Surface engineering of quantum dots for in vivo vascular imaging

Quantum dot-antibody bioconjugates (QD-mAb) were synthesized incorporating PEG cross-linkers and Fc-shielding mAb fragments to increase in vivo circulation times and targeting efficiency. Microscopy of endothelial cell cultures incubated with QD-mAb directed against cell adhesion molecules (CAMs), when shielded to reduce Fc-mediated interactions, were more specific for their molecular targets. In vitro flow cytometry indicated that surface engineered QD-mAb labeled leukocyte subsets with minimal Fc-mediated binding. Nontargeted QD-mAb nanoparticles with Fc-blockade featured 64% (endothelial cells) and 53% (leukocytes) lower nonspecific binding than non-Fc-blocked nanoparticles. Spectrally distinct QD-mAb targeted to the cell adhesion molecules (CAMs) PECAM-1, ICAM-1, and VCAM-1 on the retinal endothelium in a rat model of diabetes were imaged in vivo using fluorescence angiography. Endogenously labeled circulating and adherent leukocyte subsets were imaged in rat models of diabetes and uveitis using QD-mAb targeted to RP-1 and CD45. Diabetic rats exhibited increased fluorescence in the retinal vasculature from QD bioconjugates to ICAM-1 and VCAM-1 but not PECAM-1. Both animal models exhibited leukocyte rolling and leukostasis in capillaries. Examination of retinal whole mounts prepared after in vivo imaging confirmed the fluorescence patterns seen in vivo. Comparison of the timecourse of retinal fluorescence from Fc-shielded and non-Fc-shielded bioconjugates indicated nonspecific uptake and increased clearance of the non-Fc-shielded QD-mAb. This combination of QD surface design elements offers a promising new in vivo approach to specifically label vascular cells and biomolecules of interest.

MANNHEIMIA (PASTEURELLA) HAEMOLYTICA LEUKOTOXIN UTILIZES CD18 AS ITS RECEPTOR ON BIGHORN SHEEP LEUKOCYTES

Pneumonia caused by Mannheimia (Pasteurella) haemolytica is a highly fatal disease of bighorn sheep (Ovis canadensis). Leukotoxin (Lkt), secreted by M. haemolytica, is an important virulence factor of this organism, and is cytolytic to bighorn sheep leukocytes. Previously, we have shown that CD18, the beta subunit of beta2 integrins, serves as the receptor for Lkt on bovine leukocytes. Furthermore, anti-CD18 antibodies inhibit Lkt-induced cytotoxicity of bighorn sheep leukocytes. Therefore, we hypothesized that Lkt utilizes CD18 as its receptor on bighorn sheep leukocytes. Confirmation of bighorn sheep CD18 as a receptor for Lkt requires the demonstration that the recombinant expression of bighorn sheep CD18 in Lkt-nonsusceptible cells renders them susceptible to Lkt. Therefore, we transfected cDNA encoding CD18 of bighorn sheep into a Lkt-nonsusceptible murine cell line. Cell surface expression of bighorn sheep CD18 on the transfectants was tested by flow cytometry with anti-CD18 antibodies. Transfectants stably expressing bighorn sheep CD18 on their surface were subjected to flow cytometric analysis for detection of Lkt binding, and cytotoxicity assays for detection of Lkt-induced cytotoxicity. Leukotoxin bound to the transfectants. More importantly, the transfectants were effectively lysed by Lkt in a concentration-dependent manner, whereas the parent cells were not. These results clearly indicate that M. haemolytica Lkt utilizes CD18 as a receptor on bighorn sheep leukocytes. Identification of CD18 as a receptor for Lkt on bighorn sheep leukocytes should enhance our understanding of the pathogenesis of pneumonia, which in turn should help in the development of control measures against this fatal disease of bighorn sheep.

Bioactive hydrogel substrates: probing leukocyte receptor-ligand interactions in parallel plate flow chamber studies

The binding of activated integrins on the surface of leukocytes facilitates the adhesion of leukocytes to vascular endothelium during inflammation. Interactions between selectins and their ligands mediate rolling, and are believed to play an important role in leukocyte adhesion, though the minimal recognition motif required for physiologic interactions is not known. We have developed a novel system using poly(ethylene glycol) (PEG) hydrogels modified with either integrin-binding peptide sequences or the selectin ligand sialyl Lewis X (SLe^X) within a parallel plate flow chamber to examine the dynamics of leukocyte adhesion to specific ligands. The adhesive peptide sequences arginine–glycine–aspartic acid–serine (RGDS) and leucine–aspartic acid–valine (LDV) as well as sialyl Lewis X were bound to the surface of photopolymerized PEG diacrylate hydrogels. Leukocytes perfused over these gels in a parallel plate flow chamber at physiological shear rates demonstrate both rolling and firm adhesion, depending on the identity and concentration of ligand bound to the hydrogel substrate. This new system provides a unique polymer-based model for the study of interactions between leukocytes and endothelium as well as a platform to develop improved scaffolds for cardiovascular tissue engineering.

Promotion of Leukocyte Adhesion by a Novel Interaction Between Vitronectin and the β 2 Integrin Mac-1 (α M β 2 , CD11b/CD18)

Objective— The leukocyte integrin Mac-1 (α M β 2 , CD11b/CD18) binds a number of ligands and counter-receptors and thereby is a major determinant in regulation of leukocyte adhesion and extravasation. Vitronectin (VN) is an adhesion-promoting factor that is abundantly present as matrix molecule in vascular diseases such as atherosclerosis. Until now, only an indirect interaction between Mac-1 and VN via the urokinase receptor (urokinase plasminogen activator receptor) was known. We now propose that Mac-1 and VN can directly interact with each other.

Methods and Results— In an in vitro system with purified components, Mac-1 specifically bound the multimeric matrix form of VN but not the monomeric plasma form. Using various competitors, the interaction domains in Mac-1 and VN were localized. Mac-1–expressing but not untransfected Chinese hamster ovary cells adhered strongly on VN. Introduction of a GFFKR deletion in the α M subunit of Mac-1, which increases the constitutive activation of the integrin, led to increased adhesion on VN. Peripheral human blood neutrophils adhered and migrated on multimeric VN in a Mac-1–dependent manner.

Conclusions— These results show that there is a specific integrin-affinity–regulated interaction between Mac-1 and the matrix form but not the plasma form of VN that may significantly participate in leukocyte adhesion and extravasation.

FTY720 exerts differential effects on CD4+ and CD8+ T-lymphocyte subpopulations expressing chemokine and adhesion receptors

BACKGROUND

FTY720 (FTY), a novel immunomodulator with the potential to improve immunosuppressive therapy after organ transplantation, is currently under clinical investigation. Previous experimental animal studies have shown that FTY has a unique mechanism of action associated with altered lymphocyte recirculation.

METHODS

Participating in a phase I clinical trial, we studied the pharmacodynamic effects of FTY in stable renal allograft recipients. We analysed the effect of FTY on surface marker expression on T-cell subpopulations by flow cytometry.

RESULTS

A single oral dose of FTY (0.25-3.5 mg) significantly reduced peripheral lymphocyte counts by 30-70%. FTY reduced all T-lymphocyte subsets, CD4(+) cells more than CD8(+) cells. However, we observed that lower doses of FTY (0.25-2 mg, n = 11) did not affect peripheral CD4(+)CCR5(+) T-lymphocyte counts, while the highest FTY dose of 3.5 mg (n = 2) exerted a rapid reduction of CD4(+)CCR5(+) cells. Peripheral CD8(+)CCR5(+) T-lymphocyte counts were reduced by either low (0.25-2 mg) or high (3.5 mg) doses of FTY. In contrast to CCR5(+) cells, cells expressing CD62L were preferentially reduced after administration of FTY. In particular, CD4(+)CD62L(+) T cells declined after treatment. CD4(+) and CD8(+) T-lymphocyte subpopulations expressing the other chemokine and adhesion receptors (CXCR4, CD11a and CD49d) were reduced to a similar extent as compared with overall CD4(+) or CD8(+) T-lymphocyte counts.

CONCLUSIONS

Despite the limited number of patients, especially in the placebo (n = 3) and the high-dose groups (n = 2), our observations suggest that FTY exerts differential effects on T-cell subpopulations. FTY predominantly reduces CD4(+)CD62L(+) cells in the peripheral blood suggesting increased migration into lymph nodes. It seems that only FTY doses above 2 mg are able to reduce peripheral CD4(+)CCR5(+) T lymphocytes, which are potentially capable of infiltrating into the allograft during rejection.

Receptor-ligand binding: 'catch' bonds finally caught

Leukocyte recruitment to sites of inflammation is initiated by the selectin family of adhesion receptors. Recent research reveals that P-selectin binding to its ligand exhibits 'catch' to 'slip' bond transition that may help explain the shear threshold phenomenon.

Neutrophil airway influx by platelet-activating factor in asthma: role of adhesion molecules and LTB4 expression

Platelet-activating factor (PAF)-induced neutrophil lung sequestration may require cell surface adhesion molecules (macrophage-1 antigen (MAC-1) and lymphocyte function-associated antigen-1 (LFA-1)). In this randomised, double-blinded, crossover study, the neutrophil kinetics after PAF and Lyso-PAF (L-PAF) airway challenge were investigated in nine mild-intermittent asthmatics. Neutrophils were measured in peripheral blood (PB) before and at 5, 15, 45 and 240 min after bronchoprovocation, and in induced sputum before and at 240 min after challenge. MAC-1 and LFA-1 expression were assessed by immunocytochemistry, and leukotriene B4 (LTB4) was measured by enzyme-immunoassay in induced-sputum supernatants. Compared with baseline, neutrophils in PB decreased 5 min after PAF, while at 240 min neutrophils in induced sputum increased. Compared with baseline and L-PAF, PAF decreased the percentages of MAC-1- and LFA-1-positive neutrophils in PB at 5 min, but increased the percentages of MAC-1 and LFA-1 in neutrophil-induced sputum. Moreover, compared with baseline and L-PAF, PAF-induced sputum revealed higher LTB4 levels, a finding that correlated with the elevated number of neutrophils in induced sputum. These findings suggest that macrophage-1 antigen and lymphocyte function-associated antigen-1 are involved in platelet-activating factor-induced neutrophil lung traffic, and that this process is modulated by enhanced leukotriene B4 release within the airways.

Leukocyte trans-endothelial migration: JAMs add new pieces to the puzzle

The molecular details of leukocyte transmigration through the endothelial barrier (also called diapedesis), which is the final step of leukocyte extravasation from the circulation to a given site of inflammation, are by far not well understood. The present review will focus on the different mechanisms potentially involved in leukocyte trans-endothelial migration. Both homophilic and heterophilic interactions between leukocyte and endothelial cell receptors will be covered, with a particular focus on the growing gene family of junctional adhesion molecules (JAM). Deciphering their mechanisms of interaction will also allow to unravel novel strategies for therapeutic intervention in inflammatory or atherothrombotic diseases.

Nonsteroidal anti-inflammatory drugs prevent early diabetic retinopathy via TNF-alpha suppression

Leukocyte adhesion to the diabetic retinal vasculature results in blood-retinal barrier breakdown, capillary nonperfusion, and endothelial cell injury and death. Intercellular adhesion molecule-1 (ICAM-1) and the leukocyte integrin CD18 are required for these processes. Diabetes was induced in Long Evans rats, resulting in a two- to threefold increase in retinal leukocyte adhesion. Following one week of diabetes, neutrophil CD11a, CD11b, and CD18 expression was increased significantly, as were retinal ICAM-1 levels. Animals were treated with aspirin, a cyclooxygenase 2 (COX-2) inhibitor (meloxicam), or a soluble tumor necrosis factor alpha (TNF-alpha) receptor/Fc construct (TNFR-Fc, etanercept). High-dose aspirin, etanercept, and high-dose meloxicam each reduced leukocyte adhesion and suppressed blood-retinal barrier breakdown. High-dose aspirin also reduced the expression of CD11a, CD11b, and CD18, whereas meloxicam and etanercept did not. High-dose aspirin, etanercept, and high-dose meloxicam each reduced retinal ICAM-1 expression. Aspirin and meloxicam both lowered retinal TNF-alpha levels. Notably, aspirin, meloxicam, and etanercept did not change retinal vascular endothelial growth factor levels. High-dose aspirin, etanercept and high-dose meloxicam, each suppressed the retinal expression of eNOS and the DNA-binding capacity of retinal nuclear factor-kappaB. High-dose aspirin also suppressed Erk kinase activity, which is involved in CD18 up-regulation. Taken together, these data identify COX-2 and TNF-alpha as operative in the early signature pathologies of diabetic retinopathy, a newly recognized inflammatory disease.

Elements of cerebral microvascular ischaemia

Although neuronal cells have long been thought to be the prime target of ischaemic insults, events which occur at the blood-vascular-parenchymal interface are necessary for the initiation of ischaemic tissue injury. This cascade of microvascular events includes fibrin accumulation, endothelium expression of leukocyte adhesion receptors, breakdown of the basal laminae with loss of astrocyte and endothelial cell contacts leading to blood-brain barrier disruption and consequently oedema formation and haemorrhagic transformation. Potential stroke treatments have been studied in the clinic and many have not been particularly successful, probably due to the delicate balance between improved outcome and adverse reactions as well as the window of opportunity for drug treatment after symptom onset. The only acute intervention trial demonstrating any benefit in patients was that of intravenous tissue plasminogen activator (tPA), administered within 3 h of the onset of symptoms of ischaemic stroke. Such treatment improved clinical outcome at 3 months, although there was an increased incidence of symptomatic haemorrhage [New Engl. J. Med. 333 (1995) 1581]. The recent progress made in defining the mechanisms involved in the initiation of ischaemic events, as described in this review, may lead to the identification of new strategies for intervention in the ischaemic cascade.

Effect of LFA-1beta antibody on leukocyte adherence in response to hemorrhagic shock in rats

The activation and adherence of leukocytes to the venular endothelium are critical steps in the pathogenesis of generalized microvascular injury following hemorrhagic shock. Previous studies have shown that the integrins CD11/CD18 play a significant role in this interaction. The purpose of this study is to examine the efficacy of anti-LFA-1beta, an antibody to CD11a/CD18, in attenuating leukocyte adherence before, during, and after hemorrhagic shock. Following a control period, blood was withdrawn to reduce the mean arterial pressure to 40 mm Hg for 30 min in urethane-anesthetized rats. Mesenteric venules in a transilluminated segment of the small intestines were examined to quantitate leukocyte adherence using intravital microscopy. In sham-operated rats (control), there was minimal to no leukocyte adherence throughout the experiment. Hemorrhagic shock resulted in significant leukocyte adherence during resuscitation (10.8 +/- 1.7 cells/100 microm, P < 0.01) when compared to control. Anti-LFA-1beta, when given before hemorrhagic shock, significantly attenuated leukocyte adherence during resuscitation (1.1 +/- 0.8, P < 0.01) when compared with hemorrhagic shock alone. This protective effect of anti-LFA-1beta on leukocyte adherence was even demonstrated when it was given during (1.6 +/- 0.3, P < 0.01) and 10 min after hemorrhagic shock (5.8 +/- 0.4, P < 0.05). These results suggest that anti-LFA-1beta may be of potential therapeutic benefit against microvascular injury caused by hemorrhagic shock.

Functional relevance of activated beta1 integrins in mercury-induced nephritis

Cell adhesion through different adhesion molecules is a crucial event in the inflammatory response. Integrins can only bind and mediate cellular adhesion after their activation by different specific stimuli. The state of beta1 integrin activation can be assessed by a group of monoclonal antibodies (HUTS) that selectively recognize beta1 integrins in their active form. A similar activated epitope in the rat was defined using the anti-human monoclonal antibody HUTS-21, which recognizes an activation-dependent epitope on the beta1 chain. It was found that the divalent cations Mn(2+) and Hg(2+) were able to induce in vitro the activation of beta1 integrins on rat lymphocytes. The Hg(2+) cation induces an autoimmune disease in the Brown Norway rat characterized by synthesis and glomerular deposits of anti-glomerular basement membrane antibodies, proteinuria, and interstitial nephritis. Using the mercury model of nephritis, it was found that the expression of HUTS-21 epitope is induced in vivo in rat lymphocytes, and its appearance is correlated with the other parameters at the onset of the disease. In addition, the administration of HUTS-21 monoclonal antibody to HgCl(2)-treated rats offered evidence of its protective effects (1) against infiltration of renal interstitium by leukocytes, and (2) in the reduction of anti-glomerular basement membrane synthesis and glomerular deposition. Nevertheless, urinary protein values remained unaffected. These results demonstrate a key role of beta1-activated integrins in both leukocyte cell-cell interactions and leukocyte infiltration pathway mechanism, and also indicate that leukocyte migration may have less importance in the development of this disease than previously thought.

Integrin-mediated neutrophil adhesion and retinal leukostasis in diabetes

PURPOSE

A critical early event in the pathogenesis of diabetic retinopathy is leukocyte adhesion to the diabetic retinal vasculature. The process is mediated, in part, by intercellular adhesion molecule-1 (ICAM-1) and results in blood-retinal barrier breakdown and capillary nonperfusion. This study evaluated the expression and function of the corresponding ICAM-1-binding leukocyte beta2-integrins in experimental diabetes.

METHODS

Diabetes was induced in Long Evans rats with streptozotocin. The expression of the surface integrin subunits CD11a, CD11b, and CD18 on rat neutrophils isolated from peripheral blood was quantitated with flow cytometry. In vitro neutrophil adhesion was studied using quantitative endothelial cell-neutrophil adhesion assays. The adhesive role of the integrin subunits CD11a, CD11b, and CD18 was tested using specific neutralizing monoclonal antibodies. CD18 bioactivity was blocked in vivo with anti-CD18 F(ab')2 fragments, and the effect on retinal leukocyte adhesion was quantitated with acridine orange leukocyte fluorography.

RESULTS

Neutrophil CD11a, CD11b, and CD18 surface integrin levels were 62% (n = 5, P = 0.006), 54% (n = 5, P = 0.045), and 38% (n = 5, P = 0.009) greater in diabetic versus nondiabetic animals, respectively. Seventy-five percent more neutrophils from diabetic versus nondiabetic animals adhered to rat endothelial cell monolayers (n = 6, P = 0.02). Pretreatment of leukocytes with either anti-CD11b or anti-CD18 antibodies lowered the proportion of adherent diabetic neutrophils by 41% (n = 6, P = 0.01 for each treatment), whereas anti-CD11a antibodies had no significant effect (n = 6, P = 0.5). In vivo, systemic administration of anti-CD18 F(ab')2 fragments decreased diabetic retinal leukostasis by 62% (n = 5, P = 0.001).

CONCLUSIONS

Neutrophils from diabetic animals exhibit higher levels of surface integrin expression and integrin-mediated adhesion. In vivo, CD18 blockade significantly decreases leukostasis in the diabetic retinal microvasculature. Integrin adhesion molecules may serve as therapeutic targets for the treatment and/or prevention of early diabetic retinopathy.

Nitric oxide synthase inhibitor augments post-ischemic leukocyte adhesion in the cerebral microcirculation in vivo

The objective was to examine the effect of the nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME) on leukocyte adhesion in the cerebral microcirculation during reperfusion following partial forebrain ischemia in the rat. Intravital fluorescence video-microscopy through a closed cranial window was used to visualize leukocyte-endothelium interaction in small pial veins of 15-100 microns diameter. Forebrain ischemia was produced by the ligation of both common carotid arteries plus elevation of the intracranial pressure to 20 mmHg for 60 min. The number of leukocytes adhering to the endothelium for longer than 3 sec was determined during ischemia (5 min and 60 min) and during reperfusion (5 min and 60 min). Two experimental groups were treated with either L-NAME or its inactive enantiomer D-NAME (20 mg kg-1 i.v.) 30 min prior to reperfusion. In a third group, also treated with D-NAME, post-ischemic hyperemia was prevented by lowering the ICP without removing the occlusion of common carotid arteries (partial reperfusion). The velocity of flow adjacent to the endothelial surface of pial veins was measured by tracking the movement of fluorescently labeled red blood cells as flow markers before and after ischemia. During ischemia, the number of adhering leukocytes increased approximately two-fold at 5 min, and three-fold at 60 min. In the D-NAME-treated group with complete reperfusion, leukocyte adhesion returned to the baseline level by 60 min of reperfusion. However, in the L-NAME-treated group, leukocyte adhesion remained elevated at 60 min of reperfusion. Post-ischemic flow velocity was significantly decreased (-66%) from control after L-NAME treatment whereas it was increased (+53%) in the D-NAME-treated group. In the partial reperfusion group, leukocyte adhesion continued to increase after the first hour of ischemia and reached a level 2.7-fold over baseline at 60 min reperfusion. Flow velocity remained below control (-26%) at 60 min reperfusion. Leukocyte adhesion was absent in pial arteries and no plugging by leukocytes was observed in cortical capillaries. The results suggest that leukocyte adhesion in small pial veins increases during 1 h forebrain ischemia and continues to increase during reperfusion if the velocity of flow or shear rate is low. The increase in leukocyte adhesion is reversible if flow velocity is elevated during reperfusion. L-NAME prevents post-ischemic hyperemia and augments leukocyte adhesion principally via a decrease in velocity or shear rate.

DNA-fragmentation and apoptosis-related proteins of muscle cells in motor neuron disorders

Apoptosis has been described as one of the mechanisms of muscle fiber loss in infantile spinal muscular atrophy. In order to investigate if muscle fiber-apoptosis plays a role in other denervating disorders as well, we studied DNA-fragmentation, a hallmark of apoptosis, by the TUNEL-method and, moreover, the expression patterns of apoptosis-related proteins in 2 patients suffering from ALS and in 6 patients with polyneuropathy. We identified DNA-cleavage in muscle fibers of all these patients. Furthermore, we found strong expression of bax and ICE promoting apoptosis in muscle fibers. However, also strong expression of the anti-apoptotic factor bcl-2 was found. Our findings indicate that defective innervation may prompt muscle fibers to activate an intrinsic "suicide" programme which is promoted by the proapoptotic factors bax and ICE, which seems to induce formation of apoptotic bodies by cleavage of actin. Nevertheless, there are also anti-apoptotic strategies in muscle fibers manifested by expression of the bax-antagonist bcl-2 which is able to neutralize high bax levels.

Beta 2 (CD11/CD18) integrins can serve as signaling partners for other leukocyte receptors

Fig. 1 depicts our current thinking about the ways in which Mo1 and p150,95 form cis interactions with other leukocyte receptors. With respect to the associations of Mo1 with Fc gamma RIIIB and uPAR, the inhibitory effect of saccharides such as NADG suggests a lectin-carbohydrate interaction that may involve the recognition of Mo1's beta-glucan site for N-linked carbohydrates4 that are expressed by both Fc gamma RIIIB and uPAR. This hypothesis is supported by the results of Stockl et al., who showed that the binding of C-terminal-specific mAb VIM12 to Mo1, which enhances the phospholipase C-mediated release of Fc gamma RIIIB, was inhibited by NADG. However, unlike the sample lectin-carbohydrate interaction that appears to govern the association between Mo1 and Fc gamma RIIIB, effective Mo1-dependent uPAR signaling also depends on the binding of intact uPA to uPAR (the receptor-binding ATF of uPA proving insufficient to prime neutrophils for an enhanced burst response to FMLP). We speculate that ATF (residues 6-135) binds to uPAR while the carboxyl terminal fragment (residues 136-411), which includes a glycosylation site at residue 144, binds to the lectinlike site of Mo1, thus fostering the linkage between the two receptors. In support of this model is the fact that exposure of neutrophils to ATF reduced the degree of molecular proximity between Mo1 and uPAR (the latter probably occupied by endogenous intact uPA) and increased the molecular association between Mo1 and Fc gamma RIIIB (both as detected by quantitative RET). This hypothesis is analogous to the concept proposed by Nykjaer et al in which plasminogen activator inhibitor-1 initially binds to uPA to form a complex that secondarily binds to the alpha 2 macroglobulin receptor, leading to internalization of the complex. Whereas the contribution of intact uPA to the interaction between Mo1 and uPAR remains speculative (based on the indirect data available), no such ambiguity exists for the role of the LPS/LBP ligand in regulating the association between Mo1 and CD14. In this circumstance, no physical linkage exists between the two receptors without the ligand complex. This observation is consistent with the previously described affinity of the beta 2 integrins for LPS, leading to the notion that the LPS portion of the LPS/LPB complex binds to Mo1, serving to link it with LPS/LBP bound to CD14. The observed reversibility of the interactions between the integrin glycoproteins and uPAR or CD14 illustrates the fact that these associations can be highly dynamic and tied to cellular processes that include directed motility (Mo1-uPAR), adherence to substrates (Mo1-CD14), and energy metabolism (p150,95-uPAR). We speculate that the GPI-anchored receptor proteins serve as rapidly diffusible, expendable "scouts" for the beta 2 integrins, which serve to expand their ligand binding repertoire in a cis-acting fashion.

Animal membrane receptors and adhesive molecules

This review summarizes some important data, principles, opinions, commentaries, and modern methodology concerning the receptor structure, interactions, signaling and receptor-mediated cell functions. Three sections give a brief overview of the signaling synergy, multivariant signaling, and some reactions in phosphorylation networks. A concise report about the cytotoxic reaction of NK cells represents an example of multistage recognition reaction, involving differently acting receptors, changes in affinities of cell-cell interactions, and secretion of regulatory and cytotoxic molecules. Some interesting trends in receptor engineering, including antibody molecules as a special receptor phenomenon are mentioned in the final section.

Activation of human monocyte functions by tumor necrosis factor: rapid priming for enhanced release of superoxide and erythrophagocytosis, but no direct triggering of superoxide release

Tumor necrosis factor (TNF), like granulocyte-macrophage colony-stimul ating factor (GM-CSF), rapidly primed human monocytes for enhanced release of superoxide (O-2) stimulated by receptor-mediated agonists, N-formyl-methionyl-leucyl-phenylalanine (FMLP) and concanavalin A (Con A), but not by phorbol myristate acetate (PMA), which bypasses the receptors to stimulate the cells. The optimal priming was obtained by pretreatment of suspended monocytes with 10 U/mL TNF for 10 minutes at 37 degrees C. The potency of the maximal priming effect was TNF> GM-CSF, and the combined effect of TNF and GM-CSF was greater than that of each cytokine alone. GM-CSF induced an increase in cytoplasmic pH but TNF did not. These findings suggest that TNF and GM-CSF activate monocytes through different mechanisms. TNF and GM-CSF by themselves never triggered O-2 release in suspended monocytes or monocytes adherent to endothelial cells, although both cytokines triggered massive release of O-2 in human neutrophils. In additions, TNF and GM-CSF induced tyrosine phosphorylation of a 42-kD protein in neutrophils but not in monocytes. These findings suggest that the TNF-receptor- or GM-CSF-receptor-mediated signaling pathways for triggering O-(2) release is active in neutrophils but inactive or defective in monocytes. TNF also enhanced phagocytosis of sialidase-treated autologous erythrocytes by monocytes, and this effect was further potentiated in the presence of autologous fresh serum. The significant enhancement of erythrophagocytosis was obtained at 1 U/mL TNF. At this concentration of TNF, the expression of C3bi-receptor (CD11b/CD18) was upregulated. These findings show that TNF rapidly primes human monocytes for enhanced release of O-(2) and erythrophagocytosis and suggest that TNF activates monocytes through autocrine or paracrine mechanisms at the inflammatory sites inasmuch as TNF is primarily produced by activated monocytes/macrophages.

Effect of hemodialysis on leukocyte adhesion receptor expression

Hemodialysis with complement-activating membranes such as cuprophane is known to transiently activate leukocytes, leading to increased cellular adhesiveness, pulmonary leukostasis, and reduced functional capacity of monocytes and neutrophils. Clinically, this repetitive cell activation may contribute to the increased morbidity and mortality associated with chronic hemodialysis. To examine the effect of cuprophane hemodialysis on expression of cell-surface proteins involved in leukocyte adhesiveness, we monitored CD11b, CD18, CD14, CD54, and plasma-soluble CD54 in 10 patients during hemodialysis with cuprophan dialyzers. To test the effect of local blood recirculation, in two patients, arterial supply to the dialyzer was accessed from the peripheral arteriovenous fistula and was returned via an indwelling central venous catheter. In an attempt to examine the possible role of membrane-induced complement activation, the results were compared with those seen after incubation with C5a in vitro. Finally, the leukocyte responses to C5a and lipopolysaccharide were measured before and after hemodialysis. Leukocyte expression of CD11b and CD18 increased and CD14 decreased with hemodialysis, while CD54 remained unaltered. Plasma CD54 was markedly elevated before and remained unchanged during hemodialysis. Data obtained with C5a activation in vitro revealed identical changes in CD11b expression as that seen with hemodialysis, suggesting the role of membrane-induced complement activation. Preliminary data obtained using remote arterial and venous access sites showed only a slight increase in CD11b expression in the arterial blood, suggesting that the apparent systemic activation seen with arteriovenous access may be due to recirculation and local activation within the blood access. Finally, dialysis procedure did not impair lipopolysaccharide- or C5a-mediated upregulation of CD11b expression.

Circulating leukocyte integrin expression in Wegener's granulomatosis

Leukocyte adhesion and infiltration are important in the pathogenesis of Wegener's granulomatosis (WG). We tested the hypothesis that the expression of the beta 1-chain integrin VLA-4 (CD49d/CD29) and the beta 2-chain integrins LFA-1 (CD11a/CD18), Mac-1 (CD11a/CD18), and gp150,95 (CD11c/CD18) is increased on leukocytes in patients with active WG. Fifteen patients with active WG as defined by positive antineutrophil cytoplasmic autoantibody (cANCA) titers and biopsy, 30 patients with WG in remission as defined by negative cANCA titers and/or immunosuppressive therapy, 25 normal control subjects, and 12 patients with other inflammatory renal and systemic diseases were studied. Surface expression of LFA-1, Mac-1, p150, 95, and VLA-4 on neutrophils, lymphocytes, and monocytes was measured by fluorescent antibody cell sorting with monoclonal antibodies against CD11a, CD11b, CD11c, CD18, CD49d, and CD29 respectively. Immunocytochemistry and confocal microscopy were also utilized. beta 1 (CD29) and beta 2 (CD18) integrin subunit expression on neutrophils, monocytes, and lymphocytes from patients with acute WG was significantly increased compared with healthy persons and compared with patients with treated vasculitis. Furthermore, the alpha-integrin subunit CD11b expression was increased on granulocytes and monocytes, but not on lymphocytes. Finally, the alpha-integrin subunit CD11a expression was increased on monocytes. Immunocytochemistry showed that the increased immunoreactivity on neutrophils was evenly distributed on the plasma membrane and in the cytosol. Immunosuppression resulted in decreased expression of the beta 1 and beta 2-integrin subunits. It was concluded that the integrin adhesion molecules, particularly Mac-1 (CD11b/CD18), are upregulated on leukocytes in active WG. This finding suggests a role for integrin expression in the pathogenesis of WG and a possible clue for treatment.

Increased adhesion to vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 of eosinophils from patients with asthma

Adhesion of peripheral blood eosinophil and neutrophil granulocytes to the endothelial cell adherence receptors E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1 has been measured. The study included patients with allergic rhinitis, patients with mild allergic and nonallergic asthma, and healthy individuals; 10 persons were in each group. In addition, assay of eosinophil and neutrophil cell surface expression of the receptor complex CD11b/CD18 was performed. Increased eosinophil adhesion to vascular cell adhesion molecule-1 (p < 0.05) and intercellular adhesion molecule-1 (p < 0.05) was demonstrated in the patients with a more labile asthma, that is, a peak expiratory flow rate variability of more than 10%, suggesting a relationship to the degree of ongoing inflammation in the airways of the patients. The increased eosinophil adhesion was most probably due to a functional upregulation of the CD11b/CD18 and very late activation antigen-4 receptors, because the number of receptors measured as cell surface expression was unaltered. The increased eosinophil adhesion in the patients with high peak expiratory flow rate variability appeared independent of atopy. The increased adhesion was not entirely specific to the eosinophils, because neutrophils from patients with a peak expiratory flow rate variability of more than 10% also demonstrated increased adhesion to intercellular adhesion molecule-1 (p < 0.05) when compared with neutrophils from the patients with low peak expiratory flow rate variability. In conclusion, the demonstrated priming of eosinophil adhesion to vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 might be one contributing mechanism behind the selective accumulation of eosinophils in the lung tissue of patients with asthma.

A peptide derived from the intercellular adhesion molecule-2 regulates the avidity of the leukocyte integrins CD11b/CD18 and CD11c/CD18

beta 2 integrin (CD11a,b,c/CD18)-mediated cell adhesion is required for many leukocyte functions. Under normal circumstances, the integrins are nonadhesive, and become adhesive for their cell surface ligands, the intercellular adhesion molecules (ICAMs), or soluble ligands such as fibrinogen and iC3b, when leukocytes are activated. Recently, we defined a peptide derived from ICAM-2, which specifically binds to purified CD11a/CD18. Furthermore, this peptide strongly induces T cell aggregation mainly mediated by CD11a/CD18-ICAM-1 interaction, and natural killer cell cytotoxicity. In the present study, we show that the same ICAM-2 peptide also avidly binds to purified CD11b/CD18, but not to CD11c/CD18. This binding can be blocked by the CD11b antibody OKM10. The peptide strongly stimulates CD11b/CD18-ICAM-1-mediated cell aggregations of the monocytic cell lines THP-1 and U937. The aggregations are energy and divalent cation-dependent. The ICAM-2 peptide also induces CD11b/CD18 and CD11c/CD18-mediated binding of THP-1 cells to fibrinogen and iC3b coated on plastic. These findings indicate that in addition to induction of CD11a/CD18-mediated cell adhesion, the ICAM-2 peptide may also serve as a "trigger" for high avidity ligand binding of other beta 2 integrins.

Priming of oxidative response in human neutrophils by anti-CD18 monoclonal antibodies

Type I collagen, the most abundant protein in the body, after acid extraction adheres to and can induce a respiratory burst from neutrophils. It has been proposed that the effects of collagen are mediated via the CD18 subfamily of integrins. In the present study, adhesion was measured by affinity chromatography in a column containing collagen-coated microcarriers, while oxygen metabolite production was measured with luminol-dependent chemiluminescence. Neutrophil adherence to collagen was attenuated by anti-CD18 monoclonal antibodies. The respiratory burst in response to collagen was not affected by the antibodies. Incubation of neutrophils with anti-CD18 antibodies prior to stimulation with FMLP increased both the extra- and intracellular respiratory burst. Treatment with antibodies prior to PMA stimulation increased only the extracellular respiratory burst. In conclusion, the respiratory burst from neutrophils is primed by pretreatment with anti-CD18 monoclonal antibodies. The collagen-stimulated respiratory burst is probably also primed, but the effect is hidden by the simultaneous attenuation of adhesion.

Platelet-leukocyte activation and modulation of adhesion receptors in pediatric patients with congenital heart disease undergoing cardiopulmonary bypass

Cardiopulmonary bypass has been shown in adults to activate platelets and leukocytes, lead to the formation of circulating platelet-leukocyte conjugates, and alter adhesive receptors on both cell types. Pediatric patients with congenital heart disease undergoing cardiopulmonary bypass, however, have not been extensively studied and may represent a group at particular clinical risk for bleeding and pulmonary dysfunction. We studied 13 patients with congenital heart disease undergoing operations necessitating bypass, 7 with cyanotic and 6 with noncyanotic congenital heart disease. We determined that (1) the surface density of platelet glycoprotein Ib was significantly lower at baseline and throughout bypass in patients with cyanotic heart disease than in noncyanotic patients; (2) platelet glycoprotein Ib in both cyanotic and noncyanotic congenital heart disease decreased significantly during bypass, with a nadir of 75% of baseline values; (3) platelets were activated to a high degree, comparable with that seen in adults; (4) mean circulating monocyte-platelet conjugates rose significantly during bypass, increasing from 36% to 66% by the end of bypass, whereas neutrophil-platelet conjugates and lymphocyte-platelet conjugates declined; and (5) both monocytes and neutrophils were activated by cardiopulmonary bypass, as assessed by increased surface expression of CD11b and, in the case of monocytes, CD11b expression continued to increase even after termination of bypass. Patients with cyanotic and noncyanotic heart disease did not differ with respect to platelet or leukocyte activation or the formation of platelet-leukocyte conjugates. We conclude that in children with congenital heart disease cardiopulmonary bypass causes loss of platelet adhesion receptors, activation of platelets, formation of platelet-leukocyte conjugates, and leukocyte activation. Cyanotic and noncyanotic patients are qualitatively similarly affected; however, cyanotic patients demonstrate a baseline deficit in the platelet adhesion receptor glycoprotein Ib. These cellular changes may contribute to both the hemostatic and inflammatory complications associated with cardiopulmonary bypass.

Endothelial-leukocyte adhesive interactions in inflammatory diseases

There is evidence that vascular endothelium directs the accumulation of leukocytes in inflammation through various means, particularly by the expression of specific cell surface molecules which are adhesive for ligands on circulating leukocytes. Examples of such molecules are E-selectin and intercellular adhesion molecule 1 (ICAM-1). In an experimental model of various forms of inflammation, E-selectin and ICAM-I were induced in association with adhesion and emigration of circulating polymorphonuclear and mononuclear leukocytes. Further work in humans showed endothelium to express E-selectin in inflammation. In addition, the presence of a leukocyte ligand for E-selectin, sialyl-Lewis X, has been seen on cells accumulating in inflammation. Furthermore, sialyl-Lewis X was also unexpectedly seen on endothelium. The role of sialyl-Lewis X on endothelium is as yet uncertain, although it may function as an adhesion receptor for leukocytes. Other endothelial adhesion receptors, such as vascular cell adhesion molecule 1 (VCAM-1), are described. Atherosclerosis shows many features in common with inflammation. These are discussed, and the demonstrated and potential relevance of endothelial adhesive phenomena in routine inflammation to those in atherosclerosis are reviewed. For example, a VCAM-1 homologue has been described on the endothelium over evolving atherosclerotic lesions in rabbits.

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)