Structure and function of intercellular adhesion molecule-1.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
N Hogg
Publications and source records attributed to N Hogg.
An integrin overview.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Reactions of reduced cellobiose oxidase with oxygen. Is cellobiose oxidase primarily an oxidase?
We report rapid-mixing experiments in which cellobiose oxidase, fully reduced with cellobiose, is allowed to react with excess molecular O2. Analysis of the progress curves and their comparison with computer simulations suggests that O2 reacts only with the cytochrome b-type haem and with a rate constant of approx. 0.5 s-1. In steady state the cytochrome b is partially oxidized, whereas the flavin remains largely reduced. This situation may be contrasted with that when dichloroindophenol is substituted for O2. Under these conditions the reactions are rapid (millisecond time range), and the redox centres in the enzyme appear to be oxidized simultaneously.
Anaerobiosis↗
Activation of platelets induced by mAb P256 specific for glycoprotein IIb-IIIa. Possible evidence for a role for IIb-IIIa in membrane signal transduction.
Monoclonal antibody P256, which is specific for glycoprotein IIb-IIIa complex, was found to induce aggregation of normal platelets in plasma. The mechanism of platelet activation induced by this monoclonal antibody was thoroughly studied. The divalent binding to the IIb-IIIa molecule was necessary for triggering aggregation since Fab' fragments did not induce aggregation as did IgG and F(ab')2 fragments; however, F(ab')2 did not induce the release as did the whole IgG. P256-induced aggregation was accompanied by release of all three granule constituents, namely dense granules, alpha-granules and lysosomes, with parallel kinetics showing half-maximum release 50 s after addition of P256. Thromboxane synthesis was initiated at the same time. Using 32P-prelabeled platelets, no variation in level of [32P]phosphatidylinositol 4,5-bisphosphate could be detected in the first minute after P256 addition, indicating no activation of the calcium-independent phospholipase C specific for polyphosphoinositol phospholipid. P256 induced a calcium mobilization as measured by Indo-1 fluorescence of about the third of that measured in the presence of a thrombin concentration giving the same intensity of aggregation. P256 induced phosphorylation of the myosin light chain p20 and of the main substrate of protein kinase C, p43. Addition of aspirin inhibited almost totally calcium mobilization and partially aggregation, release and protein phosphorylations. By contrast, in the absence of external calcium, although no aggregation could occur, the release reaction was only partially reduced. In this activation, the glycoprotein IIb-IIIa complex thus appears to play a role in modulating platelet response, not only via calcium fluxes but also in activating protein kinase C responsible for p43 phosphorylation.
Animals↗
Vitronectin receptor-mediated phagocytosis of cells undergoing apoptosis.
Phagocyte recognition of cells that have undergone apoptosis (programmed cell death) is an event of broad biological significance. Characterized by endogenous endonuclease activation, which results in chromatin fragmentation and nuclear condensation, apoptosis leads to swift ingestion of intact but 'senescent' or 'unwanted' cells by phagocytes in processes as diverse as the physiological involution of organs, the remodelling of embryonic tissues, and metamorphosis. The cell-surface mechanisms by which macrophages recognize apoptotic cells as 'senescent-self' have remained obscure. Here we report that macrophage recognition of apoptotic cells (both neutrophils and lymphocytes) is mediated by the vitronectin receptor, a heterodimer belonging to the beta 3 or cytoadhesin family of the integrins. Previously, the functions of the vitronectin receptor were believed to be limited to cell anchorage, but our findings indicate that the receptor has a novel and direct role in self-senescent-self intercellular recognition leading to macrophage phagocytosis of cells undergoing apoptosis.
Humans↗
Human memory T cells express intercellular adhesion molecule-1 which can be increased by interleukin 2 and interferon-gamma.
We have shown that low levels of intercellular adhesion molecule-1 (ICAM-1) expression can be detected on approximately 40% of the resting peripheral blood T cell population. The ICAM-1+ T cells have the phenotypic markers of memory cells which can be distinguished functionally from naive T cells by their ability to respond rapidly to previously experienced antigen. These cells appear to be in a state of marginal activation in that they also express low levels of the interleukin 2 receptor (Tac antigen) and have increased cell size as compared to the naive T cells. In addition we have shown that the cytokines interleukin 2 and interferon-gamma, both of which are products of activated T cells, are able to increase the expression of ICAM-1 on T cells. Finally, pretreating T cells with an anti-ICAM-1 monoclonal antibody inhibits their response to recall antigens, strongly suggesting a functional role for this protein on the memory T cell.
Antigens, Differentiation↗
Colony-stimulating factors and interferon-gamma differentially affect cell surface molecules shared by monocytes and neutrophils.
Monocytes and neutrophils share a common progenitor and perform many similar functions, as reflected in the expression of several shared membrane molecules. We show here that such molecules can be independently regulated by the cytokines interferon-gamma (IFN-gamma) and the colony-stimulating factors (CSF) in the context of the cell type on which they are present. Thus, IFN-gamma causes neutrophils to express the high-affinity receptor for IgG, Fc gamma RI, which has been considered to be a monocyte-specific receptor. Although neutrophil Fc gamma RI never reaches the levels present on monocytes, it is induced more rapidly and by lower amounts of IFN-gamma than monocyte Fc gamma RI. Of the CSF, only macrophage (M) CSF has an effect which is to cause a decrease in expression of monocyte Fc gamma RI. Secondly, after culture monocytes express Fc gamma RIII which is constitutively expressed by neutrophils. Although neutrophil Fc gamma RIII can be readily modulated by IFN-gamma, granulocyte (G) CSF and granulocyte-macrophage (GM) CSF, these cytokines do not alter the low levels of monocyte Fc gamma RIII. Thirdly, expression of the gp55 protein recognized by CD14 monoclonal antibodies is decreased after exposure of monocytes to IFN-gamma. Neutrophils express low levels of CD14 and, in this case, IFN-gamma causes an increase in the CD14 antigen on these cells. Of all the molecules investigated, only HLA class II is confined to monocytes, with increases in expression induced by IFN-gamma but not by the CSF.
Antibodies, Monoclonal↗
Early events of the immune response mediated by leukocyte integrins.
Explore the source record for details and available documents.
Animals↗
Regulated expression of Mg2+ binding epitope on leukocyte integrin alpha subunits.
The leukocyte integrins LFA-1, CR3 and p150,95 are a family of heterodimeric receptors that mediate divalent cation-dependent cellular adhesion reactions. In this study we describe a novel antibody-defined epitope present on the leukocyte integrin alpha subunits indicating that the antibody recognizes a structural feature common to all three polypeptides. Antibody recognition further differs from that of previously described anti-leukocyte integrin antibodies in that it is strictly dependent upon the presence of Mg2+. This suggests that the epitope is located within, or in close proximity to, the three conserved cation binding domains and is therefore a measure of Mg2+ bound to the leukocyte integrins and thus reflects functionally active molecules. The epitope can be induced on polymorphonuclear leukocytes, a subset of T cells and on monocytes but is absent or much reduced at low temperature or in the presence of metabolic inhibitors. These observations have considerable implications for the regulation of leukocyte integrin function suggesting that Mg2+ binding to the extracellular domain(s) of the alpha subunits is controlled from within the cell. We suggest that one mechanism by which ligand binding by these molecules can be 'switched' on and off in response to external signals is by regulation of Mg2+ binding to these molecules, converting from the cation-free, 'inactive' to the Mg2+-bound, 'active' form.
Antibodies, Monoclonal↗
Ionomycin-regulated phosphorylation of the myeloid calcium-binding protein p14.
Two associated calcium-binding proteins (CaBPs) have recently been identified specifically in cells of myeloid origin. These proteins have relative molecular masses (Mr) of 8,000 and 14,000 and are variously referred to as the cystic fibrosis antigen, the L1 light chain, MRP-8 or p8, and the L1 heavy chain, MRP14 or p14, respectively. The expression of p8 and p14 seems to be confined to a specific stage of myeloid cell differentiation, because both proteins are expressed in circulating neutrophils and monocytes but not in normal tissue macrophages. In chronic inflammatory conditions, however, such as rheumatoid arthritis, macrophages in affected tissues express both p8 and p14. These proteins are members of a family of CaBPs of low Mr, which include S-100 alpha and beta proteins, calcyclin (2A9), intestinal CaBP and p11. All the proteins have an Mr of approximately 10,000 with the exception of p14 which has a longer C-terminal sequence after the second calcium-binding domain. Little is known about their function, although by analogy with calmodulin they could be molecules involved in intracellular signalling that are activated by an increase in the intracellular Ca2+ concentration ([Ca2+]). Here we report that p14 is phosphorylated in both monocytes and neutrophils. The level of p14 phosphorylation can be increased by elevating the [Ca2+]i using the ionophore ionomycin, but is not affected by activation of protein kinase C using phorbol 12,13-dibutyrate. The phosphorylated residue is threonine at position 113, which is the penultimate amino acid in p14 and contained in the longer 'tail' sequence. Part of this sequence is identical to the neutrophil immobilizing factors NIF-1 and NIF-2, indicating that the phosphorylation event could have a role in the generation of NIF activity in the p14 protein.
Amino Acid Sequence↗
The effect of IFN-gamma and colony-stimulating factors on the expression of neutrophil cell membrane receptors.
The recombinant cytokines IFN-gamma, granulocyte-macrophage (GM)-CSF, and granulocyte (G)-CSF are all known to affect the function of neutrophils. We have investigated their ability to alter the surface expression of neutrophil Fc gamma R and CR. FcRI, formerly considered to be mononuclear phagocyte specific, was found on a variable percentage of neutrophils after 12 h of tissue culture. These levels could be readily enhanced by IFN-gamma at 0.5 U/ml suggesting that neutrophil FcRI is extremely sensitive IFN-gamma. In addition, membrane expression of FcRIII, the most abundant receptor of neutrophils, could also be increased by IFN-gamma and by GM-CSF and G-CSF. However, the opposite effect was observed in samples in which the initial levels of FcRIII were high. In these situations IFN-gamma and GM-CSF caused a decrease in receptor expression. No consistent alterations were found in the levels of FcRII. Cytokine-induced increases in both FcRI and FcRIII were not evident within the first hour of treatment suggesting that these molecules are not available in an intracellular compartment but must be newly synthesized. In contrast, the CR, CR1 and CR3, could be rapidly induced by GM-CSF indicating that this cytokine causes the mobilization of preformed molecules to the membrane. G-CSF and IFN-gamma did not alter the expression of CR1 and CR3. Thus, the very different effects of IFN-gamma, GM-CSF, and G-CSF suggest that the neutrophil functional profile will be distinctively affected by exposure to each of these cytokines.
Antigens, Differentiation↗
Sequence identity.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Cotransfection of ICAM-1 and HLA-DR reconstitutes human antigen-presenting cell function in mouse L cells.
The initiation of a specific immune response is believed to require not only activation through antigen-specific receptors on T cells and B cells but also antigen-independent interactions between accessory molecules. One such molecule is LFA-1, which enhances the avidity of interactions between T cells and antigen-presenting cells, and is possibly involved in signal transduction across the T-cell membrane. Intercellular adhesion molecule-1 (ICAM-1), a surface glycoprotein of relative molecular mass (Mr) 80,000-110,000, has been defined as a ligand for LFA-1, and has been shown to participate in the interaction between T cells and monocytes. The determination of the precise contribution of such accessory molecules to antigen presentation, however, is complicated by the need to analyse against a background of multiple molecular interactions. We have investigated the role of LFA-1/ICAM-1 interactions in antigen presentation directly by quantifying the contribution of ICAM-1 expression to T-cell stimulation using L-cell transfectants that co-express ICAM-1 and HLA-DR. In the case of transfectants expressing modest levels of HLA-DR, co-expression of ICAM-1 is critical for effective HLA class II-restricted and allospecific T-cell activation, pointing to an important role for ICAM-1 in the induction of T-cell responses.
Animals↗
Monoclonal antibody 5.5 reacts with p8,14, a myeloid molecule associated with some vascular endothelium.
The movement of mononuclear phagocytes and neutrophils from the circulation into tissues is a process which is not completely understood. Monoclonal antibody 5.5 is specific for an 8/14-kDa molecule known variously as the CF antigen, L1 molecule or MRP8 and 14. We show that this molecule, which will be named p8,14 in this study, is expressed in all circulating monocytes and neutrophils as an intracellular product (as well as some types of epithelium). Tissue staining patterns suggest that when monocytes and neutrophils adhere to vascular endothelium, they release this molecule onto the associated endothelium. This process occurs with single monocytes and when monocytes form part of an inflammatory infiltrate. Monoclonal antibody 5.5 does not react with cultured endothelial cells even when stimulated with phorbol ester, tumor necrosis factor, interferon-gamma or interleukin 1 alpha providing further evidence that myeloid cells are the source of the p8,14 in this interactive process. Monocytes which have moved further into such tissues and tissue macrophages in general are monoclonal antibody 5.5 negative, suggesting that the ability to synthesize this molecule may be lost when monocytes leave the circulation and enter tissues. These results indicate that p8,14 plays a role in the interaction between myeloid cells and the vascular endothelium to which they adhere prior to leaving the circulation.
Antibodies, Monoclonal↗
The leukocyte integrins.
During the 1980s, various laboratories identified a rare type of patient suffering from recurrent bacterial infections whose neutrophils showed reduced spreading on surfaces. Such leukocyte adhesion deficient (LAD) patients were shown to lack a trio of molecules named either LFA-1, CR3/Mac-1/Mo1, p150,95/CR4 or CD11, CD18 or the leukocyte integrin family. In September 1988, the first meeting exclusively devoted to this topic was held.
Antigens, Surface↗
Activity of two types of Fc receptors, Fc gamma RI and Fc gamma RII, in human monocyte cytotoxicity to sensitized erythrocytes.
We investigated the cytotoxicity of human monocytes mediated by two types of receptors for the Fc portion of IgG, Fc gamma RI and Fc gamma RII. Erythrocytes sensitized with human IgG (EA-human IgG) were used to assay Fc gamma RI function, and erythrocytes sensitized with mouse IgG1 (EA-mouse IgG1) were used to assay Fc gamma RII. Both types of Fc gamma R were observed to mediate antibody-dependent cell-mediated cytotoxicity (ADCC), which was further characterized by using different monoclonal anti-Fc gamma R antibodies (MoAb) and monomeric IgG. Lysis of EA-human IgG was inhibited by both monomeric human IgG and mouse IgG2a in a dose-dependent way, and also by anti-Fc gamma RI MoAb 10.1. Cytolysis of EA-mouse IgG1 was inhibited by monomeric mouse IgG1 and by two anti-Fc gamma RII MoAb, IV.3 and CIKM5. Antibodies of the mouse IgG2b isotype affected neither type of ADCC. The effectiveness of cytotoxicity mediated by either of the Fc gamma R was studied by means of targets sensitized with a calibrated number of IgG molecules. At least 20 times more IgG molecules per target cell were necessary to obtain half-maximal cytotoxicity mediated by Fc gamma RII than for Fc gamma RI-mediated cytolysis. Furthermore, the previously described polymorphism of Fc gamma RII was also reflected in Fc gamma RII-dependent cytotoxicity. These studies demonstrate that Fc gamma RII can mediate ADCC, although a higher degree of target cell sensitization is required than for Fc gamma RI-mediated ADCC.
Animals↗
Absence of monocyte procoagulant activity during the immune response to influenza virus.
The ability of mononuclear phagocytes (MPh) to manifest procoagulant activity (PCA) resulting in the formation of fibrin is thought to be a key MPh effector function in tissue repair. The present study addresses the question of whether monocyte PCA is confined to tissue hypersensitivity reactions or is a general correlate of all immune responses. We show here that PCA is not the obligate outcome when the immune system is stimulated. In particular, under in vitro conditions in which a mitogen (phytohemagglutinin) or an antigen (purified protein derivative of tuberculin) elicits good PCA responses, incubation with influenza virus does not result in the generation of PCA, although other parameters of response to the virus appear to be intact. Moreover, influenza virus can cause suppression of PCA when cultures are stimulated with either phytohemagglutinin, purified protein derivative of tuberculin, or endotoxin, conditions which would otherwise result in good PCA responses. This lack of PCA persists throughout the culture period and is not caused by an effect of influenza virus on the viability of either MPh or leukocytes in general.
Antibody Formation↗
The Fc receptor, FcRI, and other activation molecules on human mononuclear phagocytes after treatment with interferon-gamma.
Human monocytes and the myeloid cell lines U937 and HL60 have been tested with monoclonal antibodies (MoAbs) reactive with 22 different cell surface molecules before and after treatment with interferon-gamma (IFN-gamma). An increase in the expression of the high affinity Fc receptor, FcRI, and the receptor for interleukin 2, IL-2R, were the most consistent alterations which were observed. In addition, expression of the gp55 molecule recognized by CD14 MoAbs was decreased on monocytes. Of the MHC Class II molecules, there was little expression by the myeloid cell lines and no enhancement after IFN-gamma treatment. In contrast monocytes expressed all three MHC Class II subloci with DR much greater than DQ and DP. However there was much variation in IFN-gamma-mediated increase in expression of the individual subregions. In monocytes, the alteration in expression of FcRI, IL-2R, gp55 and MHC Class II molecules took place in a co-ordinate fashion and reached a plateau only after 48 h. In U937 cells, activation proceeded more rapidly and was at maximum levels between 12-16 h. This increase in FcRI appears to be a hallmark of IFN-gamma activation for mononuclear phagocytes (Mph) as the other alterations are either not found on all types of Mph (gp55, MHC Class II) or are induced by other cytokines on Mph and on other cells (IL-2R, MHC Class II). Conversely, other cytokines do not induce FcRI on Mph. These results also suggest that the cell membrane phenotypic changes induced in Mph by IFN-gamma may not be extensive and that FcRI must play a specific role in the IFN-gamma-activated Mph.
Antigens, Surface↗