A leukocyte integrin binding peptide from intercellular adhesion molecule-2 stimulates T cell adhesion and natural killer cell activity

Adhesion is of pivotal importance for a number of leukocyte functions. Little is known about the binding between leukocyte integrins and the intercellular adhesion molecules (ICAMs). Normally integrins are nonadhesive, and require a stimulus to become active. We have now identified a peptide from ICAM-2, which binds to leukocyte integrins and activates adhesion. Furthermore, the peptide strongly increased the binding and cytotoxicity of natural killer cells. These findings show that adhesion-dependent leukocyte functions can be activated by ligand-derived peptides, and therefore provide evidence that the avidity of leukocyte integrins is up-regulated by integrin-ligand interactions.

Regulation of CD18 expression in human neutrophils as related to shape changes

The study analyses the distribution and quantitative expression of surface CD18 of neutrophils exposed to distinct stimuli that produce different types of continuous shape changes, including types that are associated with locomotion and others that are not. The chemotactic peptide N-formyl-L-norleucyl-L-leucyl-L-phenylalanine, colchicine and nocodazole were used to induce a polarized locomotor morphology, phorbol myristate acetate, 1,2-dioctanoylglycerol and 1-oleoyl-2-acetyl-glycerol to induce non-polar motile cells ruffling all over the surface and 2H2O to induce non-polar cells performing circus movements as have been previously described. Except for colchicine and nocodazole, these stimuli increased surface expression of CD18. Thus, stimulated shape changes are frequently, though not always, associated with increased surface expression of CD18. High concentrations (10(−7) to 10(−5) M) of phorbol myristate acetate but not of chemotactic peptide induced down-regulation of surface CD18. Cytochalasin D (10(−4) M) stimulated CD18 expression even though it inhibited shape changes. The surface distribution of CD18 determined by light microscopy was uniform in unstimulated cells or in various forms of stimulation except for cells treated with 10(−5) M cytochalasin D. Cytochalasin D (10(−5) M) produced CD18 accumulation at the pole opposite the F-actin cap. Experiments with colchicine, nocodazole, 2H2O and cytochalasin D suggest that microtubules as well as microfilaments modulate surface expression of CD18. The results suggest that protein kinase C and phosphatases play a role in regulating surface expression of CD18 in neutrophils.(ABSTRACT TRUNCATED AT 250 WORDS)

Heparin-coated bypass circuits reduce pulmonary injury

Heparin coating of the extracorporeal circuit not only reduces heparin requirements during cardiac operations but also may reduce organ injury associated with cardiopulmonary bypass (CPB). To examine this possibility, pulmonary injury and neutrophil adhesion molecule expression after CPB were studied in pigs undergoing CPB with a standard extracorporeal circuit (group S, n = 6) or a heparin-coated CPB circuit (Carmeda BioActive Surface) (group HC, n = 6). Pigs received heparin sodium (300 U/kg intravenously) and then underwent 90 minutes of hypothermic (28 degrees C) CPB using membrane oxygenators, followed by 2 hours of observation. Blood samples were obtained for determination of neutrophil number and expression of the neutrophil adhesion molecule subunit CD18 (by immunofluorescence flow cytometry). The CPB-associated injury was less in group HC. Two hours after CPB, the arterial oxygen tension group was higher in group HC (597.2 +/- 31.2 versus 220.5 +/- 42.3 mm Hg; p < 0.0001), the pulmonary vascular resistance was lower in these animals (408.6 +/- 69.4 versus 1,159.8 +/- 202.4 dyne.s.cm-5; p = 0.02), and the static compliance was higher in group HC (66.4 +/- 5.4 versus 39.8 +/- 5.8 mL/mm Hg; p = 0.004). After 60 minutes of CPB, both groups had similar increases in expression of the neutrophil adhesion molecule subunit CD18 (29.4% +/- 19.5% versus 26.0% +/- 24.4%, group S and group HC, respectively) and similar decreases in neutrophil counts (6,056 +/- 1,285 to 2,453 +/- 979 cells/microL versus 6,010 +/- 1,748 to 3,197 +/- 1,225 cells/microL, group S and group HC, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible opening of the blood-brain barrier by anti-bacterial antibodies

The leukocyte adhesion molecule CR3 (CD11b/CD18, Mac-1) promotes leukocyte transmigration into tissues by engaging an unknown cognate ligand on the surface of vascular endothelial cells. Filamentous hemagglutinin (FHA), an adhesin of the bacterium Bordetella pertussis, binds to CR3. We hypothesized that FHA mimics the native ligand for the CR3 integrin on endothelial cells and predicted that anti-FHA antibodies should bind to endothelial cells, interfere with leukocyte recruitment, and induce endothelial permeability. Anti-FHA monoclonal antibodies bound to cerebral microvessels in sections from human brain and upon intravenous injection into rabbits. Antibody binding correlated with the ability to recognize two polypeptides in extracts of human cerebral vessels that were also bound by CD18. In vivo, antibody binding not only interfered with transmigration of leukocytes into cerebrospinal fluid but also induced a dose-dependent reversible increase in blood-brain barrier permeability sufficient to improve delivery of intravenously administered therapeutic agents to brain parenchyma.

Increased expression of neutrophil and monocyte adhesion molecules in unstable coronary artery disease

BACKGROUND

A rapid increase in leukocyte adhesion to endothelial cells is one of the first events in the acute inflammatory response and in the pathogenesis of vascular diseases. A subgroup of cell surface glycoproteins (the CD11/CD18 complex) play a major role in the leukocyte adhesion process; in particular, the CD11b/CD18 receptor can be upregulated severalfold in response to chemotactic factors. The purpose of this study was to assess whether upmodulation of granulocyte and monocyte CD11b/CD18 receptors takes place during the passage of blood through the coronary tree of patients with clinical manifestations of ischemic heart disease.

METHODS AND RESULTS

Thirty-nine patients who underwent diagnostic coronary arteriography were studied. Group 1 (15 patients) had a clinical diagnosis of unstable angina, group 2 (14 patients) had stable exertional angina, and group 3 (10 patients) had atypical chest pain. Simultaneous sampling from the coronary sinus and aorta was obtained before coronary arteriography. Cell surface receptors were detected by direct immunofluorescence evaluated by flow cytofluorimetry using monoclonal antibodies tagged with fluorescent markers. Leukocytes were stained in unseparated blood to avoid in vitro manipulation that could activate phagocytes. Group 1 and 2 patients had significant coronary artery disease (> 50% coronary narrowing in at least one major coronary vessel), whereas group 3 patients had normal coronary arteries. In group 1, granulocytes and monocytes showed a significantly higher expression of the CD11b/CD18 adhesion receptor in the coronary sinus than in the aorta (both P < .01), whereas no difference in CD11b/CD18 expression was seen in groups 2 and 3.

CONCLUSIONS

Patients with unstable angina have an increased expression of granulocyte and monocyte CD11b/CD18 adhesion receptors, indicating that an inflammatory reaction takes place within their coronary tree. Activation of these leukocytes may induce coronary vasoconstriction, favor thrombotic processes, and further activate platelets, thus having potential implications on the pathogenesis of unstable coronary artery disease.

Activation of neutrophils within pulmonary microvessels of rabbits exposed to cigarette smoke

Previous studies have shown that polymorphonuclear leukocytes (PMN) are delayed in the pulmonary capillaries by the presence of cigarette smoke. To determine if the PMN delayed by smoking are activated, we estimated the in vivo expression of CD11/CD18 and L-selectin on the surface of PMN in lungs and peripheral blood of rabbits because these molecules are known to be upregulated and downregulated, respectively, on the surface of activated PMN. New Zealand white rabbits (3.5 +/- 0.1 kg) were exposed to either air (n = 5) or cigarette smoke (n = 5), and we used an established protocol to measure pulmonary vascular blood flow, volume, and red blood cell (RBC) transit time in the left lung. The right lungs were then fixed in 0.025% glutaraldehyde and stored in liquid nitrogen. Ultrathin sections were immuno-labeled with either the anti-CD18 monoclonal antibody 60.3 or the anti-L-selectin antibody Dreg-200, followed by a secondary antibody conjugated to 10 nm colloidal gold. The target antigens were quantified by counting the number of gold particles per micron (G/microns) of PMN surface membrane. The data show that smoke exposure had no effect on pulmonary blood flow, volume, or RBC transit time. However, it increased the expression of CD11/CD18 on intravascular PMN in the upper region of the lung (control, 7.4 +/- 1.3 G/microns; smoke-exposed, 13.2 +/- 3.3 G/microns; P < 0.05) and decreased the expression of L-selectin on intravascular PMN in both the lower (control, 5.5 +/- 2.0 G/microns; smoke-exposed, 2.6 +/- 1.5 G/microns; P = 0.05) and the upper (control, 6.8 +/- 1.4 G/microns; smoke-exposed, 2.6 +/- 1.2 G/microns; P < 0.05) regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Activated T-cell adhesion to thrombospondin is mediated by the alpha 4 beta 1 (VLA-4) and alpha 5 beta 1 (VLA-5) integrins

T lymphocytes utilize adhesion receptors in a regulated manner to interact with other cells and with components of the extracellular matrix. These cell-cell and cell-matrix interactions serve a critical role in T cell recognition of foreign Ag and in the migration of T cells to various anatomic sites in vivo. Thrombospondin is an extracellular matrix protein that is transiently expressed at high concentration in damaged and inflamed tissue. Given recent evidence implicating a role for the extracellular matrix in modulating T-cell migration and function, we analyzed T-lymphocyte interactions with thrombospondin. We show here that CD4+ T cells specifically adhere to thrombospondin predominantly via the 70 kDa core region of the thrombospondin molecule. Antibody blocking and affinity chromatography analysis suggest that T-cell adhesion to thrombospondin involves three distinct receptors: an activation-independent receptor that mediates adhesion of resting T cells, and the alpha 4 beta 1 and alpha 5 beta 1 integrins, which mediate a rapid increase in adhesion to thrombospondin upon activation. These three molecules appear to be novel thrombospondin receptors, as other receptors previously implicated in the adhesion of nonlymphoid cells to thrombospondin appear not to be involved in T-cell/thrombospondin interactions. The up-regulation of alpha 4 beta 1 and alpha 5 beta 1 functional activity upon activation is associated with the preferential adhesion of memory T cells to thrombospondin. Our results thus define three novel thrombospondin receptors, and provide additional evidence that extracellular matrix proteins play an important role in lymphocyte migration into, and retention in, inflammatory sites.

Cell adhesion molecule expression in the regenerating rat facial nucleus

Transection of the rat facial nerve leads to an intrinsic microglial reaction in the facial nucleus. In the present study, we have examined immunocytochemically the expression of cell adhesion molecules during this process. Resting microglia constitutively expressed the LFA-1 alpha and beta chain (CD11a and CD18) in the white matter, rather than in the intact, control facial nucleus. From 24 h after facial nerve transection onward, activated microglia showed an increased expression of LFA-1 alpha and beta. The immunoreactivity reached its peak around day 7 following axotomy, i.e. at a time when activated microglia are found in a close perineuronal position. In contrast, the expression of the principal ligand of LFA-1, i.e. ICAM-1, remained unchanged following axotomy; the immunoreactivity being constitutively found on cerebral blood vessels. Increased LFA-1 expression thus appears to be a general marker for microglial activation and might further be involved in the rearrangement of the microglial cytoskeleton upon activation of this cell.

Stimulation of leukocyte/endothelium interaction by oxidized low-density lipoprotein in hairless mice. Involvement of CD11b/CD18 adhesion receptor complex

BACKGROUND

The adhesion of leukocytes to the vascular endothelium has been identified as a constant, early feature of atherogenesis. Using a skinfold chamber model in hamsters for intravital microscopy, we have recently demonstrated the chemotactic and adhesion-promoting action of oxidatively modified low density lipoprotein (oxLDL) in vivo.

EXPERIMENTAL DESIGN

In order to rule out a species specificity of the experimental approach, and to investigate the involvement of leukocyte adhesion receptors in oxLDL-induced leukocyte/endothelium interaction, we have adapted the skinfold chamber model to hairless mice. Using intravital fluorescence microscopy, leukocyte/endothelium interaction in a fine striated skin muscle was assessed during the time course after intravenous injection of native human LDL (4 mg/kg body weight) and oxLDL (oxidized in vitro by 7.5 microM Cu2+, 6 hours, 37 degrees C) into control mice and into mice pretreated with either the selective inhibitor of leukotriene biosynthesis MK-886 (20 mumol/kg body weight, intravenously, 10 minutes before oxLDL) or with a monoclonal antibody directed towards the CD11b subunit of the CD11b/CD18 adhesion receptor complex on leukocytes (monoclonal antibody anti-Mac1, 0.5 mg/kg, iv, 10 minutes before oxLDL).

RESULTS

We demonstrate in this study that injection of oxLDL (4 mg LDL-cholesterol/kg, intravenously, oxidized by 7.5 microM Cu2+, 6 hours, 37 degrees C), but not of native LDL or LDL-free Cu(2+)-solution, elicits the adhesion of fluorescently stained leukocytes to the endothelium of postcapillary venules (173 +/- 75 cells/mm2 at 20 minutes after oxLDL, mean +/- SD) and arterioles (119 +/- 74 cells/mm2 at 20 minutes after oxLDL, mean +/- SD) in the mice. OxLDL-induced leukocyte adhesion was entirely prevented by pretreatment of the animals with the inhibitor of leukotriene biosynthesis or with monoclonal antibody anti-Mac-1.

CONCLUSIONS

These results demonstrate the involvement of leukotrienes and of the CD11b/CD18 adhesion receptor complex in oxLDL-induced leukocyte adhesion in vivo and rule out a species specificity of this pathophysiologic event.

Endocytosis of beta 2 integrins by stimulated human neutrophils analyzed by flow cytometry

Flow cytometry and fluorescently labeled monoclonal antibodies were used to investigate endocytosis of human neutrophil beta 2 integrins following cellular activation. CD18 initially present on the cell surface cycled in two phases after exposure to formyl peptide or platelet-activating factor. The first phase lasted 3 min at 37 degrees C; after a lag, CD18 was specifically internalized at approximately 20%/min. Subsequently a second phase was detectable consisting of exponential reduction of internal fluorescence with a half-time of approximately 2 min, representing probe reexpression. At peak endocytosis approximately 40% of CD18 was internalized. All of the internalized CD18 was associated with alpha M (CR3); no endocytosis of alpha L (LFA-1) was observed. When neutrophils were stimulated with phorbol esters or calcium ionophore, CD18 was internalized much more slowly (t1/2 = 5 min) and probe was not reexpressed. Endocytosis of CD18 may participate in regulating neutrophil adhesiveness, removing activated receptors, or permitting receptor recycling.

Regulation of VCAM-1 expression and involvement in cell adhesion to murine microvascular endothelium

The present studies were undertaken to examine the regulation of murine VCAM-1 expression and the involvement of this molecule in adhesive processes occurring on the surface of microvascular endothelium. Flow cytometric analyses revealed that murine microvascular endothelium (MME) in culture constitutively expresses VCAM-1 and that stimulation of MME by TNF, IL-1, or LPS, but not by PMA or staurosporine, strongly increased the surface expression of this cell adhesion molecule. Stimulation of VCAM-1 expression by TNF may be diminished by ionomycin as well as by inhibitors of protein kinases (H-7 and sangivamycin). However, TGF-beta, which strongly inhibited the adhesiveness of endothelium, had little effect on the expression of VCAM-1. A newly developed adhesion assay, based on the rosette technique, allowed us to distinguish between the adhesive properties of an individual endothelial cell and those of endothelial cell monolayers and demonstrated that inhibition of binding by TGF-beta resulted primarily from its influence on the adhesive properties of individual cells. Studies on the inhibition of cell binding by monoclonal antibodies against mouse VCAM-1 and mouse VLA-4 indicated that VCAM-1 plays a dominant role in mediating the adherence of a variety of cell types, including murine splenocytes and thymocytes, P815 mastocytoma cells, PT 18 mast/basophil cells, human Molt-4 cells, and human eosinophils, to cytokine-activated MME.

Three monoclonal antibodies against human LFA-1 alpha and beta chains with different biological activities

Three murine monoclonal antibodies (MAbs) directed against human lymphocyte function-associated antigen-1 (LFA-1, CD11a/CD18), designated as MAY.017, MAY.035, and MAY. 044, were newly generated. The hybridomas were screened for their ability to inhibit a phorbol ester-stimulated aggregation of Epstein-Barr virus-transformed B-lymphoblastoid cell line (B-LCL). The MAbs bound to peripheral blood leukocytes, T cell lines, B cell lines, and some of myeloid/monocytic lines, but not to B-LCL derived from a patient with leukocyte adhesion deficiency. MAY.035 immunoprecipitated a complex of proteins with molecular masses of 155 kDa and 95 kDa, while MAY.017 and MAY.044 did a complex of 130 kDa, 155 kDa and 95 kDa proteins. MAY.035 was shown as to recognize the alpha chain of LFA-1 (CD11a), and both MAY.017 and MAY.044 the beta chain of the beta 2 integrin family (CD18). All the three MAbs inhibited lymphocyte proliferative responses to mitogens or alloantigens. MAY.017 blocked cytolytic activity mediated by natural killer cells.

Expression and function of beta 2 integrins on alveolar macrophages from human and nonhuman primates

The alveolar macrophage (AM) participates in diverse, adherence-related activities required for host defense and the inflammatory response. The beta 2 integrins (the CD11/CD18 heterodimer) mediate some of these activities on circulating leukocytes and peritoneal macrophages. We investigated expression of the CD11/CD18 leukocyte integrin subunits on AMs obtained by bronchoalveolar lavage of human and nonhuman primates. We also determined the role of the CD11/CD18 complex in AM chemotaxis and adherence to A549 alveolar epithelial cell monolayers. Immunofluorescence flow cytometry indicated that the CD11a/CD18 complex was expressed in high levels and CD11b/CD18 and CD11c/CD18 in lower levels on the AM surface. Northern blot analysis indicated the presence of CD11a, CD11c, and CD18 mRNA in the AMs. Smaller quantities of CD11b mRNA were also found. AM chemotaxis to zymosan-activated serum was markedly inhibited by a monoclonal antibody to CD18. In addition, adherence of AMs to A549 cells (stimulated by tumor necrosis factor to upregulate intercellular adhesion molecule-1 expression) was decreased from 30.3 +/- 5.0 to 20.8 +/- 2.4% (P less than 0.05) by the same monoclonal antibody. We conclude that: (1) AMs obtained from human and nonhuman primates constitutively express predominantly CD11a/CD18 surface antigen and mRNA, (2) chemotaxis of AMs is CD18 dependent, and (3) adhesion of AMs to an alveolar epithelial cell monolayer is partly but not completely dependent on the beta 2 integrins.

Induction of ICAM-1 expression on human airway epithelial cells by inflammatory cytokines: effects on neutrophil-epithelial cell adhesion

Inflammation of the human airways in diseases such as chronic bronchitis, cystic fibrosis with Pseudomonas endobronchial infection, and possibly asthma during late-phase reactions involves a local influx of neutrophils (PMN) that may participate in airway epithelial injury. PMN-mediated cellular injury is most efficient under conditions of PMN-target cell adhesion. PMN express adhesive glycoproteins of the CD11/CD18 family that are counter-receptors for intercellular adhesion molecule-1 (ICAM-1), found on various cell types. We proposed that adherence by PMN to human airway epithelial cells via ICAM-1 might be an important mechanism in inflammatory airway diseases. We found that although PMN adhere poorly (less than 5%) to monolayers of human tracheal epithelial cells (TEC) in primary culture, they adhere readily (45 to 50%) to an SV40-immortalized line of human TEC, designated 9HTEo-. We also found 6-fold greater surface expression of ICAM-1 on 9HTEo- compared with primary TEC. Blocking surface ICAM-1 on 9HTEo- cells with specific monoclonal antibody inhibited PMN adherence by about 50%. Thus, ICAM-1 plays a major role in this adherence, although it is possible that other epithelial ligands contribute also. Antibodies to CD11a, CD11b, and CD18 on PMN also inhibited PMN-epithelial adherence. Treatment of primary TEC monolayers with the proinflammatory cytokines interleukin-1 (IL-1) or tumor necrosis factor-alpha (TNF-alpha) caused a 3- to 4-fold increase in both cell surface ICAM-1 expression and support of PMN adhesion.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutrophil modulation by Actinobacillus actinomycetemcomitans I. Chemotaxis, surface receptor expression and F-actin polymerization

Localized juvenile periodontitis is an early onset periodontitis, usually localized to molars and incisors. Patients usually present with decreased chemotaxis of systemic neutrophils (PMNs) and infection with Actinobacillus actinomycetemcomitans. The pathogenic mechanisms involved have not been clarified. The purpose of this study was to determine if an extract of A. actinomycetemcomitans could induce changes in PMN chemotaxis similar to those reported in LJP patients. It was demonstrated that the bacterial extract was chemotactic for neutrophils. When neutrophils were pre-incubated with the bacterial extract, chemotaxis toward zymosan-activated serum, FMLP and the bacterial extract was inhibited in two different chemotaxis assays (Boyden chamber and under-agarose). Bacterial extract had no effect on random migration in either assay. Pre-incubation with the extract induced increased expression of CD11b/CD18 (Mac-1), Gp110, and FMLP receptors and increased F-actin polymerization following FMLP or PMA stimulation compared to cells not treated with the extract. Treatment of the bacterial extract with proteinase K or phenol extraction reversed the PMN chemotaxis inhibition activity, but increased significantly the random migration of PMNs. Heating the bacterial extract to 56 degrees C had no effect on its activity. The component(s) in the bacterial extract that inhibits chemotaxis is therefore a protein(s), not sensitive to 56 degrees C, and is not endotoxin. This study suggests that A. actinomycetemcomitans may contribute to the pathogenesis of localized juvenile periodontitis by inhibiting chemotaxis. Interference with chemotaxis by A. actinomycetemcomitans, however, occurs through a mechanism other than inhibition of actin assembly, reduction of CD11b/CD18 or Gp110 expression, or blockage/downregulation of FMLP receptors.

A method of preparing blood leucocytes for flow cytometry which prevents upregulation of leucocyte integrins

LeuCAM (CD11/CD18) cell-surface antigens are easily upregulated on cell manipulation ex vivo. A procedure for preparing leucocytes, in which human blood is immediately treated ex vivo with buffered formaldehyde and then the erythrocytes and platelets are removed by lysis and differential centrifugation, has been successfully applied to the analysis of LeuCAM antigen expression by flow cytometry. We show that the increased expression of monocyte CD11/CD18, which occurs when mononuclear leucocytes are separated by a standard Lymphoprep density gradient separation, can be avoided if cells are fixed immediately. Following this fixation polymorphs are unable to upregulate CD11/CD18 in response to fMLP stimulation in vitro. The technique produces lymphocyte, polymorph and monocyte populations that can be clearly defined on the basis of forward scatter and side scatter, and preserves the expression of various surface antigens; the percentages of gated lymphocytes expressing CD3, CD4, and CD8 were similar to those obtained using a commercial fixing and lysis solution. The processing does not render cells permeable to antibodies, as evidenced by our failure to stain cells with antibodies to intracellular antigens. We believed the method to be useful for measuring CD11/CD18 expression on blood leucocytes from normal or pathological specimens and to have application to the measurement of other cells surface antigens which may also be upregulated by the separation procedures.

Differentially regulated cell surface expression of leukocyte adhesion receptors on neutrophils

To elucidate the molecular mechanisms accounting for hemodialysis-induced neutropenia, the regulation of plasma membrane expression of leukocyte adhesion glycoproteins was investigated by both flow cytometry and immunoprecipitation techniques. The members of the LFA family of integrins, Mac-1/Mo1 (CD11/CD18) and gp150/95 (CD11c/CD18), involved in adhesion of myeloid cells to endothelia and other substrates, were found to be overexpressed on the plasma membrane of neutrophils from patients undergoing hemodialysis with a Cuprophane dialyzer, whereas no change was observed in the expression of LFA-1 (CD11a/CD18). By contrast, dialysis with Cuprophane membranes, as well as in vitro treatment with different activating agents, induced a downregulation on the expression of both the Leu-8/LAM-1 antigen, the human neutrophil peripheral lymph node homing receptor, and the CD43 major sialoglycoprotein involved in leukocyte homotypic adhesion. Kinetics studies showed that these up- and downregulatory processes of antigen expression occur very rapidly, correlating with maximal neutropenia. Recovery of initial levels of expression of CD11b/CD18 and Leu-8/LAM-1 adhesion molecules was observed after one hour of hemodialysis. However, the basal expression of CD43 was not restored by that time. The coordinated upregulation of CD11b and CD11c and downregulation of LAM-1 and CD43 adhesion receptors provide molecular mechanisms for understanding leukoaggregation, adherence to endothelia, and extravasation of neutrophils ultimately leading to the hemodialysis-induced neutropenia.

Molecular mapping of functional domains of the leukocyte receptor for endothelium, LAM-1

The human lymphocyte homing receptor LAM-1, like its murine counterpart MEL-14, functions as a mammalian lectin, and mediates the binding of leukocytes to specialized high endothelial cells in lymphoid organs (HEV). LAM-1 is a member of a new family of cell adhesion molecules, termed selectins or LEC-CAMs, which also includes ELAM-1 and PAD-GEM (GMP-140/CD62). To localize the regions of LAM-1 that are involved in cell adhesion, we developed chimeric selectins, in which various domains of PAD-GEM were substituted into LAM-1, and used these chimeric proteins to define the domain requirements for carbohydrate binding, and to localize the regions recognized by several mAb which inhibit the adhesion of lymphocytes to lymph node HEV. The binding of PPME or fucoidin, soluble complex carbohydrates that specifically define the lectin activity of LAM-1 and MEL-14, required only the lectin domain of LAM-1. The LAM1-1, LAM1-3, and LAM1-6 mAb each strongly inhibit the binding of lymphocytes to HEV in the in vitro frozen section assay, and defined three independent epitopes on LAM-1. Blocking of PPME or fucoidin binding by LAM1-3 indicated that this site is identical, or in close proximity, to the carbohydrate binding site, and analysis of the binding of LAM1-3 to chimeric selectins showed that the epitope detected by LAM1-3 is located within the lectin domain. Although the LAM1-6 epitope is also located in the lectin domain, LAM1-6 did not affect the binding of PPME or fucoidin. The LAM1-1 epitope was located in, or required, the EGF domain, and, importantly, binding of LAM1-1 significantly enhanced the binding of both PPME and fucoidin. These results suggest that adhesion mediated by LAM-1 may involve cooperativity between functionally and spatially distinct sites, and support previous data suggesting a role for the EGF domain of LAM-1 in lymphocyte adhesion to HEV.

Staurosporine inhibits neutrophil phagocytosis but not iC3b binding mediated by CR3 (CD11b/CD18)

C receptor CR3 (iC3b-receptor, CD11b/CD18) plays an essential role in several phagocytic and adhesive neutrophil functions. Recent evidence suggests that stimulus-induced phosphorylation of the CR3 beta-chain, CD18, may mediate certain neutrophil functions by transiently converting the molecule to an activated state. Staurosporine, a protein kinase C inhibitor that blocks PMA-induced CD18 phosphorylation, was used to study the functional relevance of this event. Neutrophils adhered to glass were assayed for binding and phagocytosis of iC3b-opsonized sheep E (EC3bi) in the presence or absence of PMA and/or staurosporine. Binding of EC3bi was markedly increased, not only by PMA, but also by staurosporine and by a combination of both agents (three- to sevenfold). The enhancement of rosetting by staurosporine was likely caused by increased surface expression of CR3 via exocytosis of specific granular contents. In contrast, staurosporine alone did not stimulate phagocytosis of EC3bi and markedly inhibited PMA-induced phagocytosis. Staurosporine also inhibited phagocytosis of yeast beta glucan particles, a CR3 ligand that, in contrast to EC3bi, is bound and ingested without additional prior treatment with PMA. beta glucan phagocytosis was associated with a low level of CD18 phosphorylation. Staurosporine did not block phagocytosis in general, because this agent had relatively little effect on FcR-mediated phagocytosis. These data demonstrate that phagocytosis mediated by CR3 requires activation of CR3 via a staurosporine-sensitive pathway. Increased binding of EC3bi, a function of increased surface expression of CR3, does not require activation of CR3 by such a pathway, confirming previous evidence for the independence of these two phenomena. A direct role for CD18 phosphorylation in the activation of CR3 for phagocytosis is consistent with these data.

ICAM-2 peptides mediate lymphocyte adhesion by binding to CD11a/CD18 and CD49d/CD29 integrins

Three fifteen-amino-acid polypeptides designated peptides 1, 2 and 3 were synthesised as likely candidates for mimicking the role of ICAM-2 as a ligand. The ability of each peptide to bind lymphoid cells was tested. Peptide 2 largely mediated cell attachment of unstimulated cells and this binding was only marginally increased by stimulating the cells with phorbol dibutyrate (P(Bu)2). Peptide 3 mediated minimal spontaneous cell attachment, but this binding was significantly enhanced following P(Bu)2 stimulation. Peptide 1 had no effect on cell attachment with or without stimulation. The cell attachment to peptide 2 was both temperature- and cation-dependent. Studies using specific monoclonal antibodies showed that with unstimulated cells, anti-VLA-4 alpha(CD49d) or beta chain (CD29) antibodies (KD4-13 and 4B4) and anti-CD18 (1B4) each partially inhibited the cell binding. Monoclonal antibodies against CD54 (ICAM-1; 84H10 or LB2), MHC class 1 (W6/32) and control mouse IgG had no effect. When anti-CD29 and anti-CD18 monoclonal antibodies were used concurrently, there was almost complete inhibition of the cell attachment. These observations indicated that cell adhesion via ICAM-2 is mediated: (i) predominantly by peptide 2 in unstimulated and P(Bu)2-stimulated cells, and also, to some extent, by peptide 3 in P(Bu)2-stimulated cells and (ii) by binding to both CD11/CD18 and CD49d/CD29 integrins.

Induction of LFA-1-mediated homotypic adhesions in promonocytic U-937 cells occurs independently of cell differentiation

The differentiation of monocytes into macrophages occurs along with a marked increase in LFA-1-dependent intercellular adhesions. Similarly, the phorbol ester-induced differentiation of U-937 promonocytic cells into macrophage-like cells is morphologically characterized by an important increase in LFA-1/ICAM-1-dependent intercellular homotypic adhesions. Since an important functional role in activation of human T cells has been demonstrated for LFA-1-dependent adherence, we have analyzed whether the induction of LFA-1-dependent intercellular adhesion of human monocytic cells is necessarily accompanied by differentiation of these cells. We found that treatment of the promonocytic U-937 cells with the anti-LFA-1 mAb NKI-L16 induces formation of intercellular clusters, but does not induce cell differentiation as determined by several differentiation markers. These markers include the arrest of cell proliferation, production of reactive oxygen species, changes in the cell surface expression of differentiation-associated antigens such as the transferrin receptor, CD11b and CD11c and changes in the levels of several specific gene transcripts such as CD18 antigen, c-myc, ornithine decarboxylase and vimentin. These findings suggest that LFA-1-dependent adhesion and differentiation of monocytic cells are independent processes.

Expression of a soluble and functional form of the human beta 2 integrin CD11b/CD18

Polymorphonuclear cells and monocytes (phagocytes) are a critical component of host defense against infections. However, these cells also play a significant role in host tissue damage in many noninfectious diseases, such as ischemia-reperfusion injury syndromes and rejection of transplanted organs. The leukocyte adhesion molecule family CD11/CD18 (beta 2 integrins) is critical to the function of polymorphonuclear cells and monocytes in inflammation and injury. Inherited deficiency of CD11/CD18 impairs phagocyte chemotaxis, adhesion and transmigration across endothelium, and clearance of invading microorganisms through phagocytosis and cell-mediated killing. Furthermore, murine monoclonal antibodies directed against the CD11b/CD18 (CR3) heterodimer have been shown to reduce, by 50%-80%, phagocyte-mediated ischemia-reperfusion injury in several organ systems, such as the myocardium, liver, and gastrointestinal tract and to inhibit development of insulin-dependent diabetes mellitus in nonobese diabetic (NOD) mice. Expression of CD11b/CD18 in a soluble and functional form might therefore be potentially useful as an anti-inflammatory agent. We have now expressed a recombinant soluble heterodimeric form of this human beta 2 integrin, normally expressed as two noncovalently associated membrane-bound subunits. The secreted receptor exhibited direct and specific binding to its ligand, iC3b, the major complement C3 opsonin, and inhibited binding of polymorphonuclear cells to recombinant interleukin 1-activated endothelium.

Treatment with granulocyte-macrophage colony stimulating factor and the adult respiratory distress syndrome

We report a case of a patient who developed a fatal adult respiratory distress syndrome (ARDS) during treatment with rh granulocyte-macrophage colony stimulating factor (rhGM-CSF) (250 mcg/m2/day s.c.) and low-dose cytosine-arabinoside (Ara-C) (20 mg/m2/day s.c.). Several mechanisms which might explain the lung tissue damage in this patient were explored. GM-CSF increased the expression of the glycoproteins CD11B and CD18 on the surface of his neutrophils, which may have increased the adhesiveness of neutrophils to the pulmonary endothelium. In addition, GM-CSF primed the neutrophils of the patient to an enhanced release of superoxide anions. Both findings may at least partially explain why GM-CSF exerted a deleterious action on the pulmonary endothelial integrity in this patient. Other factors, such as increased platelet-activating factor production by the neutrophils or tumor necrosis factor-mediated mechanisms, may also have played a role. ARDS as a complication of low-dose Ara-C seems less plausible.

CD18 adhesion receptors, tumor necrosis factor, and neutropenia during septic lung injury

Sequestration of neutrophils (PMNs) in the pulmonary microvasculature and associated neutropenia are characteristic features of experimental models of septic lung injury. The etiology of altered PMN kinetics during septic lung injury is uncertain, but may be partially due to increased adhesiveness of activated PMNs to pulmonary endothelium. This study examines the relationship between the expression of PMN CD18 adhesion receptors, the evolving neutropenia, and plasma tumor necrosis factor (TNF) activity in a porcine model of septic lung injury. Acute lung injury was induced by infusion of live Pseudomonas aeruginosa (5 x 10(8) CFU/ml at 0.3 ml/20 kg/min) for 60 min (Group Ps, n = 6). Control animals (Group C, n = 3) received a 60-min infusion of sterile 0.9% saline. CD18 expression of circulating PMNs was measured by quantitative immunofluorescent flow cytometry. Plasma TNF activity was measured by L929 fibroblast cytolytic assay. Group Ps developed a significant neutropenia by 30 min (14.9 +/- 2.5 vs 23.4 +/- 3.3 x 10(3) cells/microliter at baseline, P less than 0.05, ANOVA) with circulating neutrophils exhibiting significantly increased CD18 expression by 60 min (6.34 +/- 0.72 vs 5.01 +/- 0.52 equivalent soluble fluorescence molecules (ESFM) x 10(3) at baseline, P less than 0.05, ANOVA). Group Ps demonstrated a significant increase in plasma TNF activity by 30 min (2.5 +/- 0.9 vs 0.7 +/- 0.3 U/ml at baseline). There was no significant change in PMN count, PMN CD18 expression, or plasma TNF activity in Group C. In complimentary in vitro studies, porcine PMNs stimulated with recombinant human TNF-alpha (n = 5) demonstrated a time- and dose-dependent increase in CD18 expression.(ABSTRACT TRUNCATED AT 250 WORDS)