Fcμ receptor as a Costimulatory Molecule for T Cells

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Evidence for non-random distribution of Fcγ receptor genotype combinations

Human IgG receptors (FcR) display considerable heterogeneity, and are crucial immune response modulating molecules. FcRIIA, FcRIIIA, and FcRIIIB display functional biallelic polymorphisms. FcR polymorphisms have been found associated with susceptibility to infectious and autoimmune diseases. Linked transmission of FcR alleles was studied by determining the distribution of FcRIIA-FcRIIIA-FcRIIIB genotype combinations in 514 Dutch Caucasian, and 149 Japanese blood donors. The structure of the FcR locus was studied by radiation hybrid mapping of FcRIA, FcRIIA, FcRIIB, FcRIIIA, FcRIIIB, and adjacent genes from the pentraxin family. In addition, crossing-over frequencies within the FcR locus were determined in 63 Dutch Caucasian families, encompassing 183 individuals. FcRII and FcRIII subclasses were mapped in close proximity (0.47–3.14 cR). Accordingly, crossing-over frequencies within the FcRII-III locus in Dutch families were low. Analysis of combined FcR genotypes strongly suggested non-random distribution of FcRIIA-FcRIIIA-, and FcRIIIA-FcRIIIB genotypes in Dutch donors (P<0.001 and P<0.00001, respectively), and of FcRIIA-FcRIIIb genotypes in Japanese blood donors (P<0.02). Frequencies of FcRII-FcRIII haplotypes differed significantly between Dutch and Japanese (P<0.00001). This study provides important information for the interpretation of studies reporting associations of FcR alleles with disease, and underscores the apparent differences in FcR heterogeneity between ethnic groups.     

Chromosomal mapping of the high affinity Fcλ receptor gene

Address correspondence and offprint requests to: M. F. Seldin.     

Molecular cloning and expression of the porcine high-affinity immunoglobulin G Fc receptor (FcγRI)

Receptors for the Fc region (FcγRs) of immunoglobulin G (IgG) play a crucial role in the immune system and host protection against infection. In this study, we describe the cloning, sequencing, and expression of the high-affinity IgG receptor from pig. By screening a translated Expressed Sequence Tags database with the human FcγRI (CD64) protein sequence, we identified a putative porcine homologue. Subsequent polymerase chain reaction amplification confirmed that the identified full-length cDNA was expressed in porcine cells. Rosetting analysis shows that COS-7 cells transfected with a plasmid containing the cloned cDNA were able to bind chicken erythrocytes sensitized with porcine IgG. Scatchard analysis indicated that monomeric IgG bound to transiently transfected cells with an affinity of approximately 4×10⁷ M⁻¹. The porcine FcγRI cDNA is 1,038 nucleotides long and is predicted to encode a 346-amino-acid transmembrane glycoprotein composed of three Ig-like domains, a transmembrane region, and a short cytoplasmic tail. The overall identity of the porcine FcγRI to its human and mouse counterparts at the level of the amino acid sequence was 75% and 57%, respectively. Identification of porcine FcγRI will aid in the understanding of the molecular basis of the porcine immune system and further studies of the receptor function.Gaiping Zhang and Songlin Qiao contributed equally to this study.The GenBank accession number of the nucleotide sequence reported here is DQ026063.     

The inhibiting Fc receptor for IgG, FcγRIIB, is a modifier of autoimmune susceptibility

FcγRIIB-deficient mice generated in 129 background (FcγRIIB(129)(-/-)) if back-crossed into C57BL/6 background exhibit a hyperactive phenotype and develop lethal lupus. Both in mice and humans, the Fcγr2b gene is located within a genomic interval on chromosome 1 associated with lupus susceptibility. In mice, the 129-derived haplotype of this interval, named Sle16, causes loss of self-tolerance in the context of the B6 genome, hampering the analysis of the specific contribution of FcγRIIB deficiency to the development of lupus in FcγRIIB(129)(-/-) mice. Moreover, in humans genetic linkage studies revealed contradictory results regarding the association of "loss of function" mutations in the Fcγr2b gene and susceptibility to systemic lupus erythematosis. In this study, we demonstrate that FcγRIIB(-/-) mice generated by gene targeting in B6-derived ES cells (FcγRIIB(B6)(-/-)), lacking the 129-derived flanking Sle16 region, exhibit a hyperactive phenotype but fail to develop lupus indicating that in FcγRIIB(129)(-/-) mice, not FcγRIIB deficiency but epistatic interactions between the C57BL/6 genome and the 129-derived Fcγr2b flanking region cause loss of tolerance. The contribution to the development of autoimmune disease by the resulting autoreactive B cells is amplified by the absence of FcγRIIB, culminating in lethal lupus. In the presence of the Yaa lupus-susceptibility locus, FcγRIIB(B6)(-/-) mice do develop lethal lupus, confirming that FcγRIIB deficiency only amplifies spontaneous autoimmunity determined by other loci.     

Monocyte-produced prostaglandin induces Fcγ receptor expression on human T cells

Incubation of human T cells for 18 hr with prostaglandin E₂ (PGE₂ 3 × 10^?6M) causes a slight but significant increase in the percentage of Tγ cells and a reduction in Tμ cells. When PGE was added to “non-Tγ” cells, the increase in the percentage of Tγ cells was more marked (from 1.5% Tγ without PGE to 11% Tγ with PGE₂, P < 0.001). Supernates from cultures of human monocytes also caused an increase in Tγ cells (10% Tγ without supernate to 18% with supernate, P < 0.01), and this increase was blocked if the monocytes were cultured with indomethacin, a prostaglandin synthetase inhibitor (9% Tγ cells). Thus, monocytes may regulate Fcγ receptors on T cells via PGE₂ production.     

N-glycan structures of a recombinant mouse soluble Fcγ receptor II

N-glycans of a recombinant mouse soluble Fc receptor II (sFcRII) expressed in baby hamster kidney cells were released from glycopeptides by digestion with glycoamidase A (from sweet almond), and the reducing ends of the oligosaccharides were reductively aminated with 2-aminopyridine. The derivatized N-glycans were separated and structurally identified by a three-dimensional high-performance liquid chromatography (HPLC) mapping technique on three kinds of HPLC columns [Takahashi, et al. (1995) Anal. Biochem. 226: 139–46]. Eighteen different major N-glycan structures were identified, of which six were neutral (45%), five mono-sialyl (49%), one di-sialyl (4.6%), five tri-sialyl (1.1%), and one tetra-sialyl (0.3%). All N-glycan structures determined were complex type with fucosylation at the N-acetylglucosamine residue of the reducing end, and N-acetylneuraminic acid, when present, was -(2,3)-linked. The existence of a unique structure containing both N-acetylgalactosamine and -(2,3)-N-acetylneuraminic acid residues at the reducing ends, as below, was confirmed by MALDI-TOF mass spectrometry.     

Functional characteristics of the high affinity IgG receptor, FcγRI

IgG FcRs are important mediators of immunity and play a key role during Ab-based immunotherapy. Within the leukocyte IgG receptor family, only FcγRI is capable of IgG binding with high affinity. FcγRI exists as a complex of a ligand binding α-chain and an FcR γ-chain. The receptors' α-chain can, furthermore, elicit several functions independent of the ITAM-bearing FcR γ-chain. Functional implications of high-affinity IgG binding and mechanisms underlying FcR γ-chain-independent signaling remain unclear to this day. In this paper, we provide an overview of past literature on FcγRI and address the implications of recently described interactions between cytosolic proteins and the FcγRI α-chain, as well as cytokine-enhanced FcγRI immune complex binding. Furthermore, an analysis of potential polymorphisms within the FCGR1A gene is provided.     

The role of CD38 in Fcγ receptor (FcγR)-mediated phagocytosis in murine macrophages

Phagocytosis is a crucial event in the immune system that allows cells to engulf and eliminate pathogens. This is mediated through the action of immunoglobulin (IgG)-opsonized microbes acting on Fcγ receptors (FcγR) on macrophages, which results in sustained levels of intracellular Ca(2+) through the mobilization of Ca(2+) second messengers. It is known that the ADP-ribosyl cyclase is responsible for the rise in Ca(2+) levels after FcγR activation. However, it is unclear whether and how CD38 is involved in FcγR-mediated phagocytosis. Here we show that CD38 is recruited to the forming phagosomes during phagocytosis of IgG-opsonized particles and produces cyclic-ADP-ribose, which acts on ER Ca(2+) stores, thus allowing an increase in FcγR activation-mediated phagocytosis. Ca(2+) data show that pretreatment of J774A.1 macrophages with 8-bromo-cADPR, ryanodine, blebbistatin, and various store-operated Ca(2+) inhibitors prevented the long-lasting Ca(2+) signal, which significantly reduced the number of ingested opsonized particles. Ex vivo data with macrophages extracted from CD38(-/-) mice also shows a reduced Ca(2+) signaling and phagocytic index. Furthermore, a significantly reduced phagocytic index of Mycobacterium bovis BCG was shown in macrophages from CD38(-/-) mice in vivo. This study suggests a crucial role of CD38 in FcγR-mediated phagocytosis through its recruitment to the phagosome and mobilization of cADPR-induced intracellular Ca(2+) and store-operated extracellular Ca(2+) influx.     

MicroRNA-127 inhibits lung inflammation by targeting IgG Fcγ receptor I

The molecular mechanisms of acute lung injury are incompletely understood. MicroRNAs (miRNAs) are crucial biological regulators that act by suppressing their target genes and are involved in a variety of pathophysiologic processes. miR-127 appears to be downregulated during lung injury. We set out to investigate the role of miR-127 in lung injury and inflammation. Expression of miR-127 significantly reduced cytokine release by macrophages. Looking into the mechanisms of regulation of inflammation by miR-127, we found that IgG FcγRI (CD64) was a target of miR-127, as evidenced by reduced CD64 protein expression in macrophages overexpressing miR-127. Furthermore, miR-127 significantly reduced the luciferase activity with a reporter construct containing the native 3' untranslated region of CD64. Importantly, we demonstrated that miR-127 attenuated lung inflammation in an IgG immune complex model in vivo. Collectively, these data show that miR-127 targets macrophage CD64 expression and promotes the reduction of lung inflammation. Understanding how miRNAs regulate lung inflammation may represent an attractive way to control inflammation induced by infectious or noninfectious lung injury.     

Functional haplotypes of Fc gamma (Fcγ) receptor (FcγRIIA and FcγRIIIB) predict risk to repeated episodes of severe malarial anemia and mortality in Kenyan children

Development of protective immunity against Plasmodium falciparum is partially mediated through binding of malaria-specific IgG to Fc gamma (γ) receptors. Variations in human FcγRIIA-H/R-131 and FcγRIIIB-NA1/NA2 affect differential binding of IgG sub-classes. Since variability in FcγR may play an important role in severe malarial anemia (SMA) pathogenesis by mediating phagocytosis of red blood cells and triggering cytokine production, the relationship between FcγRIIA-H/R131 and FcγRIIIB-NA1/NA2 haplotypes and susceptibility to SMA (Hb?相似文献   

The polymorphic Fcγ receptor II gene maps to human chromosome 1q

Human receptors for IgG (FcR) play important roles in the immune response. Expression of the human FcRII gene may be relevant in immune complex related disorders such as systemic lupus erythematosus and Sjogren's syndrome. We have used spot blot analysis of dual laser-sorted human chromosomes to localize the FcRII gene to human chromosome 1. Spot blot analysis of sorted derivative chromosomes sublocalized the gene to the chromosome 1 long arm (1q1225.1). This subchromosomal localization involved reassigning a reciprocal chromosome translocation breakpoint. We also identified Xmn I and Taq I FcRII polymorphic restriction sites that arose before the races diverged. These common Xmn I and Taq I polymorphisms are predicted to be informative for segregation analysis with human diseases in 85% of all matings.     

Genetic variants of the IgA Fc receptor (FcαR, CD89) promoter in chronic hepatitis C patients

Fc receptor for IgA (FcαR, CD89) is capable of triggering IgA-mediated immune responses to pathogens and has been proposed to function in circulating IgA clearance. Because inheritable variations modifying individual immune responses or immunoglobulin catabolism may affect the chronicity of viral infection, we investigated whether promoter polymorphisms of the FcαR gene (FCAR) affect chronic hepatitis C virus (HCV) infection and its disease progression. The two −311T/C and −142T/C single-nucleotide polymorphisms (SNPs) were studied by direct DNA sequencing in 177 Japanese patients with chronic hepatitis C (CHC). Both −311CC and −142CC genotypes were more frequent in CHC patients (15.9 and 18.6%) compared with 210 healthy controls (5.7 and 10.0%) [p = 0.001, odds ratio (OR) = 3.10, 95% confidence interval CI) = 1.53–6.30 and p = 0.014, OR = 2.06, 95% CI = 1.14–3.72, respectively], and were associated with infection with HCV genotype 2a/2b (p = 0.019 and p = 0.005, respectively). Conversely, −311CC and −142CC were decreased in 59 patients at advanced stages of disease as assessed on the basis of hepatic fibrosis markers such as decreased platelet count (PLT) ( < 150,000/μl) (5.1 and 8.5%) compared with 91 patients with normal PLT ( ≥ 150,000/μl) (24.2 and 26.4%) (p = 0.006 and p = 0.005, respectively). Moreover, among the patients with normal PLT (but not with decreased PLT), −311CC or −142CC was significantly associated with decreased serum IgA levels (p = 0.023 or p = 0.007, respectively). These results suggest that the FCAR promoter SNPs may be related to chronic HCV infection and disease progression in Japanese CHC, which might be explained by altered FcαR expression affecting IgA-mediated immune responses and/or IgA catabolism.     

Characterization of conformational deformation-coupled interaction between immunoglobulin G1 Fc glycoprotein and a low-affinity Fcγ receptor by deuteration-assisted small-angle neutron scattering

A recently developed integrative approach combining varied types of experimental data has been successfully applied to three-dimensional modelling of larger biomacromolecular complexes. Deuteration-assisted small-angle neutron scattering (SANS) plays a unique role in this approach by making it possible to observe selected components in the complex. It enables integrative modelling of biomolecular complexes based on building-block structures typically provided by X-ray crystallography. In this integrative approach, it is important to be aware of the flexible properties of the individual building blocks. Here we examine the ability of SANS to detect a subtle conformational change of a multidomain protein using the Fc portion of human immunoglobulin G (IgG) interacting with a soluble form of the low-affinity Fcγ receptor IIIb (sFcγRIIIb) as a model system. The IgG-Fc glycoprotein was subjected to SANS in the absence and presence of 75%-deuterated sFcγRIIIb, which was matched out in D₂O solution. This inverse contrast-matching technique enabled selective observation of SANS from IgG-Fc, thereby detecting its subtle structural deformation induced by the receptor binding. The SANS data were successfully interpreted by considering previously reported crystallographic data and an equilibrium between free and sFcγRIIIb-bound forms. Our SANS data thus demonstrate the applicability of SANS in the integrative approach dealing with biomacromolecular complexes composed of weakly associated building blocks with conformational plasticity.     

Effect of adenosine deaminase inhibitors on Fcμ receptor expression in human T-cell cultures

Incubation of human peripheral blood T-lymphocyte cultures with 100 μM EHNA or 1 μM pentostatin results in the delayed appearance of Fcμ, receptor-bearing cells. The percentage of Tμ-positive cells approaches control levels by 24–30 hr despite the lack of detectable adenosine deaminase activity. Tγ to Tμ transition was more effectively inhibited than To to Tμ in studies with the individual subpopulations. The inhibitory effect of pentostatin or EHNA on the appearance of Fcμ receptor-positive cells was reversible with exogenous undine or 2′-deoxycytidine. These results indicate that pyrimidine deprivation affects the appearance of Fcμ receptors in T-cell cultures, and that despite the continued inhibition of ADA the effect on Fcμ is reversible by 24 hr without the addition of exogenous pyrimidines.