Role of novel rat-specific Fc receptor in macrophage activation associated with crescentic glomerulonephritis.
ABSTRACT Crescentic glomerulonephritis (Crgn) is a complex disease where the initial insult is often the glomerular deposition of antibodies against intrinsic or deposited antigens in the glomerulus. The role of Fc receptors in the induction and progression of Crgn is increasingly recognized, and our previous studies have shown that copy number variation in Fcgr3 partially explains the genetic susceptibility of the Wistar-Kyoto (WKY) rat to nephrotoxic nephritis, a rat model of Crgn. The Fcgr3-related sequence (Fcgr3-rs) is a novel rat-specific Fc receptor with a cytoplasmic domain 6 amino acids longer than its paralogue, Fcgr3. The Fcgr3-rs gene is deleted from the WKY rat genome, and this deletion is associated with enhanced macrophage activity in this strain. Here, we investigated the mechanism by which the deletion of Fcgr3-rs in the WKY strain leads to increased macrophage activation. By lentivirus-mediated gene delivery, we generated stably transduced U937 cells expressing either Fcgr3-rs or Fcgr3. In these cells, which lack endogenous Fcgr3 receptors, we show that Fcgr3-rs interacts with the common Fc-γ chain but that Fc receptor-mediated phagocytosis and signaling are defective. Furthermore, in primary macrophages, expression of Fcgr3-rs inhibits Fc receptor-mediated functions, because WKY bone marrow-derived macrophages transduced with Fcgr3-rs had significantly reduced phagocytic activity. This inhibitory effect on phagocytosis was mediated by the novel cytoplasmic domain of Fcgr3-rs. These results suggest that Fcgr3-rs may act to inhibit Fcgr3-mediated signaling and phagocytosis and could be considered as a novel mechanism in the modulation of Fc receptor-mediated cell activation in autoimmune diseases.
Article: Nephrotoxic nephritis is mediated by Fcgamma receptors on circulating leukocytes and not intrinsic renal cells.[show abstract] [hide abstract]
ABSTRACT: There is evidence that mesangial cells express Fcgamma receptors in vitro, but the in vivo relevance of this is not known. FcRgamma-/- mice lack the gamma chain signaling subunit and therefore do not express the activator Fcgamma receptors (FcgammaRI and FcgammaRIII) or the high affinity IgE receptor, FcepsilonRI. FcRgamma-/- mice were protected from renal inflammation following the induction of accelerated nephrotoxic nephritis using sheep anti-mouse glomerular basement membrane anti-serum in mice sensitized to sheep IgG. In order to test whether Fcgamma receptors had a role on intrinsic renal cells during nephritis, bone marrow cells were transplanted between wild-type (WT) mice and mice with a gene-targeted deletion of FcRgamma. Donor marrow reconstitution was confirmed by flow cytometric analysis of peripheral blood for FcgammaRIII, and the susceptibility of the transplanted mice to accelerated nephrotoxic nephritis was tested. Following the induction of nephrotoxic nephritis, FcRgamma-/- mice transplanted with WT bone marrow developed as much renal disease as WT mice transplanted with WT bone marrow. In contrast, WT mice transplanted with FcRgamma-/- marrow were completely protected from glomerular crescents, thrombosis, albuminuria and renal impairment, as were FcRgamma-/- mice transplanted with FcRgamma-/- marrow. Mice with FcRgamma-/- marrow had prolonged survival, but by day 28 after nephrotoxic serum injection they had developed mesangial hypercellularity and a macrophage influx caused by non-FcRgamma dependent mechanisms. Despite previous evidence that mesangial cells express Fcgamma receptors in vitro, they have no role in an FcRgamma-dependent model of glomerulonephritis in vivo.Kidney International 01/2003; 62(6):2087-96. · 6.61 Impact Factor
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ABSTRACT: Exposure of macrophages to bacterial products such as lipopolysaccharide (LPS) results in activation of the NF-kappaB transcription factor, which orchestrates a gene expression programme that underpins the macrophage-dependent immune response. These changes include the induction or repression of a wide range of genes that regulate inflammation, cell proliferation, migration and cell survival. This process is tightly regulated and loss of control is associated with conditions such as septic shock, inflammatory diseases and cancer. To study this response, it is important to have in vitro model systems that reflect the behaviour of cells in vivo. In addition, it is necessary to understand the natural differences that can occur between individuals. In this report, we have investigated and compared the LPS response in macrophage derived cell lines and peripheral blood mononuclear cell (PBMC) derived macrophages. Gene expression profiles were determined following LPS treatment of THP-1 cells for 1 and 4 hours. LPS significantly induced or repressed 72 out of 465 genes selected as being known or putative NF-kappaB target genes, which exhibited 4 temporal patterns of expression. Results for 34 of these genes, including several genes not previously identified as LPS target genes, were validated using real time PCR. A high correlation between microarray and real time PCR data was found. Significantly, the LPS induced expression profile of THP-1 cells, as determined using real time PCR, was found to be very similar to that of human PBMC derived macrophages. Interestingly, some differences were observed in the LPS response between the two donor PBMC macrophage populations. Surprisingly, we found that the LPS response in U937 cells was dramatically different to both THP-1 and PBMC derived macrophages. This study revealed a dynamic and diverse transcriptional response to LPS in macrophages, involving both the induction and repression of gene expression in a time dependent manner. Moreover, we demonstrated that the LPS induced transcriptional response in the THP-1 cell line is very similar to primary PBMC derived macrophages. Therefore, THP-1 cells represent a good model system for studying the mechanisms of LPS and NF-kappaB dependent gene expression.BMC Immunology 02/2007; 8:1. · 2.53 Impact Factor
Article: In the absence of other Fc receptors, Fc gamma RIIIA transmits a phagocytic signal that requires the cytoplasmic domain of its gamma subunit.[show abstract] [hide abstract]
ABSTRACT: The transmembrane isoform of Fc gamma RIII, Fc gamma RIIIA, is found on NK cells, cultured monocytes, and tissue macrophages in association with a dimer of an accessory subunit, either gamma or zeta. Functions of individual Fc receptors have been difficult to analyze due to coexpression of the receptors on hematopoietic cells and permanent cell lines expressing Fc receptors. cDNAs for the alpha and gamma subunits of Fc gamma RIIIA were cotransfected into COS-1 cells, which lack endogenous Fc receptors, to evaluate receptor-mediated phagocytosis and changes in [Ca2+]i. Transfectants both bound and phagocytosed IgG-sensitized erythrocytes and, following activation of Fc gamma RIIIA, increased [Ca2+]i. The gamma subunit was essential both for the surface expression of the receptor and for transduction of the phagocytic signal. Truncation of the gamma subunit cytoplasmic domain (amino acids 65-80) eliminated phagocytic function. Phorbol ester inhibited phagocytosis in a concentration-dependent manner, but did not affect IgG-sensitized erythrocytes binding, suggesting that a protein kinase C-dependent pathway inhibits phagocytosis. The data indicate that a tyrosine containing cytoplasmic domain within the gamma subunit is required for phagocytosis by Fc gamma RIIIA.Journal of Clinical Investigation 11/1993; 92(4):1967-73. · 15.39 Impact Factor