The effect of fever‐like temperatures on neutrophil signaling

The effect of fever on neutrophils has not been explored. We tested the hypothesis that fever-like temperature spikes affect neutrophil signaling and function. Prior 60 min, 42 degrees C heat exposure inhibited p38 MAPK, ERK, PI3-Kinase/Akt, and NF-kappaB activation in TNF-alpha-challenged suspended neutrophils. Using pharmacological inhibitors and an inhibitory peptide transduced into neutrophils by a HIV-TAT sequence, we found that p38 MAPK and NF-kappaB mediate TNF-alpha-mediated delayed apoptosis in suspended neutrophils. Heat exposure (39-42 degrees C) did not affect constitutive apoptosis but abrogated TNF-alpha-delayed apoptosis in these suspended cells. In contrast, adhesion-dependent functions were not inhibited. Furthermore, we found that heat exposure neither blocked p38 MAPK, ERK, and NF-kappaB activation in neutrophils on fibronectin nor prevented delayed apoptosis by TNF-alpha when cells interacted with fibronectin. Above and beyond apoptosis, TNF-alpha initiated NF-kappaB-dependent gene transcription. Heat exposure blocked this effect in suspended neutrophils but not in neutrophils on fibronectin. Finally, we show that beta2-integrins, which are not necessary for TNF-alpha-induced NF-kappaB activation at 37 degrees C, transduce costimulatory signals allowing NF-kappaB activation after heat exposure. The effect could protect circulating neutrophils from TNF-alpha activation, while not interfering with activation of adherent neutrophils. Fever could make neutrophils more parsimonious.

Beta1 and beta2 integrins mediate adhesion during macrophage fusion and multinucleated foreign body giant cell formation

An in vitro system of interleukin (IL)-4-induced human monocyte-derived macrophage fusion was used to investigate the cell/substrate adhesive mechanisms that support multinucleated foreign body giant cell (FBGC) formation. Monocytes were cultured for 3 days and IL-4 was added to induce macrophage fusion and FBGC formation by day 7. Functionally defined anti-integrin antibodies demonstrated that initial monocyte adhesion is mediated by beta2 integrins, whereas during the induction of macrophage fusion by IL-4, an additional dependence on beta1 integrins is acquired. The combination of anti-beta1 plus anti-beta2 was most effective, reducing macrophage/FBGC adhesion to 10% of controls. Consistent with integrin-mediated signaling, the tyrosine kinase inhibitor genistein and the phosphatidylinositol-3-kinase inhibitors wortmannin and LY294002 also attenuated macrophage/FBGC adhesion. Confocal microscopic analysis revealed that beta2 integrins are present on monocytes after initial adhesion and are strongly expressed on fusing macrophages, particularly in peripheral cell areas, and on FBGCs. In contrast, beta1 integrins are not detected on monocytes but begin to appear during macrophage development and are strongly expressed on fusing macrophages and FBGCs. For the first time, these results demonstrate the IL-4-induced acquisition of cooperation between beta1 and beta2 integrins in the cell/substrate adhesive interactions that are required for multinucleated FBGC formation.

Platelet/polymorphonuclear leukocyte adhesion: a new role for SRC kinases in Mac-1 adhesive function triggered by P-selectin

Adhesion of polymorphonuclear leukocytes (PMNLs) to activated platelets requires a P-selectin-triggered, tyrosine kinase-dependent adhesiveness of Mac-1 and is accompanied by tyrosine phosphorylation of a 110-kd protein (P-110) in PMNLs. Inhibitors of SRC tyrosine kinases were found to inhibit PMNL adhesion to activated platelets or to P-selectin expressing Chinese hamster ovary (CHO-P) cells and the tyrosine phosphorylation of P-110. Adhesion of PMNLs to activated platelets or to CHO-P cells stimulated activity of LYN and HCK. Monoclonal antibody blockade of P-selectin or beta2-integrins reduced the activation of both kinases. In PMNLs either adherent to platelets or aggregated by P-selectin-IgG chimera, Mac-1 was rapidly redistributed to the Triton X-100-insoluble cytoskeletal fraction, and large clusters of Mac-1 colocalized with patches of F-actin at the sites of cell-cell contact. In PMNLs stimulated by P-selectin-IgG chimera, SRC kinase inhibition impaired Mac-1 clustering, F-actin accumulation, and CD18 redistribution to the cytoskeleton. Disruption of the actin filament network by cytochalasin D prevented PMNL-platelet adhesion and P-selectin-induced PMNL aggregation and impaired the clustering of Mac-1. In agreement with the requirement for the beta2-integrin in the functional up-regulation of LYN and HCK, integrin blockade by monoclonal antibodies resulted in a complete inhibition of P-selectin-induced Mac-1 clustering and F-actin accumulation. Taken together, the results indicate that, after an initial P-selectin-triggered beta2-integrin interaction with the ligand, SRC kinases are activated and allow the remodeling of cytoskeleton-integrin linkages and integrin clustering that finally strengthen cell-cell adhesion. This model highlights a new role for SRC kinases in a regulatory loop by which the Mac-1 promotes its own adhesive function.

Mechanisms of granulocytosis in the absence of CD18

Genetic deficiency in CD18 leads to disease characterized by myeloid hyperplasia, including profound granulocytosis and splenomegaly. Myeloid hyperplasia could directly result from the disruption of CD18 functions essential to granulopoiesis or basal leukocyte trafficking. Alternatively, myeloid hyperplasia could be reactive in nature, due to disruption of essential roles of CD18 in leukocyte responses to microbial challenge. To distinguish between these mechanisms, the hematopoietic systems of lethally irradiated wild-type (WT) mice were reconstituted with either WT fetal liver cells or CD18-deficient fetal liver cells, or an equal mixture of both types of cells. Granulocytosis and splenomegaly developed in mice that received CD18-deficient fetal liver cells. Splenomegaly was prevented and granulocytosis was inhibited by more than 95% in mice that had received both CD18-deficient and WT fetal liver cells, suggesting that myeloid hyperplasia was largely reactive in nature. Consistent with this postulate, the circulating life spans in the blood and the fraction of neutrophils that incorporated BrdU in the bone marrow were not increased for CD18-deficient neutrophils compared with the WT. However, these animals did develop mild granulocytosis compared with mice reconstituted with WT cells alone, and a higher percentage of CD18-deficient leukocytes were neutrophils compared with the WT leukocytes. These observations suggest that the granulocytosis observed in the absence of CD18 occurs through at least 2 mechanisms: one that is dramatically improved by the presence of WT cells, likely reactive in nature, and a second that is independent of the WT hematopoietic cells, involving an alteration in the lineage distribution of blood leukocytes.

Synergistic mobilization of hemopoietic progenitor cells using concurrent beta1 and beta2 integrin blockade or beta2-deficient mice

The hierarchy of cytoadhesion molecules involved in hematopoietic/stem progenitor cell mobilization has not yet been delineated. Previous studies have suggested an important role for alpha4beta1 integrin in this process. To test whether mobilization involves dynamic interactions of alpha4beta1 with other integrins on hematopoietic cells, especially the beta2 integrins, mice and primates were treated with anti-beta1 or anti-beta2 antibodies alone or in combination. A single injection of anti-alpha4beta1 antibody elicited reproducible mobilization in contrast to other antibodies, and 3 injections yielded higher mobilization efficiency than each of the other antibodies. When the anti-beta2 (anti-CD11a or anti-CD18) or anti-alpha5/beta1 integrin antibody was combined with anti-alpha4, an augmentation in mobilization was seen that was either additive or synergistic, depending on the potency of the antibody used. Synergy between anti-alpha4 and anti-CD18 (beta(2)) antibody blockade was seen in primates and confirmed in anti-alpha4-treated CD18-deficient mice. In the latter, there was a 49-fold increase in mobilization with anti-alpha4, much higher than in littermate control animals, in CD18 hypomorphic mice, or in other strains of mice tested. Data from both the antibody blockade and gene-targeted mice suggest that the cooperativity of alpha4beta1 with beta2 integrins becomes evident when they are concurrently inhibited. It is unclear whether this cooperativity is exerted at the stage of reversible adhesion versus migration, and enhancement of and whether the 2 integrins work in a sequential or parallel manner. Whatever the mechanism, the data provide a novel example of beta1 and beta2 integrin crosstalk in stem/progenitor cell mobilization.

Inhibitory effects of synthetic beta peptide on invasion and metastasis of liver cancer

PURPOSE

To study the inhibitory effects of synthetic beta peptide on invasion and metastasis of liver cancer.

METHODS

Membrane-type intercellular adhesion molecule-1 (ICAM-1) expression of SMMC-7721 cultured hepatoma cells (7721 cells) was detected by immunofluorescence cell flowmeter. The adhesion of 7721 cells to fibronectin (FN) was assayed by the MTT method. The adhesion of 7721 cells to 7721 cells, 7721 cells to endothelial cells, and 7721 cells to lymphocyte cells was detected by adhesion assay. LCI-D20 human liver cancer metastasis model in nude mice was used in this experiment. One hundred micrograms of beta peptide per mouse were injected subcutaneously after tumor was resected premetastatically or postmetastatically to observe its effect on liver cancer metastasis after hepatectomy.

RESULTS

Membrane-type ICAM-1 expression of SMMC-7721 cells treated by beta peptide was lower than that of the untreated cells. The adhesion of 7721 cells to FN, 7721 cells to 7721 cells, 7721 cells to endothelial cells, and 7721 cells to lymphocyte cells was also lower in the beta peptide group than in the untreated group.

CONCLUSIONS

beta Peptide can block the adhesion of 7721 cells to FN, 7721 cells to some host cells in vitro, and inhibit HCC metastasis of LCI-D20 model posthepatectomy in vivo, so it could potentially act as an antimetastasis drug.

Rapid and prominent up-regulation of high-affinity receptor for immunoglobulin G (Fc gamma RI) by cross-linking of beta 2 integrins on polymorphonuclear leukocytes

Receptors for the Fc region (FcR) of immunoglobulin (Ig)G play essential roles in effector functions of polymorphonuclear leukocytes (PMNs) including the antibody-mediated clearance of microbes. In contrast to the constitutive expression of the low-affinity receptors for IgG (Fc gamma RII [CD32] and Fc gamma RIII [CD16]), the high-affinity receptor Fc gamma RI (CD64) is barely detectable on unactivated PMNs. CD64 expression is induced in a slow kinetic manner by interferon (IFN)-gamma and granulocyte colony-stimulating factor (G-CSF) after 12 to 24 hours of exposure to these agents. We found that the cross-linking of CD11b as well as of CD18 induced comparable rapid increases in CD64 expression on the surface of PMNs, occurring within 15 minutes of exposure. Cross-linking of neither CD11a nor CD11c induced CD64 expression. In contrast to slow induction by IFN-gamma and G-CSF, the integrin-induced rapid CD64 expression did not require RNA synthesis. Genistein, herbimycin A, and 1,2-bis(o-aminophenoxy)ethan-N,N-N',N'-tetraacetic acid blocked the immediate expression of CD64 in a dose-dependent manner, suggesting that the signal is mediated through calcium mobilization and protein tyrosine kinase(s). Such rapid modulation of the high-affinity Fc gamma RI receptor by integrin cross-linking may reflect the requirement for rapid up-regulation of PMN effector functions, after interaction with endothelial cells, platelets or bacteria.

The hepatic inflammatory response after acetaminophen overdose: role of neutrophils

Acetaminophen overdose induces severe liver injury and hepatic failure. There is evidence that inflammatory cells may be involved in the pathophysiology. Thus, the aim of this investigation was to characterize the neutrophilic inflammatory response after treatment of C3Heb/FeJ mice with 300 mg/kg acetaminophen. A time course study showed that neutrophils accumulate in the liver parallel to or slightly after the development of liver injury. The number of neutrophils in the liver was substantial (209 +/- 64 PMN/50 high-power fields at 12 h) compared to baseline levels (7 +/- 1). Serum levels of TNF-alpha and the C-X-C chemokines KC and MIP-2 increased by 28-, 14-, and 295-fold, respectively, over levels found in controls during the injury process. In addition, mRNA expression of MIP-2 and KC were upregulated in livers of acetaminophen-treated animals as determined by ribonuclease protection assay. However, none of these mediators were generated in large enough quantities to account for neutrophil sequestration in the liver. There was no upregulation of Mac-1 (CD11b/ CD18) or shedding of L-selectin on circulating neutrophils. Moreover, an anti-CD18 antibody had no protective effect against acetaminophen overdose during the first 24 h. These results indicate that there is a local inflammatory response after acetaminophen overdose, including a substantial accumulation of neutrophils in the liver. Because of the critical importance of beta2 integrins for neutrophil cytotoxicity, these results suggest that neutrophils do not contribute to the initiation or progression of AAP-induced liver. The inflammation observed after acetaminophen overdose may be characteristic for a response sufficient to recruit neutrophils for the purpose of removing necrotic cells but is not severe enough to cause additional damage.

Effects of roughness, fibronectin and vitronectin on attachment, spreading, and proliferation of human osteoblast-like cells (Saos-2) on titanium surfaces

The influence of surface roughness and the presence of adhesion molecules in the culture medium were studied regarding cell adhesion, shape, and proliferation of osteoblast-like cells grown on two types of titanium disk. Type I disks were acid etched and type II disks were sandblasted and acid etched. Surface roughness was determined by contact profilometry and scanning electron microscopy. Chemical composition and oxide thickness of the superficial titanium layer were established with energy dispersive X-ray spectrometry, electron spectroscopy for chemical analysis and auger electron spectroscopy. Titanium release in the culture medium was assessed by inductively coupled plasma-optical emission spectrometry. Osteoblast-like cells (Saos-2) were cultured on both types of titanium disks (1) in standard conditions (DMEM culture medium supplemented with fetal calf serum), (FCS), (2) with the culture medium alone (DMEM alone), (3) in the presence of fibronectin or vitronectin (DMEM supplemented with fibronectin or vitronectin). Cultures were also performed in the presence of monoclonal anti-integrin (beta1, alphav) to test the cell adhesion molecules involved in the cell binding to the titanium surface. We found that sandblasting does not modify the chemical surface composition and that titanium represents only 5-6% (in the atom percentage) of surface elements. Release of titanium in the culture medium was found to increase from 24 to 72 hours. In the absence of FCS, fibronectin, or vitronectin, cells appeared scanty and packed in clusters. On the contrary, cells cultured in the presence of FCS, fibronectin, or vitronectin were flattened with large and thin cytoplasmic expansions. The addition of anti beta1 or alphav integrin subunit monoclonal antibody in the culture medium decreased adhesion and spreading of cells, particularly in the presence of fibronectin. Cell proliferation was significantly higher on culture plastic than on both types of disks, but was increased on rough but not on smooth surfaces. These results indicate that a high surface roughness and presence of fibronectin or vitronectin are critical elements for adhesion, spreading, and proliferation of cells on titanium surfaces.

[The effect of PMN adhesion mediated by CD11b/CD18 on the increasing permeability of microvascular endothelial monolayer after severe burn injury]

OBJECTIVE

To detect the effect of burn-activated PMN adhesion and its adhesion molecule CD11b/CD18 on microvascular endothelial permeability using an experimental model of endothelial monolayer on polycarbonate microporous filters.

METHODS

An experimental model for in vitro study of endothelal monolayer for permeability analysis was established. Seven groups were divided into according to the treatment of microvascular endothelial monolayer. Fluid filtration coeffecient(Kf) and albumin reflection coeffecient(delta) were measured after endothelial monolayer was perfused with albumin labelled by FITC.

RESULTS

Burn-activated PMN could increase the level of fluid filtration coeffecient(Kf) and decrease the albumin reflection coeffecient(delta). Monoclonal antibody sealing off CD11b/CD18 on PMN provented the change of delta induced by burn-activated PMN. Another microporous filter interposed between PMNs and endothelial monolayer corrected the changes of Kf and delta.

CONCLUSION

The permeability enhancing effect of PMNs may be attributed mainly to the PMN-EC adhesion mediated by CD11b/CD18. Blocking the PMN-EC over-adhesion in moderation may be helpful in reducing the lung injury due to severe burn injury.

[Effects of blocking CD18-mediated leukocyte adhesion on the survival of the island flap]

OBJECTIVE

This study was to investigate the role of leukocyte and leukocyte adhesion in tissue injury from ischemia and reperfusion.

METHODS

The experiment utilized the monoclonal antibody (mAb) directed to the leukocyte adhesion glycoprotein CD18 to block leukocyte adhesion and aggregation in an island flap model in rats. Tissue content of myeloperoxidase (MPO) and malondialdehyde (MDA) were detected after transient treatment with either saline or mAb directed to CD18. Flap survival was assessed 7 days afterwards.

RESULTS

The content of both MPO and MDA was significantly increased with 8 h ischemia and 1 h reperfusion of the flap. The treatment with anti-CD18 mAb significantly decreased the levels of MPO and MDA and also significantly improved the survival of flaps compared with the saline-treated controls.

CONCLUSION

CD18-mediated leukocyte adhesion plays an important role in tissue injury from ischemia and reperfusion. Blocking leukocyte adhesion can attenuate leukocyte-mediated injury, providing protective effects on island flaps.

Cell adhesion molecules of experimental otitis media in the rat

We examined the expression of cell adhesion molecules (CAM) in immune-mediated otitis media using keyhole limpet haemocyanin (KLH) in the rat, as well as the regulation of these CAM in peripheral blood polymorphonuclear leucocytes (PMN) and lymphocytes upon exposure to middle ear effusion (MEE). After general immunization, a topical antigen was introduced into the middle ear cavity. One day after exposure, CD18+ cells, primarily PMN, had maximally invaded the middle ear mucosa and mucosal epithelium. Mucosal epithelium strongly expressed intercellular adhesion molecule-1 (ICAM-1), only on the first day. The total number of cells in MEE reached a peak on day 3. On day 3, ICAM-1+ cells had reached a peak of 24.5% of the total cells. On day 2. CD18+ cells had reached a peak at 75.3% of the total cells. We examined the regulation of CAM in peripheral blood upon exposure to MEE. The percentage of fluorescent CD18+ PMN increased with MEE compared to those incubated in its absence, but those of L-selectin-positive PMN significantly decreased CAM on the surface lymphocytes did not change when incubated with MEE. The expression of CAM (CD18, ICAM-1) appears important for the initiation of otitis media. Moreover, it was thought that the interaction between the infiltrated PMN and MEE may modify the expression of CAM during the inflammatory process in the middle ear cavity.

Apoptosis following interleukin-2 withdrawal from T cells: evidence for a regulatory role of CD18 (beta 2-integrin) molecules

Following a successful immune response against invading microorganisms, the majority of activated T cells is eliminated, while a minor fraction survives as memory T cells. A decline in T lymphocyte growth factors such as interleukin-2 (IL-2) appears to play a role in the elimination of previously activated T cells. Thus, removal of IL-2 from proliferating T cells not only induces growth arrest, but triggers a massive cell death due to apoptosis. While the apoptotic response involves a series of well-described events, it remains less clear how apoptosis is regulated following IL-2 withdrawal. Here, we provide evidence that CD18 molecules (beta 2-integrins) play a regulatory role in the apoptotic response following removal of IL-2 from previously activated, antigen specific CD4+ T cell lines. Thus, CD18 mAb inhibited the apoptotic response to IL-2 deprivation, whereas mAb against other adhesion molecules (CD28, CD29, CD49d, CD80, CD86) did not. Secondly, IL-2 withdrawal resulted in a retarded apoptotic response in LFA-1 (CD11a/CD18) negative T cells obtained from a leukocyte adhesion deficiency (LAD) patient, as compared to LFA-1 positive T cell lines. Thirdly, co-culture of LFA-1 positive- and negative-T cells at different ratios induced apoptotic responses that were higher than expected, had the two lymphocyte populations not been interacting and significantly higher than that seen in pure LFA-1 negative T cells. Supernatants from LFA-1 positive T cell cultures undergoing apoptosis did not induce an enhanced apoptotic responses in LFA-1 negative T cells, and, reversely, culture supernatants from LFA-1 negative T cells did not rescue LFA-1 positive cells from undergoing apoptosis. The apoptotic response was partly blocked by IL-15, a newly identified T cell growth factor. Taken together, these findings suggest that CD18 molecules (beta 2-integrins) play a regulatory role in the apoptotic response following cytokine withdrawal, and that the regulation is mediated, at least partly, through T-T cell interactions. Thus, apoptotic death following IL-2 deprivation appears to be under "social" control by surrounding T cells.

Soluble intercellular adhesion molecule-1 provokes polymorphonuclear leukocyte elastase release by CD18

BACKGROUND

Elevated levels of soluble intercellular adhesion molecule-1 (sICAM-1) correlate with the development of postinjury multiple organ failure. Soluble ICAM-1 secretion is known to be induced in endothelial cells and monocytes by diverse inflammatory stimuli. We have found that incubation of quiescent polymorphonuclear leukocytes (PMNs) with sICAM-1 elicits elastase release and, more recently, that cross-linking CD18 receptors on PMNs also produces elastase release. Consequently, our study hypothesis was that sICAM-1 provokes PMN elastase release through its interaction with CD18.

METHODS

To obtain sICAM-1, Chinese hamster ovarian cells transfected with human ICAM-1 were lysed and centrifuged at 150,000 g for 1 hour; the supernatant was passed over an ICAM-1 affinity column, eluted with 0.1 mmol/L glycine HCl, and concentrated with dialysis filter. Human PMNs (2.5 x 10(5)) were saturated with specific monoclonal antibodies for the beta 2 subunits (CD11a, CD11b, CD18) or nonspecific monoclonal antibodies for 30 minutes on ice before a 1-hour incubation with sICAM-1 (75 ng/ml) at 37 degrees C. Elastase activity was measured by the cleavage of n-methoxysuccinyl-A-A-P-V-p-nitroanilide.

RESULTS

Neutrophil incubation with sICAM-1 resulted in 19.2% +/- 2.8% of total PMN elastase, compared with 2.4% +/- 0.5% in the controls. Blockade of CD18 abrogated sICAM-1 provoked elastase release with monoclonal antibodies to CD18 (TS1/18, 31H8) resulting in 4.3% +/- 1.0% and 5.5% +/- 1.4% elastase release, respectively. Blockade of CD11a, CD11b, and nonspecific antibody controls had no effect on sICAM-1 induced elastase release.

CONCLUSIONS

In vitro, sICAM-1 provokes PMN elastase release through CD18. This may represent a mechanism by which elevated levels of circulating sICAM-1, released from local injury sites, provoke distal organ dysfunction.

Kupffer cell-mediated cytotoxicity against hepatoma cells occurs through production of nitric oxide and adhesion via ICAM-1/CD18

Rat Kupffer cell (KC)-mediated cytotoxicity against both the syngeneic hepatoma cell line AH70 and hepatocytes was evaluated by changes in mitochondrial function, and the possible role of ICAM-1/CD18 in the interaction between the cells was studied. Rhodamine 123 fluorescence, a marker of the mitochondrial membrane potential, decreased in AH70 cells after co-culture with CK, while that in hepatocytes was unchanged by co-culture. This decrease was blocked by anti-ICAM-1 anti-CD18 and the inhibition of nitric oxide synthesis. Cytometric studies demonstrated that ICAM-1 expression on AH70 cells increased after addition of IFN-gamma, IL-1beta, tumor necrosis factor (TNF)-alpha or KC, while in hepatocytes ICAM-1 was not increased. Anti-ICAM-1 pretreatment inhibited the increase in ICAM-1 expression and the decrease in rhodamine 123 fluorescence on AH70 cells after co-culture with KC. CD18 on KC was increased only after co-culture with AH70. TNF-alpha but not IFN-gamma was detected in the supernatant of co-culture between KC and AH70 cells, and this production was partially inhibited by anti-ICAM-1 and anti-CD18. The activity of inducible nitric oxide synthase in Kupffer cells and the levels of nitrites and nitrates in the co-culture supernatant increased over time, and this increase was attenuated either by addition of NO synthesis inhibitors, anti-ICAM-1 or anti-CD18. These results indicate that the rat KC causes mitochondrial dysfunction in cancer cells via the production of NO and cell-to-cell adhesion via ICAM-1/CD18 has an important role in this cytotoxic process.

L- and P-selectins, but not CD49d (VLA-4) integrins, mediate monocyte initial attachment to TNF-alpha-activated vascular endothelium under flow in vitro

Monocyte adhesion to the vascular endothelium is a pivotal step during their egress to tissues at sites of inflammation and immune reactions, and during atherogenesis. In this study, an in vitro flow model and blocking mAb were used to define the role of adhesion molecules in monocyte interactions with activated HUVEC under flow conditions. By videomicroscopy, freely flowing monocytes abruptly halted (initial attachment) on 6-h TNF-alpha-activated HUVEC under flow via L- and P-selectin, whereas E-selectin was not involved. CD49d/CD29 integrin (VLA-4), which can mediate initial attachment of certain T cells to VCAM-1 under flow, did not support monocyte initial attachment. Once initially attached, a small number of monocytes began rolling at 9 microns/s through a mechanism involving L-selectin, as well as CD49d and CD11/CD18 integrins, while the remaining monocytes became firmly adherent, or released to the flow stream. Monocyte stable arrest and subsequent transendothelial migration occurred rapidly and efficiently through either CD49d or CD18 integrin adhesion pathways. Transendothelial passage was also dependent on PECAM-1 (CD31). These data reveal monocytes initially attach to activated endothelium via an L-selectin-dependent mechanism, with a smaller contribution from P-selectin and no contribution by CD49d. Subsequent monocyte rolling, arrest, and transmigration require overlapping functions between multiple members of the selectin, integrin, and Ig gene families.

Deficiency of Src family kinases p59/61hck and p58c-fgr results in defective adhesion-dependent neutrophil functions

Cross-linking of the neutrophil-beta 2- or beta 3-related leukocyte response integrins by extracellular matrix (ECM) proteins or monoclonal antibodies (mAb) stimulates cytoskeletal rearrangement leading to cell spreading and respiratory burst. Tyrosin phosphorylation of a variety of proteins and activation of the Src family kinases within polymorphonuclear leukocytes (PMN) have recently been implicated in the intracellular signaling pathways generated by leukocyte integrins (Yan, S.R., L. Fumagalli, and G Berton. 1995. J. Inflammation. 45:217-311.) To directly test whether these functional responses are dependent on the Src family kinases p59/61hck and p58c-fgr, we examined adhesion-dependent respiratory burst in PMNs isolated from hck -/-, fgr -/-, and hck -/- fgr -/- knockout mice. Purified bone marrow PMNS from wild-type mice released significant amounts of O2- when adherent to fibrinogen-, fibronectin-, or collagen-coated surfaces, in the presence of activating agents such as tumor necrosis factor (TNF) or formyl-methionyl-leucyl-phenylalanine, as described for human PMNs. PMNs from hck-/-fgr-/- double-mutant mic, however, failed to respond. This defect was specific for integrin signaling, since respiratory burst was normal in hck-/-fgr-/-PMNs stimulated by immune complexes or PMA. Stimulation of respiratory burst was observed in TNF-primed wild-type PMN plated on surfaces coated with murine intracellular adhesion molecule-1 (ICAM-1), while hck-/-fgr-/- PMNs, failed to respond. Direct cross-linking of the subunits of beta 2 and beta 2 integrins by surface-bound mAbs was elicited O2- production by wild-type PMNs, while the double-mutant hck-/-fgr-/- cells failed to respond. Photomicroscopy and cell adhesion assays revealed that the impaired functional responses of hck-/-fgr-/- PMNs were caused by defective spreading and tight adhesion on either ECM protein- or mAb-coated surfaces. In contrast, hck-/-or fgr-/-single mutant cells produced O2- at levels equivalent to wild-type cells on ECM protein, murine ICAM-1, and antiintegrin mAb-coated surfaces. Hence, either p59/61 hck and p 58c-fgr is required for signaling through leukocyte beta 2 and beta 3 integrins leading to PMN spreading and respiratory burst. This is the first direct genetic evidence of the importance of Src family kinases in integrin signaling within leukocytes, and it is also the best example of overlapping function between members of this gene family within a defined signal transduction pathway.

Lipoxin A4 and B4 inhibit leukotriene-stimulated interactions of human neutrophils and endothelial cells

Lipoxins are bioactive eicosanoids that are generated within the vascular lumen by leukocytes and transcellular biosynthetic routes during multicellular responses. Polymorphomuclear neutrophils (PMN) and endothelial cells express high affinity receptors for lipoxins, engagement of which invokes profiles of signaling events that differ from other lipid mediators. In this work, we report that lipoxins are potent inhibitors of PMN-endothelial cell interactions triggered by leukotrienes via dual-pronged actions with PMN and endothelial cells. Both lipoxin A4(LXA4) and B4(LXB4) blocked PMN migration stimulated by leukotriene B4 (LTB4), a well established agonist for PMN recruitment, a transmigration assay in vitro. Lipoxins were almost as effective in this regard as the pharmacologic LTB4 receptor antagonist, ONO 4057, and the blocking anti-CD18 mAb, R15.7. LXA4 and LXB4 blunted PMN transmigration, in part by inhibiting beta 2 integrin-dependent PMN adhesion. These modulatory actions of lipoxins were evident at subnanomolar concentrations, rapid in onset, and attenuated by prior exposure of PMN to a tyrosine kinase inhibitor, genistein. The peptidoleukotrienes, leukotriene C4 (LTC4) and leukotriene D4 (LTD4) also provoked PMN-endothelial cell adhesion, but via a different mechanism than LTB4. Both LTC4 and LTD4 enhanced endothelial adhesiveness for PMN, in part, by stimulating mobilization of P-selectin from intracellular Weibel-Palade bodies. LXA4 and LXB4, but not other lipoxygenase products, blocked P-selectin mobilization induced by peptidoleukotrienes and attenuated P-selectin-mediated PMN-endothelial cell adhesion. These results indicate that lipoxins attenuate PMN-endothelial cell interactions supported by selectins and beta 2 integrins in vitro, and are potential endogenous lipid-derived modulators of PMN trafficking in host defense, inflammation, and other vascular events.

Mechanisms and pharmacological manipulation of eosinophil accumulation in vivo

The presence of eosinophils and their products in tissues is frequently associated with the pathogenesis of allergic inflammation. A better understanding of how these cells are recruited from the microcirculation will help in the development of therapies targeted at allergic disorders. Here, Mauro Teixeira, Timothy Williams and Paul Hellewell describe the current concepts of eosinophil accumulation, examine the potential ways of modulating this process, and discuss whether antagonists of eosinophil-specific mediators or functional antagonists would be the preferred therapies.

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

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