Glucocorticoid effects in an endotoxin-induced rat pulmonary inflammation model: differential effects on neutrophil influx, integrin expression, and inflammatory mediators

To understand the basis for the refractory nature of acute respiratory distress syndrome (ARDS) to glucocorticoids, the effects of dexamethasone pretreatment (DEX, 2 mg/kg, intraperitoneally) on the kinetics of airway tumor necrosis factor-alpha (TNF alpha) and macrophage inflammatory protein 2 (MIP-2) production, and polymorphonuclear leukocyte (PMN) influx after intratracheal lipopolysaccharide (LPS) (1 mg/kg) in rats were investigated. In the absence of exogenous glucocorticoids, TNF alpha and MIP-2 levels in bronchoalveolar lavage (BAL) fluid peaked at 21 and 300 ng, respectively, by 3 h. DEX pretreatment resulted in a 74% reduction in BAL TNF alpha, yet MIP-2 accumulation was unchanged. In addition, DEX reduced PMN influx at 5 h by 58.4% to 4.1 +/- 0.7 x 10(6) PMN (n = 5). DEX, however, did not mitigate the 3-fold increase in total BAL protein observed at 5 h, attributable to albumin influx. The effects of subacute DEX treatment (3.8 mg/kg per day, for 3 days) on cell-surface expression of the adhesion molecules CD11a, CD11b, and L-selectin were determined by flow cytometric analysis of peripheral blood and autologous BAL PMN. Compared with peripheral blood PMN, exudative PMN had 4-fold greater CD11b expression, no change in CD11a, and loss of L-selectin immunoreactivity 5 h after LPS challenge. The upregulation of CD11b on exudative PMN was insensitive to DEX pretreatment, which, together with a failure to suppress MIP-2 levels, provides a possible explanation for the lack of efficacy of steroids in the management of ARDS.

Defective Peyer's patch organogenesis in mice lacking the 55-kD receptor for tumor necrosis factor

Lymphotoxin alpha (LT-alpha) may form secreted homotrimers binding to p55 and p75 tumor necrosis factor (TNF) receptors or cell surface-bound heterotrimers with LT-beta that interact with the LT-beta receptor. Genetic ablation of LT-alpha revealed that mutant mice have no detectable lymph nodes or Peyer's patches and that the organization of the splenic white pulp in T and B cell areas is disturbed. In this report we describe a novel function for the p55 TNF receptor during ontogeny and demonstrate that mice deficient for p55 completely lack organized Peyer's patches. In contrast, lymph nodes and spleen are present in p55-deficient mice and lymphocytes segregate normally into B and T cell areas in these organs. Lamina propria and intraepithelial lymphocytes of the small intestine were detected in normal number and distribution in p55 mutant mice. Lymphocytes and endothelial cells from p55-deficient mice express normal levels of adhesion molecules considered important for lymphocyte migration to mucosal organs; this indicates that the lack of Peyer's patches does not result from a defect in lymphocyte homing. In summary, the p55 receptor for TNF selectively mediates organogenesis of Peyer's patches throughout ontogeny, suggesting that the effects of LT-alpha on the development of lymphoid organs may be mediated by distinct receptors, each functioning in an organ-specific context.

In vivo T cell response to viral superantigen. Selective migration rather than proliferation

Superantigens induce T cell activation and proliferation in vitro, and some also induce cell activation in vivo. MMTV(SW) is an infectious mouse mammary tumor virus (MMTV) encoding a superantigen with the same Vbeta specificity as MIs-1a (Mtv-7), which induces a strong local response in vivo. injection of MMTV(SW) into mouse footpads leads to accumulation of superantigen-reactive T cells (Vbeta6+CD4+) and B cells in the draining lymph nodes (LN). We investigated the kinetics of this cell accumulation by measuring cell activation (blastogenesis, CD25 and CD69 expression), cell migration (using syngenic FITC-labeled CD4+ cells and L-selectin detection), and cell proliferation (using in vivo labeling with bromodeoxyuridine). Specific T cells selectively migrated to the draining LN. Accumulating Vbeta6+CD4+ T cells were large CD69+ cells, but remained CD25 negative and showed down-regulated L-selectin expression. Their DNA synthesis rate, studied by pulse labeling and continuous administration of bromodeoxyuridine, was increased, but remained too low to explain the draining LN hyperplasia. These data show that the local T cell response to MMTV(SW) mainly consists of selective migration followed by local activation of reactive T cells, and that cell proliferation is only a minor component of the response. By contrast, the optimal dose of staphylococcal enterotoxin B that, nevertheless, leads to a lower reactive T cell accumulation in the draining LN induces a very high proliferation rate.

Calcium-dependent oligonucleotide antagonists specific for L-selectin

The selectins are calcium-dependent C-type lectins that recognize complex anionic carbohydrate ligands, initiating many cell-cell interactions in the vascular system. Selectin blockade shows therapeutic promise in a variety of inflammatory and postischemic pathologies. However, the available oligosaccharide ligand mimetics have low affinities and show cross-reaction among the three selectins, precluding efficient and specific blockade. The SELEX (systematic evolution of ligands by exponential enrichment) process uses combinatorial chemistry and in vitro selection to yield high affinity oligonucleotides with unexpected binding specificities. Nuclease-stabilized randomized oligonucleotides subjected to SELEX against recombinant L-selectin yielded calcium-dependent antagonists with approximately 10(5) higher affinity than the conventional oligosaccharide ligand sialyl LewisX. Most of the isolated ligands shared a common consensus sequence. Unlike sialyl LewisX, these antagonists show little binding to E- or P-selectin. Moreover, they show calcium-dependent binding to native L-selectin on peripheral blood lymphocytes and block L-selectin-dependent interactions with the natural ligands on high endothelial venules.

The carbohydrate-recognition domain of E-selectin is sufficient for ligand binding under both static and flow conditions

Selectins are a family of adhesion molecules with a well-defined domain structure comprised of a lectin or carbohydrate-recognition domain (CRD), an epidermal growth factor (EGF)-like motif, and a variable number of consensus repeats (CRs). While it is clear from various lines of evidence that the CRD plays a pivotal role in selectin-ligand interactions, little is known about the role of the non-lectin selectin domains. We expressed a series of soluble chimeric proteins with various domains switched between E- and L-selectin and measured binding of the resulting chimeras to sialyl Lewis(a) and sulfatide, two carbohydrate structures which are specific for the E- and L-CRDs, respectively. Both CRDs bind to their respective ligands with the same affinity regardless of the origin of the other domains they are attached to. The domain-switched chimeras were assayed for their ability to support static binding and rolling of various cell lines which bind specifically to E-selectin. In these assays, the E-CRD was indispensable for both static binding and rolling under physiological flow conditions. The E-CRD alone, when substituted into L-selectin, supported rolling without the requirement for additional ligand-recognition elements. We conclude that the EGF domain or the CRs of E- and L-selectin have no influence on the CRD's specificity to carbohydrates. Furthermore, at least in the case of E-selectin, they do not contribute to the specificity of binding to cell surface ligands.

Diverse cell surface protein ectodomains are shed by a system sensitive to metalloprotease inhibitors

The extracellular domains of a diverse group of membrane proteins are shed in response to protein kinase C activators such as phorbol 12-myristate 13-acetate (PMA). The lack of sequence similarity in the cleavage sites suggests the involvement of many proteases of diverse specificity in this process. However, a mutant Chinese hamster ovary cell line recently isolated for being defective in PMA-activated shedding of the membrane-anchored growth factor transforming growth factor alpha precursor (proTGF-alpha) is concomitantly defective in the shedding of many other unrelated membrane proteins. Here we show that independent mutagenesis and selection experiments yield shedding mutants having the same recessive phenotype and belonging to the same genetic complementation group. Furthermore, two structurally distinct agents, TAPI-2 and 1,10-phenanthroline, which are known to inhibit metalloproteases, block PMA-activated shedding of proTGF-alpha, cell adhesion receptor L-selectin, interleukin 6 receptor alpha subunit, beta-amyloid precursor protein, and an entire set of anonymous Chinese hamster ovary cell surface proteins. Certain serine protease inhibitors prevent release of these proteins by interfering with their maturation and transport to the cell surface but do not inhibit ectodomain shedding from the cell surface. The results suggest the existence of a common system for membrane protein ectodomain shedding involving one or several proteolytic activities sensitive to metalloprotease inhibitors, whose ability to act can be disrupted by recessive mutations in a single gene.

Decreased L-selectin expression in CD34-positive cells from patients with chronic myelocytic leukaemia

Abnormal adhesive interaction between bone marrow stroma and progenitors, one of the causes of unregulated proliferation in chronic myelocytic leukaemia (CML), may be caused by some alterations in adhesion molecules on CML progenitors. We investigated the expression of adhesion molecules (CD44, VLA-5, VLA-4, LFA-1, ICAM-1, L-selectin and c-kit) on bone marrow CD34++ cells from 16 CML patients by three-colour flow cytometry. The mean percentage of cells expressing L-selectin in the CD34++CD38+(or)++ fraction from untreated CML patients was significantly lower, and that in the CD34++CD38- fraction tended to be lower than that from normal controls. Among 11 CML patients treated with interferon-alpha (IFN-alpha), the mean percentage of the cells expressing L-selectin in the CD34++CD38- fraction from three patients with a low percentage of Ph1(+) cells in bone marrow was significantly higher than that from five patients with a high percentage of Ph1(+) cells. In addition, L-selectin expression rate was inversely correlated to the percentage of Ph1(+) cells. There was no significant difference between the untreated patients and normal controls with regard to the expression rates of the other adhesion molecules in each CD34++ fraction except LFA-1. These data suggest that decreased L-selectin expression in CML CD34++ cells reflects one of the features of malignant CML progenitors.

Obstructive jaundice causes reduced expression of polymorphonuclear leucocyte adhesion molecules and a depressed response to bacterial wall products in vitro

BACKGROUND

Obstructive jaundice is associated with an increased incidence of infection and endotoxaemia, which may result from impaired host immunity. Neutrophil adhesion to vascular endothelium is a key part of the inflammatory response.

AIMS

To investigate neutrophil adhesion molecule expression and activation in obstructive jaundice.

PATIENTS

Nine adult patients with obstructive jaundice and 11 control subjects.

METHODS

The expression of the neutrophil adhesion receptors L-selectin, CD11a, CD11b, CD11c, and CD15 was determined using flow cytometry. CD11b expression in response to stimulation with fMLP and endotoxin was measured.

RESULTS

The basal expression of L-selectin, CD11a, and CD15 was significantly decreased in jaundiced patients (p < 0.05) and the expression of CD11b in response to stimulation with fMLP and endotoxin was significantly impaired in the jaundiced group. Endotoxin stimulation without plasma did not reverse the impaired response showing that it is not caused by endotoxin inactivation by plasma proteins.

CONCLUSIONS

Neutrophils from patients with obstructive jaundice show decreased adhesion receptor expression and an impaired response to stimulation with bacterial products. This cellular dysfunction may be responsible for the high incidence of septic complications in these patients.

CD31 (PECAM-1) is a differentiation antigen lost during human CD4 T-cell maturation into Th1 or Th2 effector cells

The CD31 antigen (PECAM-1) has been reported to be a stable marker for a human CD4 T-cell subpopulation unable to produce interleukin-4 (IL-4). We show here that CD31 expression is not stable inasmuch as CD4 T-cell lines and clones derived from cell-sorted neonatal CD31+ cells lose CD31 upon repetitive cycles of stimulation and IL-2 expansion. Moreover, various cytokines (IL-1 alpha, IL-4, IL-6, transforming growth factor-beta) fail to reinduce CD31 on CD31- clones. Whereas all CD31+ CD4 T cells rapidly express high levels of the CD45RO antigen and down-regulate the L-selectin antigen after priming, CD31 disappears more slowly because only part of the cells lose CD31 expression upon each cycle of stimulation. Loss of CD31 reflects a functional maturation of CD45RO+ cells since, in a system which favours the development of Th2 effectors, IL-4 is produced by CD31- but not CD31+ effector T cells, whereas interferon-gamma is produced by both types of cells. However, CD31 is not a Th1 marker since it is not expressed on several Th1 antigen-specific clones. We conclude that CD31 is a maturation marker expressed on the great majority of naive CD45RO- CD4 T cells and on a subset of CD45RO+ CD4 T cells that are at an intermediate stage of maturation.

Platelet-dependent primary hemostasis promotes selectin- and integrin-mediated neutrophil adhesion to damaged endothelium under flow conditions

Co-localization of blood platelets and granulocytes at sites of hemostasis and inflammation has triggered an intense interest in possible interactions between these cellular processes and induction of vessel wall injury. Leukocyte adhesion to endothelial cells decreases with increasing shear and is dependent on an initial rolling phase mediated by selectins. We hypothesized that flow-dependent platelet adhesion at an injured vessel wall will lead to P-selectin expression by platelets, thus mediating leukocyte co-localization. A perfusion chamber was used in which flowing whole blood induced platelet adhesion to a subendothelial matrix (ECM) of cultured human umbilical vein endothelial cells (HUVEC). We compared neutrophil (polymorphonuclear leukocyte [PMN]) interactions with HUVEC and their ECM with and without adhered platelets. PMNs adhered predominantly to ECM-adhered platelets and not to endothelial cells. ECM alone did not support PMN adhesion under flow conditions. PMN adhesion to unstimulated HUVEC was only substantial at low shear (up to 200 cells/mm2 at shear stress 80 mPa). In marked contrast, PMN adhesion to ECM-adhered platelets was dramatically increased, and adhesion was demonstrated at much higher shear stress (up to 640 mPa). Studies with specific antibodies showed that the platelet-dependent neutrophil adhesion was selectin-mediated. Inhibition of P-selectin caused a marked inhibition of adhesion at high shear stress, whereas the role of leukocyte L-selectin was less pronounced. beta2-Integrin-blocking antibodies inhibited static neutrophil adhesion. fMLP induced L-selectin shedding from leukocytes, resulting in decreased leukocyte adhesion. In conclusion, platelet-dependent hemostasis at the ECM appears to be a powerful intermediate in neutrophil-vessel wall interactions at shear stresses that normally do not allow neutrophil adhesion to intact endothelium.

Expression of the alpha(1,3)fucosyltransferase Fuc-TVII in lymphoid aggregate high endothelial venules correlates with expression of L-selectin ligands

Lymphocyte homing to lymph nodes and Peyer's patches is mediated, in part, by adhesive interactions between L-selectin expressed by lymphocytes and L-selectin ligands displayed at the surface of the cuboidal endothelial cells lining the post-capillary venules within lymphoid aggregates. Candidate terminal oligosaccharide structures thought to be essential for effective L-selectin ligand activity include a sulfated derivative of the sialyl Lewis x tetrasaccharide. Cell type-specific synthesis of this oligosaccharide is presumed to require one or more alpha(1,3)fucosyltransferases, operating upon common 3'-sialylated and/or sulfated N-acetyllactosamine-type precursors. The identity of the alpha(1,3)fucosyltransferase(s) expressed in cells that bear L-selectin ligands has not been defined. We report here the molecular cloning and characterization of a murine alpha(1,3)fucosyltransferase locus whose expression pattern correlates with expression of high affinity ligands for L-selectin. In situ hybridization and immunohistochemical analyses demonstrate that this cDNA and its cognate alpha(1,3)fucosyltransferase are expressed in endothelial cells lining the high endothelial venules of peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. These expression patterns correlate precisely with the expression pattern of L-selectin ligands identified with a chimeric L-selectin/IgM immunohistochemical probe and by the high endothelial venule-reactive monoclonal antibody MECA-79. Transcripts corresponding to this cDNA are also detected in isolated bone marrow cells, a source rich in the surface-localized ligands for E- and P-selectins. Sequence and functional analyses indicate that this murine enzyme corresponds to the human Fuc-TVII locus. These observations suggest that Fuc-TVII participates in the generation of alpha(1,3)fucosylated ligands for L-selectin and provide further evidence for a role for this enzyme in E- and P-selectin ligand expression in leukocytes.

Colchicine interferes with L-selectin and leukocyte function-associated antigen-1 expression on human T lymphocytes and inhibits T cell activation

Colchicine, which inhibits cell microtubule assembly by preventing polymerization of tubulin monomers, inhibits cell-mediated immune responses and promotes long-term survival of major histocompatibility complex-incompatible renal allografts in rats. Here we evaluated the effect of blocking cell microtubule assembly by colchicine on T cell and endothelial cell adhesion receptors involved in transducing signals for T cell activation. By using immunofluorescence flow cytometry analysis, evidence is presented that colchicine, in a dose-dependent fashion, downregulated L-selectin and leukocyte function-associated antigen-1, but not CD2 and CD44 on the surface of naive human peripheral blood lymphocytes. This effect was confirmed in two subsets of T lymphocytes, namely, CD45RA- and CD45RO-positive cells. However, colchicine did not influence the rapid shedding of L-selectin from T lymphocytes exposed to activating stimuli. Colchicine inhibited expression of interleukin-2 receptor on activated T lymphocytes. This effect was observed when T lymphocytes were stimulated with both anti-CD3 and anti L-selectin monoclonal antibodies. Colchicine also inhibited lymphocyte function in vitro as documented by inhibition of the human mixed lymphocyte response in a dose-dependent fashion. Moreover, colchicine downregulated surface expression of intercellular adhesion molecule-1 and E-selectin on activated human umbilical vein endothelial cells. These results indicate that blocking cell microfubule assembly inhibits surface expression of adhesion molecules on T cells and endothelial cells, and provides insights into the complex mechanisms of the action of colchicine in vivo.

High-dose IL-2 and IL-15 enhance the in vitro priming of naive CD4+ T cells for IFN-gamma but have differential effects on priming for IL-4

Cytokines play an important role for the in vitro differentiation of naive CD4+ T cells into IL-4- or IFN-gamma-producing cells. The presence of both IL-4 and IL-2 is required to prime cells for IL-4 in vitro. Using purified CD4+/LECAM-1high T cells from TCR transgenic mice as naive responder cells, the role of IL-15 was studied to see if it functioned similarly to IL-2 with regard to IL-4 priming. Purified CD4+ T cells cultured in the presence of IL-4 and anti-IL-2 failed to prime cells for IL-4 production. Addition of IL-15 to these same cultures could not restore priming for IL-4, suggesting that IL-2 and IL-15 may have different functional properties during the in vitro differentiation of IL-4-producing cells. The role of IL-15 in priming for IFN-gamma was also examined. The addition of high doses of IL-15 to priming cultures resulted in a striking increase in the amount of IFN-gamma produced following restimulation. Similarly, addition of a relatively high dose of IL-2 also produced a significant enhancement of IFN-gamma production; however, as previously reported, the presence of IL-12 in priming cultures induced the greatest increase in IFN-gamma production, leaving it as the predominant controller of Th1 differentiation in physiologic situations. Finally, IL-15 was shown to increase proliferation of activated CD4+ T cell blasts but not of naive CD4+ T cells. Moreover, cultures containing both IL-12 and IL-15 showed greater proliferation than either cytokine alone, suggesting an additive effect between these cytokines.

Mucosally activated circulating human B cells in diarrhea express homing receptors directing them back to the gut

BACKGROUND & AIMS

Recirculation of mucosal lymphocytes has been established in animals but not in humans. Specific antibody-secreting cells in the blood of patients with diarrhea, initially activated in gut mucosa, are potential recirculating cells. The aim of this study was to determine whether these cells circulate back to gut by analyzing their homing receptors.

METHODS

Blood mononuclear cells, separated with immunomagnetic cell sorting into receptor-positive and receptor-negative populations, were assayed for pathogen-specific antibody-secreting cells and all immunoglobulin-secreting cells using enzyme-linked immunospot assay.

RESULTS

The gut mucosa homing receptor alpha4beta7 was expressed more frequently on pathogen-specific antibody-secreting cells than on immunoglobulin-secreting cells of healthy controls (P<0.001). Conversely, L-selectin, a homing receptor for peripheral lymph nodes, was found on remarkably fewer antibody-secreting cells of the patients compared with immunoglobulin-secreting cells of controls (32.9% and 70.3%, respectively; P<0.001). Three to 6 months after the disease, specific antibody-secreting cells had disappeared and frequency of L-selectin-and alpha4beta7-expressing cells had returned to control levels.

CONCLUSIONS

Circulating mucosally activated antibody-secreting cells express a set of homing receptors guiding them back to the gut. This provides evidence for recirculation of mucosal lymphocytes in humans.

Shedding of the lymphocyte L-selectin adhesion molecule is inhibited by a hydroxamic acid-based protease inhibitor. Identification with an L-selectin-alkaline phosphatase reporter

Expression of the L-selectin adhesion molecule can be rapidly down-modulated by regulated proteolysis at a membrane-proximal site. The L-selectin secretase has remained undefined, and the secretase activity is resistant to a broad panel of common protease inhibitors. We have developed an L-selectin-alkaline phosphatase reporter, consisting of the ectodomain of human placental alkaline phosphatase fused to the membrane-proximal cleavage, transmembrane, and cytoplasmic domains of L-selectin, to aid in the screening for L-selectin secretase inhibitors. A hydroxamic acid-based metalloprotease inhibitor, KD-IX-73-4, inhibited release of the L-selectin-alkaline phosphatase reporter in a dose-dependent manner. The hydroxamic acid-based peptide was also found to inhibit wild type L-selectin down-regulation from the surfaces of phorbol myristate acetate-activated peripheral blood lymphocytes and phytohemagglutinin-stimulated lymphoblasts. Analysis of the proteolytic cleavage fragments of L-selectin confirmed that KD-IX-73-4 inhibited L-selectin proteolysis. Lymphocyte L-selectin was not down-regulated when co-cultured with formylmethionylleucylphenylalanine-stimulated neutrophils, suggesting that the putative secretase acts in cis with the membrane-bound L-selectin. These results suggest that the L-selectin secretase activity may involve a cell surface, zinc-dependent metalloprotease, although L-selectin shedding is not affected by EDTA and may be related to the recently described activity involved in processing of membrane-bound TNF-alpha.

Studies on selectin blocker. 1. Structure-activity relationships of sialyl Lewis X analogs

As part of our studies of selectin blockers, we prepared 1-deoxy-3'-O-sulfo LeX analogs (1-3), 1-deoxy-3'-O-phosphono LeX analogs (4), and 1-deoxy sLeX analogs (5-7), and examined their inhibitory activities against natural ligand (sLeX) binding to E-selectin, P-selectin, and L-selectin. The 1-deoxy sLeX 5 was up to 20 times more potent an inhibitor than the sLeX tetrasaccharide toward P- and L-selectin binding. This indicates that the modification of the 1 or 2 position of sLeX is useful in the design of a more potent selectin blocker.

Extracellular ATP causes of loss of L-selectin from human lymphocytes via occupancy of P2Z purinocepters

Lymphocytes from normal subjects or patients with chronic lymphocytic leukemia are known to possess receptors for extracellular ATP termed P2Z purinoceptors whose physiological role is undefined. Addition of extracellular ATP (50-500 microM) to both normal and leukemic lymphocytes caused loss of binding of monoclonal antibodies to L-selectin (CD62L) on the cell surface. UTP, ADP, and adenosine (all at 500 microM) had no effect on L-selectin expression. Several features of the ATP-induced loss of L selectin indicate that this effect is mediated by lymphocyte P2Z purinoceptors. First the loss was attenuated in isotonic NaCl medium compared to 150 mM KCl medium. Second the loss of L-selectin was immediately halted by addition of Mg2+ ions in molar excess of ATP. The most potent nucleotide causing L-selectin loss was benzoylbenzoic ATP (> 10 microM) which is also the most potent agonist for the P2Z purinoceptor. Finally preincubation of lymphocytes with oxidized ATP, an irreversible inhibitor of P2Z purinoceptors, also inhibited ATP induced loss of L-selectin. Extracellular ATP is known to open an ion channel associated with the P2Z purinoceptor on B-lymphocytes which allows influx of Ca2+. However, ATP-induced loss of L-selectin did not require extracellular Ca2+. Moreover addition of the calcium ionophore, ionomycin, had minimal effect on L-selectin expression. Staurosporine (500 nM), an inhibitor of protein kinase C, inhibited only 10% of ATP induced loss of L-selectin but completely inhibited the loss of L-selectin caused by 50 nM PMA. Thus extracellular ATP interacts with lymphocyte P2Z purinoceptors which leads to shedding of L-selectin via a pathway which requires neither Ca2+ influx nor activation of protein kinase C. ATP may have a physiological role in the loss of L-selectin which occurs during the interactions of lymphocytes with other cells.

Blood leucocyte subsets of the rat: expression of adhesion molecules and localization within high endothelial venules

Although several distinct adhesion pathways are now well characterized, it is not clear whether analysis of adhesion molecule expression on leucocytes is sufficient to predict their interaction with endothelium in vivo. Therefore, in the present study this question was addressed by investigating the interaction between blood leucocyte subsets and high endothelial venules (HEV). The expression of different types of adhesion molecule (CD44, alpha 4-integrins, LFA-1, ICAM-1, CD2 and L-selectin) on lymphocytes, NK cells, monocytes and granulocytes of rat blood was determined by flow cytometry. In the same animals the numbers of blood leucocyte subsets present in the HEV of axillary lymph nodes and Peyer's patches were analysed using immunohistology. In the HEV of both axillary lymph nodes and of Peyer's patches lymphocytes (greater than 10,000 per mm2), as well as small numbers of NK cells and monocytes (less than 500 per mm2), were found. In contrast, granulocytes were not detected here. Lymphocytes, NK cells, monocytes and granulocytes each expressed CD44, alpha 4-integrins, LFA-1, ICAM-1, CD2 and L-selectin in a pattern characteristic to cell type, but this did not correlate with the different ability of the leucocyte subsets to interact with the two types of HEV. In conclusion, determining the expression of CD44, alpha 4-integrins, LFA-1, ICAM-1, CD2 and L-selectin on blood leucocytes alone is not sufficient to predict leucocyte/endothelium interaction in vivo.

Subsets of sialylated, sulfated mucins of diverse origins are recognized by L-selectin. Lack of evidence for unique oligosaccharide sequences mediating binding

Previous studies have shown that the mucin-type polypeptides GlyCAM-1, CD34, and MAdCAM-1 can function as ligands for L-selectin only when they are synthesized by the specialized high-endothelial venules (HEV) of lymph modes. Since sialylation, sulfation, and possibly fucosylation are required for generating recognition, we reasoned that other mucins known to have such components might also bind L-selectin. We show here that soluble mucins secreted by human colon carcinoma cells, as well as those derived from human bronchial mucus can bind to human L-selectin in a calcium-dependent manner. As with Gly-CAM-1 synthesized by lymph node HEV, alpha 2-3 linked sialic acids and sulfation seem to play a critical role in generating this L-selectin binding. In each case, only a subset of the mucin molecules is recognized by L-selectin. Binding is not destroyed by boiling, suggesting that recognition may be based primarily upon carbohydrate structures. Despite this, O-linked oligosaccharide chains released from these ligands by beta-elimination do not show any detectable binding to L-selectin. Following protease treatment of the ligands, binding persists in a subset of the resulting fragments, indicating that specific recognition is determined by certain regions of the original mucins. However, O-linked oligosaccharides released from the subset of non-binding mucin fragments do not show very different size and charge profiles compared to those that do bind. Furthermore, studies with polylactosamine-degrading endoglycosidases suggest that the core structures involved in generating binding can vary among the different ligands. Taken together, these data indicate that a single unique oligosaccharide structure may not be responsible for high-affinity binding. Rather, diverse mucins with sialylated, sulfated, fucosylated lactosamine-type O-linked oligosaccharides can generate high-affinity L-selectin ligands, but only when they present these chains in unique spacing and/or clustered combinations, presumably dictated by the polypeptide backbone.

Anionic phospholipids bind to L-selectin (but not E-selectin) at a site distinct from the carbohydrate-binding site

It is known that L-selectin binds to glycoconjugates containing the tetrasaccharide sialyl Lewis X in a Ca2+-dependent manner. In addition, a number of other acidic oligosaccharides (for example heparin or chondroitin sulphate) or glycolipids (for example sulphatides) bind to L-selectin independent of cations. In this paper we have established that L-selectin binds to charged phospholipids, such as cardiolipin and phosphatidylserine, but not to neutral phospholipids such as phosphatidylcholine. No interaction between E-selectin and any phospholipid was observed. The interaction between L-selectin cardiolipin was inhibited by dextran sulphate, fucoidan, mannose 6-phosphate and monoclonal antibodies previously reported to block the interaction between L-selectin and its natural ligands. Analysis of the amino acid sequence of the selectins indicated that L-selectin, but no E-selectin, contains a sequence homologous to the putative cardiolipin-binding epitope found in plasma glycoprotein beta2I. Glycoprotein beta2I and a peptide corresponding to the putative cardiolipin-binding epitope in beta2I inhibited the binding of L-selectin to cardiolipin or fucoidin. Based on the binding characteristics, sequence analysis and structural modelling of L-selectin, we suggest that the amino acid sequence KKNKED (residues 84-89) is a novel site for the binding of acidic species to L-selectin. This motif is localized close to the putative carbohydrate-binding domain of L-selectin and may be a second site within the lectin domain for the interaction of leucocyte L-selectin with its natural endothelial ligands.

Selectin synthesis and inflammation

The selectins are a family of three cell-surface-presented glycoprotein receptors. They play a key role in the initial adhesive interaction between leukocytes and endothelial cells at sites of inflammation. The presence of selectins on the cell surface is tightly regulated and inappropriate appearance is associated with a number of inflammatory disease conditions.

Cryptococcal polysaccharides induce L-selectin shedding and tumor necrosis factor receptor loss from the surface of human neutrophils

High titers of cryptococcal polysaccharides in the serum and spinal fluid and the lack of cellular infiltrates in the infected tissues are hallmarks of disseminated cryptococcosis. Cryptococcal polysaccharides given intravenously to mice inhibit the influx of leukocytes into sites injected with inflammatory mediators. The purpose of this investigation was to determine if cryptococcal polysaccharides, i.e., glucuronoxylomannan (GXM), galactoxylomannan, and mannoprotein, affect expression of molecules on the surface of neutrophils that are important in extravasation. GXM in the absence of serum was shown to induce human neurophils to shed L-selectin, a molecule needed in the first step of neutrophil movement into tissues. In the presence of serum, GXM caused a further shedding of L-selectin. Shedding of L-selectin was evident by reduced amounts of L-selectin on the neutrophils treated with GXM and by increased levels of soluble L-selectin in the GXM-treated neutrophil supernatants. GXM also stimulated neutrophils to have reduced expression of TNF receptor. In contrast, GXM-treated neutrophils showed increased levels of CD15 and CD11b, and unchanged CD16 expression. In the absence of serum, galactoxylomannan and mannoprotein did not affect L-selectin, TNF receptor, CD15, CD11b, or CD16 on neutrophils but did induce loss of L-selectin in the presence of serum. Our results indicate that cryptococcal polysaccharides, especially GXM, can cause shedding of L-selectin from the surface of neutrophils, and this may prevent neutrophils from attaching to the endothelial cell surfaces. Blockage of this early step in cell migration from the vessels into tissues may be responsible in part for reduced cellular infiltration into infected tissues of individuals with disseminated cryptococcosis.

S100 protein CP-10 stimulates myeloid cell chemotaxis without activation

Leukocyte recruitment to inflammatory foci is generally associated with cellular activation. Recent evidence suggests that chemotactic agents can be divided into two classes, "classical chemoattractants" such as FMLP, C5a, and IL-8, which stimulate directed migration and activation events and "pure chemoattractants" such as TGF-beta 1 which influence actin polymerisation and movement but not oxidative burst and associated granular enzyme release. The studies reported here demonstrate that the murine S100 chemoattractant protein, CP-10, belongs to the "non-classical" group. Despite its potent chemotactic activity for neutrophils and monocytes/macrophages, CP-10 failed to increase [Ca2+]i in human or mouse PMN, although chemotaxis was inhibited by pertussis toxin, confirming the suggestion of a novel Ca(2+)-independent G-protein-coupled pathway for post-receptor signal transduction triggered by "pure chemoattractants." The co-ordinated up-regulation of Mac-1 and down-regulation of L-selectin induced by FMLP on human PMN in vitro was not observed with CP-10. Quantitative changes in immediate (30 s) actin polymerisation occurred with FMLP and CP-10-treated human PMN. The relative F-actin increases induced in WEHI 265 monocytoid cells by FMLP and CP-10 was optimal at 60 s and declined over 120 s. F-actin changes reflected the concentration and potencies of the agonists required to provoke chemotaxis. After 90 min, CP-10 profoundly altered cell shape and increased both cell size and F-actin within pseudopodia. These changes are typical of those mediating leukocyte deformability, and CP-10 may mediate leukocyte retention within microcapillaries and thereby contribute to the initiation of inflammation in vascular beds.

Impaired primary T cell responses in L-selectin-deficient mice

L-selectin is a homing receptor that mediates the selective attachment of leukocytes to specialized high endothelial venules. To study the potential role of L-selectin in immune responses in intact mice, we generated L-selectin-deficient mice by gene targeting. L-selectin-deficient mice are defective in cutaneous delayed-type hypersensitivity (DTH) responses when tested after conventional intervals of immunization (4 d). Primary T cell proliferative responses and cytokine production (interleukin [IL] 2, IL-4, and interferon gamma) were also compromised when tested after 5 d of immunization, indicating that L-selectin is important for the immune response to antigens. In contrast, after more prolonged immunization protocols (9 d), normal responses were observed, suggesting that L-selectin-independent compensatory mechanisms exist. Interestingly, humoral responses of L-selectin-deficient mice to keyhole limpet hemocyanin are indistinguishable from wild-type control mice, implying that L-selectin plays no rate-limiting role in T cell help of B cell function. Thus, our results suggest that L-selectin plays an important role in the generation of primary T cell responses but may not be essential for humoral and memory T cell responses. L-selectin does not appear to be rate limiting for the events leading to antigen-driven neutrophil recruitment, since normal DTH responses are obtained at late time points after immunization.

Modulation of L-selectin ligand expression during an immune response accompanying tumorigenesis in transgenic mice

Immune surveillance depends on lymphocyte access to tissue. Lymphocytes emigrate from blood when adhesion receptors such as L-selectin and the alpha 4 beta 7 integrin on these cells bind to ligands expressed on venular endothelium. Among transgenic mouse lines expressing an oncoprotein (Tag) in islet beta cells, some recognize Tag as nonself. In these mice, Tag expression elicits both beta cell hyperplasia with subsequent progression to tumors and lymphocytic infiltration. Endothelial ligands for L-selectin and alpha 4 beta 7 were upregulated in infiltrated islets in these transgenic mice. These ligands were not expressed in tumors, which were devoid of lymphocytic infiltration. In contrast, the adhesion molecules PECAM-1, ICAM-1, and VCAM-1 were expressed on endothelium in both noninfiltrated tumors and infiltrated islets. Thus, upregulation of expression of endothelial ligands for L-selectin and alpha 4 beta 7 may contribute to autoimmune infiltration. Repression of expression of these same ligands may be involved in the failure of tumor immunity.

The influence of capsulation and lipooligosaccharide structure on neutrophil adhesion molecule expression and endothelial injury by Neisseria meningitidis

Host inflammatory response to meningococcal infection is believed to be a major determinant of disease severity. Isogenic mutants of Neisseria meningitidis serogroup B1940, which differ in expression of capsular polysaccharide and lipooligosaccharide (LOS), were used to examine host responses in a whole blood model of bacteremia and a model of endothelial injury. The parent organism caused significantly less neutrophil shedding of the adhesion molecule, L-selectin, than the three mutant organisms (P < .01) and was most resistant to the bactericidal activity of whole blood. Despite marked differences in bacterial adhesion to endothelial cells (P < .05), no damage was induced by organisms alone. Endothelial injury was observed when neutrophils were incubated with adherent, capsule-deficient organisms (P < .05). The degree of endothelial damage was related to the number of neutrophils adherent to the endothelium. Thus, bacterial capsulation and LOS structure can influence neutrophil activation and endothelial injury and, as such, may be important in the pathogenesis of meningococcal sepsis.

Expression of beta-2-integrins and L-selectin by leukocytes and changes in acute-phase reactants in total hip replacement surgery

The aim of this study was to characterize the changes in the quantitative expression of beta 2-integrins and L-selectin detected by means of fluorochrome-conjugated monoclonal antibodies and flow cytometry on leukocytes in the systemic circulation after a major musculoskeletal trauma, i.e. hip replacement surgery, and to relate these changes to parameters of the acute-phase response [plasma acute-phase reactants (C-reactive protein, CRP, and interleukin-6, IL-6) and parameters of coagulation activation (thrombin-antithrombin III complexes, TAT)]. Eight patients with either primary or secondary osteoarthritis of the hip received uncemented total hip prostheses. LFA-1 (CD11a/CD18) was upregulated on granulocytes during the operation. MAC-1 (CD11b/CD18) expression on monocytes increased to peak levels 20 h after surgery, whereas the L-selectin (CD62L) expression on monocytes and granulocytes reached peak values at the end of surgery. The changes in expression of LFA-1 on monocytes, MAC-1 on granulocytes and p150,95 (CD11c/CD18) on monocytes and granulocytes during and after the operation did not reach statistical significance. TAT and IL-6 increased during surgery and reached peak values at the end of the operation and 20 h after surgery, respectively. In contrast, CPR concentrations increased after surgery with peak levels 44 h postoperatively. Significant upregulation of LFA-1 on granulocytes and L-selectin on monocytes and granulocytes preceded the increase in IL-6 which again preceded the increase in CRP. However, the up- or downregulation of leukocyte beta 2-integrins and L-selectin during and after surgery was not significantly correlated with the increase in IL-6. The increases in TAT correlated well with the upregulation of L-selectin on monocytes, but not with the beta 2-integrins known to participate in the coagulation process in vitro. The rise in CRP was inversely correlated with the maximal increase in expression of MAC-1 on monocytes. In conclusion, the changes in leukocyte adhesion molecules during and after surgery indicate changes in critical leukocyte functions. The lack of correlation between quantitative up- and downregulation of leukocyte beta 2-integrins and parameters of the acute phase response suggests that these processes are regulated through independent pathways or that functional up- and downregulation of adhesion molecules, shedding, leukocyte-endothelial adhesion and mobilization of new unactivated cells may result in a net estimate of leukocyte activation not suspected to be positively correlated to acute-phase reactants.

Type IV collagen-binding proteins of neutrophils: possible involvement of L-selectin in the neutrophil binding to type IV collagen

To isolate type IV collagen-binding proteins, 125I-labeled human-neutrophil extracts were chromatographed on a type IV collagen-Sepharose column. The affinity chromatography-separated fraction contained the four radioactive proteins with apparent molecular masses of 28, 49, 67, and 95 kD on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Western blot analysis indicated that the 95-kD proteins contained both L-selectin and nonspecific cross-reacting antigen 90 (NCA90), and that the 67-kD protein was the 67-kD elastin/laminin-binding protein (67BP). The data obtained with the type IV collagen-affinity chromatography and the immunoaffinity chromatographies using anti-L-selectin and anti-NCA90 monoclonal antibodies (MoAbs) have shown that L-selectin is closely associated with 67BP and the 49-kD protein, and that NCA90 is associated with 67BP, the 28-kD and 49-kD proteins. Among these binding proteins, sialic acid residues were contained in 67BP, L-selectin, and NCA90, but not in the 28-kD and 49-kD proteins. Sialidase treatment completely abolished both the binding affinity of the type IV collagen-binding proteins to type IV collagen and the neutrophil adherence to type IV collagen-coated plastic. Thus, the sialic acid residues of 67BP, L-selectin, and NCA90 seem to be important for the binding of neutrophils to type IV collagen. Furthermore, L-selectin IgG chimeric protein directly bound to type IV collagen-Sepharose column, and anti-L-selectin MoAb DREG56 inhibited the neutrophil adherence to type IV collagen-coated plastic by 51%. These observations suggest that L-selectin likely plays a role in the neutrophil binding to type IV collagen, although neutrophils have several kinds of adhesion molecules for type IV collagen such as L-selectin, NCA90, 67BP, and the 28-kD and 49-kD proteins.

Patterns of changes in neutrophil adhesion molecules during normothermic cardiopulmonary bypass. A clinical study

The adhesion of activated neutrophils to endothelial cells is a key feature of the inflammatory response to cardiopulmonary bypass (CPB) because it "unlocks" a cascade of cytotoxic events. This adhesion is made possibly by the sequential involvement of two sets of neutrophil cell surface receptors: L-selection and beta 2 integrins (CD 11 a/CD 18; CD 11 b/CD 18; CD 11 c/CD 18). We have assessed the changes in the expression of these adhesion molecules in ten patients who underwent various open-heart procedures with the use of "warm" (33.4 degrees-37 degrees C) CPB. Arterial blood samples were obtained before, during and after bypass and processed for immunofluorescent flow cytometric analysis. CD 11 a expression remained unchanged throughout the study period. Conversely, CD 11 b drastically increased early after the onset of bypass (at 15 min on bypass: 172 +/- 17 [mean fluorescence (arbitrary units), mean +/- SEM] versus 63 +/- 13 before bypass. P < 0.02) and was still markedly elevated 30 min after the end of bypass (160 +/- 38, P < 0.05 versus the pre-by-pass value). CD 11 c expression underwent a similar upregulation (at 15 min of bypass: 54 +/- 5 versus 34 +/- 5 at baseline, P < 0.01). L-selectin expression did not change significantly during the period of observation. Put together, these results suggest that CPB is associated with an increased adhesive potential of neutrophils, which enhances their binding to the vascular endothelium and thereby initiates tissue damage through the release of cytotoxic mediators from adherent cells. Manipulation of integrin expression could therefore represent an effective means of alleviating the component of bypass-induced inflammatory tissue damage which is more specifically neutrophil-mediated.

Analysis of bovine gamma delta T cell interactions with E-, P-, and L-selectin. Characterization of lymphocyte on lymphocyte rolling and the effects of O-glycoprotease

In earlier studies, we found that bovine gamma delta T cells avidly bind and roll under physiologic flow on E- and P-selection. In this study, we have extended our analyses of shear interactions of gamma delta T cells and have found that once gamma delta T cells permanently bind to endothelial cell monolayers they can support continued rolling of newly arriving gamma delta T cells. Anti-L-selection Abs blocked gamma delta T cell rolling on immobilized gamma delta T cells, and it was L-selection on the rolling cell, not the bound cell, that mediated the interaction. We propose, as we have for neutrophils, that lymphocyte/lymphocyte rolling represents a mechanism for amplification of the extravasation process. Having defined P-, E-, and L-selectin interactions with gamma delta T cells, we tested the susceptibility of the ligands for these selectins to treatment with O-glycoprotease, a compound that selectively cleaves mucin-like selectin ligands. O-glycoprotease treatment of gamma delta T cells blocked their interaction with P-selectin, but not E-selectin. Rolling of O-glycoprotease-treated cells on bound untreated gamma delta T cells was unaffected; however, O-glycoprotease treatment of the bound gamma delta T cells blocked their capacity to support rolling interactions. These results define a new lymphocyte/selectin interaction that may be important in amplifying lymphocyte extravasation and suggest that gamma delta T cell ligands for P- and E-selectin are distinct, whereas ligands for P- and L-selectin may be similar.

Down-regulation of adhesion receptors on cells of primate embryos as a probable mechanism of the teratogenic action of thalidomide

In spite of ongoing speculation, there has been no evidence that adhesion receptors are expressed on the cells of mammalian embryos. In this report, we provide the first proof that a variety of such receptor (beta 1-, beta 2-, and beta 3-integrins and selectin) are indeed expressed on cells of essentially all primordia of marmoset embryos at early organogenesis (developmental stages 11 to 13, or even earlier). Treatment with low doses (20 or as little as 1 mg/kg body weight) of a highly teratogenic derivative (EM12) of thalidomide, the most notorious human teratogen, triggers a dramatic and statistically highly significant down-regulation of several surface adhesion receptors (e.g. CD11a/CD18, CD49d/CD29, CD61, etc.) on early limb bud cells and on cells of some other primordia during early organogenesis of embryos of a primate (marmoset, Callithrix jacchus). Some of these receptors almost disappear, or they are expressed at a lower epitope density in the exposed embryos. These down-regulations of surface adhesion receptors may be expected to alter cell-cell- and cell-extracellular matrix interactions, and they are suggested to be a long-sought primary mechanism of the teratogenic action of thalidomide-type substances.

Synthesis of a divalent sialyl Lewis x O-glycan, a potent inhibitor of lymphocyte-endothelium adhesion. Evidence that multivalency enhances the saccharide binding to L-selectin

The recognition of cell-surface L-selectin by its carbohydrate ligands causes lymphocytes to roll on capillary endothelium at sites of inflammation. As this primary contact is a prerequisite for extravasation of the leukocytes to the tissue, its inhibition by free oligosaccharides capable of competing with the natural L-selectin ligands in an attractive therapeutic possibility. The exact structures of the biological ligands of L-selectin are not yet known, but the principal carbohydrate epitopes share some structural features: they are O-glycosidically linked mucin-type oligosaccharides with N-acetyllactosamine backbone, which is 3'-sialylated or 3'-sulfated, 3-fucosylated and sometimes 6- or 6'-sulfated at the distal N-acetyllactosamine termini. Multivalency of the ligand, which is believed to enhance the binding, is achieved by a branched polylactosamine backbone or by a clustered array of O-glycans. We report here enzymic synthesis of a large oligosaccharide fulfilling several of the features characteristic to the L-selectin ligands: it is a dodecameric O-glycosidic core-2-type oligosaccharide alditol with a branched polylactosamine backbone carrying two distal alpha-2,3'-sialylated and alpha-1,3-fucosylated N-acetyl-lactosamine groups (sialyl Lewis x, sialyl Le(x)). The structure of each saccharide on the synthesis route from disaccharide Gal beta 1-3GalNAc to the dodecasaccharide alditol was established by several methods including one- and two-dimensional 1H-NMR spectroscopy. The last step of the synthesis, the alpha-1,3-fucosylation of the 6-linked arm proceeded sluggishly, and was associated with a noticeable shift in H1 resonance of the GlcNAc residue of the branch-bearing N-acetyllactosamine unit. The final synthesis product and its analogs lacking one or both of the fucose residues were tested as inhibitors of L-selectin-mediated lymphocyte-endothelium interaction in vitro in rejecting rat kidney transplant. While the non-fucosylated O-glycosidic oligosaccharide alditol did not possess any inhibitory activity, the mono-fucosylated one (i.e. monovalent sialyl Le(x)) prevented the binding significantly and the difucosylated dodecasaccharide alditol (i.e. divalent sialyl Le(x)) was a very potent inhibitor (IC50, inhibitory concentration preventing 50% of binding = 0.15 microM). Besides the multivalency, also the Gal beta 1-3GalNAc-ol sequence of the O-glycosidic core appeared to increase the affinity of the glycan to L-selectin. This was indicated by parallel inhibition experiments, where a disialylated and difucosylated branched polylactosamine decasaccharide, similar to the divalent dodecasaccharide alditol, but lacking the reduced O-glycosidic core, was a less effective inhibitor (IC50 = 0.5 microM) than the O-glycosidic dodecasaccharide alditol.

Sulfated disaccharide inhibitors of L-selectin: deriving structural leads from a physiological selectin ligand

The selectins are a family of three adhesion molecules (L-, P-, and E-) that direct the interaction of circulating leukocytes with endothelial cells during the first step in recruitment to tissue sites. Their involvement in inflammatory disease makes the selectins attractive targets for anti-inflammatory therapy. The sialyl Lewis x tetrasaccharide binds weakly to all three selectins and has demonstrated anti-inflammatory activity in vivo. However, the synthetic difficulties inherent to sialylated and fucosylated oligosaccharides motivate the search for alternative antagonists. Here we demonstrate that information gained from the biochemical analysis of a physiological selectin ligand can provide new leads for small molecule design. Previous structural analysis of the oligosaccharide chains on GlyCAM-1, an endothelial-derived ligand for L-selectin, revealed two novel structures: 6'-sulfo sialyl Lewis x and 6-sulfo sialyl Lewis x. The sulfate esters on these structures are thought to be essential for high-affinity binding to L-selectin. By incorporating sulfate esters on the analogous positions of the disaccharide lactose, we generated a simple small molecule (lactose 6',6-disulfate) with greater inhibitory potency for L-selectin than sialyl Lewis x.

Evidence for a third component in neutrophil aggregation: potential roles of O-linked glycoproteins as L-selectin counter-structures

The homotypic aggregation of neutrophils requires the participation of L-selectin and the beta 2-integrins, but it has not been clear whether the two receptors recognize one another as counter-structures or whether other adhesion molecules are involved. We have examined aggregation of live neutrophils with target populations, manipulated to alter expression of adhesive epitopes, using flow cytometry. A target population depleted of both L-selectin and activatable beta 2-integrin displayed an ability to aggregate with live neutrophils, suggesting that these two molecules are not counter-structures. We also found that an O-sialoglycoprotease (GCP) from Pasteurella haemolytica is capable of inhibiting homotypic aggregation. Neutrophils treated with GCP lose O-glycosylated proteins but retain L-selectin and activatable beta 2-integrin. One or more of the GCP substrates appears to function in L-selectin-dependent binding but not in beta 2-integrin-dependent binding. Together the data suggest a mechanism of aggregation that is analogous to leukocyte-endothelial cell adhesion in which a low-affinity carbohydrate-dependent interaction precedes a high-affinity integrin-dependent adhesion.

Hypothermia during cardiopulmonary bypass delays but does not prevent neutrophil-endothelial cell adhesion. A clinical study

BACKGROUND

An accurate evaluation of warm heart surgery cannot be limited to the assessment of the myocardial effects of warm blood cardioplegia but should also address the effects of systemic normothermia on the inflammatory response to cardiopulmonary bypass. A major component of this response is the endothelial adhesion of neutrophils, because it is linked to the release of cytotoxic compounds. This study was designed (1) to characterize the bypass-induced changes in the expression of neutrophil adhesion molecules (L-selectin and beta 2-integrins) and (2) to assess the influence of bypass temperature on these changes.

METHODS AND RESULTS

Twenty case-matched patients undergoing open-heart procedures were divided into two equal groups according to the core temperature during cardiopulmonary bypass: warm (33.4 +/- 0.3 degrees C) or cold (27.1 +/- 0.4 degrees C, P < .0001 versus warm). Arterial blood samples were collected before, during, and 30 minutes after bypass and processed for the expression of L-selectin and beta 2-integrins (CD11a, CD11b, and CD11c) with flow cytometry. Warm bypass was associated with an early and sustained upregulation of CD11b. In contrast, hypothermia resulted in a strikingly less pronounced CD11b upregulation during bypass. However, CD11b expression sharply increased thereafter so that 30 minutes after bypass, it was no longer significantly different between the two groups. Changes in CD11c expression grossly paralleled those described for CD11b. Neither CD11a nor L-selectin changed significantly from baseline values in either group.

CONCLUSIONS

Clinical cardiopulmonary bypass is associated with a marked upregulation of the neutrophil CD11b and CD11c integrins. Hypothermia delays but does not prevent the increased expression of these adhesion molecules, which could consequently represent logical targets for interventions designed to blunt the neutrophil-mediated component of bypass-induced inflammatory tissue damage.

Effect of heparin anticoagulation on neutrophil adhesion molecules and release of IL8: C3 is not essential

OBJECTIVE

To examine the role of heparin in modulating neutrophil activation and release of cytokine.

BACKGROUND

Up-regulation of CD11b, down-regulation of L-selectin on neutrophil cell surface and release of IL8 occur in response to extracorporeal circulation (ECC) and were proposed to cause leakage of the capillaries in patients.

DESIGN

In a series of experiments, we examined the effect of heparin (4 U/ml) comparing it with ethylenediamine tetra-acetate (EDTA, 1.5 mg/ml) and citrate mixture (100 microliters/ml), heparin dose-response, IL8 (human recombinant IL8) dose-response and protamine (80 micrograms/ml) neutralisation of heparin (4 U/ml) using donor blood (total of 38). The role of complement component type 3 (C3) was tested. Neutrophils from a patient with complete C3 deficiency were stimulated by using heparin and cobra venom factor (10 micrograms/ml) and compared with controls (n = 5). CD11b and L-selectin expressions were assayed immediately and serially up to 120 min using immune fluorescence and flow cytometry. Serum concentrations of IL8 were determined by using enzyme-linked immunosorbent assay.

RESULTS

The medians of up-regulation of CD11b were 540.2 (range 235.2-653.3) for heparin vs. 186.5 (55.7-207.1) for EDTA and 192.5 (69.2-263.8) for citrate mixture, P < 0.01. The medians of down-regulation of L-selectin were 79 (32-192) for heparin vs. 18.4 (0-188) for EDTA and 36.2 (7.4-135) for citrate mixture, P < 0.05. Up-regulation of CD11b, down-regulation of L-s and release of IL8 were inversely related to heparin concentration (r = 0.87, P < 0.05). Serum concentration of IL8 had a direct relationship to the changes in CD11b and L-selectin expression (r = 0.92). Heparin-protamine complex was less stimulant to expression of CD11b and L-selectin than heparin or protamine (P < 0.05). In blood samples from C3-deficient patients, heparin and cobra venom factor caused up-regulation of CD11b and down-regulation of L-selectin similar to that of controls (P > 0.05).

CONCLUSIONS

Heparin stimulates up-regulation of neutrophil adhesion molecules CD11b, down-regulation of L-selectin and release of IL8. These effects are inversely related to heparin concentration and are independent of C3 activation. IL8 has a direct relationship to activation of neutrophil adhesion molecules. Increasing heparin dosage reduces neutrophil activation and may reduce the morbidity of patients.

De novo expression of endothelial sialyl Lewis(a) and sialyl Lewis(x) during cardiac transplant rejection: superior capacity of a tetravalent sialyl Lewis(x) oligosaccharide in inhibiting L-selectin-dependent lymphocyte adhesion

Acute organ transplant rejection is characterized by a heavy lymphocyte infiltration. We have previously shown that alterations in the graft endothelium lead to increased lymphocyte traffic into the graft. Here, we demonstrate that lymphocytes adhere to the endothelium of rejecting cardiac transplants, but not to the endothelium of syngeneic grafts or normal hearts analyzed with the in vitro Stamper-Woodruff binding assay. Concomitant with the enhanced lymphocyte adhesion, the cardiac endothelium begins to de novo express sialyl Lewis(a) and sialyl Lewis(x) (sLea and sLex) epitopes, which have been shown to be sequences of L-selectin counterreceptors. The endothelium of allografts, but not that of syngeneic grafts or normal controls, also reacted with the L-selectin-immunoglobulin G fusion protein, giving further proof of inducible L-selectin counterreceptors. The lymphocyte adhesion to endothelium could be significantly decreased either by treating the lymphocytes with anti-L-selectin antibody HRL-1, or by treating the tissue sections with sialidase or anti-sLea or anti-sLex monoclonal antibodies. Finally, we synthetized enzymatically several members of the sLex family oligosaccharides and analyzed their ability to block lymphocyte adhesion to cardiac endothelium. The monovalent sLex (a tetramer), divalent sLex (a decamer), and tetravalent sLex (a 22-mer) could all significantly reduce lymphocyte binding, but the inhibition by the tetravalent sLex-construct was clearly superior to other members of the sLex family. The crucial control oligosaccharides, sialyl lactosamines lacking fucose but being otherwise similar to the members of sLex family, had no effect on lymphocyte binding.

Selective inhibition of neutrophil function by a peptide derived from lipocortin 1 N-terminus

A multi-faceted approach was used to investigate the effect of an anti-inflammatory peptide derived from human lipocortin 1 N-terminus region (amino acid 2-26; termed human Ac2-26) on human neutrophil activation in vitro. When incubated with purified human neutrophils. human Ac2-26 produced a concentration-dependent inhibition of elastase release stimulated by formyl-Met-Leu-Phe (fMLP), platelet-activating factor, or leukotriene B4, with an approximate EC50 of 33 microM (100 micrograms/ml). At this concentration, human Ac2-26 also inhibited (77%) the release of [3H]-arachidonic acid from neutrophils stimulated with fMLP. The peptide, however, did not inhibit the up-regulation of the beta 2-integrin CD11b and the concomitant shedding of L-selectin from neutrophil plasma membrane induced by fMLP. In adhesion experiments, human Ac2-26 inhibited neutrophil adhesion to endothelial monolayers when this was stimulated with fMLP, but not when this followed endothelial cell activation with histamine or platelet-activating factor. Again, the effect of the peptide was concentration-dependent, and an approximate EC50 of 33 microM was calculated. When a preparation of 125I-labeled human Ac2-26 was incubated with the neutrophils, the peptide was internalised in an energy-dependent fashion. All together, these observations lead us to propose a model in which this peptide derived from the N-terminus of human lipocortin 1 alters a common cellular mechanism producing a selective inhibition of neutrophil activation.

Participation of the propeptide on procathepsin D activation of human peripheral lymphocytes and neutrophils

Flow cytometry was used to test the role of the propeptide of procathepsin D in the activation of human peripheral lymphocytes and neutrophils. A selective inhibition of the activation was achieved by antibodies targeted against the propeptide. Synthetic peptide corresponding to the cathepsin D propeptide had a very similar effect as procathepsin D itself. The interaction of procathepsin D with the cells was blocked by the propeptide as monitored in experiments with fluorescently labeled procathepsin D. Our data indicate that procathepsin D activation of human neutrophils and leukocytes described earlier is mediated through the propeptide of the procathepsin D.

High endothelial venules (HEVs): specialized endothelium for lymphocyte migration

High endothelial venules (HEVs) are specialized postcapillary venules found in lymphoid tissues that support high levels of lymphocyte extravasation from the blood. Here, Jean-Philippe Girard and Timothy Springer highlight the unique properties of HEV endothelium, discuss the molecular mechanisms controlling HEV specialization and review evidence suggesting that HEVs could play an important role in the pathogenesis of chronic inflammatory diseases.

Regulation of neutrophil adhesion molecules and shedding of Staphylococcus aureus in milk of cortisol- and dexamethasone-treated cows

The effects of 3 days of glucocorticoid administration on bovine blood neutrophil expression of L-selectin and CD18, and on the health status of mammary glands subclinically infected with Staphylococcus aureus were measured in 9 lactating Holsteins. The experiment was a 3 x 3 Latin square cross-over design, with 3 glucocorticoid treatments switched among groups of 3 cows/treatment during 3 periods. Treatments consisted of a vehicle (control, 10 ml of excipient/cow/d), cortisol (7.5, 15, and 7.5 mg/cow on days 1, 2, and 3, respectively), and dexamethasone (0.04 mg/kg of body weight/cow/d for total daily dosages that ranged from 21.6 to 33.2 mg). Blood samples for immunostaining and flow cytometric analysis of L-selectin and CD18 and leukograms, as well as foremilk samples for determination of S aureus shedding, somatic cell counts, protein and fat percentages, and daily milk yields were collected repeatedly before, during, and after treatment days. Dexamethasone caused a profound, acute, short-lived down-regulation of L-selectin on neutrophils, which correlated in time to leukocytosis, mature and immature neutrophilias, increased shedding of S aureus in infected glands, and onset of high percentages of fat and protein and decreased milk yields. Dexamethasone also caused profound but delayed down-regulation of neutrophil CD18, which reached nadir simultaneously with reappearance of L-selectin-bearing neutrophils, normalized blood neutrophil counts, markedly high foremilk somatic cell counts and protein percentage, decreased S aureus shedding in milk, and finally, expression of clinical mastitis in some infected quarters. Each of these variables had returned to control (vehicle) values by the ninth (and last) sample collection day. Although cortisol treatment also decreased expression of L-selectin and CD18 on neutrophils, dosages used in this study were not sufficient to alter the number of circulating cells or to convert subclinical mammary gland infections to clinical mastitis. These results suggest that mammary gland health status can be altered by sudden exposure of blood neutrophils to glucocorticoids, because these steroid hormones caused profound down-regulation of the adhesion molecules that direct neutrophil margination and migration through the vascular endothelium. The results also reinforce the potential disease risk of treating infected animals with potent synthetic glucocorticoids, such as dexamethasone.

Selective modulation of the expression of L-selectin ligands by an immune response

BACKGROUND

The adhesion molecule L-selectin is expressed on the cell surface of lymphocytes and mediates their migration from the bloodstream into lymph nodes. L-selectin is able to recognize four glycoprotein ligands, three of which--Sgp50, Sgp90, and Sgp200--are sulphated, bind specifically to L-selectin and are synthesized by the high endothelial venules of the peripheral and mesenteric lymph nodes. One of these three sulphated L-selectin ligands, Sgp90, has been shown to be identical to the known surface marker CD34 and is expressed on the cell surface of endothelial cells. The cDNA encoding Sgp50 has been cloned, and its product, which has been designated GlyCAM-1, is secreted. The third ligand, Sgp200, is both secreted and cell-associated. We have investigated how the expression of these sulphated glycoproteins is regulated during an immune response.

RESULTS

Here we demonstrated that, during a primary immune response, the expression and secretion of both GlyCAM-1 and Sgp200 are reduced, recovering to normal levels 7-10 days after antigen stimulation. In contrast, the expression of cell-associated CD34 and Sgp200 is relatively unaffected. These results may account for the modest decreases in the binding of an L-selectin-IgG fusion protein to high endothelial venules of inflamed peripheral lymph nodes that have been observed after antigen exposure. In vivo experiments show that, following the decrease in the levels of secreted GlyCAM-1 and Sgp200, migration of lymphocytes from the blood stream into lymph nodes remains L-selectin-dependent, but more lymphocytes home to antigen-primed than unprimed peripheral lymph nodes.

CONCLUSIONS

We suggest that the secreted forms of the L-selectin ligands GlyCAM-1 and Sgp200 act as modulators of cell adhesion, and that cell-associated CD34 and Sgp200 are the ligands that mediate the initial loose binding of lymphocytes to high endothelial venules.

Influence of sE-selectin and L-selectin on the regulation of cell migration during chronic periodontitis

Soluble endothelial leukocyte adhesion molecule-1 (sE-selectin) levels in peripheral blood (PB) and gingival capillary blood (GCB) of both healthy donors (HD) and patients with adult periodontitis (AP) were assayed by ELISA. Binding of sE-selectin to polymorphonuclear neutrophils (PMN) from PB, GCB and crevicular fluid (GF), and expression of L-selectin and sialyl-Lewisx (sLex) on these cells were analyzed by immunofluorescence and flow cytometry. No significantly enhanced serum levels of sE-selectin in patients with AP, compared to HD (28 +/- 5 ng/ml vs 19 +/- 3 ng/ml, respectively), and no differences in the concentration of sE-selectin in GCB (16 +/- 1 ng/ml vs 16 +/- 2 ng/ml, respectively) were observed. On PB-PMN no significant differences in the expression of L-selectin and sLex were found and binding of sE-selectin to PB-PMN was comparable between HD and patients with AP. Binding of sE-selectin to GCB-PMN was significantly higher in patients with AP compared to HD (mean channel fluorescence (MCF) = 88.5 +/- 13.2 vs MCF = 24.2 +/- 5.3, respectively). The expression of sLex on GCB-PMN did not differ significantly between the two groups. A significant decrease in the expression of the adhesion molecule L-selectin on GCB-PMNs compared to PB-PMN was found in patients with AP but not in HD. CF-PMN showed decreased expression of both L-selectin and sLex compared to PMN from PB and GCB, both in HD and patients with AP. Taken together, these data suggest that PMN from patients with AP had reduced selectin-mediated adhesive capabilities to inflamed gingival endothelium.

Exercise-induced changes in the expression of surface adhesion molecules on circulating granulocytes and lymphocytes subpopulations

This study examined the relationship between exercise-induced changes in the concentration of circulating immunocompetent cells and their surface expression of adhesion molecules: L-selectin (CD62L) and three beta 2-integrins [LFA-1(CD11a/CD18), Mac-1 (CD11b/CD18), and p150/95(CD11c/CD18)]. Eight young male volunteers exercised on a cycle ergometer for 60 min at 60% maximal oxygen uptake. Peripheral blood samples, collected every 30 min throughout exercise and during the 2-h recovery period, were used for flow-cytometric analysis. The experimental results were compared with control data obtained ever 60 min at corresponding times of the nonexercise day. The exercise regimen induced a granulocytosis and a lymphocytosis, mainly due to an elevation of CD8+ and CD16+ cells. During recovery, a further granulocytosis occurred but accompanied by a lymphopenia. The increased CD8+ cell-count during exercise was characterized by a selective mobilization of the CD62L- and CD11ahigh cells, i.e. primed CD8+ cells. A postexercise suppression of CD4+ cell-count was derived only from CD62L+ cells. The CD11b+ and CD11c+ lymphocytes also increased during exercise, largely attributable to an increase in CD16+ cells which co-expressed CD11b and CD11c molecules. The CD62L surface density of granulocytes increased significantly during recovery. This resulted from a selective influx of CD62Lhigh granulocytes into the circulation. There were no significant changes in per-cell density of the three beta 2-integrins on granulocytes and lymphocytes throughout the experimental period. These results suggest that the cell-surface expression of CD62L (and CD11a) molecules is associated with the differential mobilization of CD8+ cells during exercise, the postexercise suppression of CD4+ cell-counts and the granulocytosis following exercise.

Quantitative and qualitative changes in CD44 and MEL-14 expression by T cells in C57BL/6 mice during aging

Aging is associated with a decrease in the functional activity of T cells. We have explored age-related alterations in CD44 and MEL-14 expression by spleen cells bearing the Thy1.2, CD4 or CD8 antigens in C57BL/6 mice at 2, 8, 15 and 23 months of age. The membrane expression of CD44 and MEL-14 molecules can be used to distinguish naive (CD44low, MEL-14high) from preactivated/memory (CD44high, MEL-14low) T cells. Our results show that the proportion of CD4+ splenic cells begins to decrease at an intermediate age (8-month-old mice), whereas the proportion of CD8+ cells remains unaltered. The proportion of CD4+ and CD8+ splenic cells with the CD44high memory phenotype was increased at an early stage of aging (in 8-month-old mice) without a concomitant change in MEL-14 expression. In older mice, MEL-14 expression decreased on CD4+ but not on CD8+ subsets. Recent studies have reported that following activation, the expression of CD44 molecules containing additional, so-called variable exons can be detected. By PCR, we observed an increase in CD44 transcripts containing the v6 or v7 variable exons in murine lymph nodes at the age of 15 months. Our results suggest that v6- or v7-containing variants of CD44 may be involved in the development of memory cells. Taken together, these results suggest that the trafficking of memory T cells in aging may be altered by quantitative and/or qualitative differences in the expression of molecules involved in lymphocyte recirculation.

Chronic proliferative dermatitis in mice: neutrophil-endothelium interactions and the role of adhesion molecules

The murine chronic proliferative dermatitis mutation (cpdm/cpdm) is characterized by epidermal hyperplasia and hyperproliferation of ventral and dorsal skin sites. The expression of endothelium-associated adhesion molecules was studied in combination with the binding capacity of various cell types on frozen sections of the affected skin. In correlation with the relative absence of lymphocytes in the cpdm/cpdm skin no lymphocyte binding could be observed, but avid adhesion of neutrophils was seen. Binding of neutrophils could be blocked with antibodies against L-selectin, LFA-1, CR3 and anti ICAM-1. No expression of vascular addressins or E-selectin on endothelium in the dermis was found. The cpdm/cpdm mutation has therefore characteristics of a psoriasis-like as well as a more generalized inflammatory skin condition.