CD43 (sialophorin, leukosialin) shedding is an initial event during neutrophil migration, which could be closely related to the spreading of adherent cells

Staphylococcal superantigen-like protein 3 triggers murine mast cell adhesion by binding to CD43 and augments mast cell activation

Staphylococcus aureus is a noteworthy pathogen in allergic diseases, as four staphylococcal exotoxins activate mast cells, a significant contributor to inflammation, in an IgE-independent manner. Although the adhesion of mast cells is an essential process for their immune responses, only a small number of exotoxins have been reported to affect the process. Here, we demonstrated that staphylococcal superantigen-like (SSL) 3, previously identified as a toll-like receptor 2 agonist, induced the adhesion of murine bone marrow-derived mast cells to culture substratum. SSL3-induced adhesion was mediated by fibronectin in an Arg-Gly-Asp (RGD) sequence-dependent manner, suggesting the integrins were involved in the process. Additionally, SSL3 was found to bind to an anti-adhesive surface protein CD43. SSL3 induced the adhesion of HEK293 cells expressing exogenous CD43, suggesting that CD43 is the target molecule for adhesion induced by SSL3. Evaluation of SSL3-derived mutants showed that the C-terminal region (253-326), specifically T285 and H307, are necessary to induce adhesion. SSL3 augmented the IL-13 production of mast cells in response to immunocomplex and SSL12. These findings reveal a novel function of SSL3, triggering cell adhesion and enhancing mast cell activation. This study would clarify the correlation between S. aureus and allergic diseases such as atopic dermatitis.

The extracellular sialidase NEU3 primes neutrophils

Some extracellular glycoconjugates have sialic acid as the terminal sugar, and sialidases are enzymes that remove this sugar. Mammals have 4 sialidases and can be elevated in inflammation and fibrosis. In this report, we show that incubation of human neutrophils with the extracellular human sialidase NEU3, but not NEU1, NEU2 or NEU4, induces human male and female neutrophils to change from a round to a more amoeboid morphology, causes the primed human neutrophil markers CD11b, CD18, and CD66a to localize to the cell cortex, and decreases the localization of the unprimed human neutrophil markers CD43 and CD62-L at the cell cortex. NEU3, but not the other 3 sialidases, also causes human male and female neutrophils to increase their F-actin content. Human neutrophils treated with NEU3 show a decrease in cortical levels of Sambucus nigra lectin staining and an increase in cortical levels of peanut agglutinin staining, indicating a NEU3-induced desialylation. The inhibition of NEU3 by the NEU3 inhibitor 2-acetylpyridine attenuated the NEU3 effect on neutrophil morphology, indicating that the effect of NEU3 is dependent on its enzymatic activity. Together, these results indicate that NEU3 can prime human male and female neutrophils, and that NEU3 is a potential regulator of inflammation.

Neutrophils Release Metalloproteinases during Adhesion in the Presence of Insulin, but Cathepsin G in the Presence of Glucagon

In patients with reperfusion after ischemia and early development of diabetes, neutrophils can attach to blood vessel walls and release their aggressive bactericide agents, which damage the vascular walls. Insulin and 17β-estradiol (E2) relieve the vascular complications observed in metabolic disorders. In contrast, glucagon plays an essential role in the pathophysiology of diabetes. We studied the effect of hormones on neutrophil secretion during adhesion to fibronectin. Amino acid analysis revealed that proteins secreted by neutrophils are characterized by a stable amino acid profile enriched with glutamate, leucine, lysine, and arginine. The total amount of secreted proteins defined as the sum of detected amino acids was increased in the presence of insulin and reduced in the presence of glucagon. E2 did not affect the amount of protein secretion. Proteome analysis showed that in the presence of insulin and E2, neutrophils secreted metalloproteinases MMP-9 and MMP-8 playing a key role in modulation of the extracellular matrix. In contrast, glucagon induced the secretion of cathepsin G, a key bactericide protease of neutrophils. Cathepsin G can promote the development of vascular complications because of its proinflammatory activity and ability to stimulate neutrophil adhesion via the proteolysis of surface receptors.

Modulation of neutrophil motility by curcumin: implications for inflammatory bowel disease

BACKGROUND

Neutrophils (PMN) are the first cells recruited at the site of inflammation. They play a key role in the innate immune response by recognizing, ingesting, and eliminating pathogens and participate in the orientation of the adaptive immune responses. However, in inflammatory bowel disease (IBD) transepithelial neutrophil migration leads to an impaired epithelial barrier function, perpetuation of inflammation, and tissue destruction via oxidative and proteolytic damage. Curcumin (diferulolylmethane) displays a protective role in mouse models of IBD and in human ulcerative colitis, a phenomenon consistently accompanied by a reduced mucosal neutrophil infiltration.

METHODS

We investigated the effect of curcumin on mouse and human neutrophil polarization and motility in vitro and in vivo.

RESULTS

Curcumin attenuated lipopolysaccharide (LPS)-stimulated expression and secretion of macrophage inflammatory protein (MIP)-2, interleukin (IL)-1β, keratinocyte chemoattractant (KC), and MIP-1α in colonic epithelial cells (CECs) and in macrophages. Curcumin significantly inhibited PMN chemotaxis against MIP-2, KC, or against conditioned media from LPS-treated macrophages or CEC, a well as the IL-8-mediated chemotaxis of human neutrophils. At nontoxic concentrations, curcumin inhibited random neutrophil migration, suggesting a direct effect on neutrophil chemokinesis. Curcumin-mediated inhibition of PMN motility could be attributed to a downregulation of PI3K activity, AKT phosphorylation, and F-actin polymerization at the leading edge. The inhibitory effect of curcumin on neutrophil motility was further demonstrated in vivo in a model of aseptic peritonitis.

CONCLUSIONS

Our results indicate that curcumin interferes with colonic inflammation partly through inhibition of the chemokine expression and through direct inhibition of neutrophil chemotaxis and chemokinesis.

Galectin-3 regulates peritoneal B1-cell differentiation into plasma cells

Extracellular galectin-3 participates in the control of B2 lymphocyte migration and adhesion and of their differentiation into plasma cells. Here, we analyzed the role of galectin-3 in B1-cell physiology and the balance between B1a and B1b lymphocytes in the peritoneal cavity. In galectin-3(-/-) mice, the total number of B1a lymphocytes was lower, while B1b lymphocyte number was higher as compared to wild-type mice. The differentiation of B1a cells into plasma cells was associated with their abnormal adhesion and location on the mesentery. The B220 and CD43, constitutively expressed by B1 lymphocytes, were respectively up- and downregulated in galectin-3(-/-) mice. Mononuclear cells were strongly adhered to the mesenteric membranes of both CD43(-/-) and galectin-3(-/-) mice, but in contrast to CD43(-/-) mice, the accumulation of B1 cells in peritoneal membranes in galectin-3(-/-) mice was accompanied by their functional differentiation into plasma cells. We have shown that in the absence of galectin-3, B1-cell differentiation into plasma cells is favored and the dynamic equilibrium of B1-cell populations in the peritoneum is maintained through a compensatory increase in B1b lymphocytes.

Modulation of neutrophil function by a secreted mucinase of Escherichia coli O157:H7

Escherichia coli O157∶H7 is a human enteric pathogen that causes hemorrhagic colitis which can progress to hemolytic uremic syndrome, a severe kidney disease with immune involvement. During infection, E. coli O157∶H7 secretes StcE, a metalloprotease that promotes the formation of attaching and effacing lesions and inhibits the complement cascade via cleavage of mucin-type glycoproteins. We found that StcE cleaved the mucin-like, immune cell-restricted glycoproteins CD43 and CD45 on the neutrophil surface and altered neutrophil function. Treatment of human neutrophils with StcE led to increased respiratory burst production and increased cell adhesion. StcE-treated neutrophils exhibited an elongated morphology with defective rear detachment and impaired migration, suggesting that removal of the anti-adhesive capability of CD43 by StcE impairs rear release. Use of zebrafish embryos to model neutrophil migration revealed that StcE induced neutrophil retention in the fin after tissue wounding, suggesting that StcE modulates neutrophil-mediated inflammation in vivo. Neutrophils are crucial innate effectors of the antibacterial immune response and can contribute to severe complications caused by infection with E. coli O157∶H7. Our data suggest that the StcE mucinase can play an immunomodulatory role by directly altering neutrophil function during infection. StcE may contribute to inflammation and tissue destruction by mediating inappropriate neutrophil adhesion and activation.

Enterohemorrhagic Escherichia coli (EHEC) poses a significant threat to the U.S. food supply, causing foodborne gastrointestinal disease in humans that can progress to hemolytic uremic syndrome (HUS), a potentially fatal kidney disease. Research suggests that EHEC strains are growing more virulent, resulting in a higher incidence of hospitalization and development of HUS from recent produce-associated outbreaks. Although immune dysregulation is a feature of HUS disease, the specific mechanisms contributing to altered immune function require investigation. Furthermore, the contribution of the immune response to early intestinal disease is not known. StcE is a secreted protease of EHEC that is expressed during infection and may contribute to virulence via cleavage of mucin-like glycoproteins. In this study, we define mucinase activity toward glycoproteins on the surface of human neutrophils and find that StcE alters neutrophil activity by interacting with these proteins. StcE affected crucial neutrophil functions including oxidative burst production and migration. The effects of StcE were both cleavage-dependent and cleavage-independent, providing insight into a novel mechanism for mediating neutrophil function via mucin interactions. Our study reports an immune-modulating role for a potential EHEC virulence factor and provides a possible explanation for altered neutrophil phenotypes observed during E. coli O157∶H7-induced disease.

The cleavage of neutrophil leukosialin (CD43) by cathepsin G releases its extracellular domain and triggers its intramembrane proteolysis by presenilin/gamma-secretase

The highly negatively charged membrane sialoglycoprotein leukosialin, CD43, is shed during neutrophil activation. This is generally thought to enhance cell adhesion. We here describe two novel consequences of this shedding, during neutrophil activation by phorbol esters or by chemoattractants after TNF-alpha priming. CD43 proteolysis was investigated by Western blotting, using a polyclonal antibody to CD43 intracellular domain. Our data emphasize the importance of a juxtamembranous cleavage of about 50% of membrane CD43 molecules by cathepsin G. Indeed, it is inhibited by alpha1-antichymotrypsin and cathepsin G inhibitor I and is reproduced by exogenous purified cathepsin G. The resulting membrane-anchored C-terminal fragment, CD43-CTF, becomes susceptible to presenilin/gamma-secretase, which releases CD43 intracytoplasmic domain: preincubation with three different gamma-secretase inhibitors, before PMN treatment by agonists or by purified cathepsin G, results in the accumulation of CD43-CTF. Because CD43 binds E-selectin, we also investigated the effect of the soluble extracellular domain CD43s, released by cathepsin G juxtamembranous cleavage, on neutrophil adhesion to endothelial cells. A recombinant CD43s-Fc fusion protein inhibited neutrophil E selectindependent adhesion to endothelial cells under flow conditions, while it had no effect on neutrophil static adhesion. We thus propose that, in addition to its potential pro-adhesive role, CD43 proteolysis results in: (i) the release, by cathepsin G, of CD43 extracellular domain, able to inhibit the adhesion of flowing neutrophils on endothelial cells and thus to participate to the natural control of inflammation; (ii) the release and/or the clearance, by presenilin/gamma-secretase, of CD43 intracellular domain, thereby regulating CD43-mediated signaling.

Endpoint-attached heparin blocks neutrophil sticking and spreading

Neutrophils adhere to polymer surfaces by partly unknown mechanisms. Heparin-coating of such surfaces is employed to improve biocompatibility of extracorporeal circulation. The aim of the study was to investigate mechanisms for interactions between neutrophils and uncoated versus heparin-coated surfaces. Isolated human neutrophils were incubated in tissue culture plates. Uncoated plates induced sticking and spreading of unstimulated neutrophils. Heparin-coating reduced sticking by approximately 75%, and adherent cells were less spread (p<0.001). Experiments in plates coated with modified heparins showed that sticking and spreading were not related to anticoagulatory ability or surface charge. Unstimulated neutrophil sticking was unchanged whether the media contained divalent cations or 1mM ethylenediaminetetraacetic acid (EDTA). Spreading on uncoated plates was greater in the presence of Ca(2+) and/or Mg(2+) than with EDTA. Spreading of unstimulated neutrophils on heparin-coated plates varied little with different media. Pre-incubation with anti-CD11b/CD18 antibodies did not significantly influence adhesion to heparin-coated plates. There were no differences in expression of the antiadhesive receptor CD43 (leukosialin) on adherent neutrophils on uncoated and heparin-coated plates, and pre-incubation with anti-CD43 antibody had little effect on neutrophil sticking. These data indicate an adhesive mechanism independent of selectins, integrins, and leukosialin, and inhibition of sticking and spreading by heparin-coating.

Downhill running in rats: influence on neutrophils, macrophages, and MyoD+ cells in skeletal muscle

The accumulation of neutrophils and macrophages, as well as the activation of satellite cells, are early events following skeletal muscle injury. We examined the temporal relationship between changes in neutrophils, macrophages, and MyoD protein, a marker of satellite cell activation, after injurious exercise. Male rats ( n=47) performed an intermittent downhill (-16% grade) running (17 m/min) protocol and the solei were obtained at 0, 2, 6, 24, 48, or 72 h post-exercise. Neutrophils, macrophages (ED1 and ED2), and MyoD+ cells were determined in muscle cross sections using immunohistochemistry. Downhill running increased ( P<or=0.05) the percentage of injured fibers and elevated blood creatine kinase activity. Neutrophils were elevated 18-fold relative to controls at 24 h post-exercise. ED1 macrophages were elevated four- and twofold at 24 and 48 h post-exercise, respectively. Neither ED2 macrophages nor MyoD+ cells were elevated post-exercise. These observations may indicate that elevations in neutrophils and ED1 macrophages after injurious exercise are not temporally associated with an increase in satellite cell activation.

Regulation of CD43-induced U937 homotypic aggregation

CD43 (leukosialin, sialophorin), a prominent component of the hemopoietic cell surface, has an enigmatic role in cell-cell interaction. The observation that CD43 ligation triggers homotypic aggregation of monoblastoid U937 cells has permitted analysis of this: CD43-induced aggregation was distinguishable from CD29- (also known as beta1 integrin) or CD98- (also known as 4F2, or fusion-related protein 1) induced aggregation, with different energy requirements and with partial dependence on beta2 integrins. Previous studies have focused on the role of CD43 ligation in tyrosine phosphorylation. However, in the homotypic adhesion assay, although there is initial tyrosine phosphorylation, protein tyrosine kinase inhibitors did not block aggregation. Therefore, other signaling pathways were examined. CD43 ligation induced protein tyrosine dephosphorylation, and protein tyrosine phosphatase inhibitors blocked aggregation. Activation of MAP kinases was not necessary. Cytoskeletal inhibitors amplified aggregation. Protein kinase C (PKC) inhibitors amplified aggregation, implicating PKC as a negative regulator. CD43 ligation up-regulated surface adhesion molecules and enhanced CD29- and CD98-induced aggregation. Thus, CD43 participation in cell-cell adhesion is under stringent control, involving both surface events and several different intracellular signaling pathways, acting together to regulate the process. These mechanisms add a further dimension to the potential role of CD43 in tissue immune responses.

Modulation of neutrophil function by the tripeptide feG

BACKGROUND

Neutrophils are critical in the defense against potentially harmful microorganisms, but their excessive and inappropriate activation can contribute significantly to tissue damage and a worsening pathology. Through the release of endocrine factors submandibular glands contribute to achieving a balance in neutrophil function by modulating the state of activation and migratory potential of circulating neutrophils. A putative hormonal candidate for these effects on neutrophils was identified as a heptapeptide named submandibular gland peptide T (SGP-T; sequence = TDIFEGG). Since the tripeptide FEG, derived from SGP-T, and its D-amino acid analogue feG had similar inhibitory effects on inflammatory reactions, we investigated the effects of feG on human and rat neutrophil function.

RESULTS

With human neutrophils feG had no discernible effect on oxidative burst or phagocytosis, but in picomolar amounts it reduced PAF-induced neutrophil movement and adhesion, and the binding of CD11b by 34% and that of CD16b close to control values. In the rat feG (10-11M) reduced the binding of CD11b and CD16 antibodies to PAF-stimulated circulating neutrophils by 35% and 43%, respectively, and at 100 micrograms/kilograms intraperitoneally feG reduced neutrophil in vivo migration by 40%. With ovalbumin-sensitized rats that were challenged with antigen, feG inhibited binding of antibodies against CD16b but not CD11b, on peritoneal leukocytes.

CONCLUSIONS

The inhibitory effect of feG on neutrophil movement may be mediated by alterations in the co-stimulatory molecules CD11b and CD16.

Inhibition of Mg2+-dependent Adhesion of Polymorphonuclear Leukocytes by Serum Hemopexin: Differences in Divalent-Cation Dependency of Cell Adhesion in the Presence and Absence of Serum

Circulating and nonadherent polymorphonuclear leukocytes (PMNs) become activated to attain adhesive state in an integrin-dependent manner by various stimuli, and perform a variety of microbicidal functions such as phagocytosis and superoxide production. We found that, in the absence of serum, a physiological concentration of hemopexin has a strong inhibitory action on Mg(2+)-dependent adhesion of PMA-activated PMNs to fibrinogen- and serum-coated surfaces. Under these conditions, Ca(2+) had no effect on Mg(2+)-dependent adhesion or the adhesion-inhibitory activity of hemopexin. In contrast, PMNs suspended in serum containing sufficient amounts of hemopexin to inhibit adhesion showed marked adherence, which was inhibited by EGTA. Next, we prepared a small-molecule fraction of serum by ultrafiltration followed by boiling. PMA-activated PMNs was found to adhere in the presence of both hemopexin and the small-molecule fraction, and the adhesion was enhanced by exogenous Ca(2+). EGTA abolished the effect of the small molecule fraction. The data suggest that serum contains adhesion-promoting factor(s) which allows PMNs to adhere despite the presence of hemopexin and that Ca(2+) is required for adhesion-promoting activity. Further study of hemopexin may provide clues for new therapeutic strategies aimed at interfering with PMN adhesion to control inflammation and tissue injury.

Alteration of leukocyte motility on plasma-conditioned prosthetic biomaterial, ePTFE, via a flow-responsive cell adhesion molecule, CD43

The physiologic determinants of leukocyte migration on vascular prosthetic biomaterials remain poorly understood, despite their relevance to the control of periprosthetic infection. Using hemodynamic exposure of human polymorphonuclear leukocytes adherent to expanded polytetrafluoroethylene (ePTFE) in vitro, we investigated the role of fluid shear in regulating leukocyte migratory behavior on plasma-adsorbed, prosthetic vascular biomaterial. The presence of flow at a wall shear stress of 25 dyn/cm(2) increased the degree of leukocyte displacement along the flow direction without altering the degree of overall cell attachment. Moreover, plasma-ePTFE elicited a lower overall degree of displacement under flow in comparison with untreated ePTFE. We further probed the molecular level regulation of leukocyte migratory responses under flow through the immunocytochemical quantification of specific leukocyte adhesion molecules and determined that CD43, a cell adhesion molecule, was upregulated via flow exposure for leukocytes adherent to plasma-ePTFE, whereas basal levels of CD43 expression were not significantly altered on untreated ePTFE. When flow-exposed, adherent leukocytes were incubated in the presence of substrate immobilized anti-CD43 immunoglobulin, the degree of cell displacement along flow was found to be significantly enhanced on plasma-ePTFE. Quantification of the cell population redistribution under flow using a modified random motility model, indicated that the incorporation of anti-CD43 on plasma-ePTFE led to a significant increase (243 +/- 60%) in the cell dispersion coefficient, mu(D), whereas only a minimal increase (61 +/- 30%) was detected on non-adsorbed ePTFE. Overall, our results suggest that flow exposure can induce the migration of leukocytes adherent to prosthetic materials in a substrate-dependent manner. An important implication of our study is that, although biomaterials exposed to plasma intrinsically passivate leukocyte migration even under hemodynamic conditions, it may be possible to promote cell motility by targeting a specific, flow-responsive, adhesion molecule.

Transient resistance to B16F10 melanoma growth and metastasis in CD43-/- mice

CD43, the major transmembrane sialoglycoprotein of neutrophils, monocytes, T lymphocytes and platelets, is highly glycosylated and its high sialic acid content contributes to the strongly negative charge of cells. In this study the role of CD43 in melanoma development was addressed using CD43 -/- mice (null mutated for the corresponding gene or knockout [KO]). Growth of B16F10 melanoma was retarded in the KO mice compared with the wild-type CD43+/+ control (WT). A marked difference in lung colonization and other metastatic foci was observed in the KO and WT mice up to 15 days after intravenous injection of tumour cells. The initial resistance of KO mice was reversed with time, and in the long term there was no difference in the survival rate of the two animal groups. Transient resistance was attributed to increased adhesion of thrombin-activated platelets and leukocytes to melanoma and endothelial cells in KO mice. In the KO mice tumour emboli were found in the central portion of the lung more than at the lung periphery immediately after intravenous injection, in contrast to the WT mice. Activation of melanoma adhesion receptors by thrombin or TRAP stimulated lung colonization in WT but not KO mice. Therefore, the correlation of tumour embolism and metastasis in short-term experiments depends on the nature and stability of interactions between the tumour and the blood/endothelial cells of the host.

Reduced CD43 expression on the neutrophils of MDS patients correlates with an activated phenotype of these cells

CD43 (also known as leukosialin and sialophorin) is a surface sialoglycoprotein expressed at high levels on most leukocytes implicated in adhesion, antiadhesion, and activation/proliferation mechanisms. We studied the expression of this molecule on the leukocytes of patients with myelodysplastic syndromes (MDSs) in an effort to detect acquired deficiencies of this molecule. We used immunofluorescence flow cytometry in analyzing whole blood and isolated neutrophils from 49 MDS patients, 33 men and 16 women aged 33 to 85 years (median, 75 years), and 18 healthy individuals aged 35 to 80 years (median, 72 years). According to French-American-British classification criteria, 13 patients had refractory anemia, 18 had refractory anemia with ringed sideroblasts, 9 had refractory anemia with excess of blasts, 4 had refractory anemia with excess of blasts in transformation to acute leukemia, and 5 had chronic myelomonocytic leukemia. We found decreased expression of CD43 on the neutrophils of these patients, and we correlated this finding with the activation status of these cells as it is defined by their phenotypes. We studied the expression of CD11b, CD18, CD35, CD67, CD69, CD44, and CD53 molecules known to be changed in the activated form of neutrophils. CD43 expression correlated positively with CD53 and CD44 expression and negatively with CD11b, CD18, CD35, CD67, and CD69 expression. Additionally, increased levels of soluble vascular cell adhesion molecules were detected in these patients, suggesting endothelial cell activation. In conclusion, we believe that the decreased expression of CD43 on the neutrophils of MDS patients is associated with activation of these cells and is probably due to cleavage of the molecule from the cell surface and that the same mechanism is possibly responsible for the parallel down-regulation of CD44 and CD53.

Sialidase treatment exposes the beta1-integrin active ligand binding site on HL60 cells and increases binding to fibronectin

The migration of neutrophils from the circulation to areas of inflammation is the result of the sequential activation of multiple cellular adhesion molecules. beta1-Integrins are cell surface glycoproteins and the class of adhesion molecules responsible for binding to the extracellular matrix. The goal of this study was to determine the contribution of glycosylation, specifically the presence of sialic acid, to beta1-integrin adhesion in a neutrophil model. beta1-Integrins on differentiated HL60 cells were remodeled by treatment with the exoglycosidases, sialidase and beta-galactosidase. beta1-Integrin activity was determined by measuring adherence to the extracellular matrix protein fibronectin. The expression of beta1-integrins, beta2-integrins and activated beta1-integrins was determined by flow cytometry. Remodeling of beta1-integrins by treatment with sialidase increased adhesion by greater than 1,000%. Flow cytometric analysis of remodeled beta1-integrins demonstrated an increased expression of the activated beta1-integrin, but only minor increases in the expression of total beta1- and beta2-integrins. We postulate that glycosidase treatment increases adhesion and expression of activated beta1-integrins by exposure of the normally hidden ligand-binding site. The glycosylation of beta1-integrins on neutrophils may act to hide the ligand-binding site in unstimulated cells thereby contributing to the affinity modulation observed in neutrophil beta1-integrin function.

Leukocyte chemosensory migration on vascular prosthetic biomaterial is mediated by an integrin beta2 receptor chain

The ability of adherent activated leukocytes to migrate on implanted prosthetic biomaterial surfaces may be an early rate-limiting step in eliminating periprosthetic infection. The goal of this study was to explore the molecular mechanism governing leukocyte migration on the implantable cardiovascular prosthetic biomaterial, expanded polytetrafluoroethylene (ePTFE), in response to stimulation by the soluble chemokine, N-formyl-methionyl-leucyl-phenylalanine (fMLP). We used a population level migration assay to study the migration of polymorphonuclear leukocytes (PMN) on ePTFE, overlaid by a gelatin/agar composite. A theoretical random walk model was applied to describe fMLP-induced PMN migration on ePTFE in terms of an objective random cell migration coefficient, mu. Our results show that following stimulation with 0-10(-7) M fMLP, the value of mu ranged from 5.43 x 10(-9) to 1.08 x 10(-7) cm2/s, with a maximum value obtained at 10(-8) M fMLP. We probed the expression levels of various beta2 integrin receptor subunits and their contribution to the migratory function of ePTFE-adherent PMN over a wide range of fMLP concentration. We found that the expression of the integrin beta-chain, CD18, was also maximized at 10(-8) M fMLP, along with only slight changes in the expression of integrin alpha-chains (CD11a,b,c). We report that treatment with antibodies against either beta or combined alpha chains, but not individual alpha chains, inhibited PMN attachment to ePTFE at 10(-8) M fMLP, suggesting the likely role of combined beta2 receptor subunits in early adhesion events following stimulation. However, treatment with only anti-CD18 significantly lowered PMN migration on ePTFE (mu = 5.98 x 10(-9) cm2/s), and this degree of inhibition was much greater than that elicited by the combined treatment with antibodies recognizing all possible alpha-chains. Overall, we conclude that migratory behavior of chemokinetically stimulated PMN on ePTFE is mediated by the integrin beta chain pool, and is only weakly regulated by the integrin alpha chain.

Distinctive roles of neutrophils and monocytes in anti-thy-1 nephritis

Anti-Thy-1.1 glomerulonephritis as an experimental model for mesangial proliferative glomerulonephritis was induced in Wistar rats by a single injection of monoclonal IgG2a-anti-Thy-1.1 antibody (ER4G). This transient model is complement-mediated and leads to mesangial-cell (MC) lysis followed by MC proliferation, glomerular microaneurysm formation, glomerular influx of polymorphonuclear leukocytes (PMNs) and macrophages, proteinuria, and hematuria. In this study we investigated the distinctive roles of infiltrating PMNs or monocytes/macrophages by treating rats with an antibody against rat integrin CD11b/CD18 (ED7) or by depletion of monocytes with multilamellar clodronate liposomes, respectively. ED7 administration resulted in reduction of the influx of PMNs in glomeruli during the first 6 days after induction of Thy-1.1 nephritis, whereas treatment with an isotype-matched irrelevant antibody (PEN9) or with phosphate-buffered saline had no effect on macrophage influx. Increased glomerular C3 and C6 deposition on days 1 and 3 was seen in the ED7-treated rats but not seen in the control groups. In addition, the ED7-treated group showed an increased number of aneurysmatic glomeruli and more severe hematuria. Monocyte/macrophage depletion led to a significant reduction of mesangial matrix expansion, although mesangial proliferation, proteinuria, and hematuria remained unaltered. These results, together with the known effects of PMN-derived enzymes on C3 cleavage, suggest that a reduction in the influx of PMNs results in sparing of C3 and consequently of more complement activation in the glomerulus with increased complement-mediated damage. Our data indicate that infiltrating PMNs and monocytes/macrophages play distinctive roles during inflammation in this model of MC glomerulonephritis.

The CBF.78 monoclonal antibody to human sialophorin has distinct properties giving new insights into the CD43 marker and its activation pathway

We confirm here the CD43 specificity of the CBF.78 monoclonal antibody (mAb) and compare its phenotypic and functional capacities to classical group-A mAbs (DFT1, MEM-59) and to 2 other CD43 mAbs (RDP/AD9, 161-46). It reacts with stable human CD43 transfectants in a sialic acid independent way and blocks completely cell binding of RDP/AD9 or 161-46 more or less but not DFT1 and MEM-59. Its distribution differs from all other CD43. B lymphocytes, but surprisingly the majority of granulocytes or monocytes are CBF.78 negative. CBF.78 is expressed on all T lymphocytes, but the number of CBF.78 molecules/cell is low and equally represented on resting T CD4 and CD8 cells. In comparison to naive T lymphocytes, CD45RO cells increase their CBF.78 epitopes much more than other CD43 epitopes. At a single cell level, confocal microscopy shows that CBF.78 can exist independently of other epitopes. CBF.78 is able to induce homotypic adhesion in different cell lines but not in peripheral blood lymphocytes and is unable to relocalise the targeted molecules. U937 cell line that is not agglutinated by CBF.78 (or RDP/AD9) undergoes a stronger adhesion with PMA, when this reagent is combined with this mAb. By itself CBF.78 is unable to activate T lymphocytes and to costimulate CD3 mAbs but partially blocks PMA. The phosphorylation of the tyrosine kinase p59fyn and p56lck, driven by CBF.78, is weak and almost blocked by PMA. Altogether these data support the hypothesis that there are at least 3 modes of interaction between PKC and CD43 pathways: each pathway is inhibitory towards the other but the CD43 one can also be synergistic.

Actin polymerization induces shedding of FcgammaRIIIb (CD16) from human neutrophils

FcgammaRIIIb (CD16) is a glycosyl phosphatidylinositol (GPI)-anchored low-affinity IgG receptor, exclusively expressed on human neutrophils. FcgammaRIIIb associates with complement receptor 3 (CR3, Mac-1, CD11b/CD18), which may indirectly link FcgammaRIIIb to the actin cytoskeleton. Upon neutrophil activation, apoptosis, or chemotaxis, FcgammaRIIIb is shed from the cell surface. In all of these events, actin rearrangements play an important role. To establish a role for the actin cytoskeleton in the control of FcgammaRIIIb shedding, we treated human neutrophils with jasplakinolide, an actin-polymerizing peptide. We show that enhanced actin polymerization induces time- and dose-dependent shedding of FcgammaRIIIb. This effect was not restricted to FcgammaRIIIb, because the cell surface expression of CD43, CD44, and L-selectin was also downregulated after induction of actin polymerization. This actin-dependent pathway is staurosporine sensitive but does not appear to involve activation of PKC or CR3. These data show that the actin cytoskeleton can regulate protein ectodomain shedding from human neutrophils.