The cutaneous reverse Arthus reaction requires intercellular adhesion molecule 1 and L-selectin expression

The Art of Mast Cell Adhesion

Cell adhesion is one of the basic phenomena occurring in a living organism, affecting many other processes such as proliferation, differentiation, migration, or cell viability. Mast cells (MCs) are important elements involved in defending the host against various pathogens and regulating inflammatory processes. Due to numerous mediators, they are contributing to the modulation of many basic cellular processes in a variety of cells, including the expression and functioning of different adhesive molecules. They also express themselves many adhesive proteins, including ICAM-1, ICAM-3, VCAM-1, integrins, L-selectin, E-cadherin, and N-cadherin. These molecules enable MCs to interact with other cells and components of the extracellular matrix (ECM), creating structures such as adherens junctions and focal adhesion sites, and triggering a signaling cascade. A thorough understanding of these cellular mechanisms can create a better understanding of MC biology and reveal new goals for MC targeted therapy. This review will focus on the current knowledge of adhesion mechanisms with the involvement of MCs. It also provides insight into the influence of MCs or MC-derived mediators on the adhesion molecule expression in different cells.

Inhibitory role of interleukin-10 in the cutaneous reverse Arthus reaction

The formation and deposition of immune complexes (IC) containing immunoglobulin (Ig)G antibodies induces an acute inflammatory response with tissue injury. One of the experimental models of IC-related vasculitis is the cutaneous reverse passive Arthus reaction, in which IgG antibodies are injected i.d., followed immediately by the i.v. application of the corresponding antigen. This reaction is characterized by edema, hemorrhage and neutrophil infiltration. To assess the role of the anti-inflammatory cytokine interleukin (IL)-10 in IC-related vasculitis, we investigated the cutaneous Arthus reaction using IL-10 knockout (IL-10KO) mice. Edema, which was quantified macroscopically by measuring the vascular leakage of Evans blue dye at 4 h after IC challenge, was significantly increased in IL-10KO mice compared with wild-type mice. In addition, hemorrhage, which was assessed by the average diameter of purpuric spots at 8 h after IC challenge, was enhanced significantly in IL-10KO mice compared with wild-type mice. Histological examination showed that the number of extravascular neutrophils was significantly increased in IL-10KO mice compared with wild-type mice at 4 and 8 h after IC challenge. Analysis of pro-inflammatory cytokine mRNA expression showed that IL-6 mRNA levels were significantly increased in IL-10KO mice compared with wild-type mice at 4 and 8 h after IC challenge. These results showed that IC-induced inflammation and vascular damage were significantly enhanced in the absence of IL-10. Thus, IL-10 may limit tissue disruption by suppressing the excessive infiltration of neutrophils and cytokine expression in a mouse model of type III vasculitis.

The reversed passive Arthus reaction as a model for investigating the mechanisms of inflammation-associated hemostasis

In recent years, accumulating evidence has indicated that platelets continuously repair vascular damage at sites of inflammation and/or infection. Studies in mouse models of inflammation have highlighted the fact that the mechanisms underlying bleeding prevention by platelets in inflamed organs can substantially differ from those supporting primary hemostasis following tail tip transection or thrombus formation in models of thrombosis. As a consequence, exploration of the hemostatic function of platelets in inflammation, as well as assessment of the risk of inflammation-induced bleeding associated with a platelet deficit and/or the use of anti-thrombotic drugs, require the use of dedicated experimental models. In the present review, we present the pros and cons of the cutaneous reversed passive Arthus reaction, a model of inflammation which has been instrumental in studying how inflammation causes vascular injury and how platelets continuously intervene to repair it. The limitations and common issues encountered when working with mouse models of inflammation for investigating platelet functions in inflammation are also discussed.

In vivo migration of Fe3O4@polydopamine nanoparticle-labeled mesenchymal stem cells to burn injury sites and their therapeutic effects in a rat model

Mesenchymal stem cell (MSC)-based therapy has emerged as a promising therapeutic strategy for tissue regeneration and repair. However, efficient targeted delivery to specific tissues remains an open challenge. Here, we non-invasively monitored the migration of MSCs labeled with Fe3O4@polydopamine nanoparticles (Fe3O4@PDA NPs) toward laser burn injury sites in a living rat model and evaluated the effects of the labeled MSCs at the injury site. The Fe3O4@PDA NPs could be effectively incorporated into the MSCs without any negative effects on stem cell properties. Furthermore, they enhanced the migration ability of the MSCs by up-regulating the expression level of C-X-C chemokine receptor type 4 (CXCR4). They also increased the secretion of some cytokines and the expression of healing-related genes in comparison with unlabeled MSCs. Labeled MSCs were intravenously administered into injured rats, and live imaging was performed to monitor MSC migration. Fluorescent signals of the labeled MSCs appeared at burn injury lesions 1 day after injection and then gradually increased up to 7 days. After 7 days, the group injected with the labeled MSCs showed less inflammation compared with those injected with the unlabeled MSCs. Additionally, the labeled MSC group showed increased cytokines and reduced pro-inflammatory factors compared with the unlabeled MSC group. The Fe3O4@PDA NPs enhanced stromal cell-derived factor-1/CXCR4-mediated MSC migration in vivo. Thus, we demonstrated the safety, feasibility, and potential efficacy of using the Fe3O4@PDA NPs for optimizing MSC-based therapeutic strategies for burn wound healing.

Sphingosine 1-Phosphate Receptor 1 Signaling Maintains Endothelial Cell Barrier Function and Protects Against Immune Complex-Induced Vascular Injury

OBJECTIVE

Immune complex (IC) deposition activates polymorphonuclear neutrophils (PMNs), increases vascular permeability, and leads to organ damage in systemic lupus erythematosus and rheumatoid arthritis. The bioactive lipid sphingosine 1-phosphate (S1P), acting via S1P receptor 1 (S1P₁ ), is a key regulator of endothelial cell (EC) barrier function. This study was undertaken to investigate whether augmenting EC integrity via S1P₁ signaling attenuates inflammatory injury mediated by ICs.

METHODS

In vitro barrier function was assessed in human umbilical vein endothelial cells (HUVECs) by electrical cell-substrate impedance sensing. Phosphorylation of myosin light chain 2 (p-MLC-2) and VE-cadherin staining in HUVECs were assessed by immunofluorescence. A reverse Arthus reaction (RAR) was induced in the skin and lungs of mice with S1P₁ deleted from ECs (S1P₁ EC-knockout [ECKO] mice) and mice treated with S1P₁ agonists and antagonists.

RESULTS

S1P₁ agonists prevented loss of barrier function in HUVECs treated with IC-activated PMNs. S1P₁ ECKO and wild-type (WT) mice treated with S1P₁ antagonists had amplified RAR, whereas specific S1P₁ agonists attenuated skin and lung RAR in WT mice. ApoM-Fc, a novel S1P chaperone, mitigated EC cell barrier dysfunction induced by activated PMNs in vitro and attenuated lung RAR. Expression levels of p-MLC-2 and disruption of VE-cadherin, each representing manifestations of cell contraction and destabilization of adherens junctions, respectively, that were induced by activated PMNs, were markedly reduced by treatment with S1P₁ agonists and ApoM-Fc.

CONCLUSION

Our findings indicate that S1P₁ signaling in ECs modulates vascular responses to IC deposition. S1P₁ agonists and ApoM-Fc enhance the EC barrier, limit leukocyte escape from capillaries, and provide protection against inflammatory injury. The S1P/S1P₁ axis is a newly identified target to attenuate tissue responses to IC deposition and mitigate end-organ damage.

Molecular imaging reveals time course of matrix metalloproteinase activity in acute cutaneous vasculitis in vivo

Matrix metalloproteinases (MMPs) play a critical role in various pathological conditions including cutaneous inflammation. Thus far, serial assessment of MMP activity in ongoing inflammation is hampered due to technical limitations. Here, we present an innovative method for longitudinal detection of MMP activity by in vivo imaging. First, we analysed skin sections from patients suffering from leucocytoclastic vasculitis (LcV) and detected a significant MMP signal via immunofluorescence staining. Then, we mimicked LcV in mice in a well-studied model of immune complex-mediated vasculitis (ICV). This acute inflammatory process was serially visualized in vivo using the fluorescence-labelled MMP tracer Cy5.5-AF443. The deposition of fluorescence-labelled immune complexes and MMP tracer distribution was visualized repeatedly and non-invasively by fluorescence reflectance imaging. In correlation with the presence of MMP-2 and MMP-9 in immunofluorescence stainings, Cy5.5-AF443 accumulated in ICV spots in the skin of C57BL/6 mice. This tracer accumulation could also be observed in mice equipped with a dorsal skinfold chamber, where microscopic observations revealed an increased recruitment of fluorescence-labelled leucocytes during ICV. The specificity of the MMP tracer was supported by (i) analysis of mice deficient in functional β2 -integrins (CD18(-/-) ) and (ii) subsequent MMP immunofluorescence staining. These findings let us conclude that MMP accumulation in the acute phase of ICV depends on β2 -mediated leucocyte recruitment. In summary, we show that MMPs are involved in ICV as determined by Cy5.5-AF443, a new optical marker to longitudinally and non-invasively follow MMP activity in acute skin inflammation in vivo.

A crucial role of L-selectin in C protein-induced experimental polymyositis in mice

OBJECTIVE

To investigate the role of adhesion molecules in C protein-induced myositis (CIM), a murine model of polymyositis (PM).

METHODS

CIM was induced in wild-type mice, L-selectin-deficient (L-selectin(-/-) ) mice, intercellular adhesion molecule 1 (ICAM-1)-deficient (ICAM-1(-/-) ) mice, and mice deficient in both L-selectin and ICAM-1 (L-selectin(-/-) ICAM-1(-/-) mice). Myositis severity, inflammatory cell infiltration, and messenger RNA expression in the inflamed muscles were analyzed. The effect of dendritic polyglycerol sulfate, a synthetic inhibitor that suppresses the function of L-selectin and endothelial P-selectin, was also examined.

RESULTS

L-selectin(-/-) mice and L-selectin(-/-) ICAM-1(-/-) mice developed significantly less severe myositis compared to wild-type mice, while ICAM-1 deficiency did not inhibit the development of myositis. L-selectin(-/-) mice that received wild-type T cells developed myositis. Treatment with dendritic polyglycerol sulfate significantly diminished the severity of myositis in wild-type mice compared to treatment with control.

CONCLUSION

These data indicate that L-selectin plays a major role in the development of CIM, whereas ICAM-1 plays a lesser role, if any, in the development of CIM. L-selectin-targeted therapy may be a candidate for the treatment of PM.

Blocking von Willebrand factor for treatment of cutaneous inflammation

Von Willebrand factor (VWF), a key player in hemostasis, is increasingly recognized as a proinflammatory protein. Here, we found a massive accumulation of VWF in skin biopsies of patients suffering from immune complex (IC)-mediated vasculitis (ICV). To clarify the impact of VWF on cutaneous inflammation, we induced experimental ICV either in mice treated with VWF-blocking antibodies or in VWF(-/-) mice. Interference with VWF led to a significant inhibition of the cutaneous inflammatory response. We confirmed the major findings in irritative contact dermatitis, a second model of cutaneous inflammation. In vivo imaging of cutaneous inflammation in the dorsal skinfold chamber revealed unaffected leukocyte rolling on anti-VWF treatment. However, we identified that reduced leukocyte recruitment is accompanied by reduced vascular permeability. Although VWF-mediated neutrophil recruitment to the peritoneum was described to require the VWF receptor on platelets (glycoprotein Ibα (GPIbα)), the VWF/GPIbα axis was dispensable for cutaneous inflammation. As assessed in tail bleeding assays, we could exclude interference of VWF blockade with hemostasis. Of particular importance, anti-VWF treatment was effective both in prophylactic and therapeutic administration. Thus, VWF represents a promising target for the treatment of cutaneous inflammation, e.g., leukocytoclastic vasculitis.

Neutrophils in local and systemic antibody-dependent inflammatory and anaphylactic reactions

Neutrophils are notorious for their efficacy in microbial killing. Various mechanisms, such as phagocytosis, production of ROS, cytokines/chemokines and lipid mediators, degranulation of antimicrobials and enzymes, as well as NETosis contribute to this capacity. However, every incidence of neutrophil activation bears a risk to cause damage to the host. Several distinct steps, i.e., adhesion to endothelial cells, transmigration, chemotaxis, cytokine stimulation, and TLR signaling, are thought to control the extent of neutrophil activation. In the absence of a microbial stimulus, other pathways can induce neutrophil activation, among which FcR-induced activation when neutrophils encounter ICs. In these situations (inflammation, autoimmunity, allergy), neutrophils may act as primary or secondary effectors of immune reactions. In the presence of circulating ICs, neutrophils can indeed get stimulated directly in the bloodstream and trigger an immune response. Upon deposition of antibody complexes inside of tissues, neutrophils are first recruited and primed before being highly activated to amplify the ongoing inflammation. This review focuses on the engagement, activation, and responses of neutrophils to antibody ICs, inside of tissues or in the vasculature.

Interaction between CX3CL1 and CX3CR1 regulates vasculitis induced by immune complex deposition

A type III hypersensitivity reaction induced by an immune complex, such as leukocytoclastic vasculitis, is mediated by inflammatory cell infiltration that is highly regulated by multiple adhesion molecules. CX3CL1, a ligand for CX3C chemokine receptor 1 (CX3CR1), has recently been identified as a key mediator of leukocyte adhesion that functions without the recruitment of integrins or selectin-mediated rolling. To elucidate the role of CX3CL1 and CX3CR1 in the development of leukocytoclastic vasculitis, the cutaneous and peritoneal reverse Arthus reactions, classic experimental models for immune complex-mediated tissue injury, were examined in mice lacking CX3CR1. CX3CL1 expression in sera and lesional skin of patients with polyarteritis nodosa (PN) and healthy controls was also examined. Edema and hemorrhage were significantly reduced in CX3CR1(-/-) mice compared with wild-type mice. Infiltration of neutrophils and mast cells and expression of IL-6 and tumor necrosis factor-α were also decreased in CX3CR1(-/-) mice. CX3CL1 was expressed in endothelial cells during the cutaneous reverse Arthus reactions. Furthermore, serum CX3CL1 levels were significantly higher in patients with PN than in healthy controls. Endothelial cells in lesional skin of patients with PN strongly expressed CX3CL1. These results suggest that interactions between CX3CL1 and CX3CR1 may contribute to the development of leukocytoclastic vasculitis by regulating neutrophil and mast cell recruitment and cytokine expression.

Exogenous application of hydrogen sulfide donor attenuates inflammatory reactions through the L-selectin-involved pathway in the cutaneous reverse passive Arthus reaction

H2S has been highlighted recently as an endogenous, gaseous signaling molecule, especially in inflammations. The deposition of IC induces an acute inflammatory response with tissue injury. To assess the roles of H2S in the IC-induced diseases, the cutaneous, reverse passive Arthus reaction was conducted using NaHS as a H2S donor. Furthermore, we conducted similar experiments using selectin(-/-) mice to determine the involvement of selectin molecules in the H2S-mediated pathway. Exogenous application of NaHS dramatically attenuated inflammatory reactions in WT mice associated with Arthus reaction. Namely, mRNA expressions of TNF-α, IFN-γ, and neutrophil numbers were reduced significantly in the lesional skins of NaHS-treated WT mice relative to untreated ones. NaHS treatment significantly reduced these three parameters in the lesional skins of E- and P-selectin(-/-) mice but not in those of L-selectin(-/-) mice. Quite similar results were obtained in the blocking study using WT mice injected with mAb to E-, P-, and L-selectin. Our results indicated that the exogenous application of NaHS attenuates inflammatory responses in reverse passive Arthus reaction through a L-selectin-involved pathway but not through E- or P-selectin pathways.

Isoflurane inhibits neutrophil recruitment in the cutaneous Arthus reaction model

PURPOSE

Neutrophil recruitment to the inflammatory sites is regulated by a variety of adhesion molecules including β2 integrins. The dependency of neutrophil recruitment on β2 integrins is variable in different tissues, but has not yet been verified in the cutaneous passive reverse Arthus reaction. We examined this question and also evaluated the impact of isoflurane on neutrophil recruitment to the skin because we previously showed in vitro that isoflurane binds and inhibits β2 integrins.

METHODS

The dependency on β2 integrins in neutrophil recruitment to the skin in the Arthus reaction was examined using αL, αM and β2 knockout mice. Then, we evaluated the effect of isoflurane on neutrophil recruitment to the skin. In addition, the effects of isoflurane on neutrophil binding to intercellular adhesion molecule-1 (ICAM-1), one of the β2 integrin ligands, were studied in vitro using cell adhesion assays.

RESULTS

Neutrophil recruitment to the skin in the Arthus reaction model was totally dependent on β2 integrins, as β2 knockout mice completely abolished it. However, the defect of only one of the β2 integrins was not sufficient to abolish neutrophil recruitment. Isoflurane reduced neutrophil recruitment to the skin by approximately 90 %. Also, isoflurane inhibited neutrophil adhesion to β2 integrin ligand ICAM-1.

CONCLUSIONS

We demonstrated that (1) neutrophil recruitment to the skin was totally dependent on β2 integrins, and (2) isoflurane significantly impaired neutrophil recruitment. Based on the previous studies on the contribution of other adhesion molecules in neutrophil recruitment, it is likely that isoflurane at least partially affects on β2 integrins in this model.

Basophils and mast cells play critical roles for leukocyte recruitment in IgE-mediated cutaneous reverse passive Arthus reaction

BACKGROUND

The pathogenic role of IgE has been implicated in a variety of allergic and inflammatory diseases. We have previously established an IgE-mediated cutaneous reverse passive Arthus model in which eosinophil infiltration is a prominent feature. This uniquely provides a model of type III hypersensitivity in which Fc classes of Ig that forms immune complex differentially determine the disease manifestation.

OBJECTIVE

To investigate the mechanisms of how mast cells and basophils regulate this IgE-mediated Arthus reaction.

METHODS

IgE-mediated cutaneous reverse passive Arthus reaction was induced in wild-type C57BL/6 or WBB6F1-+/+ mice and mast-cell-deficient WBB6F1-W/W(v) mice by intradermal injection of IgE anti-trinitrophenyl antibodies followed immediately by intravenous administration of trinitrophenyl bovine serum albumin. Basophils were depleted in vivo using anti-CD200R3 monoclonal antibody prior to the IC challenge.

RESULTS

Hemorrhage and infiltration of eosinophils, neutrophils, and basophils were significantly reduced but were not completely abrogated in WBB6F1-W/W(v) mice compared with those in wild-type WBB6F1-+/+ mice. Wild-type C57BL/6 mice treated by basophil-depleting mAb also showed significantly decreased hemorrhage and inflammatory cell infiltration, especially that of eosinophils, compared with control mice. Furthermore, basophil depletion in WBB6F1-W/W(v) mice led to nearly complete inhibition of eosinophil recruitment. By contrast, basophil depletion did not further decrease neutrophil infiltration in WBB6F1-W/W(v) mice.

CONCLUSION

While mast cells play a central role, basophils also have an important function, especially for eosinophil recruitment, in IgE-mediated cutaneous reverse passive Arthus reaction.

α-1-Antitrypsin and IFN-γ reduce the severity of IC-mediated vasculitis by regulation of leukocyte recruitment in vivo

IC-mediated vasculitis (ICV) can be life threatening. The cellular and immune mechanisms controlling ICV are poorly understood. Therefore, we investigated the role of α-1-antitrypsin (α1AT) and IFN-γ in reducing the severity of ICV in a mouse model in vivo. To induce ICV, mice were challenged with the reverse passive Arthus reaction (RPA), the prototypic in vivo model for leukocytoclastic vasculitis (LcV), and the modulation of vascular permeability, edema formation, and leukocyte recruitment was studied. To further analyze the dynamics of RPA, we applied intravital microscopy in the dorsal skinfold chamber. α1AT continuously led to reduced leukocyte recruitment. α1AT interfered with neutrophil recruitment through a KC-dependent mechanism and reduced KC-elicited neutrophil activation. In contrast to α1AT, IFN-γ-reduced leukocyte recruitment during RPA was clearly independent of KC. We also revealed that the recruitment of neutrophils during RPA was a prerequisite for full KC expression. Thus, therapeutic administration of α1AT and IFN-γ might be beneficial for limiting the duration and severity of ICV.

Platelets control leukocyte recruitment in a murine model of cutaneous arthus reaction

Platelets have been shown to be important in inflammation, but their role in the cutaneous Arthus reaction remains unclear. To assess the role of platelets in this pathogenetic process, the cutaneous Arthus reaction was examined in wild-type mice and mice lacking E-selectin, P-selectin, or P-selectin glycoprotein ligand-1 (PSGL-1) with or without platelet depletion by busulfan, a bone marrow precursor cell-specific toxin. Edema and hemorrhage induced by immune complex challenge significantly decreased in busulfan-treated wild-type mice compared with untreated mice. Busulfan treatment did not affect edema and hemorrhage in P-selectin- or PSGL-1-deficient mice, suggesting that the effect by busulfan is dependent on P-selectin and PSGL-1 expression. The inhibited edema and hemorrhage paralleled reduced infiltration of neutrophils and mast cells and reduced levels of circulating platelets. Increased cutaneous production of interleukin-6, tumor necrosis factor-alpha, and platelet-derived chemokines during Arthus reaction was inhibited in busulfan-treated wild-type mice relative to untreated mice, which paralleled the reduction in cutaneous inflammation. Flow cytometric analysis showed that immune complex challenge generated blood platelet-leukocyte aggregates that decreased by busulfan treatment. In thrombocytopenic mice, the cutaneous inflammation after immune complex challenge was restored by platelet infusion. These results suggest that platelets induce leukocyte recruitment into skin by forming platelet-leukocyte aggregates and secreting chemokines at inflamed sites, mainly through the interaction of P-selectin on platelets with PSGL-1 on leukocytes.

L-selectin: role in regulating homeostasis and cutaneous inflammation

The maintenance of immune surveillance and the generation of normal immune responses are dependent on leukocyte migration to appropriate lymphoid and non-lymphoid tissues. The process of leukocyte migration occurs through complex and highly regulated interactions between the circulating leukocytes and the vascular endothelium. Multiple families of adhesion molecules as well as specific chemoattractants and their cognate receptors function to stabilize these interactions and induce migration into the tissue. L-selectin is a key adhesion molecule that regulates both the migration of leukocytes at sites of inflammation and the recirculation of lymphocytes between blood and lymphoid tissues. L-selectin-mediated lymphocyte recirculation is required for maintaining the appropriate tissue distribution of lymphocyte subpopulations including naïve and effector subsets such as regulatory T cells. In addition, L-selectin-mediated entry into peripheral lymph nodes is required for optimal induction of lymphocyte homeostatic proliferation during lymphopenia. Importantly, L-selectin has been shown to have both adhesive and signaling functions during leukocyte migration. Specifically, L-selectin is highly efficient at capturing free-flowing leukocytes from the blood and supporting subsequent fast rolling interactions along the vascular endothelium. During rolling, synergistic interactions between L-selectin and integrin functions slow leukocyte rolling velocities allowing for chemoattractant-induced activation and eventual firm adhesion of the leukocyte to the vascular endothelium. Engagement of L-selectin by ligand generates transmembrane signals leading to activation of intracellular signaling pathways, increased integrin binding affinity, and enhanced chemotaxis. L-selectin has also been shown to mediate leukocyte recruitment during chronic inflammatory and autoimmune diseases and thus is a potential therapeutic target for drug development.

Establishment of experimental eosinophilic vasculitis by IgE-mediated cutaneous reverse passive arthus reaction

Prominent eosinophil infiltration is a characteristic of some forms of vasculitis, such as Churg-Strauss syndrome, also known as allergic granulomatous vasculitis. In the current study, we established a mouse model of cutaneous eosinophilic vasculitis by the cutaneous reverse passive Arthus reaction using IgE injection instead of IgG. Wild-type C57BL/6 mice were injected with IgE anti-trinitrophenyl antibodies, followed immediately by intravenous administration of trinitrophenyl bovine serum albumin. IgE-mediated immune complex challenge induced substantial hemorrhage with marked infiltration of eosinophils in which neutrophils, mast cells, and macrophages were also mixed. This finding contrasted remarkably with the neutrophil-dominant infiltration pattern in IgG-mediated immune complex challenge. In the lesion, the expression level of monocyte chemotactic protein-3 was increased, and anti-monocyte chemotactic protein-3 treatment resulted in a significant but incomplete blockade of eosinophil recruitment. Furthermore, mice lacking E-selectin, P-selectin, L-selectin, or intercellular adhesion molecule-1, as well as wild-type mice that received anti-vascular cell adhesion molecule-1-blocking antibodies were assessed for the IgE-mediated Arthus reaction. After 24 hours, the loss of P-selectin resulted in a significant reduction in eosinophil accumulation compared with both wild-type mice and other mouse mutants. Collectively, the Fc class of immunoglobulins, which forms these immune complexes, critically determines the disease manifestation of vasculitis. The IgE-mediated cutaneous reverse passive Arthus reaction may serve as an experimental model for cutaneous eosinophilic infiltration in vasculitis as well as in other diseases.

Involvement of gaseous low molecular monoxides in the cutaneous reverse passive Arthus reaction: cytoprotective action of carbon monoxide

The deposition of immune complexes (IC) induces an acute inflammatory response with tissue injury, for which the involvement of nitric oxide (NO) and carbon monoxide (CO) has been suggested. NO is induced by NO synthase (NOS) and CO is generated by haeme oxygenase (HO). Among HO isoenzymes, HO-1 is an induced type. To assess the role of NO and CO in the pathogenic process, the cutaneous reverse passive Arthus reaction was examined using NOS inhibitor, HO-1 stimulator and HO-1 inhibitor. To evaluate the reaction we considered oedema, tumour necrosis factor-alpha, interleukin-6, and neutrophil number. The values of these four parameters were significantly reduced in mice treated with HO-1 stimulator as compared with the positive control mice. Quite the reverse was observed in mice treated with HO-1 inhibitor. These results suggest that the HO-1/CO signalling pathway is a therapeutic target for human IC-mediated disease.

Intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 cooperatively contribute to the cutaneous Arthus reaction

Immune complex (IC)-induced inflammation is mediated by inflammatory cell infiltration, a process that is highly regulated by expression of multiple adhesion molecules. The roles and interactions of ICAM-1 and VCAM-1, the major regulators of leukocyte firm adhesion, were examined in the cutaneous reverse-passive Arthus reaction using ICAM-1-deficient (ICAM-1-/-) mice and blocking mAb against VCAM-1. Within 8 h, IC challenge of wild-type mice induced edema, hemorrhage, interstitial accumulation of neutrophils and mast cells, as well as production of TNF-alpha and IL-6. All of these inflammatory parameters were reduced significantly in ICAM-1-/- mice. The blockade of VCAM-1 in wild-type mice did not affect any inflammatory parameters. In contrast, ICAM-1-/- mice treated with anti-VCAM-1 mAb had significantly reduced edema, hemorrhage, and neutrophil infiltration. Furthermore, VCAM-1 blockade in ICAM-1-/- mice suppressed cutaneous TNF-alpha and IL-6 production. Thus, VCAM-1 plays a complementary role to ICAM-1 in the cutaneous Arthus reaction by regulating leukocyte accumulation and proinflammatory cytokine production.

Cutaneous vasculitis: diagnosis and management

Vasculitis is histologically defined as inflammatory cell infiltration and destruction of blood vessels. Vasculitis is classified as primary (idiopathic, eg, cutaneous leukocytoclastic angiitis, Wegener's granulomatosis) or secondary, a manifestation of connective tissue diseases, infections, adverse drug eruptions, or a paraneoplastic phenomenon. Cutaneous vasculitis, manifested as urticaria, purpura, hemorrhagic vesicles, ulcers, nodules, livedo, infarcts, or digital gangrene, is a frequent and often significant component of many systemic vasculitic syndromes such as lupus or rheumatoid vasculitis and antineutrophil cytoplasmic antibody-associated primary vasculitic syndromes such as Churg-Strauss syndrome. In most instances, cutaneous vasculitis represents a self-limited, single-episode phenomenon, the treatment of which consists of general measures such as leg elevation, warming, avoidance of standing, cold temperatures and tight fitting clothing, and therapy with antihistamines, aspirin, or nonsteroidal anti-inflammatory drugs. More extensive therapy is indicated for symptomatic, recurrent, extensive, and persistent skin disease or coexistence of systemic disease. For mild recurrent or persistent disease, colchicine and dapsone are first-choice agents. Severe cutaneous and systemic disease requires more potent immunosuppression (prednisone plus azathioprine, methotrexate, cyclophosphamide, cyclosporine, or mycophenolate mofetil). In cases of refractory vasculitis, plasmapheresis and intravenous immunoglobulin are viable considerations. The new biologic therapies that work via cytokine blockade or lymphocyte depletion such as tumor alpha inhibitor infliximab and the anti-B-cell antibody rituximab, respectively, are showing benefit in certain settings such as Wegener's granulomatosis, antineutrophil cytoplasmic antibody-associated vasculitis, Behçet's disease, and cryoglobulinemic vasculitis.

Regulation of local and metastatic host-mediated anti-tumour mechanisms by L-selectin and intercellular adhesion molecule-1

Malignant melanoma is often accompanied by a host response of inflammatory cell infiltration that is highly regulated by multiple adhesion molecules. To assess the role of adhesion molecules, including L-selectin and intercellular adhesion molecule-1 (ICAM-1), in this process, subcutaneous primary growth and metastasis to the lung of B16 melanoma cells not expressing L-selectin, ICAM-1 or their ligands were examined in mice lacking L-selectin, ICAM-1 or both. Primary subcutaneous growth of B16 melanoma was augmented by loss of L-selectin, ICAM-1 or both, while pulmonary metastasis was enhanced by the loss of L-selectin or combined loss of L-selectin and ICAM-1. In both situations, the combined loss of L-selectin and ICAM-1 exhibited the greatest effect. This enhancement was associated generally with a reduced accumulation of natural killer (NK) cells, CD4+ T cells and CD8+ T cells and also with a diminished release of interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha but not interleukin (IL)-6. Cytotoxicity against melanoma was not defective by the absence of ICAM-1, L-selectin or both, suggesting that the enhancement of tumour growth and metastasis caused by the loss of adhesion molecules results from an impaired migration of effector cells into the tissue rather than from a suppression of the cytotoxic response. The results indicate that L-selectin and ICAM-1 contribute co-operatively to the anti-tumour reaction by regulating lymphocyte infiltration to the tumour.

Cutaneous Vasculitis Update: Diagnostic Criteria, Classification, Epidemiology, Etiology, Pathogenesis, Evaluation and Prognosis

Vasculitis, inflammation of the vessel wall, can result in mural destruction with hemorrhage, aneurysm formation, and infarction, or intimal-medial hyperplasia and subsequent stenosis leading to tissue ischemia. The skin, in part due to its large vascular bed, exposure to cold temperatures, and frequent presence of stasis, is involved in many distinct as well as un-named vasculitic syndromes that vary from localized and self-limited to generalized and life-threatening with multi-organ disease. To exclude mimics of vasculitis, diagnosis of cutaneous vasculitis requires biopsy confirmation where its acute signs (fibrinoid necrosis), chronic signs (endarteritis obliterans), or past signs (acellular scar of healed arteritis) must be recognized and presence of extravascular findings such as patterned fibrosis or collagenolytic granulomas noted. Although vasculitis can be classified by etiology, many cases have no identifiable cause, and a single etiologic agent can elicit several distinct clinicopathologic expressions of vasculitis. Therefore, the classification of cutaneous vasculitis is best approached morphologically by determining vessel size and principal inflammatory response. These histologic patterns roughly correlate with pathogenic mechanisms that, when coupled with direct immunofluorescent examination, anti-neutrophil cytoplasmic antibody (ANCA) status, and findings from work-up for systemic disease, allow for specific diagnosis, and ultimately, more effective therapy. Herein, we review cutaneous vasculitis focusing on diagnostic criteria, classification, epidemiology, etiology, pathogenesis, and evaluation of the cutaneous vasculitis patient.

Involvement of chemokines and type 1 cytokines in the pathogenesis of hepatitis C virus-associated mixed cryoglobulinemia vasculitis neuropathy

OBJECTIVE

To examine the expression profiles of a large number of genes within typical vasculitic nerve lesions in patients with mixed cryoglobulinemia (MC) vasculitis in order to better characterize the molecules involved in cellular tissue activation and trafficking.

METHODS

The quantitative expression of 19 genes coding for cytokines, chemokines, and their receptors in the nerve lesions of 9 patients with hepatitis C virus (HCV)-associated MC vasculitis, 7 with idiopathic polyarteritis nodosa (PAN) (rheumatic disease controls), and 8 patients with noninflammatory idiopathic neuropathy (noninflammatory neuropathy controls) was assessed using a real-time reverse transcriptase-polymerase chain reaction procedure.

RESULTS

Compared with the noninflammatory controls, HCV-MC vasculitis patients had a significantly higher expression of Th1 cytokines in vasculitic nerve lesions (mean +/- SEM fold increase 33.7 +/- 11.6 for interferon-gamma and 7.2 +/- 1.9 for tumor necrosis factor alpha), whereas Th2 cytokines were absent (interleukin-4 [IL-4], IL-5, and IL-13) or were not significantly different (IL-10). Chemokines involved in T cell and monocyte trafficking were also significantly up-regulated in the HCV-MC vasculitis patients (mean +/- SEM fold increase 27.4 +/- 8.3 for macrophage inflammatory protein 1alpha [MIP-1alpha], 19.9 +/- 5.7 for MIP-1beta, and 7.2 +/- 1.5 for CXCR3). Compared with patients with idiopathic PAN, there was a trend toward higher expression of MIP-1alpha and CXCR3 in HCV-MC vasculitis patients (mean +/- SEM fold increase 27.4 +/- 8.3 versus 5.3 +/- 3.4 for MIP-1alpha and 7.2 +/- 1.5 versus 2.5 +/- 0.9 for CXCR3).

CONCLUSION

This study is the first to demonstrate a role of cellular immunity and Th1 lymphocytes in the pathogenesis of HCV-MC vasculitic nerve lesions.

Manifestations of inflammatory arthritis are critically dependent on LFA-1

Leukocyte infiltration of synovial fluid and tissues is the hallmark of inflammatory arthritis. Selectins and beta2 integrins have been implicated in the multistep process of leukocyte adhesion to vascular endothelium. However, previous work has revealed disparate requirements for leukocyte recruitments to specific anatomic locales. Moreover, the mechanisms regulating recruitment of leukocytes to the joint in inflammatory arthritis models are not fully understood. We hypothesized that beta2 integrins, expressed on leukocytes, might play a pathogenic role in synovial inflammation. Using mice deficient in all beta2 integrins (CD18 null mice), we demonstrate that expression of these heterodimeric adhesion molecules is critical for arthritis induction in the K/B x N serum transfer model. Using null-allele mice and blocking mAbs, we demonstrate specifically that CD11a/CD18 (LFA-1) is absolutely required for the development of arthritis in this model. Blocking mAbs further revealed an ongoing requirement for LFA-1 I-domain adhesive function in disease perpetuation. These findings suggest that the LFA-1 I-domain forms an attractive target for treatment of human inflammatory arthritis.

Vascular cell adhesion molecule-1 (VCAM-1) plays a central role in the pathogenesis of severe forms of vasculitis due to hepatitis C-associated mixed cryoglobulinemia

BACKGROUND/AIMS

To better characterize the molecules involved in leukocyte tissue infiltration during hepatitis C-mixed cryoglobulinemia (HCV-MC)-associated vasculitis.

METHODS

The involvement of ELAM, ICAM-1 and VCAM-1 was evaluated in 36 patients with HCV-MC vasculitis using three different approaches: concentrations of soluble forms by specific ELISA, tissue expression by immunohistochemistry on patients nerve biopsies, endothelial expression by FACS analysis, on cells activated in vitro by cryoprecipitates purified from HCV-MC patients.

RESULTS

Concentrations of sVCAM-1 were significantly elevated in the serum of HCV-MC patients compared to HCV patients without MC, the highest concentrations being found in severe vasculitis. VCAM-1 expression was detected on blood vessels from nerve biopsies performed in patients with severe vasculitis. When added to endothelial cells in vitro, HCV-MC patients cryoprecipitate induced VCAM-1 but also ELAM and ICAM-1 expression possibly through a mechanism due to the C1q complement fraction interaction with endothelial cells, since C1q was consistently present in the cryoprecipitates.

CONCLUSIONS

VCAM-1 is mainly involved in the pathogenesis of HCV-MC-associated severe vasculitis and may be a potential interesting therapeutic target.

Tumor necrosis factor-alpha up-regulates the expression of beta1,4-galactosyltransferase I in primary human endothelial cells by mRNA stabilization

During the course of an inflammatory response, the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFalpha) triggers endothelial cells to increase the expression levels of adhesion molecules that are pivotal for the rolling, adhesion, and transmigration of leukocytes over the endothelial cell wall. Here we show that TNFalpha, in addition, has a regulatory function in the biosynthesis of proper carbohydrate molecules on endothelial cells that constitute ligands for adhesion molecules on leukocytes. Our data show that TNFalpha induced an increase in the expression of beta1,4-galactosyltransferase-1 (beta4GalT-1) in primary human umbilical vein endothelial cells in a time- and concentration-dependent manner. The beta4GalT-1 mRNA up-regulation correlated with an increase in the Golgi expression and catalytic activity of the enzyme. Furthermore, an enhanced incorporation of galactose was observed in newly synthesized glycoproteins. Analysis of the molecular mechanism behind the up-regulation of beta4GalT-1 showed that the increase in mRNA levels is due to an enhanced stability of the transcripts. These data strongly demonstrate that TNFalpha modulates the glycosylation of endothelial cells by a mechanism that directly enhances the stability of beta4GalT-1 mRNA transcripts.

Role of C-C chemokine receptors?1 and?5 and CCL3/macrophage inflammatory protein-1? in the cutaneous Arthus reaction: possible attenuation of their inhibitory effects by compensatory chemokine production

The deposition of immune complexes induces an acute inflammatory response with tissue injury. Immune complex-induced tissue injury is mediated by inflammatory cell infiltration that is highly regulated by multiple chemokines. To assess the role of the chemokine receptors CCR1 and CCR5, and a ligand for these receptors CCL3/macrophage inflammatory protein-1alpha, in this pathogenic process, the reverse passive cutaneous Arthus reaction was induced in mice lacking CCR1, CCR5, or CCL3. Edema was significantly attenuated in CCR1-deficient (CCR1(-/-)) and CCL3(-/-) mice but not CCR5(-/-) mice, compared with wild-type mice. Numbers of infiltrating neutrophils and mast cells were reduced in CCL3(-/-) and CCR1(-/-) mice, respectively, compared with wild-type mice. CCR1 and CCR5 were expressed on neutrophils and mast cells. Remarkably, the intradermal mRNA expression of CCL5/RANTES, another ligand for CCR1 and CCR5, was increased in CCR5(-/-) and CCL3(-/-) mice, compared with wild-type mice, while the cutaneous CCL3 mRNA expression was augmented in CCR1(-/-) and CCR5(-/-) mice. These results indicate that CCR1, CCR5, and CCL3 cooperatively contribute to the cutaneous Arthus reaction, and also suggest that enhanced expression of CCL3 and CCL5 compensates for the loss of CCR1, CCR5, and CCL3 in the reaction.

Expression of L-selectin, but not CD44, is required for early neutrophil extravasation in antigen-induced arthritis

L (leukocyte)-selectin (CD62L) and CD44 are major adhesion receptors that support the rolling of leukocytes on endothelium, the first step of leukocyte entry into inflamed tissue. The specific contribution of L-selectin or CD44 to the regulation of cell traffic to joints in arthritis has not been investigated. We used CD44-deficient, L-selectin-deficient, and CD44/L-selectin double knockout mice to determine the requirement for these receptors for inflammatory cell recruitment during Ag-induced arthritis. Intraperitoneal immunization resulted in similar activation status and Ag-specific responses in wild-type and gene-targeted mice. However, extravasation of neutrophil granulocytes, but not the emigration of T cells, into the knee joints after intra-articular Ag injection was significantly delayed in L-selectin-deficient and double knockout mice. Intravital videomicroscopy on the synovial microcirculation revealed enhanced leukocyte rolling and diminished adherence in mice lacking either CD44 or L-selectin, but CD44 deficiency had no significant effect on the recruitment of L-selectin-null cells. Compared with wild-type leukocytes, expression of L-selectin was down-regulated in CD44-deficient cells in the spleen, peripheral blood, and inflamed joints, suggesting that reduced expression of L-selectin, rather than the lack of CD44, could be responsible for the delayed influx of granulocytes into the joints of CD44-deficient mice. In conclusion, there is a greater requirement for L-selectin than for CD44 for neutrophil extravasation during the early phase of Ag-induced arthritis.

P-selectin glycoprotein ligand-1 is required for the development of cutaneous vasculitis induced by immune complex deposition

Immune complex (IC)-induced tissue injury is mediated by inflammatory cell infiltration that is highly regulated by various adhesion molecules. To assess the contribution of P-selectin glycoprotein ligand-1 (PSGL-1) and selectins in the pathogenetic process, the cutaneous reverse-passive Arthus reaction was examined in mice treated with monoclonal antibodies (mAb) to PSGL-1 or P- and/or E-selectin. Edema and hemorrhage were significantly reduced in mice treated with anti-P-selectin mAb compared with control mice while they were not inhibited in mice treated with anti-E-selectin mAb. It is remarkable that blocking PSGL-1 by mAb resulted in significant, further reduction in edema and hemorrhage compared with blocking anti-P- or anti-E-selectin. However, blockade of E- and P-selectins exhibited more significant reduction relative to PSGL-1 blockade. The inhibited edema and hemorrhage paralleled reduced infiltration of neutrophils and mast cells. Reduced infiltration of neutrophils and mast cells was observed in the peritoneal Arthus reaction and was associated with the decreased production of tumor necrosis factor alpha and interleukin-6. The results of this study indicate that PSGL-1 contributes to the Arthus reaction mainly as a ligand of P-selectin and partly as a ligand of E- and/or L-selectin by regulating neutrophil and mast-cell recruitment and that PSGL-1 would be a therapeutic target for human IC-mediated diseases.

Overlapping roles of endothelial selectins and vascular cell adhesion molecule-1 in immune complex-induced leukocyte recruitment in the cremasteric microvasculature

Many adhesion molecule pathways have been invoked as mediating leukocyte recruitment during immune complex-induced inflammation. However the individual roles of these molecules have not been identified via direct visualization of an affected microvasculature. Therefore, to identify the specific adhesion molecules responsible for leukocyte rolling and adhesion in immune complex-dependent inflammation we used intravital microscopy to examine postcapillary venules in the mouse cremaster muscle. Wild-type mice underwent an intrascrotal reverse-passive Arthus model of immune complex-dependent inflammation and subsequently, leukocyte-endothelial cell interactions and P- and E-selectin expression were assessed in cremasteric postcapillary venules. At 4 hours, the reverse-passive Arthus response induced a significant reduction in leukocyte rolling velocity and significant increases in adhesion and emigration. P-selectin expression was increased above constitutive levels whereas E-selectin showed a transient induction of expression peaking between 2.5 to 4 hours and declining thereafter. While E-selectin was expressed, rolling could only be eliminated by combined blockade of P- and E-selectin. However, by 8 hours, all rolling was P-selectin-dependent. In contrast, inhibition of vascular cell adhesion molecule-1 had a minimal effect on leukocyte rolling, but significantly reduced both adhesion and emigration. These observations demonstrate that immune complex-mediated leukocyte recruitment in the cremaster muscle involves overlapping roles for the endothelial selectins and vascular cell adhesion molecule-1.

Ultraviolet light exposure suppresses contact hypersensitivity by abrogating endothelial intercellular adhesion molecule-1 up-regulation at the elicitation site

Hapten sensitization through UV-exposed skin induces systemic immune suppression, which is experimentally demonstrated by inhibition of contact hypersensitivity (CHS). Although this UV-induced effect has been shown to be mediated by inhibition of the afferent phase of the CHS, the UV effects on the efferent (elicitation) phase remain unknown. In this study, UV effects on endothelial ICAM-1 expression at elicitation sites were first examined. Mice were sensitized by hapten application onto UV-exposed back skin, and ears were challenged 5 days later. ICAM-1 up-regulation at nonirradiated elicitation sites following hapten challenge was eliminated by UV exposure on sensitization sites distant from elicitation sites. To assess whether loss of the ICAM-1 up-regulation at elicitation sites contributed to UV-induced immunosuppression, we examined CHS responses in UV-exposed ICAM-1-deficient (ICAM-1(-/-)) mice that genetically lacked the ICAM-1 up-regulation. ICAM-1(-/-) mice exhibited reduced CHS responses without UV exposure, but UV exposure did not further reduce CHS responses in ICAM-1(-/-) mice. Furthermore, ICAM-1 deficiency did not affect the afferent limb, because ICAM-1(-/-) mice had normal generation of hapten-specific suppressor and effector T cells. This UV-induced immunosuppression was associated with a lack of TNF-alpha production after Ag challenge at elicitation sites. Local TNF-alpha injection before elicitation abrogated the UV-induced CHS inhibition with increased endothelial ICAM-1 expression. TNF-alpha production at elicitation sites was down-regulated by IL-10, a possible mediator produced by hapten-specific suppressor T cells that are generated by UV exposure. These results indicate that UV exposure inhibits CHS by abrogating up-regulation of endothelial ICAM-1 expression after Ag challenge at elicitation sites.

Relative contributions of selectins and intercellular adhesion molecule-1 to tissue injury induced by immune complex deposition

Immune complex-induced tissue injury is mediated by inflammatory cell infiltration that is highly regulated by multiple adhesion molecules. To assess the relative contribution of adhesion molecules, including selectins and ICAM-1, in this pathogenetic process, the cutaneous passive Arthus reaction was examined in mice lacking E-selectin, P-selectin, or both L-selectin and ICAM-1 with anti-P- or E-selectin mAbs. Edema and hemorrhage were significantly reduced in P-selectin(-/-) mice compared with wild-type mice while they were not inhibited in E-selectin(-/-) mice. Combined E- and P-selectin blockade resulted in more significant reduction relative to L-selectin/ICAM-1(-/-) as well as P-selectin(-/-) mice. Remarkably, both E- and P-selectin blockade in L-selectin/ICAM-1(-/-) mice completely abrogated edema and hemorrhage. The inhibited edema and hemorrhage paralleled reduced infiltration of neutrophils and mast cells that expressed significant levels of P-selectin glycoprotein ligand-1. Similarly reduced infiltration of neutrophils and mast cells was observed in the peritoneal Arthus reaction and was associated partly with the decreased production of tumor necrosis factor-alpha and interleukin-6. The results of this study indicate that both endothelial selectins contribute predominantly to the Arthus reaction by regulating mast cell and neutrophil infiltration and that the full development of the Arthus reaction is mediated cooperatively by all selectins and ICAM-1.

A peptide derived from the parasite receptor, complement C2 receptor inhibitor trispanning, suppresses immune complex-mediated inflammation in mice

Complement C2 receptor inhibitor trispanning (CRIT) is a Schistosoma protein that binds the human complement protein, C2. We recently showed that peptides based on the ligand binding region of CRIT inhibit the classical pathway (CP) of complement activation in human serum, using hemolytic assays and so speculated that on the parasite surface CRIT has the function of evading human complement. We now show that in vitro the C2-binding 11-aa C terminus of the first extracellular domain of CRIT, a 1.3-kDa peptide termed CRIT-H17, inhibits CP activation in a species-specific manner, inhibiting mouse and rat complement but not that from guinea pig. Hitherto, the ability of CRIT to regulate complement in vivo has not been assessed. In this study we show that by inhibiting the CP, CRIT-H17 is able to reduce immune complex-mediated inflammation (dermal reversed passive Arthus reaction) in BALB/c mice. Upon intradermal injection of CRIT-H17, and similarly with recombinant soluble complement receptor type 1, there was a 41% reduction in edema and hemorrhage, a 72% reduction in neutrophil influx, and a reduced C3 deposition. Furthermore, when H17 was administered i.v. at a 1 mg/kg dose, inflammation was reduced by 31%. We propose that CRIT-H17 is a potential therapeutic agent against CP complement-mediated inflammatory tissue destruction.

L-selectin or ICAM-1 deficiency reduces an immediate-type hypersensitivity response by preventing mast cell recruitment in repeated elicitation of contact hypersensitivity

Repeated Ag exposure results in a shift in the time course of contact hypersensitivity (CH) from a typical delayed-type to an immediate-type response followed by a late phase reaction. Chronic CH responses are clinically relevant to human skin allergic diseases, such as atopic dermatitis, that are usually caused by repeated stimulation with environmental Ags. Chronic inflammatory responses result in part from infiltrating leukocytes. To determine the role of leukocyte adhesion molecules in chronic inflammation, chronic CH responses were assessed in mice lacking L-selectin, ICAM-1, or both adhesion molecules. Following repeated hapten sensitization for 24 days at 2-day intervals, wild-type littermates developed an immediate-type response at 30 min after elicitation, followed by a late phase reaction. By contrast, loss of ICAM-1, L-selectin, or both, eliminated the immediate-type response and inhibited the late phase reaction. Similar results were obtained when wild-type littermates repeatedly exposed to hapten for 22 days were treated with mAbs to L-selectin and/or ICAM-1 before the elicitation on day 24. The lack of an immediate-type response on day 24 paralleled a lack of mast cell accumulation after 30 min of elicitation and decreased serum IgE production. Repeated Ag exposure in wild-type littermates resulted in increased levels of serum L-selectin, a finding also observed in atopic dermatitis patients. The current study demonstrates that L-selectin and ICAM-1 cooperatively regulate the induction of the immediate-type response by mediating mast cell accumulation into inflammatory sites and suggests that L-selectin and ICAM-1 are potential therapeutic targets for regulating human allergic reactions.