Giant Cell Vasculitis Is a T Cell-Dependent Disease

[Pathogenesis of primary large vessel arteritis]

Giant cell arteritis (GCA) and Takayasu's arteritis (TA) are the two primary large-vessel arteritides. Recent advances in cellular immunology have allowed better understanding of pathogenesis of these diseases. In GCA and TA, resident adventitial dendritic cells are activated by unidentified stimuli. This activation induces chemokine synthesis which enhances recruitment of inflammatory cells. T-cells infiltrate the vascular wall and specifically recognize one or a few antigens presented by shared epitopes associated with specific HLA molecules on dendritic cells. Activated T-cells produce IFNgamma stimulating two distinct populations of macrophages. Macrophages located in the intima produce pro-inflammatory cytokines (IL-1, IL-6). Macrophages located in the media differentiate into giant cells and/or produce reactive oxygen species, nitric oxide and matrix metallo-proteinases. Macrophages of the media also produce VEGF, which leads to neovascularization and PDGF, which induces intimal hyperplasia and vascular occlusion. In TA, cytotoxic T cells infiltrate the vascular wall and induce apoptosis of the vascular cells. Better understanding of the pathogenesis of large-vessel arteritis may lead to development of immunosuppressive drugs specifically targeting the immunological mechanisms implicated in GCA and TA.

Prolonged urticaria with purpura: the spectrum of clinical and histopathologic features in a prospective series of 22 patients exhibiting the clinical features of urticarial vasculitis

BACKGROUND

Biopsy specimens of lesions with clinical features of urticarial vasculitis often show a predominantly lymphocytic infiltrate with eosinophils and red blood cell extravasation. Only occasionally is a leukocytoclastic vasculitis encountered, confirming a diagnosis of urticarial vasculitis.

OBJECTIVE

The aim of this study was to assess the clinical presentation and histologic features of patients who meet the clinical criteria for urticarial vasculitis.

METHODS

Patients were recruited who had persistent urticarial lesions individually lasting longer than 24 hours, associated with at least 2 of 3 of the following: pain or tenderness; purpura or dusky changes; and resolution with hyperpigmentation. Patients were interviewed based on a standard questionnaire with regard to their symptoms. Blood tests and chest radiographs were performed to exclude systemic involvement and hypocomplementemia. Skin biopsy specimens were sent for histology and direct immunofluorescence.

RESULTS

Of 22 patients recruited, 19 (86.4%) showed a predominantly lymphocytic infiltrate on histology. Three cases (13.6%) had a neutrophil-predominant infiltrate associated with a leukocytoclastic vasculitis. Twenty (90.9%) had a superficial perivascular infiltrate, and two (9.1%) had a superficial and deep perivascular infiltrate. In all, 21 biopsy specimens (95.5%) showed inflammatory cells within dermal blood vessel walls, obscuring the vessel outline in some. Endothelial cell swelling was seen in 20 biopsy specimens (90.9%), erythrocyte extravasation in 17 (77.3%), nuclear dust in 5 (22.7%), and fibrin extravasation in 2 (9.1%). Multivariate analysis revealed the following features to be independently associated with neutrophil predominance: fulfillment of all 3 minor criteria for urticarial vasculitis-like lesions (P = .007); presence of fibrin on histology (P < .001); presence of nuclear dust on histology (P = .001); hypocomplementemia (P = .001); and anemia (P = .015). There was a trend toward lesions not clearing as readily in the neutrophil-predominant group (P = .071), even with two-modality treatment (P = .089).

LIMITATIONS

Serum immunoelectrophoresis was not done to exclude Schnitzler's syndrome. Electronmicroscopy and cytokine profiling were not performed.

CONCLUSION

Biopsy specimens of lesions with clinical features of urticarial vasculitis reveal that only a minority of patients has leukocytoclastic vasculitis. The majority has a lymphocyte-predominant histology, associated with varying numbers of eosinophils. We favor a lymphocytic vasculitis as a causative explanation in the lymphocyte-predominant group.

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.

Immunopathways in giant cell arteritis and polymyalgia rheumatica

Giant cell arteritis (GCA), a vasculitis that targets medium- and large-size arteries, is ranked as a medical emergency because of its potential to cause blindness and stroke. The typical lesions, granulomas in the vessel wall, are formed by IFN-gamma-producing CD4+ T cells and macrophages. CD4+ T cells undergo in situ activation in the adventitia, where they interact with indigenous dendritic cells. Tissue injury is mediated by several distinct sets of macrophages that are committed to diverse effector functions. The dominant tissue injury in the media results from oxidative stress and leads to smooth muscle cell apoptosis and nitration of endothelial cells. Macrophage-derived growth factors are instrumental in driving the response-to-injury program of the artery that causes intimal hyperplasia and vessel occlusion. Clinical manifestations are those of tissue ischemia or a syndrome of exuberant systemic inflammation. The vascular and the systemic components of GCA contribute differentially to the disease, leading to distinct clinical phenotypes of this arteritis. Immunologically most interesting is polymyalgia rheumatica, in which the systemic component is combined with aborted vasculitis, suggesting a role for artery-specific tolerance mechanisms.

Activation of arterial wall dendritic cells and breakdown of self-tolerance in giant cell arteritis

Giant cell arteritis (GCA) is a granulomatous and occlusive vasculitis that causes blindness, stroke, and aortic aneurysm. CD4(+) T cells are selectively activated in the adventitia of affected arteries. In human GCA artery-severe combined immunodeficiency (SCID) mouse chimeras, depletion of CD83(+) dendritic cells (DCs) abrogated vasculitis, suggesting that DCs are critical antigen-presenting cells in GCA. Healthy medium-size arteries possessed an indigenous population of DCs at the adventitia-media border. Adoptive T cell transfer into temporal artery-SCID mouse chimeras demonstrated that DCs in healthy arteries were functionally immature, but gained T cell stimulatory capacity after injection of lipopolysaccharide. In patients with polymyalgia rheumatica (PMR), a subclinical variant of GCA, adventitial DCs were mature and produced the chemokines CCL19 and CCL21, but vasculitic infiltrates were lacking. Human histocompatibility leukocyte antigen class II-matched healthy arteries, PMR arteries, and GCA arteries were coimplanted into SCID mice. Immature DCs in healthy arteries failed to stimulate T cells, but DCs in PMR arteries could attract, retain, and activate T cells that originated from the GCA lesions. We propose that in situ maturation of DCs in the adventitia is an early event in the pathogenesis of GCA. Activation of adventitial DCs initiates and maintains T cell responses in the artery and breaks tissue tolerance in the perivascular space.

HLA-DRB1 allele distribution in polymyalgia rheumatica and giant cell arteritis: Influence on clinical subgroups and prognosis

OBJECTIVE

To evaluate HLA-DRB1 associations in patients with polymyalgia rheumatica (PMR) and giant cell arteritis (GCA) in the Spanish population, especially those alleles that include the disease-linked sequence motif DRYF (positions 28 to 31 of the HVR2).

METHODS

We performed a PCR based HLA-DRB1 genotyping in 89 PMR patients, 44 GCA patients, and 99 unrelated healthy controls from the same geographic area.

RESULTS

We did not find any significant difference between the whole group of PMR/GCA patients (n = 133) compared with the healthy controls with the exception of a lower frequency of HLA-DRB1*0405 in the patient group (odds ratio [OR], 0.1 [CI0.02 to 1.2]; P =.04). The distribution of DRB1 alleles was very similar between PMR patients and controls. However, DRB1*0401 (OR, 3.1 [1.1 to 8.6]; P =.02) and DRB1*0404 (OR, 3.5 [0.97 to 12.9]; P =.04) were overrepresented in patients with GCA compared with the control group. DRB1*04 (OR, 1.9 [0.96 to 3.8]; P =.06), especially *0401 (OR, 2.8 [1 to 7.7]; P =.04), and DRB1*07 (OR, 2.3 [1.2 to 4.6]; P =.01) were more frequent in GCA than in PMR. Frequency of the DRYF 28-31 motif was similar among GCA (79.5%), PMR (89.9%), and controls (87.9%) and did not confer any significant risk of the development of systemic vasculitis. We also compared the DRB1 allele distribution in patients with classic PMR (n = 58) and those with an erythrocyte sedimentation rate (ESR) <40 mm/hour (n = 31). Patients with classic PMR expressed DRB1*07 less frequently (OR, 0.4 [0.1 to 1]; P =.04) and had a higher frequency of the DRYF 28-31 motif (94.8% vs 80.6%; P =.03) than patients with ESR < 40. Within the GCA group, DRB1 alleles were not predictive for the development of severe ischemic complications. However, the development of relapses in patients with PMR was associated with a higher frequency of DRB1*09 (5.6% vs 0%; P =.04).

CONCLUSIONS

Our data suggest that the HLA-DRB1 alleles associated with susceptibility for developing PMR and GCA are different. Whether PMR with low ESR represents a different clinical subset of the disease should be clarified in a larger sample of patients. HLA-DRB1 genes might predict the presence of relapses in PMR, but they do not seem to be indicators of severe disease in GCA patients.

[Physiopathological data of Horton's syndrome]

GREAT PROGRESS: The understanding of the physiopathology of Horton's syndrome has been made in view of the prevalence of the disease, the access to affected tissue and new molecular biology techniques. And it is now possible to specify the intricacy between the genetic, immunological and vascular components. HORTON'S SYNDROME, A GENETIC DISEASE: The preferential association of the disease with some alleles pf the HLA DR4 group has helped to emphasize the fundamental role of a few amino acids of the second hypervariable area of the HLA-DR molecule. An immunogenetic predisposition appears favourable, or even necessary, for the development of the disease. HORTON'S SYNDROME, AN IMMUNOLOGICAL DISEASE: The temporal arteries of patients presenting with Horton's syndrome are infiltrated by polymorphous inflammatory cells, fundamentally including CD4 T-cell lymphocytes, macrophages, and a few giant cells. Some CD4 lymphocytes have undergone clonal proliferation and show signs of recent antigenic recognition. A fraction of them secrete interferon gamma, which plays a crucial role in the onset, maintenance and orientation of the immunological response. The macrophages play multiple roles notably in maintaining the inflammatory reaction, but also in the destruction of certain structures of the arterial wall. HORTON'S SYNDROME, A VASCULAR DISEASE: The destruction of the arterial wall at the acute stage of the disease appears responsible, sometimes later on, for aneurismal dilatations observed on the aorta of certain patients. Moreover, intimal hyperplasia (mediated by the PDGF (platelet derived growth factor) A and B) and thrombosis (related to the inflammation) join up in reducing the arterial flow and enhancing the risk of ischemic complications during the acute stage. PATHOGENESIS, HYPOTHESES: Various candidate-antigens have been incriminated in the onset of the inflammatory reaction during Horton's syndrome. Some epidemiological and molecular studies are in favour of an exogenous antigen, possibly infectious, but no evidence has been demonstrated in the studies published. A parietal, endogenous antigen might also be at the origin of the cascade of events described during this disease.

Immunobiologic analysis of arterial tissue in Buerger's disease

INTRODUCTION

the cause of thromboangiitis obliterans (TAO) still remains unknown. We have reported that immunologic injury associated with T lymphocytes infiltration might be the initial etiologic mechanism in TAO. The present study was undertaken to examine further the mechanism of immune injury.

METHODS

arterial walls affected by TAO were obtained from eight patients with eight non-pulsatile arteries and one patent artery. Immunohistochemical and TUNEL studies were performed for phenotyping of the infiltrating cells with CD4 (helper T cell), CD8 (cytotoxic T cell), CD56 (natural killer cell), and CD68 (macrophage), for identification of cell activation with VCAM-1 and i -NOS, for the presence of cell death with TUNEL analysis, and for inflammatory cytokine detection with RT-PCR.

RESULTS

the characteristic features were luminal obliteration, together with a varying degree of recanalization. T cells infiltrated mainly in thrombus, intima, and adventita. Among infiltrating cells, CD4 T cells greatly outnumbered CD8 cells. VCAM-1 and i -NOS were expressed in endothelial cells around the intima (patent segment) or vaso vasorum (occluded segment). Endothelial cells in vaso vasorum stained positive with TUNEL. Interferon-gamma mRNA was detected in two specimens.

CONCLUSIONS

our results suggest that T cell mediated immune inflammation is a significant event in the development of TAO.

Trapping of misdirected dendritic cells in the granulomatous lesions of giant cell arteritis

Immature dendritic cells (DCs) are scattered throughout peripheral tissues and act as sentinels that sample the antigenic environment. After activation, they modify their chemokine receptor profile and migrate toward lymphoid tissues. On arrival, they have matured into chemokine-producing DCs that express co-stimulatory molecules and can prime naive T cells. Normal temporal arteries contain immature DCs that are located at the media-adventitia border. In temporal arteries affected by giant cell arteritis, DCs are highly enriched and activated and have matured into fully differentiated cells producing the chemokines, CCL18, CCL19, and CCL21. In keeping with their advanced maturation, DCs in the granulomatous lesions possess the chemokine receptor, CCR7. CCR7 binds CCL19 and CCL21, causing the highly activated DCs to be trapped in the peripheral tissue site. The co-stimulatory molecule, CD86, which is critical for DC/T-cell interaction, is expressed by a subset of DCs captured in the arterial wall. DC/T-cell interaction does not involve interleukin-12; transcripts for interleukin-12 p40 are absent in the vasculitic infiltrates. We propose that differentiation of DCs and the autocrine and paracrine actions of chemokines in granulomatous lesions misdirect DCs away from their usual journey to lymphoid organs and are critical in maintaining T-cell activation and granuloma formation in giant cell arteritis.

Reactive nitrogen intermediates in giant cell arteritis: selective nitration of neocapillaries

Arterial wall damage in giant cell arteritis (GCA) is mediated by several different macrophage effector functions, including the production of metalloproteinases and lipid peroxidation. Tissue-invading macrophages also express nitric oxide synthase (NOS)-2, but it is not known whether nitric oxide-related mechanisms contribute to the disease process. Nitric oxide can form nitrating agents, including peroxynitrite, a nitric oxide congener formed in the presence of reactive oxygen intermediates. Protein nitration selectively targets tyrosine residues and can result in a gain, as well as a loss, of protein function. Nitrated tyrosine residues in GCA arteries were detected almost exclusively on endothelial cells of newly formed microcapillaries in the media, whereas microvessels in the adventitia and the intima were spared. Nitration correlated with endothelial NOS-3 expression and not with NOS-2-producing macrophages, which preferentially homed to the hyperplastic intima. The restriction of nitration to the media coincided with the production of reactive oxygen intermediates as demonstrated by the presence of the toxic aldehyde, 4-hydroxynonenal. Depletion of tissue-infiltrating macrophages in human temporal artery-SCID mouse chimeras disrupted nitrotyrosine generation, demonstrating a critical role of macrophages in the nitration process that targeted medial microvessels. Thus, protein nitration in GCA is highly compartmentalized, reflecting the production of reactive oxygen and reactive nitrogen intermediates in the inflamed arterial wall. Heterogeneity of microvessels in NOS-3 regulation may be an additional determinant contributing to this compartmentalization and could explain the preferential targeting of newly generated capillary beds.

Therapeutic effects of acetylsalicylic acid in giant cell arteritis

OBJECTIVE

In giant cell arteritis (GCA), inflammatory lesions typically produce interferon-gamma(IFNgamma)-- and nuclear factor kappaB (NF-kappaB)-dependent monokines. Corticosteroids influence disease activity by repressing NF-kappaB-dependent genes but have only marginal effects on IFNgamma. The current study explored whether acetylsalicylic acid (ASA) had cytokine-repressing activity in GCA and could function as a steroid-sparing agent.

METHODS

Temporal artery-severe combined immunodeficiency (SCID) mouse chimeras were created by engrafting inflamed temporal arteries into SCID mice. Chimeras were treated with ASA, indomethacin, or dexamethasone for 3 weeks. Temporal artery grafts were harvested and cytokine message was semiquantified by polymerase chain reaction-enzyme-linked immunosorbent assay. The ability of dexamethasone and ASA to suppress IFNgamma and interleukin-1beta (IL-1beta) messenger RNA and protein production was also tested in vitro using T cell clones and monocytes derived from patients with GCA. Drug-induced effects on the transcription factors NF-kappaB and activator protein 1 (AP-1) were assessed by electrophoretic mobility shift assays (EMSAs).

RESULTS

At clinically relevant doses, 20-100 mg/kg, ASA was a highly effective inhibitor of cytokine transcription in temporal arteries. While dexamethasone preferentially targeted NF-kappaB-regulated monokines, ASA acted predominantly by suppressing IFNgamma. Indomethacin failed to reduce tissue IFNgamma transcription, which therefore excluded the inhibition of cyclooxygenases as a critical mechanism. IFNgamma production by T cell clones was highly sensitive to ASA-mediated suppression, whereas IL-1beta production by lipopolysaccharide-stimulated monocytes responded primarily to dexamethasone. The combination of ASA and dexamethasone had synergistic effects. EMSAs demonstrated that ASA interfered with the formation of AP-1, whereas dexamethasone suppressed the nuclear translocation of NF-kappaB.

CONCLUSION

The results of this study provide evidence of the complementary action of ASA and corticosteroids in suppressing proinflammatory cytokines in the vascular lesions of GCA.

Giant cell arteritis: diagnosis and management

Visual loss caused by giant cell arteritis is a medical emergency that requires prompt recognition and treatment with systemic corticosteroids. A delay in diagnosis can lead to devastating ophthalmic and systemic complications. Recent advances in genetic and immunocytochemical research techniques have led to greater understanding of the underlying pathomechanisms of giant cell arteritis. Giant cell arteritis is a systemic condition with a strong predilection for the ocular vasculature. Visual symptoms are often the presenting manifestation of the disease, placing the ophthalmologist in a critical position for early diagnosis and treatment. Maintenance of a high clinical suspicion in the appropriate clinical setting is important in establishing an early diagnosis. Because of the complex nature of the disease process, many cases may be a therapeutic challenge requiring prolonged immunosuppression.

Leukocyte-endothelial interactions in antineutrophil cytoplasmic antibody-associated systemic vasculitis

The etiology of ANCA-associated vasculitis is unknown. Currently, it is believed that disease may be triggered by infection with the release of proinflammatory cytokines in genetically susceptible individuals. Priming of PMNs and endothelial cells by these cytokines allows ANCAs to activate PMNs, with damage localized to the endothelium, resulting in early lesions. Damage and activation of endothelial cells produces proinflammatory chemokines and cytokines with influxes of monocytes and T cells that intensify endothelial damage. In the kidney, these changes eventually lead to crescent formation. Antigen-specific memory T cells persist after disease remission with the potential of reactivation and disease relapse. Although our understanding of the pathophysiologic mechanisms of ANCA-associated vasculitis is far greater now than when ANCAs were first identified in 1982, more experimental work in combination with clinical observations is required to further elucidate these mechanisms.

New therapeutic aspects: haemopoietic stem cell transplantation

Primary systemic vasculitis responds well to intensive immunosuppression, particularly with cyclophosphomide. Use of the latter is restricted by side-effects, particularly in relapsing disease. Techniques which allow more complete immunosuppression have an obvious attraction in autoimmune disease. They are particularly suitable for vasculitis which can go into long-lasting remission even with standard therapy in many cases. The conditioning used for stem cell transplantation allows more complete deletion of auto aggressive T-cell clones, with subsequently haemopoietic rescue by previously harvested stem cell precursors. The procedure also has immune potentiating effects, perhaps by promoting peripheral suppressor mechanisms. These may be important even though immune ablation is not achieved. With rigorous patient selection, experience with this technique in vasculitis may be broadened.

Circulating CD8+ T cells in polymyalgia rheumatica and giant cell arteritis: a review

BACKGROUND AND OBJECTIVE

During the last few years, there have been several studies on T cell subsets in polymyalgia rheumatica (PMR) and giant cell arteritis (GCA), with conflicting results. Whereas some authors have found normal values of circulating CD8+ T cells, others have found a decreased number. Furthermore, in some studies, the level of CD8+ cells was found to be related to disease activity, and it has been proposed that a decrease of CD8+ T cells be used as a diagnostic criterion for PMR. The purpose of our study was to determine the value of assessing T cell subsets in PMR and GCA.

METHODS

T lymphocyte subsets were determined by flow cytometry using a whole blood lysis technique in the following groups: 28 PMR and 6 GCA patients before corticosteroid treatment, 20 PMR and 12 GCA patients in clinical remission with steroid treatment, 55 PMR patients in remission without steroid treatment, 17 rheumatoid arthritis (RA) patients before treatment, and 18 age-matched controls with noninflammatory conditions. Total white cell, lymphocyte, and platelet counts, hemoglobin, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) were measured by routine techniques. Comparisons were made by the Student's t-test and the Mann-Whitney test. A MEDLINE database search for studies published between 1983 and 1997 was performed.

RESULTS

Compared with noninflammatory controls, CD8+ T cells were not reduced before steroid treatment in patients with active PMR/GCA in proportion (P =.7) or absolute numbers (P =.1). Patients with active disease had significantly lower hemoglobin levels and higher platelet counts, CRP, and ESR than noninflammatory controls (P <.05). When compared with active RA, CD8+ T cells were not reduced in patients with active PMR in proportion (P =.5) or absolute numbers (P =.2). Between these two groups, RA patients were significantly younger (P =.003) and had lower ESR values (P =.003). We did not find significant differences between patients with active PMR/GCA and those in remission with steroid therapy, except for the lower hemoglobin levels and higher platelet count, CRP, and ESR in the active disease group (P <.05). The same results were found when patients with active disease were compared with PMR in remission and no longer on steroid therapy, the only significant differences were those parameters reflecting the acute phase response (hemoglobin levels, platelet count, CRP and ESR).

CONCLUSIONS

This study does not confirm the previous findings that the proportion or number of circulating CD8+ T cells are reduced in patients with active PMR/GCA. The utility of the determination of CD8+ T cells for diagnostic and prognostic purpose should be evaluated in a large multicenter study.

[Risk factors for irreversible cerebral ischemia complications from Horton's disease: prospective study of 178 patients]

PURPOSE

To search for risk factors of developing irreversible cranial ischemic complications (ICIC) in patients with giant cell arteritis (GCA) and to explore whether two subsets of patients (high risk and low risk of developing ICIC) can be defined.

METHODS

One-hundred seventy-eight consecutive patients with temporal arteritis (149 biopsy-proven) were diagnosed and followed up in a department of Internal Medicine between 1976 and 1999. The patients were separated into two groups, according to the presence or absence of ICIC, with comparison of 17 clinical and biological parameters prospectively recorded for each patient using a pre-established comprehensive questionnaire.

RESULTS

ICIC occurred in 25 patients (14%), with amaurosis in 22 cases. Suggestive symptoms and/or signs of temporal arteritis were present in 92% of the patients, lasting 50 days (median) before the onset of ICIC. Forty-three patients (24%) complained of transient visual ischemic symptoms (TVIS), which preceded acute blindness in 11 cases. A multivariate logistic regression, from which 28 cases with upper limb artery involvement were excluded for technical reasons (no CCII in any case, thus predicting perfectly the lack of ischemic risk, P = 0.02), indicated that the only independent variables associated with the ischemic risk were: a history of TVIS (P = 0.05), the lack of signs of polymyalgia rheumatica (PMR; P = 0.02), lower blood levels of fibrinogen (P = 0.024) and higher mean blood platelets levels (P = 0.006). However, these five variables predicted only 30% of the variability of the model. Sensitivity, specificity, positive and negative predictive values of the model reached respectively 36, 96, 64 and 88%. Overall, 86% of the cases were correctly classified with respect to the ischemic risk.

CONCLUSION

The rate of ICIC should be reduced by an earlier recognition of the usual signs of temporal arteritis. Several independent risk factors of ICIC have been identified. However, the logistic model failed to predict accurately the ischemic risk in 14% of the cases, indicating that as yet unrecognised factors probably exist that play a role in the occurrence of ICIC. Nevertheless, regarding the strong association between platelet levels and ICIC, patients with thrombocytosis should receive initially both corticosteroids and antiplatelet agents.

Pathogenic principles in giant cell arteritis

In giant cell arteritis, an immune insult in the vascular wall initiates a reaction in the artery that leads to structural changes, intimal hyperplasia, and luminal occlusion. The mechanisms triggering the immune stimulation are unknown; however, the process is strictly dependent on T cells that are found in the vicinity of the vasa vasorum in the adventitia and that produce interferon-gamma. The major effector cells in the artery are macrophages and giant cells that are ultimately under T-cell control but assume different functions depending on their location in the arterial wall. The response of the artery to the injury is maladaptive and includes mobilization and proliferation of smooth muscle cells in conjunction with matrix production and neoangionesis, resulting in the formation of a lumen-obstructive neointima. Heterogeneity in the immune insult and the resulting arterial response patterns correlate with variations in clinical disease.

Pathogenesis of ANCA-associated systemic vasculitis

The aetiology of primary systemic vasculitides remains unknown. Recent advances have been made in the understanding of relevant mechanisms of inflammation, particularly the role of the endothelium and interactions with inflammatory mediators and immune effector cells. In Wegener's granulomatosis and microscopic polyangiitis the evidence suggests an autoimmune inflammatory process, characterized by an early lesion involving neutrophils and endothelial cells as both targets and active participants; priming of neutrophils and endothelial cells allows ANCA to activate neutrophils with damage localized to the endothelium. In the absence of immune complex deposition, the role of the ANCA is particularly intriguing. Endothelial cell damage and activation produces pro-inflammatory mediators with influx monocytes and T cells intensifying damage. Increased understanding of the pathogenesis of systemic vasculitis is likely to provide the basis for the use of more selective immunomodulatory therapies in the future.

Are animal models of vasculitis suitable tools?

Several rodent models have been proposed for various forms of systemic vasculitis. The MRL-lpr mouse has been studied extensively as a model for systemic lupus erythematosus. Backcross experiments in combination with genetic linkage studies have firmly established that the phenotype of autoimmune disease is dependent on the combination of various background genes. It has also become apparent that environmental factors, particularly infections, modulate the disease phenotype. Specific interventions, such as the treatment of Brown Norway rats with agents resulting in polyclonal B cell stimulation or immunization with human myeloperoxidase and subsequent localized perfusion with neutrophil lysosomal extract and H2O2, have provided substantial insights into the cellular and molecular mechanisms leading to the development of vasculitis and glomerulonephritis. Even though the existing models may not exactly mirror any specific human disease, they offer reproducible, highly controlled conditions to answer specific questions about pathogenesis and novel therapeutic approaches.

Formation of new vasa vasorum in vasculitis. Production of angiogenic cytokines by multinucleated giant cells

Inflammation of the arterial wall in giant cell arteritis induces a series of structural changes, including the formation of new vasa vasorum. To study the regulation of neoangiogenesis in giant cell arteritis, temporal arteries were examined for the extent and localization of microvessel generation and for the production of angiogenic factors. In normal arteries, vasa vasorum were restricted to the adventitia, but in inflamed arteries, capillaries emerged in the media and the intima. These capillaries displayed a distinct topography with a circumferential arrangement in the external one-third of the intima. Neovascularization was closely correlated with the formation of lumen-obstructing intima, the fragmentation of the internal elastic lamina, and the presence of multinucleated giant cells. Comparison of tissue cytokine transcription in temporal arteries of giant cell arteritis patients with and without up-regulated neoangiogenesis identified interferon-gamma and vascular endothelial growth factor but not fibroblast growth factor-2 as mediators associated with vasa vasorum proliferation. Giant cells and CD68-positive macrophages at the media-intima junction were found to be the major cellular sources of vascular endothelial growth factor. These data demonstrate that formation of new vasa vasorum in vasculitis is regulated by inflammatory cells and not by arterial wall cells, raising the possibility that it represents a primary disease mechanism and not a secondary hypoxia-induced event. Increased neovascularization in interferon-gamma-rich arteries suggests that the formation of new vasa vasorum is determined by the nature of the immune response in the arterial wall, possibly resulting from the generation and functional activity of multinucleated giant cells.

Tissue-destructive macrophages in giant cell arteritis

Giant cell arteritis (GCA) is an inflammatory vasculopathy in which T cells and macrophages infiltrate the wall of medium and large arteries. Clinical consequences such as blindness and stroke are related to arterial occlusion. Formation of aortic aneurysms may result from necrosis of smooth muscle cells and fragmentation of elastic membranes. The molecular mechanisms of arterial wall injury in GCA are not understood. To identify mechanisms of arterial damage, gene expression in inflamed and unaffected temporal artery specimens was compared by differential display polymerase chain reaction. Genes differentially expressed in arterial lesions included 3 products encoded by the mitochondrial genome. Immunohistochemistry with antibodies specific for a 65-kDa mitochondrial antigen revealed that increased expression of mitochondrial products was characteristic of multinucleated giant cells and of CD68+ macrophages that cluster in the media and at the media-intima junction. 4-Hydroxy-2-nonenal adducts, products of lipid peroxidation, were detected on smooth muscle cells and on tissue infiltrating cells, in close proximity to multinucleated giant cells and CD68+ macrophages. Also, giant cells and macrophages with overexpression of mitochondrial products were able to synthesize metalloproteinase-2. Our data suggest that in the vascular lesions characteristic for GCA, a subset of macrophages has the potential to support several pathways of arterial injury, including the release of reactive oxygen species and the production of metalloproteinase-2. This macrophage subset is topographically defined and is also identified by overexpression of mitochondrial genes. Because these macrophages have a high potential to promote several mechanisms of arterial wall damage, they should be therapeutically targeted to prevent blood vessel destruction.

IL-16 as an Anti-Inflammatory Cytokine in Rheumatoid Synovitis

T lymphocytes are a major component of the inflammatory infiltrate in rheumatoid synovitis, but their exact role in the disease process is not understood. Functional activities of synovial T cells were examined by adoptive transfer experiments in human synovium-SCID mouse chimeras. Adoptive transfer of tissue-derived autologous CD8+ T cells induced a marked reduction in the activity of lesional T cells and macrophages. Injection of CD8+, but not CD4+, T cells decreased the production of tissue IFN-γ, IL-1β, and TNF-α by &gt;90%. The down-regulatory effect of adoptively transferred CD8+ T cells was not associated with depletion of synovial CD3+ T cells or synovial CD68+ macrophages, and it could be blocked by Abs against IL-16, a CD8+ T cell-derived cytokine. In the synovial tissue, CD8+ T cells were the major source of IL-16, a natural ligand of the CD4 molecule that can anergize CD4-expressing cells. The anti-inflammatory activity of IL-16 in rheumatoid synovitis was confirmed by treating synovium-SCID mouse chimeras with IL-16. Therapy for 14 days with recombinant human IL-16 significantly inhibited the production of IFN-γ, IL-1β, and TNF-α in the synovium. We propose that tissue-infiltrating CD8+ T cells in rheumatoid synovitis have anti-inflammatory activity that is at least partially mediated by the release of IL-16. Spontaneous production of IL-16 in synovial lesions impairs the functional activity of CD4+ T cells but is insufficient to completely abrogate their stimulation. Supplemental therapy with IL-16 may be a novel and effective treatment for rheumatoid arthritis.

Aldose reductase functions as a detoxification system for lipid peroxidation products in vasculitis

Giant cell arteritis (GCA) is a systemic vasculitis preferentially affecting large and medium-sized arteries. Inflammatory infiltrates in the arterial wall induce luminal occlusion with subsequent ischemia and degradation of the elastic membranes, allowing aneurysm formation. To identify pathways relevant to the disease process, differential display-PCR was used. The enzyme aldose reductase (AR), which is implicated in the regulation of tissue osmolarity, was found to be upregulated in the arteritic lesions. Upregulated AR expression was limited to areas of tissue destruction in inflamed arteries, where it was detected in T cells, macrophages, and smooth muscle cells. The production of AR was highly correlated with the presence of 4-hydroxynonenal (HNE), a toxic aldehyde and downstream product of lipid peroxidation. In vitro exposure of mononuclear cells to HNE was sufficient to induce AR production. The in vivo relationship of AR and HNE was explored by treating human GCA temporal artery-severe combined immunodeficiency (SCID) mouse chimeras with the AR inhibitors Sorbinil and Zopolrestat. Inhibition of AR increased HNE adducts twofold and the number of apoptotic cells in the arterial wall threefold. These data demonstrate that AR has a tissue-protective function by preventing damage from lipid peroxidation. We propose that AR is an oxidative defense mechanism able to neutralize the toxic effects of lipid peroxidation and has a role in limiting the arterial wall injury mediated by reactive oxygen species.

Disease pattern in cranial and large-vessel giant cell arteritis

OBJECTIVE

To identify variables that distinguish large-vessel giant cell arteritis (GCA) with subclavian/axillary/brachial artery involvement from cranial GCA.

METHODS

Seventy-four case patients with subclavian/axillary GCA diagnosed by angiography and 74 control patients with temporal artery biopsy-proven GCA without large vessel involvement matched for the date of first diagnosis were identified. Pertinent initial symptoms, time delay until diagnosis, and clinical symptoms, as well as clinical and laboratory findings at the time of diagnosis, were recorded by retrospective chart review. Expression of cytokine messenger RNA in temporal artery tissue from patients with large-vessel and cranial GCA was determined by semiquantitative polymerase chain reaction analysis. Distribution of disease-associated HLA-DRB1 alleles in patients with aortic arch syndrome and cranial GCA was assessed.

RESULTS

The clinical presentation distinguished patients with large-vessel GCA from those with classic cranial GCA. Upper extremity vascular insufficiency dominated the clinical presentation of patients with large-vessel GCA, whereas symptoms related to impaired cranial blood flow were infrequent. Temporal artery biopsy findings were negative in 42% of patients with large-vessel GCA. Polymyalgia rheumatica occurred with similar frequency in both patient groups. Large-vessel GCA was associated with higher concentrations of interleukin-2 gene transcripts in arterial tissue and overrepresentation of the HLA-DRB1*0404 allele, indicating differences in pathogenetic mechanisms.

CONCLUSION

GCA is not a single entity but includes several variants of disease. Large-vessel GCA produces a distinct spectrum of clinical manifestations and often occurs without involvement of the cranial arteries. Large-vessel GCA requires a different approach to the diagnosis and probably also to treatment.

Giant cell arteritis

In many populations giant cell arteritis (GCA) is the most common form of vasculitis. Genetic markers, ethnic factors, and increasing age over 50 years appear to enhance susceptibility and an infection may trigger its onset. Recent investigations provide evidence that the vasculitic reaction is part of an immune response to an antigen residing in involved artery walls. These studies along with the description of an experimental model of the disease have significantly increased out understanding of GCA.