Hisashi Arase

Resistance of Fc receptor- deficient mice to fatal glomerulonephritis.

Immune complex-mediated inflammation is a common mechanism of various autoimmune diseases. Glomerulonephritis (GN) is one of these diseases, and the main mechanism of the induction of GN has been unclear. We examined the contribution of Fc receptors in the induction of nephrotoxic GN by establishing and analyzing mice deficient in the Fc receptor gamma chain (FcRgamma). Whereas all wild-type mice died from severe glomerulonephritis with hypernitremia by administration of anti-glomerular basement membrane (GBM) antibodies, all FcRgamma-deficient mice survived. Histologically, wild-type mice showed glomerular hypercellularity and thrombotic changes, whereas the renal tissue in FcRgamma-deficient mice was almost intact. Deposition of anti-GBM antibody as well as complement components in the GBM were equally observed in both wild-type and knockout mice. These results demonstrate that the triggering of this type of glomerulonephritis is completely dependent on FcR+ cells.

NKG2D-mediated Natural Killer Cell Protection Against Cytomegalovirus Is Impaired by Viral gp40 Modulation of Retinoic Acid Early Inducible 1 Gene Molecules

Natural killer (NK) cells play a critical role in the innate immune response against cytomegalovirus (CMV) infections. Although CMV encodes several gene products committed to evasion of adaptive immunity, viral modulation of NK cell activity is only beginning to be appreciated. A previous study demonstrated that the mouse CMV m152-encoded gp40 glycoprotein diminished expression of ligands for the activating NK cell receptor NKG2D on the surface of virus-infected cells. Here we have defined the precise ligands that are affected and have directly implicated NKG2D in immune responses to CMV infection in vitro and in vivo. Murine CMV (MCMV) infection potently induced transcription of all five known retinoic acid early inducible 1 (RAE-1) genes (RAE-1α, RAE-1β, RAE-1δ, RAE-1ɛ, and RAE-1γ), but not H-60. gp40 specifically down-regulated the cell surface expression of all RAE-1 proteins, but not H-60, and diminished NK cell interferon γ production against CMV-infected cells. Consistent with previous findings, a m152 deletion mutant virus (Δm152) was less virulent in vivo than the wild-type Smith strain of MCMV. Treatment of BALB/c mice with a neutralizing anti-NKG2D antibody before infection increased titers of Δm152 virus in the spleen and liver to levels seen with wild-type virus. These experiments demonstrate that gp40 impairs NK cell recognition of virus-infected cells through disrupting the RAE-1–NKG2D interaction.

Cutting edge : the mouse NK cell-associated antigen recognized by DX5 monoclonal antibody is CD49b (alpha 2 integrin, very late antigen 2)

DX5 mAb is a useful reagent because it stains NK cells from all mouse strains examined. We have identified the molecule recognized by DX5 mAb by using a retrovirus-mediated expression cloning system. A 5-kb cDNA encoding a protein that is reactive with the DX5 mAb was isolated from a NK cell cDNA library, and this molecule was identical with CD49b (very late Ag-2, α2 integrin). The DX5 mAb reacted with transfectants expressing CD49b, and binding of DX5 to the NK cells and CD49b transfectants was blocked in the presence of other anti-CD49b mAbs. When NK1.1+ NK cells were cultured with IL-2, they progressively lost reactivity with DX5 mAb as a consequence of cellular proliferation. Cytotoxicity mediated by the DX5+ NK cells was dramatically higher as compared with DX5− NK cells. Therefore, DX5 mAb recognizes CD49b and can be used to define functionally distinct subsets of NK cells.

PILRα Is a Herpes Simplex Virus-1 Entry Coreceptor That Associates with Glycoprotein B

Glycoprotein B (gB) is one of the essential components for infection by herpes simplex virus-1 (HSV-1). Although several cellular receptors that associate with glycoprotein D (gD), such as herpes virus entry mediator (HVEM) and Nectin-1, have been identified, specific molecules that mediate HSV-1 infection by associating with gB have not been elucidated. Here, we found that paired immunoglobulin-like type 2 receptor (PILR) alpha associates with gB, and cells transduced with PILRalpha become susceptible to HSV-1 infection. Furthermore, HSV-1 infection of human primary cells expressing both HVEM and PILRalpha was blocked by either anti-PILRalpha or anti-HVEM antibody. Our results demonstrate that cellular receptors for both gB and gD are required for HSV-1 infection and that PILRalpha plays an important role in HSV-1 infection as a coreceptor that associates with gB. These findings uncover a crucial aspect of the mechanism underlying HSV-1 infection.

Binding and uptake of H-ferritin are mediated by human transferrin receptor-1

Ferritin is a spherical molecule composed of 24 subunits of two types, ferritin H chain (FHC) and ferritin L chain (FLC). Ferritin stores iron within cells, but it also circulates and binds specifically and saturably to a variety of cell types. For most cell types, this binding can be mediated by ferritin composed only of FHC (HFt) but not by ferritin composed only of FLC (LFt), indicating that binding of ferritin to cells is mediated by FHC but not FLC. By using expression cloning, we identified human transferrin receptor-1 (TfR1) as an important receptor for HFt with little or no binding to LFt. In vitro, HFt can be precipitated by soluble TfR1, showing that this interaction is not dependent on other proteins. Binding of HFt to TfR1 is partially inhibited by diferric transferrin, but it is hindered little, if at all, by HFE. After binding of HFt to TfR1 on the cell surface, HFt enters both endosomes and lysosomes. TfR1 accounts for most, if not all, of the binding of HFt to mitogen-activated T and B cells, circulating reticulocytes, and all cell lines that we have studied. The demonstration that TfR1 can bind HFt as well as Tf raises the possibility that this dual receptor function may coordinate the processing and use of iron by these iron-binding molecules.

Cutting Edge: Negative Regulation of Immune Synapse Formation by Anchoring Lipid Raft to Cytoskeleton Through Cbp-EBP50-ERM Assembly

Ag recognition by T lymphocytes induces immune synapse formation and recruitment of signaling molecules into a lipid raft. Cbp/PAG is a Csk-associated membrane adapter protein exclusively localized in a lipid raft. We identified NHERF/EBP50 as a Cbp-binding molecule, which connects the membrane raft and cytoskeleton by binding to both Cbp through its PDZ domain and ezrin-radixin-moesin through the C terminus. Overexpression of Cbp reduced the mobility of the raft on the cell surface of unstimulated T cells and prevented synapse formation and subsequent T cell activation, whereas a mutant incapable of EBP50 binding restored both synapse formation and activation. These results suggest that anchoring of lipid raft to the cytoskeleton through Cbp-EBP50-ezrin-radixin-moesin assembly regulates membrane dynamism for synapse formation and T cell activation.

Efficient Leukocyte Ig-like Receptor Signaling and Crystal Structure of Disulfide-linked HLA-G Dimer

HLA-G is a nonclassical major histocompatibility complex class I (MHCI) molecule, which is expressed in trophoblasts and confers immunological tolerance in the maternal-fetal interface by binding to leukocyte Ig-like receptors (LILRs, also called as LIR/ILT/CD85) and CD8. HLA-G is expressed in disulfide-linked dimer form both in solution and at the cell surface. Interestingly, MHCI dimer formations have been involved in pathogenesis and T cell activation. The structure and receptor binding characteristics of MHCI dimers have never been evaluated. Here we performed binding studies showing that the HLA-G dimer exhibited higher overall affinity to LILRB1/2 than the monomer by significant avidity effects. Furthermore, the cell reporter assay demonstrated that the dimer formation remarkably enhanced the LILRB1-mediated signaling at the cellular level. We further determined the crystal structure of the wild-type dimer of HLA-G with the intermolecular Cys42-Cys42 disulfide bond. This dimer structure showed the oblique configuration to expose two LILR/CD8-binding sites upward from the membrane easily accessible for receptors, providing plausible 1:2 (HLA-G dimer:receptors) complex models. These results indicated that the HLA-G dimer conferred increased avidity in a proper structural orientation to induce efficient LILR signaling, resulting in the dominant immunosuppressive effects. Moreover, structural and functional implications for other MHCI dimers observed in activated T cells and the pathogenic allele, HLA-B27, are discussed.

Heme-mediated SPI-C induction promotes monocyte differentiation into iron-recycling macrophages

Splenic red pulp macrophages (RPM) degrade senescent erythrocytes and recycle heme-associated iron. The transcription factor SPI-C is selectively expressed by RPM and is required for their development, but the physiologic stimulus inducing Spic is unknown. Here, we report that Spic also regulated the development of F4/80(+)VCAM1(+) bone marrow macrophages (BMM) and that Spic expression in BMM and RPM development was induced by heme, a metabolite of erythrocyte degradation. Pathologic hemolysis induced loss of RPM and BMM due to excess heme but induced Spic in monocytes to generate new RPM and BMM. Spic expression in monocytes was constitutively inhibited by the transcriptional repressor BACH1. Heme induced proteasome-dependent BACH1 degradation and rapid Spic derepression. Furthermore, cysteine-proline dipeptide motifs in BACH1 that mediate heme-dependent degradation were necessary for Spic induction by heme. These findings are the first example of metabolite-driven differentiation of a tissue-resident macrophage subset and provide new insights into iron homeostasis.

Cutting Edge: KIR3DS1, a Gene Implicated in Resistance to Progression to AIDS, Encodes a DAP12-Associated Receptor Expressed on NK Cells That Triggers NK Cell Activation

The killer cell Ig-like receptor (KIR) gene, KIR3DS1, has been implicated in slowing disease progression in HIV infection; however, little is known about its expression, function, or ligand specificity. Using retrovirally transduced NKL cells and peripheral blood NK cells from KIR3DS1-positive donors we assessed expression of this gene by flow cytometry and its function by in vitro assays measuring KIR3DS1-induced cell-mediated cytotoxicity and cytokine production. In the present study, we demonstrate that KIR3DS1 is expressed on peripheral blood NK cells and triggers both cytotoxicity and IFN-γ production. Using cotransfection and coimmunoprecipitation, we found that KIR3DS1 associates with the ITAM-bearing adaptor, DAP12. Soluble KIR3DS1-Ig fusion proteins did not bind to EBV-transformed B lymphoid cell lines transfected with HLA-Bw4 80I or 80T allotypes, suggesting that if KIR3DS1 does recognize HLA-Bw4 ligands, this may be peptide dependent.

Non-muscle myosin IIA is a functional entry receptor for herpes simplex virus-1

Herpes simplex virus-1 (HSV-1), the prototype of the α-herpesvirus family, causes life-long infections in humans. Although generally associated with various mucocutaneous diseases, HSV-1 is also involved in lethal encephalitis. HSV-1 entry into host cells requires cellular receptors for both envelope glycoproteins B (gB) and D (gD). However, the gB receptors responsible for its broad host range in vitro and infection of critical targets in vivo remain unknown. Here we show that non-muscle myosin heavy chain IIA (NMHC-IIA), a subunit of non-muscle myosin IIA (NM-IIA), functions as an HSV-1 entry receptor by interacting with gB. A cell line that is relatively resistant to HSV-1 infection became highly susceptible to infection by this virus when NMHC-IIA was overexpressed. Antibody to NMHC-IIA blocked HSV-1 infection in naturally permissive target cells. Furthermore, knockdown of NMHC-IIA in the permissive cells inhibited HSV-1 infection as well as cell–cell fusion when gB, gD, gH and gL were coexpressed. Cell-surface expression of NMHC-IIA was markedly and rapidly induced during the initiation of HSV-1 entry. A specific inhibitor of myosin light chain kinase, which regulates NM-IIA by phosphorylation, reduced the redistribution of NMHC-IIA as well as HSV-1 infection in cell culture and in a murine model for herpes stromal keratitis. NMHC-IIA is ubiquitously expressed in various human tissues and cell types and, therefore, is implicated as a functional gB receptor that mediates broad HSV-1 infectivity both in vitro and in vivo. The identification of NMHC-IIA as an HSV-1 entry receptor and the involvement of NM-IIA regulation in HSV-1 infection provide an insight into HSV-1 entry and identify new targets for antiviral drug development.