Acetylcholinesterase-associated inflammation in patients with giant cell arteritis. Evaluation by histology and 11C-donepezil PET/CT.

OBJECTIVES: To investigate the in-situ expression of acetylcholinesterase (AChE) in the inflamed vessel wall of patients with biopsy-positive giant cell arteritis (GCA) as compared to biopsy-negative non-GCA patients, and to evaluate the in-vivo expression of AChE in patients with large-vessel GCA (LVGCA) by 11C-donepezil (AChE inhibitor) positron emission tomography/computed tomography (PET/CT). METHODS: Twenty-four biopsy-positive GCA and 44 biopsy-negative non-GCA patients were included for AChE histology. Immunohistochemical methods were used to determine the AChE expression. The histological inflammation and the AChE expression were assessed by an experienced pathologist on a 3-point scale. Two patients with newly diagnosed 18F-fluorodeoxyglucose (18F-FDG) PET/CT verified LVGCA were included for 11C-donepezil PET/CT. PET images were assessed by an experienced nuclear medicine physician. RESULTS: AChE was expressed in all 24 positive temporal artery biopsies, 10/24 showed high AChE expression (grade 2) and 14/24 showed moderate AChE expression (grade 1). No AChE expression was observed outside the media smooth muscle cells (grade 0) in any of the biopsy-negative non-GCA patients. The AChE expression was in 86% agreement with the histological inflammation. The AChE expression was not associated with any clinical or biochemical findings. In both LV-GCA patients, PET/CT revealed extensive vascular FDG uptake but no 11C-donepezil uptake. CONCLUSIONS: AChE is highly expressed in the inflamed vessel wall of patients with GCA. Although, 11C-donepezil PET/CT showed no vascular uptake in the FDG PET/CT verified LV-GCA patients, histological findings raise the possibility that AChE can be used in the development of new diagnostic and disease monitoring tools for GCA.

MMP (Matrix Metalloprotease)-9-Producing Monocytes Enable T Cells to Invade the Vessel Wall and Cause Vasculitis.

RATIONALE: Giant cell arteritis (GCA)-a primary vasculitis of medium and large arteries-is associated with vessel wall damage, elastic membrane fragmentation, and vascular remodeling. Proteinases are believed to contribute to pathogenesis by degrading extracellular matrix and causing tissue injury. OBJECTIVE: The MMP (matrix metalloproteinase)-9-a type IV collagenase-is produced in the vasculitic lesions of GCA. It is unknown which pathogenic processes are MMP-9 dependent. METHODS AND RESULTS: The tissue transcriptome of GCA-affected temporal arteries contained high amounts of MMP-9 transcripts, and immunostaining for pro-MMP-9 localized the enzyme to wall-infiltrating macrophages. MMP-2 and MMP-9 transcripts were also abundant in monocytes and monocyte-derived macrophages from patients with GCA. Patient-derived monocytes outperformed healthy monocytes in passing through engineered basement membranes. GCA CD (cluster of differentiation) 4+ T cells required MMP-9-producing monocytes to penetrate through matrix built from type IV collagen. In vivo functions of MMP-9 were tested in a human artery-SCID (severe combined immunodeficiency) chimera model by blocking enzyme activity with a highly specific monoclonal antibody or by injecting rMMP-9 (recombinant MMP-9). Inhibiting MMP-9 activity profoundly suppressed vascular injury, decreased the density of inflammatory infiltrates ( P<0.001), reduced intramural neoangiogenesis ( P<0.001), and prevented intimal layer hyperplasia ( P<0.001). rMMP-9 amplified all domains of vasculitic activity, promoted assembly of T-cell infiltrates ( P<0.05), intensified formation of new microvessels ( P<0.001), and worsened intimal thickening ( P<0.001). Systemic delivery of N-acetyl-proline-glycine-proline-a matrikine produced by MMP-9-mediated gelatinolysis-had limited vasculitogenic effects. CONCLUSIONS: In large vessel vasculitis, MMP-9 controls the access of monocytes and T cells to the vascular wall. T cells depend on MMP-9-producing monocytes to pass through collagen IV-containing basement membrane. Invasion of vasculitogenic T cells and monocytes, formation of neoangiogenic networks, and neointimal growth all require the enzymatic activity of MMP-9, identifying this protease as a potential therapeutic target to restore the immunoprivilege of the arterial wall in large vessel vasculitis.

Inhibition of JAK-STAT Signaling Suppresses Pathogenic Immune Responses in Medium and Large Vessel Vasculitis.

BACKGROUND: Giant cell arteritis, a chronic autoimmune disease of the aorta and its large branches, is complicated by aneurysm formation, dissection, and arterial occlusions. Arterial wall dendritic cells attract CD4+ T cells and macrophages to form prototypic granulomatous infiltrates. Vasculitic lesions contain a diverse array of effector T cells that persist despite corticosteroid therapy and sustain chronic, smoldering vasculitis. Transmural inflammation induces microvascular neoangiogenesis and results in lumen-occlusive intimal hyperplasia. We have examined whether persistent vessel wall inflammation is maintained by lesional T cells, including the newly identified tissue-resident memory T cells, and whether such T cells are sensitive to the cytokine-signaling inhibitor tofacitinib, a Janus kinase (JAK) inhibitor targeting JAK3 and JAK1. METHODS: Vascular inflammation was induced in human arteries engrafted into immunodeficient mice that were reconstituted with T cells and monocytes from patients with giant cell arteritis. Mice carrying inflamed human arteries were treated with tofacitinib or vehicle. Vasculitic arteries were examined for gene expression (reverse transcription polymerase chain reaction), protein expression (immunohistochemistry), and infiltrating cell populations (flow cytometry). RESULTS: Tofacitinib effectively suppressed innate and adaptive immunity in the vessel wall. Lesional T cells responded to tofacitinib with reduced proliferation rates (<10%) and minimal production of the effector molecules interferon-γ, interleukin-17, and interleukin-21. Tofacitinib disrupted adventitial microvascular angiogenesis, reduced outgrowth of hyperplastic intima, and minimized CD4+CD103+ tissue-resident memory T cells. CONCLUSIONS: Cytokine signaling dependent on JAK3 and JAK1 is critically important in chronic inflammation of medium and large arteries. The JAK inhibitor tofacitinib effectively suppresses tissue-resident memory T cells and inhibits core vasculitogenic effector pathways.

NADPH oxidase deficiency underlies dysfunction of aged CD8+ Tregs.

Immune aging results in progressive loss of both protective immunity and T cell-mediated suppression, thereby conferring susceptibility to a combination of immunodeficiency and chronic inflammatory disease. Here, we determined that older individuals fail to generate immunosuppressive CD8+CCR7+ Tregs, a defect that is even more pronounced in the age-related vasculitic syndrome giant cell arteritis. In young, healthy individuals, CD8+CCR7+ Tregs are localized in T cell zones of secondary lymphoid organs, suppress activation and expansion of CD4 T cells by inhibiting the phosphorylation of membrane-proximal signaling molecules, and effectively inhibit proliferative expansion of CD4 T cells in vitro and in vivo. We identified deficiency of NADPH oxidase 2 (NOX2) as the molecular underpinning of CD8 Treg failure in the older individuals and in patients with giant cell arteritis. CD8 Tregs suppress by releasing exosomes that carry preassembled NOX2 membrane clusters and are taken up by CD4 T cells. Overexpression of NOX2 in aged CD8 Tregs promptly restored suppressive function. Together, our data support NOX2 as a critical component of the suppressive machinery of CD8 Tregs and suggest that repairing NOX2 deficiency in these cells may protect older individuals from tissue-destructive inflammatory disease, such as large-vessel vasculitis.

Role of chitin and chitinase/chitinase-like proteins in inflammation, tissue remodeling, and injury.

The 18 glycosyl hydrolase family of chitinases is an ancient gene family that is widely expressed from prokaryotes to eukaryotes. In mammals, despite the absence of endogenous chitin, a number of chitinases and chitinase-like proteins (C/CLPs) have been identified. However, their roles have only recently begun to be elucidated. Acidic mammalian chitinase (AMCase) inhibits chitin-induced innate inflammation; augments chitin-free, allergen-induced Th2 inflammation; and mediates effector functions of IL-13. The CLPs BRP-39/YKL-40 (also termed chitinase 3-like 1) inhibit oxidant-induced lung injury, augments adaptive Th2 immunity, regulates apoptosis, stimulates alternative macrophage activation, and contributes to fibrosis and wound healing. In accord with these findings, levels of YKL-40 in the lung and serum are increased in asthma and other inflammatory and remodeling disorders and often correlate with disease severity. Our understanding of the roles of C/CLPs in inflammation, tissue remodeling, and tissue injury in health and disease is reviewed below.

[Role of matrix metalloproteinases in primary systemic vasculitis]. / Rola metaloproteinaz macierzy w pierwotnych ukladowych zapaleniach naczyn.

Primary systemic vasculitis comprise a group of diseases such as Wegener's granulomatosis, Kawasaki disease, Takayasu arteritis, giant cell arteritis with various clinical manifestations, and an etiology not fully understood. The pathogenesis involves an inflammatory infiltration of the vessel wall, which results in its damage. Matrix metalloproteinases seem to participate not only in the degradation of structural components of a vessel wall which leads to bleeding and/or aneurysmal dilatation. In addition, they play a significant role in the in inflammatory cells migration and development of inflammatory infiltration. This process, and the proliferation and migration of smooth muscle cells may result in the narrowing of the affected vessels. This article outlines the role of matrix metalloproteinases in primary systemic vasculitis.

Association of a nonsynonymous single-nucleotide polymorphism of matrix metalloproteinase 9 with giant cell arteritis.

OBJECTIVE: Giant cell arteritis (GCA) is the most common type of primary vasculitis. Matrix metalloproteinase 9 (MMP-9) is present in arterial lesions of GCA and may be involved in its pathogenesis. We investigated whether certain genotypes of 4 single-nucleotide polymorphisms (SNPs) of MMP-9 are overrepresented in patients with histologically confirmed GCA. METHODS: Four SNPs of MMP-9, rs3918242 in the promoter region and 3 nonsynonymous coding SNPs (rs3918252, rs17576, and rs2250889) were genotyped by polymerase chain reaction-restriction fragment length polymorphism analysis in 58 white patients for whom there was a clinical suspicion of GCA. Thirty of these patients had histologically confirmed GCA (group 1), and 28 patients had negative results of a temporal artery biopsy for GCA (group 2). Estimates of the genotype distributions of each of these SNPs in a white population were determined using publicly available genotype data for a panel of 23 individuals (group 3). RESULTS: Although 1 SNP was monomorphic in all 3 groups, we observed statistically significant differences in the genotype distributions for rs2250889 between group 1 and group 2 (P = 0.005) and between group 1 and group 3 (P = 0.009), but not between groups 2 and 3 (P = 0.965). CONCLUSION: These data derived from a sample of patients with GCA suggest that the G allele of MMP-9 polymorphism rs2250889 is overrepresented in patients with histologically confirmed GCA. Clearly, larger sample sizes will be necessary to confirm this suggestive association and better characterize a possible linkage disequilibrium structure among polymorphisms.

Gelatinase expression and proteolytic activity in giant-cell arteritis.

OBJECTIVES: Gelatinases (MMP2 and MMP9) are expressed in giant-cell arteritis (GCA) and are thought to play a role in vessel disruption. However, their activation status and enzymatic activity have not been evaluated. Our aim was to investigate the distribution and proteolytic activity of gelatinases in GCA lesions at different stages. METHODS: Expression of MMP2, MMP9, MMP2-activator MMP14 and their natural inhibitors TIMP1 and TIMP2 was determined by real-time PCR and immunohistochemistry in temporal artery sections from 46 patients and 12 controls. MMP activation status and enzymatic activity were assessed by gelatin and film in situ zymography. RESULTS: Vascular smooth muscle cells from normal specimens constitutively expressed pro-MMP2 and its inhibitor TIMP2 with no resulting proteolytic activity. In GCA MMP2, MMP9 and MMP14 were strongly expressed in their active form by infiltrating leucocytes. Inflamed arteries also expressed TIMP1 and TIMP2. However, the MMP9/TIMP1 and MMP2/TIMP2 ratios were higher in patients compared with controls, indicating an increased proteolytic balance in GCA which was confirmed by in situ zymography. Maximal gelatinase expression and activity occurred at the granulomatous areas surrounding the internal elastic lamina (IEL). Myointimal cells also expressed MMPs and exhibited proteolytic activity, suggesting a role for gelatinases in vascular remodelling and repair. CONCLUSIONS: GCA lesions show intense expression of gelatinases. Activators and inhibitors are regulated to yield enhanced gelatinase activation and proteolytic activity. Distribution of expression and proteolytic activity suggests that gelatinases have a major role not only in the progression of inflammatory infiltrates and vessel destruction but also in vessel repair.

Metalloproteinase-2 and -9 in giant cell arteritis: involvement in vascular remodeling.

BACKGROUND: Both matrix metalloproteinase-2 (MMP-2) and -9 (MMP-9) have been postulated to play roles in the pathophysiology of giant cell arteritis (GCA) because of their ability to degrade elastin. Understanding the specific mediators of arterial damage in GCA could lead to new therapeutic targets in this disease. METHODS AND RESULTS: Temporal artery biopsy specimens were obtained from 147 consecutive patients suspected of GCA. Clinical and histopathological data were collected according to protocol. Using immunohistochemistry, we compared the expression of MMP-2 and MMP-9 in the temporal artery biopsies of both GCA cases (n=50) and controls (n=97). MMP-9 was found more frequently in positive than in negative temporal artery biopsies (adjusted odds ratio [OR], 3.20; P=0.01). In contrast, the frequency of MMP-2 was not significantly different between positive and negative biopsies (adjusted OR, 2.18; P=0.22). Both MMP-2 and MMP-9 were found in macrophages and giant cells near the internal elastic lamina and in smooth muscle cells and myofibroblasts of the media and intima. MMP-9 was also found in the vasa vasorum. MMP-9 but not MMP-2 was associated with internal elastic lamina degeneration, intimal hyperplasia, and luminal narrowing, even after adjustment for possible confounding variables. CONCLUSIONS: MMP-9 appears more likely than MMP-2 to be involved in the pathophysiology of GCA. MMP-9 not only participates in the degradation of elastic tissue but also is associated with intimal hyperplasia, subsequent luminal narrowing, and neoangiogenesis. The expression of MMP by smooth muscle cells implicates these cells as potential secretory cells in GCA.

Endothelial nitric oxide synthase gene polymorphisms in giant cell arteritis.

OBJECTIVE: To examine potential associations of the Glu/Asp(298) polymorphism in exon 7 and the 4a/b polymorphism in intron 4 of the endothelial nitric oxide synthase (eNOS) gene with susceptibility to and clinical expression of giant cell arteritis (GCA), particularly in patients with versus those without ischemic complications. METHODS: Ninety-one consecutive patients with biopsy-proven GCA, who were residents of Reggio Emilia, Italy, and 133 population-based controls from the same geographic area were genotyped by polymerase chain reaction and allele-specific oligonucleotide techniques for eNOS polymorphisms in exon 7 and intron 4. The patients were separated into 2 subgroups according to the presence or absence of ischemic complications (visual loss and/or jaw claudication and/or aortic arch syndrome). RESULTS: The distribution of the Glu/Asp(298) genotype differed significantly between GCA patients and controls (corrected P [P(corr)] = 0.003). Carriers of the Asp(298) allele (Asp/Asp or Glu/Asp) were significantly more frequent among the GCA patients than among the controls (P(corr) = 0.0002, odds ratio 3.3, 95% confidence interval 1.7-6.3). The distribution of the 4a/b genotype was similar in GCA patients and controls. No significant associations were found when GCA patients with and without ischemic complications were compared. CONCLUSION: Our findings show that the Glu/Asp(298) polymorphism of the eNOS gene is associated with GCA susceptibility.

Giant cell arteritis with an erythrocyte sedimentation rate lower than 50.

A high erythrocyte sedimentation rate (ESR) is considered to be a hallmark of giant cell arteritis (GCA) and one of the 1990 American College of Rheumatology classification criteria. We studied 248 patients with GCA to assess the frequency and clinical features of patients with GCA and an ESR <50 mm/h. Ten patients had a low ESR (43.1 +/- 4.9 mm/h) and in the remaining 238, the ESR was > or = 50 mm/h (96.4 +/-23.6). None of the patients with an ESR less than 50 had a completely normal ESR. The spectrum of the disease in both groups was very similar. Both groups required similar corticosteroid therapy and had a similar outcome. The ESR, analysed as a continuous variable, showed a significant positive correlation with other parameters reflecting the acute-phase response such as presence of anaemia, weight loss and fever. We suggest that in patients with a clinical picture compatible with GCA, the use of an ESR > or = 30 mm/h as the main laboratory parameter to consider the possibility of GCA would be enough to arise the suspicion and prevent cases of GCA being missed.

[Activity of chymotrypsin-like proteinases in patients with ischemic heart disease, arterial hypertension and nonspecific aortic arteritis]. / Aktivnost' khimotripsinopodobnykh proteinaz u bol'nykh ishemicheskoi bolezn'iu serdtsa, arterial'nymi gipertoniiami i nespetsificheskim aortoarteritom.

AIM: To analyze activity of chymotrypsin-like plasma proteinases (CTP) in patients with various cardiovascular diseases. MATERIAL AND METHODS: CTP activity was studied in 82 patients with various cardiovascular diseases: 13 coronary heart disease patients with normal arterial pressure, 49 patients with essential hypertension (EH) and secondary arterial hypertension, 20 patients with nonspecific aortic arteritis. 28 donors served control. RESULTS: CTP activity in plasma of patients with EH rose 4 times compared to donors. If EH patients had concurrent diseases (CHD, chronic pyelonephritis, atherosclerosis of extracranial arteries), CTP activity may increase by 30-300%. In patients with nonspecific aortic arteritis CTP activity in blood plasma is 17.5 times higher than in donors. CONCLUSION: High CTP activity in cardiovascular patients may be explained by chymase and cathepsin G release into blood flow indicating activation of alternative to ACE pathway of angiotensin II production or the presence of the inflammatory process.

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.

Matrix metalloproteinases and tissue inhibitors of metalloproteinases in giant cell arteritis: an immunocytochemical study.

Giant cell arteritis (GCA) is a relatively common granulomatous arteritis of unknown etiology which mainly occurs in elderly people. Using histopathological findings from-seven biopsy cases of temporal artery and one autopsy case of GCA, and performing immunocytochemical staining for matrix metalloproteinase (MMP)-2 and -9 and tissue inhibitor of matrix metalloproteinase (TIMP)-1 and -2, we tested the hypothesis that an imbalance between MMPs and TIMPs may be a critical determinant in developing severe intimal hyperplasia and luminal stenosis. All biopsy cases revealed nearly complete luminal occlusion of the temporal artery with active lymphocytic infiltrate, fragmentation of internal lamina and median elastic fibers. Four of seven cases revealed typical GCA. The autopsy case was systematically sampled for histological examination, revealing GCA in the ascending aorta, main branches of aorta and coronary artery. Immunocytochemical staining revealed intense staining for MMP-2 and -9 in fragmented media of the aorta and artery, and less positive staining for TIMP-1 and -2 at the MMP-positive media. In situ hybridization revealed intense positive staining for TIMPs in GCA despite weak immunocytochemical staining for TIMPs. Control cases were negative for TIMPs by immunocytochemical staining whereas RNA message level was mildly positive at a lesser intensity than that of GCA. Granulomatous tissue of fibroblasts and giant cells were most intensely positive for MMPs. The presence of markedly increased MMPs and less increased TIMPs in GCA may implicate an MMPs-TIMPs imbalance in the pathogenesis of GCA.

Human neutrophil elastase in temporal (giant cell) arteritis: plasma and immunohistochemical studies.

OBJECTIVE: Few enzymes are able to attack the internal elastic lamina, which is destroyed in temporal arteritis (TA). Because human neutrophil elastase (HNE) is one of these, its role in the pathogenesis of TA was examined in patients undergoing temporal artery biopsy for suspected TA. METHODS: Over a 6 month period, 33 patients undergoing temporal artery biopsy were prospectively included in the study. TA was diagnosed in 15 patients; 9 of them had positive temporal artery biopsy. The other 18 patients made up the non-TA group. Nineteen healthy age matched subjects (mean age 74 +/- 9 yrs) served as controls. Levels of plasma HNE bound to alpha1-antitrypsin (pHNE-alpha1AT) were measured by ELISA. The presence of HNE in the temporal artery wall of 7 TA and 7 non-TA patients was evaluated immunohistochemically. RESULTS: Age, neutrophil counts, and erythrocyte sedimentation rates were similar in TA and non-TA patients. The mean pHNE-alpha1AT concentration in the TA group (84 +/- 20 microg/l) was significantly higher (p < 0.001) than in the non-TA group (51 +/- 26 microg/l) or in healthy controls (52 +/- 23 microg/l). The diagnostic sensitivity of pHNE-alpha1AT > 50 microg/l was 100%. Immunohistochemistry detected no HNE within the temporal artery wall of any patient. CONCLUSION: High levels of pHNE-alpha1AT were associated with TA. Our preliminary results indicate this could be a diagnostic marker for TA. Further studies are needed to confirm its reliability. Because HNE was not detected locally, no conclusions can be drawn as to its pathogenic role in TA.

Macrophages contain 92-kd gelatinase (MMP-9) at the site of degenerated internal elastic lamina in temporal arteritis.

Inflammation precedes erosion and rupture of atherosclerotic atheromas and aneurysms. Inflammatory infiltrates of macrophages have been shown to secrete proteolytic enzymes, including matrix metalloproteinases (MMPs), that weaken the arterial wall. The effect of inflammation on arterial structure and remodeling can be studied in primary vascular inflammatory diseases such as in temporal arteritis. We examined the 72-kd gelatinase (MMP-2) and the 92-kd gelatinase (MMP-9) in inflamed and uninvolved temporal arteries from 10 patients with temporal arteritis and 5 controls by immunohistochemistry. The substrates of these enzymes, type IV collagen and elastin, were detected by immunohistochemistry and histochemical staining, respectively. Both diseased and normal artery specimens had moderate staining for immunoreactive MMP-2. Temporal arteritis specimens had clearly enhanced immunostaining for MMP-9 compared with normal arteries. MMP-9 was specifically localized to macrophages in regions of internal elastic lamina disruption, which may thus be of pathological significance.

Elevated levels of 92-kd type IV collagenase (matrix metalloproteinase 9) in giant cell arteritis.

OBJECTIVE: To determine if circulating gelatinase activity and matrix metalloproteinase 9 (MMP-9) (gelatinase B, or 92-kd type IV collagenase) antigenic levels are elevated in sera of patients with giant cell arteritis (GCA), and to ascertain if MMP-9 messenger RNA (mRNA) is deposited in situ at sites of disease involvement. METHODS: Serum samples were collected from 12 patients with GCA and 12 healthy volunteers. Vascular tissue was obtained at the time of temporal artery biopsy. Type IV collagenase activity was determined by gelatin substrate zymography and the quantitative biotinylated gelatin substrate degradation assay. A double-sandwich immunoassay utilizing 2 different isotypes of monoclonal antibodies generated against MMP-9 was used for measuring serum MMP-9 antigenic levels. Finally, to localize sites of MMP-9 mRNA transcription in inflamed arteries, the method of reverse transcriptase in situ polymerase chain reaction (RTisPCR) was utilized. RESULTS: Serum gelatinase activity and MMP-9 titers were significantly increased in patients with GCA (mean +/- SEM 198.9 +/- 36.9 micrograms gelatin/hour/ml serum, versus 21.2 +/- 4.0 in controls; P = 0.0006). The differences in antigenic MMP-9 levels were even more prominent (3005.4 +/- 900.6 ng/ml and 31.6 +/- 9.8 ng/ml in GCA and control sera, respectively; P = 0.007). By RTisPCR, MMP-9 mRNA was mainly detected in cytoplasm of cells resembling smooth muscle cells and fibroblasts in regions of fragmented elastic tissue in the lamina media. CONCLUSION: Gelatinase activity, and specifically MMP-9 levels, are substantially elevated in sera of patients with GCA. Detection of MMP-9 mRNA in the lamina media of inflamed vasculature suggests that degradation of intercellular matrix, particularly elastic fibers, may play a key role in the pathogenesis of GCA. Further studies are needed to determine if the circulating MMP-9 level could be utilized as a clinical marker of disease activity.