CLEC4F, a member of C-type lectin, was first purified from rat liver extract with high binding affinity to fucose, galactose (Gal), N-acetylgalactosamine (GalNAc), and un-sialylated glucosphingolipids with GalNAc or Gal terminus. However, the biological functions of CLEC4F have not been elucidated. To address this question, we examined the expression and distribution of murine CLEC4F, determined its binding specificity by glycan array, and investigated its function using CLEC4F knockout (Clec4f−/−) mice. We found that CLEC4F is a heavily glycosylated membrane protein co-expressed with F4/80 on Kupffer cells. In contrast to F4/80, CLEC4F is detectable in fetal livers at embryonic day 11.5 (E11.5) but not in yolk sac, suggesting the expression of CLEC4F is induced as cells migrate from yolk cells to the liver. Even though CLEC4F is not detectable in tissues outside liver, both residential Kupffer cells and infiltrating mononuclear cells surrounding liver abscesses are CLEC4F-positive upon Listeria monocytogenes (L. monocytogenes) infection. While CLEC4F has strong binding to Gal and GalNAc, terminal fucosylation inhibits CLEC4F recognition to several glycans such as Fucosyl GM1, Globo H, Bb3∼4 and other fucosyl-glycans. Moreover, CLEC4F interacts with alpha-galactosylceramide (α-GalCer) in a calcium-dependent manner and participates in the presentation of α-GalCer to natural killer T (NKT) cells. This suggests that CLEC4F is a C-type lectin with diverse binding specificity expressed on residential Kupffer cells and infiltrating monocytes in the liver, and may play an important role to modulate glycolipids presentation on Kupffer cells.

IntroductionDecoy receptor 3 (DcR3) is a soluble tumor necrosis factor receptor (TNFR) overexpressed in various tumors, including lung cancers, 1 gastrointestinal tract tumors, 2 virus-associated lymphomas, 3 malignant gliomas, 4 and pancreatic cancers. 5 DcR3 suppresses the activation and differentiation of dendritic cells (DCs) 6 and macrophages, 7 and enhances osteoclast differentiation 8 and angiogenesis. 9 Moreover, DcR3 is shown to sensitize cells to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. 10 Moreover, almost all serum DcR3 ϩ individuals (98.8%; 82 of 83 patients) had malignancy, 11 and DcR3 overexpression was found to be associated with shortened duration of overall survival in patients with cancer. 12 Therefore, DcR3 is an important immunosuppressive factor in promoting tumor growth in patients with cancer.DCs are the most potent antigen-presenting cells capable of priming tumor-specific T cells. The sentinel lymph node (SLN) is the first draining lymph node from the area in which a tumor is located, and the numbers of DC are reduced in SLNs from some patients with cancer. 13 In our previous study, we found the total numbers of CD14 ϩ monocytederived DCs decreased significantly when incubated with DcR3. 6 Thus, we are interested to know whether DcR3 is one of the tumor-associated factors that affect DC survival, as well as to dissect the signaling cascades leading to DC apoptosis.Apart from neutralizing endogenous TL1A to promote angiogenesis, the pleiotropic effects of DcR3 described here are independent of its interaction with 3 known ligands-FasL, LIGHT, and TL1A. Moreover, recombinant protein comprising the heparin-binding domain (HBD) of DcR3 and Fc portion of human IgG 1 (HBD.Fc), which is unable to interact with LIGHT, FasL, or TL1A, has same effect as DcR3.Fc to modulate macrophage differentiation and to activate PKC. 14,15 This indicates that DcR3-triggered signaling cascade is mediated by interaction with the heparan sulfate proteoglycans (HSPGs) on cell surfaces.PKC is a family of serine/threonine kinases grouped into 3 subfamilies based on their structures and cofactors required for activation: the conventional (␣, ␤I, ␤II, and ␥), the novel (␦, ⑀, , and ), and the atypical ( and /) isoforms. 16 The conventional PKCs are activated by diacylglycerol and phosphatidylserine in the presence of Ca 2ϩ . The novel PKCs are activated by diacylglycerol and phosphatidylserine but are independent of Ca 2ϩ , and the atypical PKCs appear to respond only to phosphatidylserine. It is interesting to note that the selective inhibitor of PKC-␦, rottlerin, and a dominant-negative mutant of PKC-␦ attenuate apoptosis induced by phorbol ester, H 2 O 2 , UV radiation, taxol and etoposide, 17,18 indicating that PKC-␦ is involved in cell apoptosis. Previously, we have shown that DcR3.Fc (3 g/mL) modulates CD14 ϩ monocyte-derived DC differentiation. 6 Recently, we further observed that a higher concentration of DcR3.Fc (10 g/mL) induces DC apoptosis. Therefore, we compared the effects of DcR...

Chronic kidney disease (CKD) is an emerging worldwide public health problem. Inflammatory cell infiltration and activation during the early stages in injured kidneys is a common pathologic feature of CKD. Here, we determined whether an important inflammatory regulator, triggering receptor expressed on myeloid cells (TREM)-1, is upregulated in renal tissues collected from mouse ureteral obstruction-induced nephritis. TREM-1 is crucial for modulating macrophage polarization, and has a pivotal role in mediating tubular injury and interstitial collagen deposition in obstructive nephritis. Lysates from nephritic kidneys triggered a TREM-1-dependent M1 polarization ex vivo, consistent with the observation that granulocyte-macrophage colony-stimulating factor (GM-CSF)-derived M1 macrophages express higher levels of TREM-1 in comparison with M-CSF-derived cells. Moreover, agonistic TREM-1 cross-link significantly strengthens the inductions of iNOS and GM-CSF in M1 cells. These observations are validated by a strong clinical correlation between infiltrating TREM-1-expressing/iNOS-positive macrophages and renal injury in human obstructive nephropathy. Thus, TREM-1 may be a potential diagnostic and therapeutic target in human kidney disease.

Tumor-associated macrophages (TAMs) are the major component of tumor-infiltrating leukocytes. TAMs are heterogeneous, with distinct phenotypes influenced by the microenvironment surrounding tumor tissues. Decoy receptor 3 (DcR3), a member of the TNFR superfamily, is overexpressed in tumor cells and is capable of modulating host immunity as either a neutralizing decoy receptor or an effector molecule. Upregulation of DcR3 has been observed to correlate with a poor prognosis in various cancers. However, the mechanisms underlying the DcR3-mediated tumor-promoting effect remain unclear. We previously demonstrated that DcR3 modulates macrophage activation toward an M2-like phenotype in vitro and that DcR3 downregulates MHC class II expression in TAMs via epigenetic control. To investigate whether DcR3 promotes tumor growth, CT26-DcR3 stable transfectants were established. Compared with the vector control clone, DcR3-transfectants grew faster and resulted in TAM infiltration. We further generated CD68 promoter-driven DcR3 transgenic (Tg) mice to investigate tumor growth in vivo. Compared with wild-type mice, macrophages isolated from DcR3-Tg mice displayed higher levels of IL-10, IL-1ra, Ym1, and arginase activity, whereas the expression of IL-12, TNF-α, IL-6, NO, and MHC class II was downregulated. Significantly enhanced tumor growth and spreading were observed in DcR3-Tg mice, and the enhanced tumor growth was abolished by arginase inhibitor N-ω-hydroxy-l-norarginine and histone deacetylase inhibitor sodium valproate. These results indicated that induction of TAMs is an important mechanism for DcR3-mediated tumor progression. Our findings also suggest that targeting DcR3 might help in the development of novel treatment strategies for tumors with high DcR3 expression.

Klebsiella pneumoniae magA (for mucoviscosity-associated gene A) is linked to the pathogenesis of primary pyogenic liver abscess, but the underlying mechanism by which magA increases pathogenicity is not well elucidated. In this study, we investigated the role of the capsular polysaccharides (CPS) in the pathogenesis of magA ؉ K. pneumoniae by comparing host immunity to magA ؉ K. pneumoniae and a ⌬magA mutant. We found that Toll-like receptor 4 recognition by magA ؉ K. pneumoniae was hampered by the mucoviscosity of the magA ؉ K. pneumoniae CPS. Interestingly, monoclonal antibodies (MAbs) against magA ؉ K. pneumoniae CPS recognized all of the K1 strains tested but not the ⌬magA and non-K1 strains. Moreover, the anti-CPS MAbs protected mice from magA ؉ K. pneumoniae-induced liver abscess formation and lethality. This indicates that the K1 epitope is a promising target for vaccine development, and anti-CPS MAbs has great potential to protect host from K1 strain-induced mortality and morbidity in diabetic and other immunocompromised patients in the future.