The melanocortin MC(1) receptor agonist BMS-470539 inhibits leucocyte trafficking in the inflamed vasculature.

BACKGROUND AND PURPOSE: Over three decades of research evaluating the biology of melanocortin (MC) hormones and synthetic peptides, activation of the MC type 1 (MC(1)) receptor has been identified as a viable target for the development of novel anti-inflammatory therapeutic agents. Here, we have tested a recently described selective agonist of MC(1) receptors, BMS-470539, on leucocyte/post-capillary venule interactions in murine microvascular beds. EXPERIMENTAL APPROACH: Intravital microscopy of two murine microcirculations were utilized, applying two distinct modes of promoting inflammation. The specificity of the effects of BMS-470539 was assessed using mice bearing mutant inactive MC(1) receptors (the recessive yellow e/e colony). KEY RESULTS: BMS-470539, given before an ischaemia-reperfusion protocol, inhibited cell adhesion and emigration with no effect on cell rolling, as assessed 90 min into the reperfusion phase. These properties were paralleled by inhibition of tissue expression of both CXCL1 and CCL2. Confocal investigations of inflamed post-capillary venules revealed immunostaining for MC(1) receptors on adherent and emigrated leucocytes. Congruently, the anti-inflammatory properties of BMS-470539 were lost in mesenteries of mice bearing the inactive mutant MC(1) receptors. Therapeutic administration of BMS-470539 stopped cell emigration, but did not affect cell adhesion in the cremasteric microcirculation inflamed by superfusion with platelet-activating factor. CONCLUSIONS AND IMPLICATIONS: Activation of MC(1) receptors inhibited leucocyte adhesion and emigration. Development of new chemical entities directed at MC(1) receptors could be a viable approach in the development of novel anti-inflammatory therapeutic agents with potential application to post-ischaemic conditions.

Role of neutrophil elastase in LTB4-induced neutrophil transmigration in vivo assessed with a specific inhibitor and neutrophil elastase deficient mice.

BACKGROUND AND PURPOSE: The serine protease neutrophil elastase (NE) appears to regulate inflammatory responses at multiple levels but its role in leukocyte transmigration in vivo remains unclear. The present study aimed to address this issue by using both an NE inhibitor (ONO-5046) and NE deficient (NE(-/-)) mice. EXPERIMENTAL APPROACH: A number of inflammatory mediators (LTB(4), KC and PAF) were investigated in vitro for their ability to stimulate the release and the surface expression of NE by neutrophils. In addition, the role of NE in leukocyte migration elicited by topical LTB(4) was investigated in vivo in mouse cremasteric venules as observed by intravital microscopy. KEY RESULTS: Amongst the mediators tested in vitro, LTB(4) was found to be a highly potent and efficacious inducer of NE cell surface expression on murine neutrophils. Furthermore, in wild-type mice (WT), LTB(4)-induced leukocyte transmigration was reduced by intravenous ONO-5046 (66% inhibition), an effect that appeared to occur at the level of the perivascular basement membrane. Interestingly, LTB(4)-induced responses were normal in NE(-/-) mice and, while ONO-5046 had no inhibitory effect in these animals, the broad-spectrum serine protease inhibitor aprotinin suppressed leukocyte transmigration in both WT and NE(-/-) mice. CONCLUSIONS AND IMPLICATIONS: The findings demonstrate the potent ability of LTB(4) to induce cell-surface expression of NE and provide evidence for the involvement of NE in LTB(4)-induced neutrophil transmigration in vivo. The results also suggest the existence of compensatory mechanisms in NE(-/-) mice, highlighting the added value of investigating pharmacological blockers in parallel with genetic deletion.

Neutrophil chemorepulsion in defined interleukin-8 gradients in vitro and in vivo.

We report for the first time that primary human neutrophils can undergo persistent, directionally biased movement away from a chemokine in vitro and in vivo, termed chemorepulsion or fugetaxis. Robust neutrophil chemorepulsion in microfluidic gradients of interleukin-8 (IL-8; CXC chemokine ligand 8) was dependent on the absolute concentration of chemokine, CXC chemokine receptor 2 (CXCR2), and was associated with polarization of cytoskeletal elements and signaling molecules involved in chemotaxis and leading edge formation. Like chemoattraction, chemorepulsion was pertussis toxin-sensitive and dependent on phosphoinositide-3 kinase, RhoGTPases, and associated proteins. Perturbation of neutrophil intracytoplasmic cyclic adenosine monophosphate concentrations and the activity of protein kinase C isoforms modulated directional bias and persistence of motility and could convert a chemorepellent to a chemoattractant response. Neutrophil chemorepulsion to an IL-8 ortholog was also demonstrated and quantified in a rat model of inflammation. The finding that neutrophils undergo chemorepulsion in response to continuous chemokine gradients expands the paradigm by which neutrophil migration is understood and may reveal a novel approach to our understanding of the homeostatic regulation of inflammation.

Intravital microscopy in the study of ANCA-associated systemic vasculitis.

In addition to being useful clinical markers of systemic vasculitis, anti-neutrophil cytoplasm antibodies (ANCA) may play a role in the initiation of vasculitic injury. These autoantibodies can induce neutrophil degranulation, dysregulated neutrophil apoptosis and neutrophil adhesion to endothelium in static cellular systems. This mini-review will place these sentinel findings in the context of more recent studies using the parallel plate flow chamber and novel animal models of ANCA-associated vasculitis (AASV). Rodent models lend themselves well to investigation of leukocyte endothelial interaction using intravital microscopy. In this way, one can study ANCA-induced leukocyte adhesion/transmigration, and microvascular injury in real time. These studies may then be extended to look at the impact of novel therapeutic agents on these processes.

MRL/lpr lupus-prone mice show exaggerated ICAM-1-dependent leucocyte adhesion and transendothelial migration in response to TNF-alpha.

OBJECTIVE: Endothelial activation and dysfunctional leucocyte-endothelial interactions are thought to play key roles in the pathogenesis of systemic lupus erythematosus (SLE). The object of this study was to investigate directly the effect of increased endothelial adhesion molecule expression on leucocyte-endothelial cell interactions, using the MRL/lpr mouse model. METHODS: Leucocyte rolling, arrest and transendothelial migration were quantified in the cremaster muscle microcirculation of 20-week-old MRL/lpr mice, using intravital microscopy. Endothelial adhesion molecule expression was quantified using intravenously injected radiolabelled monoclonal antibodies. RESULTS: Basal expression of intercellular adhesion molecule 1 (ICAM-1) by cremaster endothelium was 2-fold greater in MRL/lpr than in MRL/++ mice (P<0.05). There was a 1.6-fold increase in expression of vascular adhesion molecule 1 (VCAM-1), but no increase in E-selectin or P-selectin expression. Following intrascrotal injection of saline, no difference was detected in leucocyte-endothelial interactions between MRL/lpr and control MRL/++ mice. In contrast, intrascrotal injection of tumour necrosis factor alpha (TNF-alpha) (2 h test period) led to significantly increased numbers of adherent and extravasated leucocytes in MRL/lpr (5.98+/-0.71 and 5.45+/-0.34 leucocytes per 100 micro m vessel segment respectively) compared with MRL/++ mice (3.63+/-0.26 and 2.97+/-0.24 respectively, each P<0.05). Treatment of TNF-alpha-stimulated mice with anti-ICAM-1 F(ab')2 (YN1) abolished the difference between MRL/lpr and MRL/++ mice, whereas a negative control anti-DNP F(ab')2 had no effect. CONCLUSIONS: MRL/lpr lupus-prone mice show exaggerated ICAM-1-dependent leucocyte-endothelial interactions in response to TNF-alpha. Increased leucocyte-endothelial interactions due to endothelial priming could contribute to the clinical link between infection and flares of lupus disease activity.

Divergent mechanisms of action of the inflammatory cytokines interleukin 1-beta and tumour necrosis factor-alpha in mouse cremasteric venules.

1. Protein synthesis dependency and the role of endogenously generated platelet activating factor (PAF) and leukotriene B(4) (LTB(4)) in leukocyte migration through interleukin-1beta (IL-1beta)- and tumour necrosis factor-alpha (TNFalpha)-stimulated mouse cremasteric venules was investigated using established pharmacological interventions and the technique of intravital microscopy. 2. Based on previously obtained dose-response data, 30 ng rmIL-1beta and 300 ng rmTNFalpha were injected intrascrotally (4 h test period) to induce comparable levels of leukocyte firm adhesion and transmigration in mouse cremasteric venules. 3. Co-injection of the mRNA synthesis inhibitor, actinomycin D (0.2 mg kg(-1)), with the cytokines significantly inhibited firm adhesion (49+/-13.6%) and transmigration (67.2+/-4.2%) induced by IL-1beta, but not TNFalpha. 4. In vitro, TNFalpha (1-100 ng ml(-1)), but not IL-1beta, stimulated L-selectin shedding and increased beta(2) integrin expression on mouse neutrophils, as quantified by flow cytometry. 5. The PAF receptor antagonist, UK-74,505 (modipafant, 0.5 mg kg(-1), i.v.), had no effect on adhesion induced by either cytokine, but significantly inhibited transmigration induced by IL-1beta (66.5+/-4.5%). 6. The LTB(4) receptor antagonist, CP-105,696 (100 mg kg(-1), p.o.), significantly inhibited both IL-1beta induced adhesion (81.4+/-15.2%) and transmigration (58.7+/-7.2%), but had no effect on responses elicited by TNFalpha. Combined administration of the two antagonists had no enhanced inhibitory effects on responses induced by either cytokine. 7. The data indicate that firm adhesion and transmigration in mouse cremasteric venules stimulated by IL-1beta, but not TNFalpha, is protein synthesis dependent and mediated by endogenous generation of PAF and LTB(4). Additionally, TNFalpha but not IL-1beta, can directly stimulate mouse neutrophils in vitro. The findings provide further evidence to suggest divergent mechanisms of actions of IL-1beta and TNFalpha, two cytokines often considered to act via common molecular/cellular pathways.

Platelet-endothelial cell adhesion molecule-1 (PECAM-1)-deficient mice demonstrate a transient and cytokine-specific role for PECAM-1 in leukocyte migration through the perivascular basement membrane.

Studies with neutralizing antibodies have indicated roles for platelet-endothelial cell adhesion molecule-1 (PECAM-1) in leukocyte migration through the endothelium and the perivascular basement membrane. Because some of these findings have been contentious, this study aimed to explore the role of PECAM-1 in leukocyte migration by analyzing leukocyte responses in interleukin 1beta (IL-1beta)- and tumor necrosis factor-alpha (TNFalpha)-activated cremasteric venules of PECAM-1-deficient mice using intravital and electron microscopy. Although no differences in levels of leukocyte rolling flux or firm adhesion were observed, a delay in leukocyte transmigration in response to IL-1beta, but not TNFalpha, was detected in PECAM-1-deficient mice. Electron microscopy indicated that this delay occurred at the level of perivascular basement membrane. To address the cytokine specificity of PECAM-1 dependence, in vitro experiments demonstrated that TNFalpha, but not IL-1beta, could induce rapid adhesion of murine neutrophils to protein-coated surfaces, suggesting that TNFalpha elicited leukocyte transmigration in wild-type mice via direct stimulation of leukocytes. In summary, the results suggest a regulatory role for PECAM-1 in leukocyte migration through the perivascular basement membrane, a role that appears to be cytokine-specific and associated with the ability of the cytokine to stimulate rapid neutrophil adhesion.

Effect of aprotinin (trasylol) on the inflammatory and thrombotic complications of conventional cardiopulmonary bypass surgery.

Before the discovery of its hemostatic properties, aprotinin was thought of as a potential anti-inflammatory agent. Its clinical introduction in 1987 to prevent blood loss during cardiac surgery [Royston 1987, van Oeveren 1987] led to its anti-inflammatory benefits being largely overlooked in favor of a vigorous debate centering on whether aprotinin may be pro-thrombotic when given to patients. In this article, we summarize evidence for the anti-inflammatory activity of aprotinin and discuss our recent contributions in this area. We also summarize the state of the thrombosis debate and discuss our recent evidence from purified platelets which shows that aprotinin is simultaneously hemostatic yet anti-thrombotic.

VCAM-1 has a tissue-specific role in mediating interleukin-4-induced eosinophil accumulation in rat models: evidence for a dissociation between endothelial-cell VCAM-1 expression and a functional role in eosinophil migration.

Eosinophil accumulation has been associated with the pathogenesis of numerous allergic inflammatory disorders. Despite the great interest in this response, many aspects of eosinophil accumulation remain unknown. This is particularly true with respect to tissue-specific mechanisms that may regulate the accumulation of eosinophils in different organs. This study addressed this issue by investigating and comparing the roles of alpha(4)-integrins and vascular cell adhesion molecule 1 (VCAM-1) adhesion pathways in interleukin 4 (IL-4)-induced eosinophil accumulation in 2 different rat models of inflammation, namely pleural and cutaneous inflammation. Similar to our previous findings in studies in rat skin, locally administered IL-4 induced a time- and dose-dependent accumulation of eosinophils in rat pleural cavities, a response that was associated with generation of the chemokine eotaxin. The IL-4-induced eosinophil accumulation in skin and pleural cavities was totally inhibited by an antirat alpha(4)-integrins monoclonal antibody (mAb) (TA-2). In contrast, whereas an antirat VCAM-1 mAb (5F10) totally blocked the response in skin, IL-4-induced eosinophil accumulation in rat pleural cavities was not affected by VCAM-1 blockade. A radiolabeled mAb technique demonstrated that endothelial-cell VCAM-1 expression was induced in response to IL-4 in both skin and pleural membrane. The results indicate that although endothelial-cell VCAM-1 is present in skin and pleura, a functional role for it in IL-4-induced eosinophil accumulation was evident only in skin. These findings suggest the existence of tissue-specific adhesive mechanisms in regulating leukocyte migration in vivo and demonstrate a dissociation between VCAM-1 expression and eosinophil accumulation.

An anti-inflammatory property of aprotinin detected at the level of leukocyte extravasation.

BACKGROUND: Aprotinin is a serine protease inhibitor used extensively in cardiac operations to reduce postoperative bleeding. It has also been used in trials aimed at reducing the systemic inflammatory response to cardiopulmonary bypass. It remains unclear whether the anti-inflammatory action of aprotinin is related to its general ability to suppress leukocyte activation or whether aprotinin can exercise effects during the leukocyte-endothelial cell adhesion cascade. METHODS: We used intravital microscopy to study the 3 main stages of the adhesion cascade (leukocyte rolling, firm adhesion, and extravasation) within the mesenteric microcirculation of rats. This in vivo technique allows leukocyte recruitment to be viewed directly through the transparent mesentery of anesthetized animals. RESULTS: Aprotinin, given by continuous infusion at a clinically relevant dose, exerted no effect on the rolling or firm adhesion responses toward local chemoattractant N -formyl-methyl-leucyl-phenylalanine but significantly inhibited extravasation of leukocytes (73% at 40 minutes, P =.04) into surrounding tissues. In parallel in vitro experiments, aprotinin (used at 200, 800, and 1600 kIU/mL) dose dependently inhibited neutrophil transmigration through cultured endothelial cells in response to 3 different chemoattractants: N -formyl-methyl-leucyl-phenylalanine (P <.001 at 800 and 1600 kIU/mL), interleukin 8 (P <.05 at 200 kIU/mL and P <.001 at 800 and 1600 kIU/mL), and platelet-activating factor (P <.05 at 1600 kIU/mL). CONCLUSIONS: Our studies have therefore revealed a novel anti-inflammatory mechanism of aprotinin operating at the level of leukocyte extravasation. These findings may be relevant in the prevention of systemic inflammation after cardiopulmonary bypass through the use of protease inhibitors.

Divergent effects of platelet-endothelial cell adhesion molecule-1 and beta 3 integrin blockade on leukocyte transmigration in vivo.

The final stage in the migration of leukocytes to sites of inflammation involves movement of leukocytes through the endothelial cell layer and the perivascular basement membrane. Both platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) and the integrin alphavbeta3 have been implicated in this process, and in vitro studies have identified alphavbeta3 as a heterotypic ligand for PECAM-1. In the present study we have addressed the roles of these molecules by investigating and comparing the effects of PECAM-1 and alphavbeta3 blockade on leukocyte migration in vivo. For this purpose we have examined the effects of neutralizing Abs directed against PECAM-1 (domain 1-specific, mAb 37) and beta3 integrins (mAbs 7E3 and F11) on leukocyte responses in the mesenteric microcirculation of anesthetized rats using intravital microscopy. The anti-PECAM-1 mAb suppressed leukocyte extravasation, but not leukocyte rolling or firm adhesion, elicited by IL-1beta in a dose-dependent manner (e.g., 67% inhibition at 10 mg/kg 37 Fab), but had no effect on FMLP-induced leukocyte responses. Analysis by electron microscopy suggested that this suppression was due to an inhibition of neutrophil migration through the endothelial cell barrier. By contrast, both anti-beta3 integrin mAbs, 7E3 F(ab')2 (5 mg/kg) and F11 F(ab')2 (5 mg/kg), selectively reduced leukocyte extravasation induced by FMLP (38 and 46%, respectively), but neither mAb had an effect on IL-1beta-induced leukocyte responses. These findings indicate roles for both PECAM-1 and beta3 integrins in leukocyte extravasation, but do not support the concept that these molecules act as counter-receptors in mediating leukocyte transmigration.

VCAM-1 contributes to rapid eosinophil accumulation induced by the chemoattractants PAF and LTB4: evidence for basal expression of functional VCAM-1 in rat skin.

The aim of the present study was to investigate the role of the adhesion pathway alpha4 integrins/vascular cell adhesion molecule type 1 (VCAM-1) in rapid eosinophil accumulation induced by the chemoattractants PAF and LTB4. For this purpose we have used an in vivo model of local 111In-eosinophil accumulation to quantify eosinophil accumulation induced by intradermal administration of platelet-activating factor (PAF) and leukotriene B4 (LTB4) in rats. Initial experiments carried out over 4 hr demonstrated that intravenous administration of an anti-VCAM-1 monoclonal antibody (mAb; 5F10) or an anti-alpha4 integrin mAb (TA2) caused a significant reduction in PAF- or LTB4-induced 111In-labelled eosinophil accumulation. Time-course experiments demonstrated that the anti-VCAM-1 mAb was effective at suppressing early phases of the 111In-labelled eosinophil accumulation induced by PAF and LTB4 (e.g. within the first 60 min). In contrast, 111In-labelled eosinophil accumulation induced by these chemoattractants was unaffected by the local administration of the transcriptional inhibitor actinomycin D, suggesting a role for basally expressed VCAM-1. Indeed, basal expression of VCAM-1 in rat skin sites was demonstrated by the localization of intravenously administered radiolabelled mAb. The localization of the radiolabelled antibody was not altered in skin sites injected with PAF or LTB4. Finally, the inhibitory effects seen with the anti-VCAM-1 mAb were enhanced when the antibody was co-injected into rats with an anti-intercellular adhesion molecule-1 (ICAM-1) mAb (1A29). The combination of these two mAb also caused a significant inhibition of PAF-induced oedema, as quantified by the local accumulation of 125I-labelled human serum albumin. The results indicate a role for alpha4 integrins/VCAM-1 and ICAM-1, in PAF- and LTB4-induced eosinophil accumulation in vivo and suggest that basally expressed VCAM-1 may have a functional role in rapid accumulation of eosinophils induced by chemoattractants.

Human eotaxin induces eosinophil extravasation through rat mesenteric venules: role of alpha4 integrins and vascular cell adhesion molecule-1.

Eotaxin is a potent eosinophil-specific CC-chemokine, which has been shown to play a role in the selective induction of eosinophil accumulation in a number of allergic models of inflammation. Many aspects of the mechanism by which eotaxin induces eosinophil accumulation in vivo remain unresolved. In the present study, we investigated the direct effect of synthetic human eotaxin on leucocyte/endothelial cell interactions within rat mesenteric venules, as quantified by intravital microscopy. Topical eotaxin (30 pmol) induced rapid firm adhesion and extravasation of leucocytes within the rat mesentery, the extravasated leucocytes all being eosinophils, as determined by histological analysis. Whilst eotaxin was unable to stimulate the interaction of rat eosinophils with vascular cell adhesion molecule-1 (VCAM-1) under static conditions in vitro, eotaxin-induced responses in vivo were significantly suppressed by anti-alpha4 integrin and anti-VCAM-1 monoclonal antibodies (mAbs). The anti-alpha4 integrin mAb, HP2/1 (3.5 mg/kg), inhibited the eotaxin-induced firm adhesion and extravasation, 60 min postapplication of the chemokine, by 89% and 84%, respectively. In the same set of experiments, the anti-VCAM-1 mAb, 5F10 (3.5 mg/kg), inhibited leucocyte adhesion and extravasation by 61% and 63%, respectively. These results demonstrate that eotaxin-induced migration of eosinophils through rat mesenteric venules in vivo is dependent on an alpha4 integrin/VCAM-1 adhesion pathway, the significance of which may only be evident under flow conditions and/or following the ligation of other adhesion molecules expressed on eosinophils.

IL-4-induced eosinophil accumulation in rat skin is dependent on endogenous TNF-alpha and alpha 4 integrin/VCAM-1 adhesion pathways.

IL-4 has been implicated in the pathogenesis of a number of allergic inflammatory disease states where the accumulation of eosinophils is a prominent feature. The aim of the present study was to use an isotopic in vivo model to investigate the ability of recombinant rat IL-4 in inducing eosinophil accumulation in rat skin. 111In-eosinophil accumulation in response to intradermally injected IL-4 was measured during 0 to 4 h, 24 to 28 h, and 48 to 52 h. Accumulation was detected during the first two periods, but not at the later time point. The accumulation during 24 to 28 h, which was dose dependent, was investigated in detail. Administration i.v. of an anti-rat VCAM-1 mAb, but not an anti-rat ICAM-1 mAb, inhibited the accumulation of 111In-eosinophils induced by IL-4 (maximum inhibition, 80%). Further, when the 111In-eosinophils were pretreated in vitro with an anti-beta 2 integrin mAb, an anti-alpha 4 integrin mAb, or a combination of both mAbs, before their injection into recipient rats, the IL-4-induced cell accumulation was inhibited by 63, 60, and 74%, respectively. Finally, coadministration of IL-4 with the soluble TNF receptor (p55)-IgG fusion protein significantly reduced the 111In-eosinophil accumulation induced by the cytokine, and TNF-alpha was detected in IL-4-injected skin sites by both immunostaining and bioassay. Our results demonstrate that IL-4 is a potent inducer of eosinophil accumulation in vivo, the response being dependent on the endogenous generation of TNF-alpha, beta 2 integrins, and alpha 4 integrin/VCAM-1 interactions.

Human eotaxin induces alpha 4 and beta 2 integrin-dependent eosinophil accumulation in rat skin in vivo: delayed generation of eotaxin in response to IL-4.

The CC chemokine eotaxin, originally purified from bronchoalveolar lavage fluid of sensitized guinea pigs following allergen challenge, is a potent eosinophil-selective chemoattractant. In the present study, we have used (111)In-eosinophils and human eotaxin to characterize the profile of chemokine-induced eosinophil accumulation in vivo in rat skin. Intradermally injected eotaxin caused a dose-dependent accumulation of (111)In-eosinophils. Time course studies indicated that the response was rapid, since all the accumulation occurred within the first 1 to 2 h of eotaxin injection. The i.v. administration of anti-intercellular adhesion molecule-1, anti-vascular cell adhesion molecule-1, or anti-alpha4 integrin mAbs significantly inhibited the eosinophil accumulation induced by 100 pmol of human eotaxin by 73, 43, and 67%, respectively. Further, when (111)In-eosinophils were pretreated in vitro with anti-alpha4 integrin or anti-beta2 integrin mAbs, or with a combination of both mAbs, eotaxin-induced responses in vivo were reduced by 52, 49, and 68%, respectively. Eosinophil accumulation induced by intradermal IL-4, but not that induced by TNF-alpha or leukotriene B4, appeared to be mediated in part by endogenously generated eotaxin. Anti-eotaxin Abs significantly inhibited (54%) the later phases (24-28 h) but not the early phase (0-4 h) of the response to IL-4. This was consistent with eotaxin mRNA expression peaking at 18 h after IL-4 injection. Our findings show that human eotaxin is a potent inducer of eosinophil accumulation in vivo, this response being dependent on alpha4 integrin/vascular cell adhesion molecule-1 and beta2 integrin/intercellular adhesion molecule-1 adhesion pathways. Further, the eosinophil accumulation in response to IL-4 is partly mediated by endogenously generated eotaxin.

Tumor necrosis factor alpha-induced eosinophil accumulation in rat skin is dependent on alpha4 integrin/vascular cell adhesion molecule-1 adhesion pathways.

Tumor necrosis factor alpha (TNFalpha) is a cytokine implicated in the pathogenesis of numerous chronic and acute inflammatory conditions. In the present study, we have characterized the ability of TNFalpha in inducing eosinophil accumulation in rat skin and have shown the inhibitory effects of anti-alpha4 integrin and anti-vascular cell adhesion molecule-1 (VCAM-1) antibodies on this response. The intradermal injection of recombinant human TNFalpha induced a slowly developing, dose-dependent accumulation of 111In-eosinophils in rat skin that was maximal at the dose of 10(-11) mol/site. Coadministration of TNFalpha with the soluble TNFalpha receptor (p55)-IgG fusion protein (TNFR-IgG) totally inhibited the 111In-eosinophil accumulation induced by the cytokine. The TNFalpha-induced 111In-eosinophil accumulation was not affected after pretreatment of rats with the platelet-activating factor (PAF) receptor antagonist UK-74,505 or the antihuman interleukin-8 monoclonal antibody (MoAb) DM/C7. In contrast, the intravenous administration of an anti-alpha4 integrin MoAb, HP2/1 (3.5 mg/kg), or an anti-VCAM-1 MoAb, 5F10 (2 mg/kg), greatly inhibited the 111In-eosinophil accumulation induced by TNFalpha (the responses detected at 10(-11) mol/site were inhibited by 78% and 50%, respectively). These results show that TNFalpha is an effective inducer of eosinophil accumulation in vivo, with this response being dependent on an interaction between alpha4 integrins and VCAM-1.

An anti-platelet-endothelial cell adhesion molecule-1 antibody inhibits leukocyte extravasation from mesenteric microvessels in vivo by blocking the passage through the basement membrane.

Platelet-endothelial cell adhesion molecule-1 (PECAM-1, CD31) plays an active role in the process of leukocyte migration through cultured endothelial cells in vitro and anti-PECAM-1 antibodies (Abs) inhibit accumulation of leukocytes into sites of inflammation in vivo. Despite the latter, it is still not clear at which stage of leukocyte emigration in vivo PECAM-1 is involved. To address this point directly, we studied the effect of an anti-PECAM-1 Ab, recognizing rat PECAM-1, on leukocyte responses within rat mesenteric microvessels using intravital microscopy. In mesenteric preparations activated by interleukin (IL)-1 beta, the anti-PECAM-1 Ab had no significant effect on the rolling or adhesion of leukocytes, but inhibited their migration into the surrounding extravascular tissue in a dose-dependent manner. Although in some vessel segments these leukocytes had come to a halt within the vascular lumen, often the leukocytes appeared to be trapped within the vessel wall. Analysis of these sections by electron microscopy revealed that the leukocytes had passed through endothelial cell junctions but not the basement membrane. In contrast to the effect of the Ab in mesenteric preparations treated with IL-1 beta, leukocyte extravasation induced by topical or intraperitoneal administration of the chemotactic peptide formyl-methionyl-leucyl-phenylalanine was not inhibited by the anti-PECAM-1 Ab. These results directly demonstrate a role for PECAM-1 in leukocyte extravasation in vivo and indicate that this involvement is selective for leukocyte extravasation elicited by certain inflammatory mediators. Further, our findings provide the first in vivo indication that PECAM-1 may have an important role in triggering the passage of leukocytes through the perivascular basement membrane.

Molecular and cellular interactions mediating granulocyte accumulation in vivo.

An inflammatory response, either beneficial in host defence or detrimental resulting in an inflammatory disease, is associated with alterations in vascular tone and blood flow, enhanced vascular permeability to macromolecules and the extravasation of leucocytes from the vascular lumen into extravascular tissue. The adhesive interaction of granulocytes with venular endothelial cells is an essential step in the process of granulocyte accumulation at sites of inflammation in vivo. Recent advances made in the field of chemokines and adhesion molecules have led to a better understanding of the molecular events mediating this important component of the inflammatory response. The defined molecular interactions that mediate and regulate these events, in the process of neutrophil accumulation, will be discussed in this article. Recently, the eosinophil has come into focus because of its prominence in allergic reactions. This cell will be discussed in comparison.

Interleukin-1-induced leukocyte extravasation across rat mesenteric microvessels is mediated by platelet-activating factor.

Although our understanding of the molecular interactions that mediate the adhesion of leukocytes to venular endothelial cells has greatly expanded, very little is known about the mechanisms that mediate the passage of leukocytes across the vessel wall in vivo. The aim of the present study was to investigate the role of endogenously formed platelet-activating factor (PAF) in the process of leukocyte extravasation induced by interleukin-1 (IL-1). To determine at which stage of emigration PAF was involved, we studied the behavior of leukocytes within rat mesenteric microvessels by intravital microscopy. Rats were injected intraperitoneally with saline, recombinant rat IL-1 beta (IL-1 beta), or the peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) 4 hours before the exteriorization of the mesenteric tissue. In animals treated with IL-1 beta there was a significant increase in the number of rolling and adherent leukocytes within venules (20- to 40-micron diameter) and in the number of extravasated leukocytes in the tissue. Pretreatment of rats with the PAF receptor antagonist UK-74,505 had no effect on the leukocyte responses of rolling and adhesion, but significantly inhibited the migration of the leukocytes across the vessel wall induced by IL-1 beta (76% inhibition). A structurally unrelated PAF antagonist, WEB-2170, produced the same effect (64% inhibition). However, in contrast, UK-74,505 had no effect on the leukocyte extravasation induced by FMLP, indicating selectivity for the response elicited by certain mediators. These results provide the first line of direct evidence for the involvement of endogenously formed PAF in the process of leukocyte extravasation induced by IL-1 in vivo.