Cytokines and adhesion molecules in the pathogenesis of vasculitis

Ovalbumin/lipopolysaccharide induced vasculitis in rats: a new predictive model

OBJECTIVES

Currently, there are several animal models for vasculitis. Ovalbumin and lipopolysaccharide (OVA, LPS) are well established for causing inflammation and used as an adjunct in the vasculitis induction. However, to date, none has established the effect of OVA and LPS in disease induction. Therefore, in the present study, an attempt has been made to develop a new animal model for vasculitis using OVA/LPS in rats.

METHODS

A total of 42 Wistar rats were divided randomly into seven groups (n=6/group), normal control, and three different doses (0.5, 1, and 5 mg/kg) of OVA and LPS treated groups. Half of the rats in each group received only intraperitoneal sensitization, while the remaining half rats were additionally subjected to a one-week intranasal challenge.

RESULTS

Results showed that both OVA/LPS in their respective groups have significantly increased circulating inflammatory cells, C-reactive protein (CRP), Inflammatory cytokines (IL-1β, IL-6, TNF-α), Kidney damage markers (BUN, Creatinine), and liver function enzymes (AST, ALT) in a dose-dependent manner.

CONCLUSIONS

OVA/LPS induced vascular inflammation in a dose-dependent manner. However, the higher (5 mg/kg) dose of ovalbumin and lipopolysaccharide has contributed to severe vascular inflammation through increasing inflammatory cytokines. These findings suggest that OVA/LPS may contribute as a possible model for vasculitis in rats.

The effects of anthrax lethal toxin on host barrier function

The pathological actions of anthrax toxin require the activities of its edema factor (EF) and lethal factor (LF) enzyme components, which gain intracellular access via its receptor-binding component, protective antigen (PA). LF is a metalloproteinase with specificity for selected mitogen-activated protein kinase kinases (MKKs), but its activity is not directly lethal to many types of primary and transformed cells in vitro. Nevertheless, in vivo treatment of several animal species with the combination of LF and PA (termed lethal toxin or LT) leads to morbidity and mortality, suggesting that LT-dependent toxicity is mediated by cellular interactions between host cells. Decades of research have revealed that a central hallmark of this toxicity is the disruption of key cellular barriers required to maintain homeostasis. This review will focus on the current understanding of the effects of LT on barrier function, highlighting recent progress in establishing the molecular mechanisms underlying these effects.

Elevated serum levels of macrophage migration inhibitory factor and their significant correlation with rheumatoid vasculitis disease activity

Macrophage migration inhibitory factor (MIF) is recognized to be an important mediator in several inflammatory disorders, including rheumatoid arthritis (RA) and vasculitis. To evaluate the role of MIF in rheumatoid vasculitis (RV), we determined serum levels of MIF by enzyme-linked immunosorbent assay in RA patients with and without vasculitis and assessed their relationship to disease activity. Serum was obtained from 95 RA patients during active disease states [49 without vasculitis, 35 with extra-articular manifestations without histologically proven vasculitis, and 11 with histologically proven vasculitis] and from 22 healthy individuals. Vasculitis disease activity was assessed using the Birmingham Vasculitis Activity Score (BVAS). MIF levels were significantly higher in RA patients than in controls. Moreover, MIF levels were significantly higher in RA patients with vasculitis than in those without vasculitic complications. In all RA patients, a statistically significant positive correlation was observed between serum MIF levels and each of the following: serum levels of C-reactive protein, rheumatoid factor, and thrombomodulin; and the erythrocyte sedimentation rate. In the RV group, the elevation of MIF levels correlated with the BVAS. Our findings suggest that MIF may serve as an additional serologic inflammatory marker of disease activity in RV, and it may be implicated in the pathogenesis of RV.

Macrophage migration inhibitory factor: a multifunctional cytokine in rheumatic diseases

Macrophage migration inhibitory factor (MIF) was originally identified in the culture medium of activated T lymphocytes as a soluble factor that inhibited the random migration of macrophages. MIF is now recognized to be a multipotent cytokine involved in the regulation of immune and inflammatory responses. Moreover, the pivotal nature of its involvement highlights the importance of MIF to the pathogenesis of various inflammatory disorders and suggests that blocking MIF may be a useful therapeutic strategy for treating these diseases. This paper discusses the function and expressional regulation of MIF in several rheumatic diseases and related conditions.

Increased serum levels of macrophage migration inhibitory factor (MIF) in patients with microscopic polyangiitis

OBJECTIVE

To test the hypothesis that macrophage migration inhibitory factor (MIF) is involved in the disease activity of systemic vasculitis.

METHODS

Patients with systemic vasculitis were divided into three groups based on the size of the affected vessels. Microscopic polyangiitis (MPA) was considered as small vessel vasculitis (SVV), polyarteritis nodosa as medium-sized vessel vasculitis (MVV), and giant cell arteritis and Takayasu arteritis as large vessel vasculitis (LVV). Sera from patients with systemic vasculitis and healthy individuals were collected, and MIF levels were measured using an enzyme-linked immunosorbent assay. Disease activity of vasculitis was assessed using the Birmingham Vasculitis Activity Score (BVAS).

RESULTS

Serum MIF levels were significantly higher in the vasculitis patients than in healthy individuals. Among the vasculitis patients, MIF levels were significantly higher in patients in the SVV group (median; 4161.7 pg/ml) than in the other groups (MVV; 1443.2 pg/ml and LVV; 1576.7 pg/ml). In patients with MPA, a positive correlation was observed between serum MIF levels and CRP levels and disease activity (BVAS). Notably, serum MIF levels were significantly diminished after clinical improvement.

CONCLUSIONS

Our findings suggest that MIF may have an important role in small vessel vasculopathy and serve as a useful serologic marker of MPA disease activity.

Role of interleukin-6 in a glucan-induced model of granulomatous vasculitis

The role of interleukin-6 (IL-6) in granulomatous vasculitis is not well understood. To investigate its involvement in this type of vasculitis a model of glucan-induced pulmonary vasculitis employed interleukin-6 deficient (IL-6-/-) mice. Briefly, IL-6-/- mice and C57B/J6 wild type (IL-6+/+) mice were injected intravenously with a suspension of glucan isolated from the cell wall of bakers yeast which results in a granulomatous vasculitis primarily in the pulmonary vasculature. Histological examination demonstrated no significant difference in the number of infiltrating leukocytes between the IL-6+/+ and IL-6-/- glucan-injured mice. Similar numbers of granulomas were noted in both the IL-6+/+ and IL-6-/- injured animals, while no granulomas were seen in saline injected control mice. Cells recovered from the bronchoalveolar lavage (BAL) fluid were differentially stained and counted. While there was a significant increase in infiltrating leukocytes recovered from the BAL following glucan-induced injury, there was no significant difference between the IL-6+/+ and IL-6-/- mice. In addition, no difference was demonstrated in total protein content in the BAL fluid between IL-6+/+ and IL-6-/- mice. However, myeloperoxidase (MPO) activity in the lungs of the IL-6-/- mice was less than in their IL-6+/+ counterparts suggesting that these animals have a partial defect in their ability to recruit neutrophils in this model. Studies done to look for levels of other cytokines/chemokines in these animals to compensate for the loss of IL-6 revealed that only IL-10 in the sera (p<0.016) and BAL fluid (p<0.05) of IL-6-/- mice was significantly higher then their IL-6+/+-injured counterparts. These studies suggest that IL-6, while possibly involved in early neutrophil accumulation in this model does not appear critical to the development of the TH-2 mediated granulomatous vasculitis.

Role of interleukin-6 in immune complex induced models of vascular injury

Previous studies have suggested that Interleukin-6 (IL-6) acts as a marker of vasculitis. To determine the role of IL-6 in vasculitis we utilized two models of immune complex induced vascular injury (dermal Arthus and acute pulmonary alveolitis) in IL-6 deficient (IL-6(-/-)) and IL-6 sufficient (IL-6(+/+)) mice. Plasma and bronchoalveolar lavage (BAL) levels of IL-6 were elevated in the injured IL-6(+/+) mice with acute alveolitis and in the plasma of IL-6(+/+) mice with dermal Arthus vasculitis. While, IL-6 levels in IL-6(-/-) mice were near or below the levels of detection. Histological examination of the intensity of vascular injury response demonstrated no significant differences between IL-6(-/-) and IL6(+/+) mice. More specifically, lung permeability (total protein in the BAL) in the lung injury model in IL-6(-/-) mice was the same as injured IL-6(+/+) mice. As a corollary, assessment of vascular permeability in both models was the same in the IL-6(-/-) as the IL-6(+/+) mice. Quantification of leukocyte influx into the injured tissues in both models also revealed no differences between the IL-6(-/-) and IL-6(+/+) mice. These data demonstrate that while IL-6 is upregulated in acute vascular injury it does not appear to be critical in the development of the vascular inflammatory response.

Cutaneous IgA-associated vasculitis induced by alcohol

A patient with elevated levels of serum IgA developed purpuric lesions histologically resembling Henoch-Schönlein purpura brought on by consuming alcohol. Alcohol challenge with 5 units of alcohol reproduced the lesions, with a rapid rise of circulating CD4+ and CD8+ T cells followed by a fall of serum IgA and C3 concentration. The skin lesions and serum abnormalities resolved spontaneously within 6 weeks of the alcohol challenge.

Anthrax lethal toxin enhances cytokine-induced VCAM-1 expression on human endothelial cells

Vascular endothelial dysfunction is thought to play a prominent role in systemic anthrax pathogenesis. We examined the effect of anthrax lethal toxin (LTx), a key virulence factor of Bacillus anthracis, on the expression of vascular cell adhesion molecule-1 (VCAM-1) on normal and cytokine-stimulated human lung microvascular endothelial cells. Confluent endothelial monolayers were treated with lethal factor (LF), protective antigen (PA), or both (LTx) in the presence or absence of tumor necrosis factor-alpha (TNFalpha). LTx enhanced cytokine-induced VCAM-1 expression and monocyte adhesion. LTx alone had no effect on VCAM-1 expression. LF, PA or the combination of a catalytically inactive mutant LF and PA failed to enhance cytokine-induced VCAM-1 expression. Treatment with inhibitors of mitogen-activated protein kinase kinases (MEKs) and mitogen-activated protein kinases did not reproduce the VCAM-1 enhancement effect of LTx, a known MEK metalloprotease, suggesting LTx-mediated MEK cleavage may not be a contributing factor.

Cutaneous vasculitis

Vasculitis is defined as inflammation of blood vessels and can affect multiple organs. Several classification systems exist to categorize vasculitis such as vessel size, presence of anti-neutrophil cytoplasmic antibody, pathogenesis of the inflammation, and type of inflammatory cell infiltrate. Cutaneous vasculitis occurs as a manifestation of many diseases including rheumatologic diseases, hypersensitivity syndromes, infections, and malignancies. The diagnosis of the cutaneous vasculitis and the underlying cause requires a complete history and physical exam and usually a biopsy or angiogram. The treatment depends on the etiology of the inflammation and includes immunosuppression, withdrawal of the offending agent, antibacterial/antiviral agents, and chemotherapies. A clear understanding and approach to this condition will improve the physician's ability to provide optimal patient care.

Peripheral neuropathy in systemic vasculitides

PURPOSE OF REVIEW

Peripheral nervous system (PNS) involvement is of great diagnostic value in systemic vasculitides, because it occurs frequently and often early during the course of these diseases, despite the supposed blood-nerve barrier that should prevent or at least minimize PNS damage. However, it carries no poor prognostic value in vasculitides. Recent advances have been made in understanding the pathogenetic mechanisms of PNS involvement.

RECENT FINDINGS

Vasculitic neuropathy may result from primary or secondary systemic vasculitides, or may be restricted to the PNS, in a form that is now also considered to be a systemic vasculitis. The blood-nerve barrier is not as efficient as the blood-brain barrier. Inflammatory cell infiltration into the vasa nervorum and epineurial arteries leads to ischemic axonal nerve injury and is facilitated by additional breaches in the blood-nerve barrier, induced by proinflammatory cytokines, oxidative stress-derived molecules, and matrix metalloproteinases. Although animal models of myeloperoxidase or, now, proteinase 3-antineutrophil cytoplasmic autoantibody-inducing vasculitis have been developed, they do not support a role for antineutrophil cytoplasmic autoantibodies in PNS involvement. Treatment should be chosen based on the other organ involvement and the patient's general condition. When PNS involvement is isolated, corticosteroids alone should be used as first-line treatment.

SUMMARY

Apart from the so-called nonsystemic nerve vasculitis, PNS involvement is rarely the sole clinical sign of systemic necrotizing vasculitis, and its association with other typical manifestations is often suggestive of the diagnosis of vasculitis. Herein are summarized recent advances that have clarified but not yet fully elucidated the pathogenesis of peripheral neuropathy in systemic vasculitides, together with the latest clinical findings and therapeutic strategies.

Endothelial dysfunction and activation as an expression of disease: role of prostacyclin analogs

The endothelium is now considered a real endocrine-paracrine organ, important not only as a structural barrier between the circulation and surrounding tissue, but also because it plays an essential role for local hemodynamics, releasing substances that modulate the vascular calibre and blood cell activation. Here, after a brief but detailed analysis of the importance of the endothelium in vascular homeostasis, in the control of coagulation and in the relations with the different blood cells, we will explain the concept of endothelial dysfunction (altered NO release) and activation (amplified adhesion molecule expression) in inflammatory, connective tissue and post-trasplantation diseases. Furthermore, this review will focus on the activity of prostacyclin and synthetic analogs, especially their ability to interact with the vasodilatation system and their role in modulating cell interaction by surface adhesion molecule expression, cytokines and growth factors release as well as gene transcription factors. Finally, we will consider the therapeutic role of prostacyclin analogs in the prevention and treatment of connective tissue diseases.

Endothelial microparticles and the diagnosis of the vasculitides

Recently there has been considerable interest in a novel surrogate marker of endothelial injury, endothelial microparticles (EMP), in a number of diseases characterised by endothelial injury. This review examines the data relating to EMP in human disease states, and examines the potential for EMP to provide a window onto the activated endothelium in primary systemic vasculitides. The utility of EMP for the diagnosis and monitoring of active vasculitis is discussed.

Impaired clearance of apoptotic cells promotes synergy between atherogenesis and autoimmune disease

To clarify the link between autoimmune disease and hypercholesterolemia, we created the gld.apoE^−/− mouse as a model of accelerated atherosclerosis. Atherosclerotic lesion area was significantly increased in gld.apoE^−/− mice compared with apoE^−/− mice. gld.apoE^−/− mice also displayed increases in lymphadenopathy, splenomegaly, and autoantibodies compared with gld mice, and these effects were exacerbated by high cholesterol diet. gld.apoE^−/− mice exhibited higher levels of apoptotic cells, yet a reduced frequency of engulfed apoptotic nuclei within macrophages. Infusion of lysophosphatidylcholine, a component of oxidized low density lipoprotein, markedly decreased apoptotic cell clearance in gld mice, indicating that hypercholesterolemia promotes autoimmune disease in this background. These data suggest that defects in apoptotic cell clearance promote synergy between atherosclerotic and autoimmune diseases.

Endothelial and platelet microparticles in vasculitis of the young

OBJECTIVE

Microparticles are released from endothelial cells in response to a variety of injurious stimuli and recently have been shown to be increased in a number of diseases associated with endothelial dysfunction. This study examined endothelial microparticle (EMP) and platelet microparticle (PMP) profiles in children with systemic vasculitis to test the hypothesis that EMPs may provide a noninvasive means of examining endothelial activation or injury.

METHODS

The study cohort comprised 39 children with systemic vasculitis at various stages of disease activity, 24 control children with febrile disease, and a control group of 43 healthy subjects. Plasma was ultracentrifuged at 17,000g for 60 minutes, and the microparticle pellets were examined using flow cytometry.

RESULTS

Plasma from patients with active systemic vasculitis contained significantly higher numbers of E-selectin-positive EMPs compared with that from patients in remission, healthy controls, or febrile disease controls (P = 0.000 for each). A similar result was obtained for the numbers of EMPs expressing the marker CD105. There was also a significant increase in PMPs expressing CD42a in the active vasculitis group as compared with the other groups, but this difference was not significant for PMPs expressing P-selectin. The EMP counts correlated with the Birmingham Vasculitis Activity Score and the acute-phase reactant levels in the patients with systemic vasculitis, but there was a poor correlation overall between EMP counts and the acute-phase reactant levels in the febrile disease controls.

CONCLUSION

EMPs may provide a window to the activated endothelium and could provide important pathophysiologic insights into the vascular injury associated with vasculitis of the young.

Cytokines in sural nerve biopsies from inflammatory and non-inflammatory neuropathies

Proinflammatory cytokines are supposed to play a major role in the pathophysiology of vasculitis and in the development of neuropathic pain. Here we studied the cytokine expression in sural nerve biopsy specimens from patients with vasculitic and other inflammatory and non-inflammatory neuropathies, and investigated whether an increased cytokine expression was correlated with the presence of neuropathic pain. We used immunohistochemistry including double labeling and morphometry to localize and quantify the expression of interleukin-1 beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF) in sural nerve biopsy samples of 41 patients with vasculitic neuropathy (VANP), chronic inflammatory demyelinating neuropathy (CIDP), non-inflammatory chronic axonal neuropathy (CANP), and 3 controls. Overall cytokine immunoreactivity was highest in VANP, less strong in CIDP and lowest in CANP. Cytokine immunoreactivity was directly correlated with the degree of axonal degeneration, endoneurial macrophages and epineurial T cells. In VANP and CANP, a higher cytokine content was associated with neuropathic pain.

Antineutrophil cytoplasmic antibodies induce decreased CD62L expression and enhanced metabolic activity in monocytes

Monocyte in vitro activation by antimyeloperoxidase (anti-MPO)- and antiproteinase-3 (anti-PR3)-positive sera, corresponding immunoglobulin G (IgG) fractions and monoclonal antibodies against MPO and PR3 was evaluated. The expression of adhesion molecules, l-selectin (CD62L) and CR3 (CD11b), involved in leucocyte endothelial adhesion, and metabolic activity, measured as the production of hydrogen peroxide, were analysed. Decreased expression of CD62L was demonstrated in monocytes after incubation with antineutrophil cytoplasmic antibody (ANCA)-positive sera. This finding was not accompanied by changes in CD11b expression. Metabolic activity was increased in monocytes after incubation with ANCA-positive IgG fractions as well as after incubation with monoclonal anti-MPO and anti-PR3. These findings support the concept that the pathophysiological effect of ANCA is partly mediated through the action on crucial events in monocyte activation, such as CD62L downregulation and oxygen radical production.

A new in vitro model to study endothelial injury

BACKGROUND

Endothelial dysfunction or "endothelialitis" is a prominent feature in several disease states ranging from atherosclerosis to transplant rejection. This dysfunction is also caused by drugs such as cyclosporin A (CyA) and leads to allograft vasculopathy and eventual graft loss. Despite the frequency and importance of this injury, there is no model to study the morphological effects of endothelial injury and dysfunction in vitro.

METHODS

We utilized a model in which mouse endothelial cells (SVEC 4-10) can be induced to form capillary tubes by culturing on a laminin-rich matrix (Matrigel). In this morphological model of endothelial cell function, we studied the effect of varying doses of CyA on two parameters of tube formation: initiation of tube formation and disruption of mature capillary tubes. As a positive control we used IFN-gamma, which inhibited capillary tube formation. We developed this assay in 96-well culture plates to test several samples simultaneously.

RESULTS

The assay could be adapted to a 96-well format by optimizing the cell density. Endothelial dysfunction was seen when the endothelial cells were incubated with cyclosporin A, which affected both morphological parameters of tube formation. At higher doses (2-20 microg/ml) CyA both inhibited capillary tube formation and disrupted mature capillary tubes. At lower doses CyA only inhibited the initiation of tube formation; it did not disrupt mature capillary tubes. IL-2 (400-1000 pg/ml) and IFN-gamma (10-400 pg/ml) inhibited initiation of tube formation but did not disrupt mature capillary tubes. None of these agents, including high doses of CyA, impaired endothelial cell viability.

CONCLUSION

CyA-induced endothelial dysfunction can be modeled in vitro by this novel morphological assay of capillary tube formation. This assay can discern mild and severe degrees of endothelial dysfunction. The different effects of low and high levels of CyA on capillary tube formation imply that similar dysfunction in vivo may be responsible for allograft vasculopathy caused by CyA. This novel model can also be utilized to study other forms of vasculitis.

Lupus vasculitis: differential diagnosis with antiphospholipid syndrome

The inflammatory process of systemic lupus erythematosus (SLE) vasculitis occurs in up to 56% of patients with SLE, whereas the vaso-occlusive incidence of antiphospholipid syndrome in SLE (which is not exclusive of SLE vasculitis) reaches up to 15%. Both situations can be life-threatening, requiring the appropriate therapeutic approach. Aggressive anti-inflammatory therapy is used in the case of SLE vasculitis and aggressive antithrombotic/anticoagulant treatment in the other. However, often the differential diagnosis between the two entities is difficult to achieve, especially when a tissue biopsy to help establish the diagnosis is topographically difficult to obtain or is clinically contraindicated. Such situations are discussed and appropriate guidelines for a correct diagnosis suggested.

Immunopathogenesis of vasculitis

Vasculitis is defined by the presence of leukocytes in the vessel wall with reactive damage to mural structures, leading to tissue ischemia and necrosis. The immunopathologic events that initiate the process of vascular inflammation and blood vessel damage are unclear. Damage of vascular endothelial cells and the recruitment and accumulation of the inflammatory infiltrate are determined by the endothelial cell and the bystanders, including the expression of adhesion molecules, the secretion of peptides and hormones, and the specific interaction with inflammatory cells. In addition to the endothelial cells, which provide costimulatory function, other cellular components and nonendothelial structures of the vessel wall are involved in controlling the inflammatory process, serve as antigen-presenting cells, and contribute with inflammatory mediators.