Novel roles for the IgG Fc glycan Anthony, Robert M.; Wermeling, Fredrik; Ravetch, Jeffrey V.
Annals of the New York Academy of Sciences,
April 2012, Volume:
1253, Issue:
1
Journal Article
Peer reviewed
IgG antibodies trigger leukocyte activation and inflammation by forming immune complexes that crosslink activating Fcγ receptors (FcγRs). This is essential to combat infection, but detrimental if ...antibodies target or cross‐react with autoantigens. The high specificity and long serum half‐life of IgG antibodies confers tremendous therapeutic potential. Indeed, antibodies have been successfully employed to target cancers, autoreactive B cells, and pro‐inflammatory cytokines. Conversely, IgG antibodies can also initiate anti‐inflammatory responses. In the form of intravenous immunoglobulin (IVIG), IgGs are routinely administered to treat inflammatory autoimmune diseases. Importantly, the N‐linked glycans on the IgG Fc are absolutely required for initiating these IgG effector functions. In fact, the Fc glycan composition dictates IgG affinity to individual FcγRs, and in a broader sense, binding to different FcγRs classes: activating, inhibitory, and anti‐inflammatory (dendritic cell‐specific ICAM‐3 grabbing nonintegrin, DC‐SIGN). The Fc glycan requirements to initiate and suppress inflammation will be discussed herein.
The anti-inflammatory activity of intravenous Ig (IVIG) results from a minor population of the pooled IgG molecules that contains terminal α2,6-sialic acid linkages on their Fc-linked glycans. These ...anti-inflammatory properties can be recapitulated with a fully recombinant preparation of appropriately sialylated IgG Fc fragments. We now demonstrate that these sialylated Fcs require a specific C-type lectin, SIGN-R1, (specific ICAM-3 grabbing non-integrin-related 1) expressed on macrophages in the splenic marginal zone. Splenectomy, loss of SIGN-R1⁺ cells in the splenic marginal zone, blockade of the carbohydrate recognition domain (CRD) of SIGN-R1, or genetic deletion of SIGN-R1 abrogated the anti-inflammatory activity of IVIG or sialylated Fc fragments. Although SIGN-R1 has not previously been shown to bind to sialylated glycans, we demonstrate that it preferentially binds to 2,6-sialylated Fc compared with similarly sialylated, biantennary glycoproteins, thus suggesting that a specific binding site is created by the sialylation of IgG Fc. A human orthologue of SIGN-R1, DC-SIGN, displays a similar binding specificity to SIGN-R1 but differs in its cellular distribution, potentially accounting for some of the species differences observed in IVIG protection. These studies thus identify an antibody receptor specific for sialylated Fc, and present the initial step that is triggered by IVIG to suppress inflammation.
We aimed to search for common features in the autoreactive T cell receptor (TCR) repertoire in patients with rheumatoid arthritis (RA), focusing on the newly identified candidate antigen ...citrullinated Tenascin C (cit-TNC). Mononuclear cells from peripheral blood or synovial fluid of eight RA-patients positive for the RA-associated HLA-DRB1*04:01 allele were in-vitro cultured with recently identified citrullinated peptides from Tenascin C. Antigen-specific T cells were isolated using peptide-HLA tetramer staining and subsequently single-cell sequenced for paired alpha/beta TCR analyses by bioinformatic tools. TCRs were re-expressed for further studies of antigen-specificity and T cell responses. Autoreactive T cell lines could be grown out from both peripheral blood and synovial fluid. We demonstrate the feasibility of retrieving true autoreactive TCR sequences by validating antigen-specificity in T cell lines with re-expressed TCRs. One of the Tenascin C peptides, cit-TNC22, gave the most robust T cell responses including biased TCR gene usage patterns. The shared TCR-beta chain signature among the cit-TNC22-specific TCRs was evident in blood and synovial fluid of different patients. The identification of common elements in the autoreactive TCR repertoire gives promise to the possibility of both immune monitoring of the autoimmune components in RA and of future antigen- or TCR-targeted specific intervention in subsets of patients.
FNDC4 is a secreted factor sharing high homology with the exercise-associated myokine irisin (FNDC5). Here we report that Fndc4 is robustly upregulated in several mouse models of inflammation as well ...as in human inflammatory conditions. Specifically, FNDC4 levels are increased locally at inflamed sites of the intestine of inflammatory bowel disease patients. Interestingly, administration of recombinant FNDC4 in the mouse model of induced colitis markedly reduces disease severity compared with mice injected with a control protein. Conversely, mice lacking Fndc4 develop more severe colitis. Analysis of binding of FNDC4 to different immune cell types reveals strong and specific binding to macrophages and monocytes. FNDC4 treatment of bone marrow-derived macrophages in vitro results in reduced phagocytosis, increased cell survival and reduced proinflammatory chemokine expression. Hence, treatment with FNDC4 results in a state of dampened macrophage activity, while enhancing their survival. Thus, we have characterized FNDC4 as a factor with direct therapeutic potential in inflammatory bowel disease and possibly other inflammatory diseases.
Proteins subjected to post-translational modifications, such as citrullination, carbamylation, acetylation or malondialdehyde (MDA)-modification are targeted by autoantibodies in seropositive ...rheumatoid arthritis (RA). Epidemiological and experimental studies have both suggested the pathogenicity of such humoral autoimmunity, however, molecular mechanisms triggered by anti-modified protein antibodies have remained to be identified.
Here we describe in detail the pathways induced by anti-MDA modified protein antibodies that were obtained from synovial B cells of RA patients and that possessed robust osteoclast stimulatory potential and induced bone erosion in vivo. Anti-MDA antibodies boosted glycolysis in developing osteoclasts via an FcγRI, HIF-1α and MYC-dependent mechanism and subsequently increased oxidative phosphorylation. Osteoclast development required robust phosphoglyceride and triacylglyceride biosynthesis, which was also enhanced by anti-MDA by modulating citrate production and expression of the glycerol-3-phosphate dehydrogenase 1 (GPD1) and glycerol-3-phosphate acyltransferase 2 (GPAT2) genes. In summary, we described novel metabolic pathways instrumental for osteoclast differentiation, which were targeted by anti-MDA antibodies, accelerating bone erosion, a central component of RA pathogenesis.
•Anti-MDA antibodies are inducers of osteoclast maturation and bone erosion in RA.•Anti-MDA antibodies boost glycolysis via FcγRI, HIF-1α and MYC in pre-osteoclast.•Osteoclast glycolysis fuels mitochondrial oxidation and overproduction of citrate.•Anti-MDA boosts lipid biosynthesis via regulating citrate and the GPD1/GPAT2 genes.•Glycerolipid biosynthesis is crucial for osteoclast development.
Activation of p53 by small molecule MDM2 inhibitors can induce cell cycle arrest or death in p53 wildtype cancer cells. However, cancer cells exposed to hypoxia can develop resistance to other small ...molecules, such as chemotherapies, that activate p53. Here, we evaluated whether hypoxia could render cancer cells insensitive to two MDM2 inhibitors with different potencies, nutlin-3a and navtemadlin. Inhibitor efficacy and potency were evaluated under short-term hypoxic conditions in human and mouse cancer cells expressing different p53 genotypes (wild-type, mutant, or null). Treatment of wild-type p53 cancer cells with MDM2 inhibitors reduced cell growth by > 75% in hypoxia through activation of the p53-p21 signaling pathway; no inhibitor-induced growth reduction was observed in hypoxic mutant or null p53 cells except at very high concentrations. The concentration of inhibitors needed to induce the maximal p53 response was not significantly different in hypoxia compared to normoxia. However, inhibitor efficacy varied by species and by cell line, with stronger effects at lower concentrations observed in human cell lines than in mouse cell lines grown as 2D and 3D cultures. Together, these results indicate that MDM2 inhibitors retain efficacy in hypoxia, suggesting they could be useful for targeting acutely hypoxic cancer cells.
Inhibition of microsomal prostaglandin E synthase-1 (mPGES-1) results in decreased production of proinflammatory PGE2 and can lead to shunting of PGH2 into the prostaglandin D2 ...(PGD2)/15-deoxy-Δ12,14-prostaglandin J2 (15dPGJ2) pathway. 15dPGJ2 forms Michael adducts with thiol-containing biomolecules such as GSH or cysteine residues on target proteins and is thought to promote resolution of inflammation. We aimed to elucidate the biosynthesis and metabolism of 15dPGJ2 via conjugation with GSH, to form 15dPGJ2-glutathione (15dPGJ2-GS) and 15dPGJ2-cysteine (15dPGJ2-Cys) conjugates and to characterize the effects of mPGES-1 inhibition on the PGD2/15dPGJ2 pathway in mouse and human immune cells. Our results demonstrate the formation of PGD2, 15dPGJ2, 15dPGJ2-GS, and 15dPGJ2-Cys in RAW264.7 cells after lipopolysaccharide stimulation. Moreover, 15dPGJ2-Cys was found in lipopolysaccharide-activated primary murine macrophages as well as in human mast cells following stimulation of the IgE-receptor. Our results also suggest that the microsomal glutathione S-transferase 3 is essential for the formation of 15dPGJ2 conjugates. In contrast to inhibition of cyclooxygenase, which leads to blockage of the PGD2/15dPGJ2 pathway, we found that inhibition of mPGES-1 preserves PGD2 and its metabolites. Collectively, this study highlights the formation of 15dPGJ2-GS and 15dPGJ2-Cys in mouse and human immune cells, the involvement of microsomal glutathione S-transferase 3 in their biosynthesis, and their unchanged formation following inhibition of mPGES-1. The results encourage further research on their roles as bioactive lipid mediators.
High‐throughput drug screening enables the discovery of new anticancer drugs. Although monolayer cell cultures are commonly used for screening, their limited complexity and translational efficiency ...require alternative models. Three‐dimensional cell cultures, such as multicellular tumor spheroids (MCTS), mimic tumor architecture and offer promising opportunities for drug discovery. In this study, we developed a neuroblastoma MCTS model for high‐content drug screening. We also aimed to decipher the mechanisms underlying synergistic drug combinations in this disease model. Several agents from different therapeutic categories and with different mechanisms of action were tested alone or in combination with selective inhibition of prostaglandin E2 by pharmacological inhibition of microsomal prostaglandin E synthase‐1 (mPGES‐1). After a systematic investigation of the sensitivity of individual agents and the effects of pairwise combinations, GFP‐transfected MCTS were used in a confirmatory screen to validate the hits. Finally, inhibitory effects on multidrug resistance proteins were examined. In summary, we demonstrate how MCTS‐based high‐throughput drug screening has the potential to uncover effective drug combinations and provide insights into the mechanism of synergy between an mPGES‐1 inhibitor and chemotherapeutic agents.
This study highlights the value of spheroids for screening drug combinations and selecting appropriate hits for preclinical testing. A low‐cost spheroid model was developed that combines viability testing and confocal imaging to increase the reliability of results. Further research is needed to fully investigate the mechanisms underlying the synergies between microsomal prostaglandin E synthase‐1 inhibitors and chemotherapeutic agents.
Faulty activation of autoreactive B cells is a hallmark of autoimmune diseases like systemic lupus erythematosus (SLE). An important feature restricting activation of autoreactive B cells is ...efficient removal of apoptotic material. Mounting evidence also connects a primary defect in invariant natural killer T (iNKT) cells to autoimmune disease development. However, exactly how this unconventional T cell subset is involved remains to be defined. Here, we identify a suppressive role for iNKT cells in a model where autoantibody production is triggered by an increased load of circulating apoptotic cells, resembling the situation in SLE patients. Absence or reduction of iNKT cells as well as absence of CD1d-expression on B cells, needed for direct iNKT-B cell interaction, leads to increased autoreactive B cell activation and symptoms of disease. The suppression mediated by the iNKT cells is observed before B cell entry into germinal centers and can be rescued by transferring iNKT cells to deficient mice. This links iNKT cells to handling of dying cells and identifies a novel peripheral tolerance checkpoint relevant for autoimmune disease. Thus, these observations connect two clinical observations in SLE patients previously considered to be unrelated and define a new target for immunotherapy.
The initiation, commitment, and terminal differentiation of the B cell lineage is stringently controlled by the coordinated action of various transcription factors. Among these,
has previously been ...implicated in regulating early B lymphopoiesis, humoral immune responses to phosphocholine, and furthermore to promote the B1 over the B2 cell lineage. We have now interrogated the function of
in the adult mouse using conditional mutagenesis. We demonstrate that loss of
does not affect early B cell development or lineage commitment but rather loss of this transcription factor results in a broad expansion of bone marrow B lymphopoiesis in a manner that reflects its developmental expression pattern. Furthermore, loss of
resulted in expanded splenic B cell numbers with the exception of the B1 lineage that was maintained at normal numbers. However, B1a lymphoyctes were reduced in the peritoneal cavity. In addition, antibody responses to phosphocholine were attenuated in the absence of
. Hence, functional
is required in mature B cells for specific immune responses and for generating normal numbers of B cells in a subset dependent manner.
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