent autoimmune responses, Toll-like receptor 9 is excluded from the cell surface and silenced until the N-terminal half of the ectodomain (TLR9N) is cleaved off in the endolysosome. Truncated Toll-like receptor 9 (TLR9C) senses ingested microbial DNA, although the precise role of the truncation remains controversial. Here we show that TLR9 is expressed on the surface of splenic dendritic cells. Following the cleavage of TLR9 in the endolysosome, N-terminal half of the ectodomain remains associated with truncated TLR9, forming the complex TLR9N+C. The TLR9-dependent cytokine production by Tlr9(-/-) dendritic cells is rescued by a combination of TLR9N and TLR9C, but not by TLR9C alone. These results demonstrate that the TLR9N+C complex is a bona fide DNA sensor.

Essential role for Toll-like receptor 7 (TLR7)-unique cysteines in an intramolecular disulfide bond, proteolytic cleavage and RNA sensing

Toll-like receptor 7 (TLR7) an innate immune sensor for microbial RNA, erroneously responds to self-derived RNA. To avoid autoimmune responses, TLR7 is suggested to be silenced until the N-terminal half of the TLR7 ectodomain (TLR7N) is cleaved off. Resultant truncated TLR7 (TLR7C) is thought to signal microbial RNA. We here show that TLR7N remains associated with TLR7C through a disulfide bond. By N-terminal amino acid sequencing, TLR7C was found to start at 461E or 462A. The newly established monoclonal anti-TLR7N showed that endogenous TLR7 in bone marrow-derived dendritic cells was almost all cleaved and cleaved TLR7N remained in endolysosomes. TLR7N in endolysosomes was linked with TLR7C by a disulfide bond. In contrast, TLR9 did not have a disulfide bond between TLR9N and TLR9C fragments. Among the cysteines unique to the ectodomain of TLR7 but not TLR9 (Cys98, Cys445, Cys475 and Cys722), Cys98 in TLR7N and Cys475 in TLR7C were required for an intramolecular disulfide bond. These cysteines were also needed for proteolytic cleavage of and RNA sensing by TLR7, but not for TLR7 trafficking from endoplasmic reticulum to endosomes. No response was seen in TLR7 mutants lacking the proteolytic cleavage site or TLR7C alone. These results demonstrate requirement for proteolytic cleavage and TLR7N in TLR7 responses and indicate RNA sensing by TLR7N + TLR7C.

Targeting cell surface TLR7 for therapeutic intervention in autoimmune diseases

Toll-like receptor 7 (TLR7) senses microbial-derived RNA but can also potentially respond to self-derived RNA. To prevent autoimmune responses, TLR7 is thought to localize in endolysosomes. Contrary to this view, we show here that TLR7 is present on the cell surface of immune cells and that TLR7 responses can be inhibited by an anti-TLR7 antibody. The anti-TLR7 antibody is internalized with TLR7 and accumulates in endolysosomes as an immune complex. TLR7 responses in dendritic cells, macrophages and B cells are all inhibited by the anti-TLR7 antibody. Furthermore, the anti-TLR7 antibody inhibits in vivo cytokine production induced by a TLR7 ligand. Spontaneous TLR7 activation in Unc93b1(D34A/D34A) mice causes lethal inflammation. Progressive inflammation such as splenomegaly, thrombocytopenia and chronic active hepatitis are ameliorated by anti-TLR7 antibody treatment. These results demonstrate that cell surface TLR7 is a promising target for therapeutic intervention in autoimmune diseases.

Endocytosis-free DNA sensing by cell surface TLR9 in neutrophils: rapid defense with autoimmune risks.

TLR9 senses microbial DNA, but may also respond to self‐DNA. To prevent the initiation of innate immune responses to self‐DNA, TLR9 is thought to sense microbial DNA in endolysosomes, and not at the cell surface. A report by Lindau et al. in this issue of the European Journal of Immunology [Eur. J. Immunol. 2013. 43: 2101–2113] shows that TLR9 is expressed on the surface of human and mouse neutrophils and, furthermore, shows that cell surface TLR9, instead of endosomal TLR9, senses DNA in neutrophils. These findings demonstrate that DNA sensing by TLR9 in neutrophils is quite distinct from that in DCs or macrophages. The unique DNA sensing by cell surface TLR9 in neutrophils may reflect their role in inducing rapid inflammation by degranulation with a minimal role in engulfing microbial products for antigen presentation.

Clinical characteristics of drug‐induced liver injury in the elderly

Aim:  The average age of Japanese patients with drug‐induced liver injury (DILI) is expected to rise as the population ages. The aim of this study was to evaluate the clinical characteristics of DILI in elderly Japanese subjects.

Cleavage of Toll-Like Receptor 9 Ectodomain Is Required for In Vivo Responses to Single Strand DNA

Mouse toll-like receptor 9 (TLR9) is an endosomal sensor for single-stranded DNA. TLR9 is transported from the endoplasmic reticulum to endolysosomes by a multiple transmembrane protein Unc93 homolog B1, and proteolytically cleaved at its ectodomain. The structure of TLR9 and its biochemical analyses have shown that the proteolytic cleavage of TLR9 ectodomain enables TLR9-dimerization and TLR9 activation. However, the requirement of TLR9 cleavage in vivo has not been studied. We here show that the 13 amino acids deletion at the cleavage site made TLR9 resistant to proteolytic cleavage. The deletion mutation in the Tlr9 gene impaired TLR9-dependent cytokine production in conventional dendritic cells from the mutant mice. Not only in vitro, in vivo production of inflammatory cytokines (TNF-α and IL-12p40), chemokine (CCR5/RANTES), and type I interferon (IFN-α) induced by administration of TLR9 ligand was also impaired. These results demonstrate that the TLR9 cleavage is required for TLR9 responses in vivo.

Serum-inducible protein (IP)-10 is a disease progression-related marker for non-alcoholic fatty liver disease

BackgroundThe molecular pathogenesis of non-alcoholic steatohepatitis (NASH) is not well defined. The objective of the present study was to identify disease progression-related cytokines and investigate the molecular pathogenesis of such changes in NASH.MethodsA study population of 20 non-alcoholic fatty liver (NAFL) and 59 NASH patients diagnosed by liver biopsy and 15 healthy volunteers was recruited. The serum pro- and anti-inflammatory cytokines were measured by a multiple enzyme-linked immunosorbent assay. The hepatic mRNA expressions of cytokines were measured by real-time PCR. A monocyte cell line was stimulated with Toll-like receptor (TLR) ligand under a high glucose and insulin condition, and cellular cytokine mRNA expression was quantified.ResultsOne group of cytokines was higher in NAFL and NASH than in controls, while another group was higher in NASH than in NAFL and controls. The NASH-specific second group included interleukin (IL)-15 and interferon-γ-inducible protein (IP)-10. In particular, IP-10 was higher in NAFL than in controls and higher in NASH than in NAFL and controls. The sensitivity to diagnose NASH was 90%, with specificity of 50%. Insulin resistance reflecting a high glucose and insulin condition resulted in higher IP-10 mRNA expression in the monocyte cell line only with concomitant TLR-2 stimulation.ConclusionsIP-10 is a sensitive marker of the need for liver biopsy. Insulin resistance with bacteria-related TLR-2 stimulation might induce IP-10 production from monocytes. Insulin resistance and intestinal barrier function should be intensively controlled to prevent progression from NAFL to NASH.

Oxidative stress controlling agents are effective for small intestinal injuries induced by non-steroidal anti-inflammatory drugs.

Video‐capsule endoscopy (VCE) has shown that intestinal ulcers are common in non‐steroidal anti‐inflammatory drugs (NSAIDs) users, although the mechanisms and management have not been clearly defined. To explore the contribution of oxidative stress and potential of anti‐oxidants for NSAIDs‐induced intestinal ulcers, we assessed human serum oxidative stress balance and the effect of anti‐oxidants using a mouse model.