Biomedical subjects

M A Arnaout

Publications and source records attributed to M A Arnaout.

At least 19 recordsLinked to original sources

PubMed1995

Intercellular adhesion molecule-2 (CD102) binds to the leukocyte integrin CD11b/CD18 through the A domain.

The interactions between the leukocyte-specific beta 2-integrins cluster of differentiation (CD) Ag CD11/CD18 and their ligands, the intercellular adhesion molecules (ICAMs), play important roles in many adhesion-dependent leukocyte functions. ICAM-1 is known to be a ligand for both CD11a/CD18 and CD11b/CD18. ICAM-2, whose two extracellular Ig domains show the highest homology to the two NH2-terminal domains of ICAM-1, has been previously shown to be a ligand for CD11a/CD18. We recently found that a 22-amino acid CD11a/CD18-binding peptide, P1, derived from the first domain of ICAM-2, also binds to purified CD11b/CD18. In the present study, we demonstrate that the ICAM-2 protein interacts with CD11b/CD18, and the binding is through the CD11b A domain.

Animals↗

PubMed1995

Direct interaction of filamin (ABP-280) with the beta 2-integrin subunit CD18.

beta 2-Integrins mediate leukocyte extravasation into inflamed tissues, phagocytosis, and target cell killing, functions that require an intact actin cytoskeleton. Previous studies have focused on elucidating interactions of the cytoplasmic tails of integrins with the cytoskeleton at focal contacts in stationary cells. As integrins are also located at other types of cell-substratum junctions, such as the leading edge of migrating cells, additional cytosolic proteins abundant at these sites may also interact with integrins. In this study, we have identified the actin-binding protein, filamin (ABP-280), as a major cytoskeletal protein that binds to the cytoplasmic tail of the beta 2-integrin subunit CD18. Filamin bound to cytoplasmic CD18 directly and specifically, co-immunoprecipitated with beta 2-integrins in detergent cell lysate and co-immunolocalized with cross-linked beta 2-integrins in intact cells. The filamin binding site in CD18 was localized to the N-terminal (amino acids (aa) 724 to 747) but not to the C-terminal (aa 743 to 769) half of cytoplasmic CD18. Filamin did not bind to the major alpha-actinin binding site (aa 733 to 742), however, suggesting that these two cytoskeletal proteins bind to distinct but overlapping sites. Given the conservation of the filamin binding region among beta-integrin subunits, these findings suggest the presence of similar associations between filamin and other integrins. These associations may be important in the spreading and extension of lamellipodia at the leading edge during cell movement and, if interrupted, may contribute to the dramatic decrease in cell locomotion observed in genetic deletions involving filamin or integrins.

Actinin↗

PubMed1995

Crystal structure of the A domain from the alpha subunit of integrin CR3 (CD11b/CD18).

We have determined the high resolution crystal structure of the A domain from the alpha chain of integrin CR3. The domain adopts a classic alpha/beta "Rossmann" fold and contains an unusual Mg2+ coordination site at its surface. One of the coordinating ligands is the glutamate side chain from another A domain molecule. We suggest that this site represents a general metal ion-dependent adhesion site (MIDAS) for binding protein ligands. We further propose that the beta subunits of integrins contain a MIDAS motif within a modified A domain. Our crystal structure will allow reliable models to be built for other members of the A domain superfamily and should facilitate development of novel adhesion modulatory drugs.

Amino Acid Sequence↗

PubMed1995

Inhibition of proteinase 3 by ANCA and its correlation with disease activity in Wegener's granulomatosis.

Detection of circulating antineutrophil cytoplasmic antibodies (ANCA) to the neutrophil serine proteinase, proteinase 3 (PR3), has proven valuable for the diagnosis of Wegener's granulomatosis (WG). However, the importance of these autoantibodies in the pathogenesis of WG remains unknown. It was recently reported that anti-PR3 autoantibodies (PR3-ANCA) from some patients with WG inhibit the proteolytic activity of PR3 and interfere with the inactivation of PR3 by the physiologic inhibitor, alpha 1-proteinase inhibitor (alpha 1-PI). We have studied the effect of PR3-ANCA on the enzymatic activity of PR3 and its correlation with disease activity in patients with WG. We purified IgG from 21 PR3-ANCA positive sera obtained from 17 patients with WG, and determined its effect on the esterolytic and proteolytic activity of purified human PR3 using Boc-Ala-O-Nitrophenyl ester and fluoresceinated-elastin as enzyme substrates. Controls included seven sera containing anti-MPO autoantibodies (MPO-ANCA) from patients with systemic vasculitis and seven ANCA-negative sera obtained from healthy individuals. We found that PR3-ANCA from 9 of the 17 patients significantly inhibited the activity of PR3. There was no correlation between the titers of PR3-ANCA and their inhibitory activity. For one extensively characterized autoantibody, the inhibition reached 70 to 95% at 20-fold molar excess of IgG to enzyme, with an apparent Kiapp of 56.5 microM. This inhibition was non-competitive in nature, and was additive to that produced by alpha 1-PI. A review of the clinical histories of the patients revealed a strong association between active WG and inhibitory autoantibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Antineutrophil Cytoplasmic↗

PubMed1995

Pendred's syndrome: a study of patients and relatives.

Four families, 29 members, with Pendred's syndrome were studied to clarify hearing loss and hormonal status. The ages ranged from 3 to 50 years. Complete Pendred's syndrome was found in 9 patients. They had bilateral profound hearing loss with residual hearing at low frequencies. Goiter was diagnosed at the age of 1 to 14 years with a positive perchlorate discharge test. Twelve of the patients' relatives showed partial Pendred's syndrome. Mild sensorineural hearing losses occurred in the low- and medium-range frequencies with normal perchlorate discharge test results in 6 cases. The other 6 had a slight drop in the perchlorate discharge test results with normal hearing. Five subjects were normal and 3 had normal hormonal and normal perchlorate discharge test results, but were not tested audiologically. This paper shows that patients with Pendred's syndrome may have goiter at birth or develop it between 8 and 14 years, that their deafness is bilateral and profound, and that their perchlorate discharge tests are positive. Relatives of Pendred's syndrome patients showed mild low-frequency sensorineural hearing loss without goiter and normal perchlorate discharge test results in half the cases, and a slight drop in the perchlorate discharge test results with normal hearing and without goiter in the other half. A correlation between these findings and genetic studies needs further investigation.

Adolescent↗

PubMed1995

Preventing the infiltration of leukocytes by monoclonal antibody blocks the development of progressive ischemia in rat burns.

Tissue loss as a consequence of thermal trauma occurs in two stages. There is immediate necrosis in tissues directly killed by the thermal energy, followed by a delayed secondary necrosis in neighboring tissues. The infiltration of neutrophils into traumatized tissues is a hallmark of the inflammatory response. Neutrophils have the machinery to kill invading microorganisms, but these same weapons have the capacity to destroy the host's viable tissues as well. Leukocyte infiltration requires their adherence to the vascular endothelial cell surface. Masking these adhesion sites on neutrophils will block the adhesion of neutrophils to the endothelium. A monoclonal antibody (mAb) was developed to guinea pig leukocyte adhesion sites CD11b/ CD18, and this mAb cross-reacts with rat leukocytes, blocking their adherence. Rats received a "comb burn" composed of four rectangular full-thickness burns placed in a row and separated by three areas left unburned. The four individual burns convert into a single large wound because the blood flow to the interspaces was terminated, blood vessels were occluded, and leukocytes were present in the extravascular space. The systemic administration of the mAb (50 to 150 microliters) immediately following a comb burn promoted the survival of the interspace, demonstrated by the prevention of loss of blood flow by laser Doppler monitoring, maintained patent vessels by latex vascular casts, blocked extravascular migration of neutrophils histologically at 2 hours, and limited the tissue loss to the original four burns.

Animals↗

PubMed1994

Identification of the complement iC3b binding site in the beta 2 integrin CR3 (CD11b/CD18).

The divalent cation-dependent interaction of the beta 2 integrin CR3 (CD11b/CD18) with the major complement opsonic C3 fragment iC3b is an important component of the central role of CR3 in inflammation and immune clearance. In this investigation we have identified the iC3b binding site in CR3. A recombinant fragment representing the CR3 A-domain, a 200-amino acid region in the ectodomain of the CD11b subunit, bound to iC3b directly and in a divalent cation-dependent manner. The iC3b binding site was further localized to a short linear peptide that also bound iC3b directly and inhibited iC3b binding to the A-domain as well as to CR3 expressed by human neutrophils. These data establish a major recognition function for the integrin A-domain and have important implications for development of novel antiinflammatory therapeutics.

Amino Acid Sequence↗

PubMed1994

The A-domain of beta 2 integrin CR3 (CD11b/CD18) is a receptor for the hookworm-derived neutrophil adhesion inhibitor NIF.

The A-domain is a approximately 200-amino acid peptide present within structurally diverse proadhesive proteins including seven integrins. A recombinant form of the A-domain of beta 2 integrins CR3 and LFA-1 has been recently shown to bind divalent cations and to contain binding sites for protein ligands that play essential roles in leukocyte trafficking to inflammatory sites, phagocytosis and target cell killing. In this report we demonstrate that the neutrophil adhesion inhibitor, NIF produced by the hookworm Ancyclostoma caninium is a selective CD11b A-domain binding protein. NIF bound directly, specifically and with high affinity (Kd of approximately 1 nM) to recombinant CD11b A-domain (r11bA). The binding reaction was characterized by rapid association and very slow dissociation, and was blocked by an anti-r11bA monoclonal antibody. No binding was observed to rCD11aA. The NIF-r11bA interaction required divalent cations, and was absent when the mutant r11bA D140GS/AGA (that lacks divalent cation binding capacity) was used. The NIF binding site in r11bA was mapped to four short peptides, one of which being an iC3b binding site. The interaction of NIF with CR3 in intact cells followed similar binding kinetics to those with r11bA, and occurred with similar affinity in resting and activated human neutrophils, suggesting that the NIF epitope is activation independent. Binding of NIF to CR3 blocked its ability to bind to its ligands iC3b, fibrinogen, and CD54, and inhibited the ability of human neutrophils to ingest serum opsonized particles. NIF thus represents the first example of a disintegrin that targets the integrin A-domain, and is likely to be used by the hookworm to evade the host's inflammatory response. The unique structure of NIF, which lacks a disintegrin motif, emphasizes basic structural differences in antagonists targeting A+ and A- integrins, that should be valuable in drug design efforts aimed at generating novel therapeutics. Identification of the region in NIF mediating A-domain binding should also be useful in this regard, and may, as in the case of disintegrins, unravel a new structural motif with cellular counterparts mediating important physiologic functions.

Amino Acid Sequence↗

PubMed1994

The human beta 2 integrin CD18 promoter consists of two inverted Ets cis elements.

To define the minimal promoter responsible for expression of CD18 in myeloid and lymphoid cells, we generated 5' and 3' deletion constructs of a segment extending 785 bp upstream and 19 bp downstream of a major transcription start site and determined their effects on driving expression of the luciferase reporter gene in transfected hematopoietic cell lines. A region extending from nucleotides (nt) -302 to +19 was sufficient for cell-restricted and phorbol ester-inducible expression. DNase I footprinting of this region revealed two adjacent protected segments extending from nt -81 to -68 (box A) and -55 to -41 (box B). When a construct of 47 nt in length containing box A and box B and lacking other 3' or 5' elements was cloned into a promoterless vector, it conferred tissue-specific and phorbol ester-inducible expression. Gel retardation revealed that the protein components of two major protein-DNA complexes that form on both box A and box B and are required for transcriptional activation are members of the Ets oncoprotein family; one is related to the GA-binding protein (GABP), and the other is related to PU.1/Spi-1. The minimal CD18 promoter, lacking TATA, CAAT, and initiator elements and consisting primarily of Ets repeats, may exemplify an emerging class of promoters with which the concerted binding of Ets factors is necessary and sufficient to mediate transcriptional activation through direct recruitment of the basal transcription machinery.

Antigens, CD↗

PubMed1994

Prevalence of abnormal thyroid function tests in connective tissue disease.

The prevalence of thyroid function tests' abnormalities in 170 patients with various connective tissue diseases (CTD) was examined and compared to a group of 100 age- and sex-matched controls. The overall prevalence of diagnosed thyroid disease was 3.5%. Categorizing the patients into 5 "functional groups" by the concurrent thyroid function test/results showed normal thyroid function tests in 14%, isolated elevated TSH levels with normal T4 and T3 levels in 4% and findings consistent with the laboratory diagnosis of primary hypothyroidism in 3%. The "euthyroid sick syndrome" was evidenced in 54% and elevated T4 levels and/or increased or normal T3 values with normal TSH in 25%. Antimicrosomal antibodies were noted in 12 patients (7%), with the highest incidence in systemic lupus erythromatosus patients (10%). patients with mixed connective tissue disease had significantly (p < 0.0005) higher frequency of hypothyroidism, whereas patients with systemic vasculities had higher frequency of hyperthyroxinemia. In conclusion, CTD patients frequently have abnormal results of one or more of thyroid function tests. Hypothyroidism and hyperthyroidism should be considered when evaluating symptoms and signs in CTD and a significant subset of CTD patients appears to be predisposed to the development of hyperthyroidism.

Adolescent↗

PubMed1992

Wegener granulomatosis.

Explore the source record for details and available documents.

Antibodies, Antineutrophil Cytoplasmic↗

PubMed1992

Genetic cause of leukocyte adhesion molecule deficiency. Abnormal splicing and a missense mutation in a conserved region of CD18 impair cell surface expression of beta 2 integrins.

Patients with leukocyte adhesion molecule (CD11/CD18, beta 2 integrins) deficiency have structural defects in the common beta subunit (CD18), which prevent heterodimer formation and normal cell surface expression of these receptors, leading to life-threatening bacterial infections. To elucidate the nature of these defects in a patient with partial (type II) deficiency, abnormal CD18 cDNA clones were isolated, using the polymerase chain reaction to amplify the patient's B cell-derived cDNAs. Sequence analysis revealed two mutant alleles. cDNA clones, representing a maternal allele, contained both a 12-base pair insertion resulting in an in-frame addition of four amino acids between P247 and E248 and a C1756----T nucleotide transition, resulting in an R586----W substitution in the normal CD18 protein. The inframe insertion arose by a single nucleotide C----A transversion in the 3' terminus of an intron, generating aberrant splice acceptor site. Other cDNA clones contained an A1052----G nucleotide transition not present in either parent which resulted in an N351----S substitution. To determine the functional importance of these changes, cDNA encoding a normal alpha chain (CD11b) was cotransfected into COS with CD18 cDNAs encoding for wild-type, maternal mutant allele, or CD18 containing N351----S substitution. Immunostaining of transfectants with anti-CD18 monoclonal antibodies revealed no cell surface expression of the maternal mutant CD18, and 22% surface expression of N351----S CD18. Both the insertion and the N351----S mutations occurred in a 250 amino acid extracellular region of CD18 that is highly conserved among beta integrins supporting a role for this region in heterodimer formation.

Amino Acid Sequence↗

PubMed1992

Antineutrophil cytoplasmic autoantibody-associated vasculitis presenting as Sjögren's syndrome.

A 63-year-old woman, in whom a diagnosis of Sjögren's syndrome was initially made, proved to have systemic vasculitis with salivary gland involvement and necrotizing and crescentic glomerulonephritis. Antineutrophil cytoplasmic autoantibodies (ANCA) against myeloperoxidase were positive. ANCA-associated vasculitis should be considered in the differential diagnosis of Sjögren's syndrome. A positive finding on immunoassay for ANCA against myeloperoxidase or proteinase 3 may help establish the diagnosis.

Antibodies, Antineutrophil Cytoplasmic↗

PubMed1992

On the regulation of beta 2 integrins.

The complex functions played by beta 2 integrins in mediating a large variety of adhesive interactions of leukocytes are highly regulated. This regulation results in transient adaptations/associations, permitting physical and functional recycling of these receptors during chemotaxis, phagocytosis and target-cell killing. The structural definition of these adaptations will lead not only to a better understanding of how these receptors are regulated in leukocytes but also shed valuable light on how these integrins integrate diverse extracellular signals into spatially and temporaly coordinated cellular responses.

Amino Acid Sequence↗

PubMed1992

Neutrophil migration across a cultured epithelial monolayer elicits a biphasic resistance response representing sequential effects on transcellular and paracellular pathways.

Migration of polymorphonuclear leukocytes across epithelia is a hallmark of many inflammatory disease states. Neutrophils traverse epithelia by migrating through the paracellular space and crossing intercellular tight junctions. We have previously shown (Nash, S., J. Stafford, and J.L. Madara. 1987. J. Clin. Invest. 80:1104-1113), that leukocyte migration across T84 monolayers, a model human intestinal epithelium, results in enhanced tight junction permeability--an effect quantitated by the use of a simple, standard electrical assay of transepithelial resistance. Here we show that detailed time course studies of the transmigration-elicited decline in resistance has two components, one of which is unrelated to junctional permeability. The initial decrease in resistance, maximal 5-13 min after initiation of transmigration, occurs despite inhibition of transmigration by an antibody to the common beta subunit of neutrophil beta 2 integrins, and is paralleled by an increase in transepithelial short-circuit current. Chloride ion substitution and inhibitor studies indicate that the early-phase resistance decline is not attributable to an increase in tight junction permeability but is due to decreased resistance across epithelial cells resulting from chloride secretion. Since T84 cells are accepted models for studies of the regulation of Cl- and water secretion, our results suggest that neutrophil transmigration across mucosal surfaces (for example, respiratory and intestinal tracts) may initially activate flushing of the surface by salt and water. Equally important, these studies, by providing a concrete example of sequential transcellular and paracellular effects on transepithelial resistance, highlight the fact that this widely used assay cannot simply be viewed as a direct functional probe of tight junction permeability.

Cell Movement↗

PubMed1992

Late-onset congenital adrenal hyperplasia in women with hirsutism.

Hirsutism in women is a clinical manifestation of excessive production of androgens. The source of the excess androgen may be either the ovaries or the adrenal glands, or increased peripheral conversion of weak androgenic hormones to more potent androgens. Late-onset (non-classic) congenital adrenal hyperplasia is a cause of hirsutism in adult women, but its frequency and the patterns of abnormalities in adrenal hormone secretion are not well understood. The frequency of non-classical adrenal hyperplasia due to deficiencies of 3 beta-hydroxy-delta 5-steroid dehydrogenase, 21-hydroxylase, and 11 beta-hydroxylase among 65 women with hirsutism were determined. All enzyme defects were identified by comparing the patients' hormonal responses to 0.25 mg intravenous bolus of alpha 1-24-ACTH with those of age-matched normal women. The hormones measured in plasma during the ACTH stimulation tests were progesterone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, DHEA-sulfate, androstenedione, testosterone, 11-deoxycortisol, and cortisol. Similarly these hormones were measured after overnight 1 mg oral dexamethasone. Twelve women (18.5%) had 3 beta-hydroxy-delta 5-steroid dehydrogenase deficiency, 24 (37%) 21-hydroxylase deficiency, and 14 (21.5%) 11 beta-hydroxylase deficiency. Women with 21-hydroxylase deficiency also had evidence of a partial deficiency in 11 beta-hydroxylase activity (12 of the 24 patients). Similarly, most (11 of the 14) of the women with 11 beta-hydroxylase deficiency also had evidence of a deficiency in 3 beta-hydroxy-delta 5-steroid dehydrogenase activity. Among the 15 patients with no adrenal biosynthetic defect, eight had high plasma androgen concentrations, and seven had normal concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗

PubMed1992

Effect of an anti-Mo1 MAb on ozone-induced airway inflammation and airway hyperresponsiveness in dogs.

Ozone inhalation causes neutrophil migration into the airway and airway hyperresponsiveness in dogs. The leukocyte adhesion molecule Mo1 (CD11b/CD18) is a heterodimeric glycoprotein the expression of which is necessary for neutrophil adhesion to endothelium. To evaluate the contribution of Mo1 to ozone-induced neutrophil influx and airway hyperresponsiveness, six dogs were treated intravenously with an Anti-Mo1 monoclonal antibody (3.75 mg/kg in normal saline) that binds to both human and canine Mo1, or the diluent alone, 1.5 h before inhaling ozone (3 ppm for 30 min), or dry air. Airway responses to doubling doses of inhaled acetylcholine (ACh) were measured before and after inhalation of ozone. Neutrophil influx was assessed by bronchoalveolar lavage (BAL) performed after the second ACh inhalation. Treatment with anti-Mo1 prevented the ozone-induced influx of neutrophils into BAL. After diluent and inhaled dry air, the neutrophil count in BAL was 1.49 +/- 1.26 (SE) x 10(4) (5.0% of total cells). After diluent and inhaled ozone, the neutrophil count increased to 7.27 +/- 3.22 (SE) x 10(4) (22.6% of total cells) (P < 0.05). After anti-Mo1 and inhaled ozone, the neutrophil count was 1.48 +/- 0.62 (SE) x 10(4) (8.5% of total cells). Treatment with anti-Mo1 also significantly reduced the number of eosinophils in BAL after ozone. Ozone-induced ACh airway hyperresponsiveness was not prevented by treatment with anti-Mo1. These results indicate that expression of Mo1 is necessary for ozone-induced neutrophil migration into the airway lumen.

Acetylcholine↗

PubMed1992

Arginine-vasopressin and endothelium-associated proteins in thyroid disease.

Plasma concentrations of endothelium-derived proteins (fibronectin and von Willebrand factor), liver synthesized proteins (haptoglobin, transferrin, ceruloplasmin, alpha 1-antitrypsin, antithrombin III and factor VIII-coagulant) and plasma arginine-vasopressin (AVP) were measured in 12 hyperthyroid, 9 hypothyroid and 15 age- and sex-matched normal controls. In hyperthyroid patients the plasma concentrations of AVP and endothelium-associated proteins (EAP) were significantly higher than in the control group (p less than 0.05 and p less than 0.01 respectively). Rendering hyperthyroid patients into the euthyroid state significantly lowered AVP (p less than 0.01), fibronectin (p less than 0.05) and von Willebrand factor (p less than 0.01) compared with pretreatment levels. Hypothyroid patients were studied at diagnosis and after replacement therapy with levothyroxine. Compared with pretreatment values, significant increases were noted in plasma concentrations of von Willebrand factor, fibronectin and AVP (p less than 0.01). With the exception of factor VIII-coagulant, the concentrations of hepatic synthesized proteins did not deviate from normal values in hyperthyroid and hypothyroid patients. Significant correlations were found between serum-free thyroxine on the one hand and the plasma concentrations of fibronectin (p less than 0.005), von Willebrand factor (p less than 0.001) and AVP (p less than 0.0001). Similarly, there was significant correlation between the plasma concentrations of AVP on the one hand and fibronectin (p less than 0.002) and von Willebrand factor (p less than 0.01). The results demonstrate elevated plasma levels of AVP in hyperthyroid patients and an increase during levothyroxine treatment of hypothyroid patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗