Neutrophilic Granule Protein Is a Novel Murine LPS Antagonist.

Neutrophilic granule protein (NGP) was previously reported as a granular protein of neutrophils in mouse, but the function has not been known clearly. We found the presence of the possible signal peptide in NGP and validated this protein is circulating in the bloodstream. In our findings, NGP is being modified post-translationally in Golgi apparatus and endoplasmic reticulum, which is a universal character of secretory molecules with a signal peptide. The secreted NGP protein could be detected both in vitro and in vivo. NGP has sequence similarity with an antimicrobial protein cathelicidin, and we observed the aspect of inflammation of NGP. Interestingly, NGP interacts with the complex of LPS and LPS binding protein (LBP). This interaction blocks the binding of the complex of LPS and LBP to TLR4 and the downstream inflammatory signals. Furthermore, the inhibitory function of NGP against the inflammatory effect of LPS could be observed in both in vitro and in vivo. With these findings, we report NGP is a novel secretory protein to mask LPS and inhibit its function.

Oxygen Tension Regulates Lysosomal Activation and Receptor Tyrosine Kinase Degradation.

Oxygen sensing is crucial for adaptation to variable habitats and physiological conditions. Low oxygen tension, or hypoxia, is a common feature of solid tumors, and hypoxic tumors are often more aggressive and resistant to therapy. Here we show that, in cultured mammalian cells, hypoxia suppressed lysosomal acidification/activation and receptor tyrosine kinase (RTK) degradation. Hypoxia down-regulated mTORc1, reducing its ability to activate transcription factor EB (TFEB), a master regulator of V-ATPase, the lysosomal proton pump. Hypoxia prevented epidermal growth factor receptor (EGFR) degradation in tumor tissues, whereas activation of lysosomes enhanced tumor cell response to anti-EGFR treatment. Our results link oxygen tension and lysosomal activity, provide a molecular explanation of the malignant phenotype associated with hypoxic tumors, and suggest activation of lysosomes may provide therapeutic benefit in RTK-targeted cancer therapy.

CXCL10 expressing hematopoietic-derived cells are requisite in defense against HSV-1 infection in the nervous system of CXCL10 deficient mice.

The chemokine CXCL10 is crucial for the control of viral replication through the regulation of mobilization of antigen-specific T cells to sites of infection. CXCL10 is highly expressed both at sites of inflammation as well as constitutively within lymphoid organs by both bone marrow (BM)-derived and non-BM-derived cells. However, the relative immunologic importance of CXCL10 expressed by these divergent sources relative to HSV-1 infection is unknown. Using mouse chimeras reconstituted with either wild type or CXCL10 deficient mouse BM, we show BM-derived, radiation-sensitive cells from wild type mice were solely responsible for resistance to HSV-1 in the trigeminal ganglia and brain stem. The resistance was not reflected by a deficiency in the recruitment of effector cells to sites of inflammation or expression of chemokines or IFN-gamma and likely results from additional, yet-to-be-determined factors emanating from wild type, BM-derived cells.

VEGF-A expression by HSV-1-infected cells drives corneal lymphangiogenesis.

Inflammatory lymphangiogenesis plays a crucial role in the development of inflammation and transplant rejection. The mechanisms of inflammatory lymphangiogenesis during bacterial infection, toll-like receptor ligand administration, and wound healing are well characterized and depend on ligands for the vascular endothelial grow factor receptor (VEGFR) 3 that are produced by infiltrating macrophages. But inflammatory lymphangiogenesis in nonlymphoid tissues during chronic viral infection is unstudied. Herpes simplex virus 1 (HSV-1) infection of the cornea is a leading cause of blindness and depends on aberrant host immune responses to antigen within the normally immunologically privileged cornea. We report that corneal HSV-1 infection drives lymphangiogenesis and that corneal lymphatics persist past the resolution of infection. The mechanism of HSV-1-induced lymphangiogenesis was distinct from the described mechanisms of inflammatory lymphangiogenesis. HSV-1-elicited lymphangiogenesis was strictly dependent on VEGF-A/VEGFR-2 signaling but not on VEGFR-3 ligands. Macrophages played no role in the induction of lymphangiogenesis and were not a detectable source of VEGF-A. Rather, using VEGF-A reporter transgenic mice, we have identified infected epithelial cells as the primary source of VEGF-A during HSV-1 infection. Our results indicate that HSV-1 directly induces vascularization of the cornea through up-regulation of VEGF-A expression.

Dysregulation of CXCR3 signaling due to CXCL10 deficiency impairs the antiviral response to herpes simplex virus 1 infection.

The chemokine, CXCL10, chemotactic for NK cells, activated T cells, and dendritic cells is highly expressed during viral infections, including HSV-1. The importance of this chemokine to the control of HSV-1 infection was tested using mice deficient in CXCL10 (CXCL10(-/-)). Following corneal infection, HSV-1 viral titers were elevated in the nervous system of CXCL10(-/-) mice, which correlated with defects in leukocyte recruitment including dendritic cells, NK cells, and HSV-1-specific CD8(+) T cells to the brain stem. In the absence of NK cells and HSV-1-specific CD8(+) T cells in wild-type (WT) or CXCL10(-/-) mice, similar levels of virus were recovered in the nervous system, suggesting these cells are responsible for the observed defects in the control of viral replication in CXCL10(-/-) mice. Leukocyte mobilization was also compared between WT, CXCL10(-/-), and mice deficient in the only known receptor for CXCL10, CXCR3 (CXCR3 (-/-)). NK cell mobilization was comparably reduced in both CXCL10(-/-) and CXCR3(-/-) mice relative to WT animals. However, the reduction in mobilization of HSV-1-specific CD8(+) T cells in CXCL10(-/-) was not observed in CXCR3(-/-) mice following HSV-1 infection. The defect was not the result of an alternative receptor for CXCL10, as Ag-specific CD8(+) T cell recruitment was not reduced in mice which were deficient in both CXCL10 and CXCR3. Thus, CXCL10 deficiency results in reduced mobilization of HSV-1-specific CD8(+) T cells as a result of dysregulation of CXCR3 signaling.

Lymphoid precursors are directed to produce dendritic cells as a result of TLR9 ligation during herpes infection.

Hematopoietic stem and progenitor cells were previously found to express Toll-like receptors (TLRs), suggesting that bacterial/viral products may influence blood cell formation. We now show that common lymphoid progenitors (CLPs) from mice with active HSV-1 infection are biased to dendritic cell (DC) differentiation, and the phenomenon is largely TLR9 dependent. Similarly, CLPs from mice treated with the TLR9 ligand CpG ODN had little ability to generate CD19+ B lineage cells and had augmented competence to generate DCs. TNFalpha mediates the depletion of late-stage lymphoid progenitors from bone marrow in many inflammatory conditions, but redirection of lymphopoiesis occurred in TNFalpha-/- mice treated with CpG ODN. Increased numbers of DCs with a lymphoid past were identified in Ig gene recombination substrate reporter mice treated with CpG ODN. TLR9 is highly expressed on lymphoid progenitors, and culture studies revealed that those receptors, rather than inflammatory cytokines, accounted for the production of several types of functional DCs. Common myeloid progenitors are normally a good source of DCs, but this potential was reduced by TLR9 ligation. Thus, alternate differentiation pathways may be used to produce innate effector cells in health and disease.

The role of chemokines during herpes simplex virus-1 infection.

Herpes simplex virus-type 1 is among the most prevalent and successful humans pathogens. Although infection is largely uncomplicated in the immunocompetent human host, HSV-1 infection can cause blinding corneal disease, and individuals with defects in innate or adaptive immunity are susceptible to herpes simplex encephalitis. Chemokines regulate leukocyte trafficking to inflamed tissues and play a crucial role in orchestrating the immune response to HSV-1 infection. In this review we will focus on the pathways that induce chemokine expression during HSV-1 infection and the implications of chemokine signaling on control of viral replication.