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R A Ezekowitz

Publications and source records attributed to R A Ezekowitz.

At least 73 records · Page 4Linked to original sources
PubMed1993

Human mannose-binding protein functions as an opsonin for influenza A viruses.

Influenza A viruses (IAVs) cause substantial morbidity and mortality in yearly epidemics, which result from the ability of the virus to alter the antigenicity of its envelope proteins. Despite the rapid replication of this virus and its ability to infect a wide variety of cell types, viremia is rare and the infection is generally limited to the upper respiratory tract. The preimmune host defense response against IAV is generally, therefore, successful. We have previously provided (and summarized) evidence that neutrophils contribute to defense against IAV, although neutrophil dysfunction and local tissue damage may be less salutory byproducts of this response. Here we provide evidence that the serum lectin mannose-binding protein directly inhibits hemagglutinin activity and infectivity of several strains of IAV. In addition mannose-binding protein acts as an opsonin, enhancing neutrophil reactivity against IAV. Opsonization of IAV by mannose-binding protein also protects the neutrophil from IAV-induced dysfunction. These effects are observed with physiologically relevant concentrations of mannose-binding protein. Two different allelic forms of recombinant mannose-binding protein are found to have similar effects. We believe, on the basis of these data, that mannose-binding protein alone and in conjunction with phagocytic cells is an important constituent of natural immunity (i.e., preimmune defense) against IAV.

Acute-Phase Proteins↗
PubMed1992

Phagocytic chimeric receptors require both transmembrane and cytoplasmic domains from the mannose receptor.

Phagocytosis has traditionally been viewed as a specialized function of myeloid and monocytic cells. The mannose receptor (MR) is an opsonin-independent phagocytic receptor expressed on tissue macrophages. When human MR cDNA is transfected into Cos cells, these usually non-phagocytic cells express cell surface MR and bind and ingest MR ligands such as zymosan, yeast, and Pneumocystis carinii. Expression of cDNA for Fc gamma RI (CD64), the high-affinity Fc receptor, in Cos cells confers binding but barely detectable phagocytosis of antibody-opsonized erythrocytes (EA). We report here that chimeric receptors containing the ligand-binding ectodomain of the Fc receptor and the transmembrane and cytoplasmic domains of the MR ingest bound EA very efficiently, whereas chimeras with the Fc receptor ecto- and transmembrane domains and the MR tail, or the Fc receptor ecto- and cytoplasmic domains and the MR transmembrane region, are significantly less phagocytic. All of the chimeric receptors bind ligand with equal avidity, but gain of functional phagocytosis is only conferred by the MR transmembrane and cytoplasmic domains. Endocytosis of monomeric immunoglobulin G by chimeric receptors demonstrates a similar pattern, with optimal uptake by the chimera containing both tail and transmembrane regions from the MR. The chimeric receptors with only the transmembrane or the cytoplasmic domain contributed by the MR were less efficient. Site-directed mutagenesis of the single tyrosine residue in the cytoplasmic tail (which is present in a motif homologous to an endocytosis consensus motif in the LDL receptor cytoplasmic tail [Chen, W.-J., J. L. Goldstein, and M. S. Brown. 1990. J. Biol. Chem. 265:3116]) reduces the efficiency of phagocytosis and endocytosis to a similar extent.

Animals↗
PubMed1992

Characterization of the murine macrophage mannose receptor: demonstration that the downregulation of receptor expression mediated by interferon-gamma occurs at the level of transcription.

The macrophage mannose receptor (MMR) is a 175-Kd cell-surface transmembrane glycoprotein that is expressed on tissue macrophages where it functions both to mediate the uptake of mannose-rich glycoproteins and as a phagocytic receptor for bacteria, yeasts, and other pathogenic microorganisms. In this report we describe the cloning of the full-length cDNA of the mouse macrophage mannose receptor and we investigate the level at which interferon gamma (IFN-gamma) downregulates mannose receptor expression. The latter is a marker of the functional state of the cell as high levels are expressed on resident and inflammatory macrophages, whereas cells activated by treatment with IFN-gamma have decreased-to-absent cell-surface mannose receptor expression. The murine MMR cDNA contains an open reading frame that predicts a protein of 1,456 amino acids. Transient expression of the protein in heterologous cells shows that this cDNA encodes a functional mannose receptor. The deduced amino acid sequence of this protein has an overall 82% homology with the human mannose receptor and as such, the ectodomain contains an N-terminus that is cysteine-rich followed by a fibronectin type II domain and eight carbohydrate recognition domains (CRDs). The ectodomain is linked to a hydrophobic transmembrane region and a 46-amino acid cytoplasmic tail. All of the eight CRDs are particularly well conserved, especially CRD4, which shows 92% homology with the equivalent region of the human protein. Steady-state levels of murine MMR mRNA were measured in the macrophage cell line J774E, which is known to express the protein at the cell surface. These levels were decreased by a 4- to 8-hour incubation with IFN-gamma, but were almost abolished by overnight treatment with this cytokine. Nuclear run-on experiments showed that IFN-gamma inhibits MMR gene transcription. Therefore, the regulation of mannose receptor expression by IFN-gamma provides a novel system in which to study the mechanisms by which this cytokine represses gene expression.

Amino Acid Sequence↗
PubMed1992

Definition of interferon gamma-response elements in a novel human Fc gamma receptor gene (Fc gamma RIb) and characterization of the gene structure.

The human Fc gamma RI (CD64) is a high affinity receptor for the Fc portion of immunoglobulin (Ig), and its constitutively low expression on the cell surface of monocyte/macrophage and neutrophils is selectively upregulated by interferon gamma (IFN-gamma) treatment (Perussia, B., E. T. Dayton, R. Lazarus, V. Fanning, and G. Trinchieri. 1983. J. Exp. Med. 158:1092). Three distinct cDNAs have been cloned and code for proteins that predict three extracellular Ig-like domains (Allen, J.M., and B. Seed. 1989. Science [Wash. DC]. 243:378). Several differences in the coding region of these cDNAs suggest that in addition to polymorphic differences a second Fc gamma RI gene could possibly exist. This alternative Fc gamma RI gene (Fc gamma RIb) was defined by the lack of a genomic HindIII restriction site (van der Winkel, J. G. J., L. U. Ernst, C. L. Anderson, and I. M. Chiu. 1991. J. Biol. Chem. 266:13449). We describe the characterization a second gene (Fc gamma RIb) that has a termination codon in the third extracellular domain and therefore predicts a soluble form of a termination codon in the third extracellular domain and therefore predicts a soluble form of the receptor. We also define two distinct IFN-gamma-responsive regions in the 5' flanking sequence of Fc gamma RIb that resemble motifs that have been defined in the class II major histocompatibility complex promoter. The Fc gamma RIb promoter does not possess canonical TATA or CCAAT boxes, but does possess a palindromic motif that closely resembles the initiator sequence identified in the terminal deoxynucleotidyl transferase/human leukocyte IFN/adeno-associated virus type II P5 gene promoters (Smale, S. T., and D. Baltimore. 1989. Cell. 57:103; Seto, E., Y. Shi, and T. Shenk. 1991. Nature [Lond.]. 354:241; Roy, A. L., M. Meisterernst, P. Pognonec, and R. C. Roeder. 1991. Nature [Lond.]. 354:245) virus type II P5 gene promoters raising interesting questions as to its role in the basal and myeloid-specific transcription of this gene.

Amino Acid Sequence↗
PubMed1992

Interferon alfa-2a therapy for life-threatening hemangiomas of infancy.

BACKGROUND AND METHODS: Most hemangiomas are small, harmless birthmarks that appear soon after birth, proliferate for 8 to 18 months, and then slowly regress over the next 5 to 8 years, leaving normal or slightly blemished skin. In rare cases, hemangiomas can endanger vital structures, with a mortality of up to 60 percent. About a third of these life-threatening hemangiomas respond to treatment with corticosteroids, but for the others there is no safe and effective treatment. We evaluated the effects of daily subcutaneous injections of interferon alfa-2a (up to 3 million units per square meter of body-surface area) in 20 neonates and infants with life-threatening or vision-threatening hemangiomas that failed to respond to corticosteroid therapy. RESULTS: In 18 of the 20 patients the hemangiomas regressed by 50 percent or more after an average of 7.8 months of treatment (range, 2 to 13). One infant died of refractory proliferation of a lesion and consumptive coagulopathy. The condition of three other patients who had large hemangiomas associated with consumptive coagulopathies that were unresponsive to conventional therapies stabilized after seven days of treatment with interferon alfa-2a alone. Transient side effects of treatment with interferon alfa-2a included fever, neutropenia (one patient), and skin necrosis (one patient). No long-term toxicity has been observed after a mean follow-up of 16 months. CONCLUSIONS: Interferon alfa-2a appears to induce the early regression of life-threatening corticosteroid-resistant hemangiomas of infancy.

Disseminated Intravascular Coagulation↗
PubMed1992

Monocytes from patients with atopic dermatitis are primed for superoxide production.

To determine the potential role of monocytes (peripheral blood monocytes, PBMs) in the pathogenesis of atopic dermatitis (AD), we investigated whether PBMs from patients with severe AD are primed to generate toxic oxygen metabolites. To induce in vitro superoxide anion (O2-) production, we used either particulate (e.g., opsonized bacteria or zymosan) or soluble (e.g., phorbol esters) stimuli, which allowed us to test two distinct pathways for reduced nicotinamide-adenine dinucleotide phosphate activation. In addition, PBMs from the same patients were also examined for their levels of expression of the low-affinity receptor for IgE, Fc epsilon receptor 2 (CD23). We found that PBMs, but not peripheral blood neutrophils, from patients with AD were primed for O2- production as compared to PBMs from either normal control subjects or patients with allergic rhinitis. These cells also expressed increased levels of CD23, and there was a significant correlation between these two parameters. Since the monocytes infiltrating into the AD lesions bear CD23, our data suggest that in vivo priming of PBMs and increased O2- production may participate in the pathogenesis of this skin disease.

Adolescent↗
PubMed1992

Distinct and overlapping functions of allelic forms of human mannose binding protein.

Human mannose binding protein (MBP) is a C-type serum lectin involved in first-line host defense against a variety of bacterial, fungal and viral pathogens. Recently an association was found between low levels of serum MBP and an increased frequency of recurrent infections in infants. A particular genotype, in which glycine is substituted by aspartic acid at codon 54 of MBP in the fifth collagen repeat, shows apparent concordance with the clinical phenotype. We report, however, that this genotype occurs in 5% of the population and encodes a functional protein. Our results indicate that the Gly54Asp allele does not account for a deficiency state, but instead suggest that MBP may have two predominant allelic forms that have overlapping function and differ only in their ability to activate the classical pathway of complement.

Alleles↗
PubMed1992

The role of mannose-binding proteins in host defense.

The human mannose-binding protein (MBP) appears to function as an "ante-antibody" as its physiological role is in first line host defense. Low baseline serum levels are rapidly increased as part of the acute phase reactant and circulating MBP can act as a direct opsonin or activate the classical alternative complement pathway. MBP appears to selectively recognize an array of apparently disparate oligosaccharides that decorate gram-negative and gram-positive bacteria as well as certain parasites, yeasts, and fungi. MBP may be considered a "pattern" recognition molecule that has homologs in primitive life forms. Its ability to distinguish self from nonself indicates that it may play an important role in innate immunity.

Amino Acid Sequence↗
PubMed1991

Molecular characterization of the mouse mannose-binding proteins. The mannose-binding protein A but not C is an acute phase reactant.

Mannose-binding proteins play a role in first line host defense against a variety of pathogens. We report the molecular cloning of two mouse mannose-binding proteins designated A and C based on their close identity with their rat homologues. The deduced amino acid sequence of the mouse mannose-binding proteins, as with rat and the human forms, have an NH2 terminus that is rich in cysteine that stabilizes a collagen alpha helix followed by a carboxyl- terminal carbohydrate binding domain. We further show that the mouse mannose-binding protein A mRNA, as with the human, is induced like the acute phase reactant serum amyloid P protein, yet the expression of mouse mannose-binding protein C mRNA is not regulated above its low baseline level. The expression of both mannose-binding proteins A and C mRNA is restricted to the liver under basal and stress conditions.

Acute-Phase Proteins↗
PubMed1991

Mouse IL-1 receptor antagonist protein. Molecular characterization, gene mapping, and expression of mRNA in vitro and in vivo.

The IL-1R antagonist protein (IL-1RN/IL-1rn) is a member of the IL-1 family of inflammatory mediators. We have isolated and analyzed a mouse IL-1rn cDNA clone and established that the derived mouse IL-1rn protein sequence is highly homologous to the human counterpart molecule. Mouse IL-1rn mRNA may be induced in P388D1 monocytic cells with PMA and in mouse liver in vivo by development of an experimental inflammation via s.c. injection of azocasein. This latter observation implies the existence of an autocrine hepatic negative feedback loop that down-regulates the acute phase response and is itself induced at the same time as the major acute-phase proteins. The mouse Il 1rn gene was mapped to the proximal region of chromosome 2 between the centromere and Spna2; the other known members of the mouse IL-1 gene family, Il 1a and Il 1b, both map to the same chromosome, although not in close linkage.

Amino Acid Sequence↗
PubMed1991

Uptake of Pneumocystis carinii mediated by the macrophage mannose receptor.

Human exposure to Pneumocystis carinii is common but, in the absence of acquired or genetic dysfunction of either cellular or humoral immunity, exposure rarely leads to illness. Although alveolar macrophages can degrade P. carinii, macrophage receptors involved in P. carinii recognition have not been clearly defined. Characterization of a predominant surface glycoprotein of the high mannose type led us to investigate the role of the macrophage mannose receptor in this process. We report here that binding and uptake of cultured rat P. carinii by human and rat alveolar macrophages is reduced by 90% in the presence of competitive inhibitors of mannose receptor activity and by adherence of alveolar macrophages to mannan-coated surfaces. Further, only those COS cells transfected with the human macrophage mannose receptor complementary DNA that express surface mannose receptors bind and ingest P. carinii. These studies establish that the macrophage mannose receptor is sufficient for uptake of P. carinii and emphasize the role of the alveolar macrophage in first-line host defence against P. carinii.

Animals↗
PubMed1991

Interferon-gamma and chronic granulomatous disease.

The molecular and biochemical characterization of many components of the phagocyte oxidase complex that generates superoxide have greatly advanced our understanding of this important pathway. Genetic defects in one or more of the components of this host defense system result in the chronic granulomatous disease phenotype. Biochemical advances and the results of a clinical trial that established the efficacy of recombinant human interferon-gamma for prophylaxis of infections in chronic granulomatous disease are the highlights of recent achievements in this area of phagocyte biology.

Clinical Trials as Topic↗
PubMed1991

The gene for mannose-binding protein maps to chromosome 10 and is a marker for multiple endocrine neoplasia type 2.

Human mannose-binding lectin (MBL) is a serum protein which appears to function as an opsonin in first line host defense. In situ hybridization studies assign the human MBL gene to chromosome 10q11.2----q21. A restriction fragment length polymorphism (RFLP) was found using TaqI with a 0.8-kb cDNA probe for MBL (probe 48-11), yielding heterozysity in 34% of individuals tested. Using this biallelic RFLP, linkage analysis of 30 families confirms the assignment of MBL to the region of multiple endocrine neoplasia, type 2a (MEN2A) with a maximum lod score of 7.54 at a recombination fraction of 0.00 (males) and 0.097 (females). The presence of two crossovers between MEN2A and MBL in these families indicates that a defect of MBL itself is not the cause of the hereditary thyroid cancer syndrome. The addition of MBL to the genetic map of the pericentromeric region of chromosome 10 should prove useful for improved localization of the MEN2A mutation.

Biomarkers, Tumor↗
PubMed1990

Restoration of phagocyte function by interferon-gamma in X-linked chronic granulomatous disease occurs at the level of a progenitor cell.

Phagocytes from X-linked chronic granulomatous disease (X-CGD) patients are deficient in their ability to generate superoxide because of a defective gene that encodes a heavy chain of cytochrome b, a critical component in the superoxide-generating pathway. Previously we have shown that a single in vivo treatment of selected X-CGD patients with interferon-gamma (INF-gamma) resulted 14 days later in near-normal levels of superoxide generation by phagocytes. The effect persisted for 28 days. This prolonged effect suggested that the lymphokine affected progenitor cells. In this study, we examined progenitor-derived colonies from the peripheral blood from this unusual X-CGD kindred. Progenitor-derived colonies examined before treatment were unable to generate superoxide as visualized by lack of nitro blue tetrazolium (NBT) reduction compared with normal controls. By contrast, colonies derived 7 days after a single INF-gamma injection were able to generate superoxide as shown by increased NBT reduction. Colonies harvested 21 days after treatment contained only rare cells capable of NBT reduction. Our results indicate that INF-gamma can reprogram the myeloid progenitor cells to express a partially corrected phenotype. This corrected phenotype is later expressed in daughter cells.

Cell Differentiation↗