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Background: Porcine vascular endothelial cells are a major participant in xenograft rejection. The Toll-like receptor 2 (TLR2) pathway plays an important role in both innate and adaptive immunity. The specific role of TLR2 in the response to a xenograft has not been reported. Whether the TLR2 pathway in pig vascular endothelial cells is involved in acute rejection needs to be investigated, and the mechanism is explored., Methods: We used a modified antibody-dependent complement-mediated cytotoxicity (ADCC) assay to conduct in vitro experiments. In porcine iliac artery endothelial cells (PIECs), siRNA was used to knock down the expression of TLR2, CXCL8, and CCL2. The effect of human serum or inactivated human serum on the expression of TLR2 was analyzed by real-time PCR and Western blotting, and transwell assays were used to assess the chemotactic efficiency of PIECs on human monocyte-macrophages (THP-1 cells) and human neutrophils. The downstream signaling pathways activated by human serum were detected by Western blotting, and the regulation of proinflammatory chemokines and cytokines by TLR2 signaling was assessed by real-time PCR and ELISA., Results: TLR2 was significantly upregulated in PIECs after exposure to human serum, and porcine proinflammatory chemokines, CXCL8 and CCL2, were induced, at least partially, in a TLR2-dependent pattern; the upregulated chemokines participated in the chemotaxis of human neutrophils and THP-1 cells across the species barrier., Conclusions: (i) TLR2 is significantly upregulated in PIECs by human serum, (ii) the elevated TLR2 participates in the chemotaxis of inflammatory cells through the secretion of chemokine CCL2 and CXCL8, and (iii) blockade of TLR2 would be beneficial for xenograft survival., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Even with drug-eluting stents, the risk of in-stent restenosis (ISR) remains high. The goal of this study was to investigate the use of an endothelial progenitor cell (EPC) capture stent plus regional EPC transplantation to reduce the ISR rate., Methods: Endothelial progenitor cell capture stents were fabricated using fibrin gel and anti-CD34 plus anti-VEGFR-2 dual antibodies. Twenty male New Zealand white rabbits established as an atherosclerotic model were randomly divided into two groups: group 1 (n = 10), in which EPC capture stents were deployed into the right iliac artery; and group 2 (n = 10), in which sirolimus-eluting stents were placed. In both groups, EPCs were transplanted into target vessels beyond the stents, with outflow blocked. Radiologic-pathologic correlation outcomes were reviewed after 2 months., Results: The technical success rate of EPC capture stent placement plus EPC transplantation was 100%. The ISR rate in group 1 was lower than in group 2 (1/10 vs. 4/10; p > 0.05). Minimal luminal diameters were larger in group 1 than in group 2 (computed tomographic angiography, 1.85 ± 0.15 mm vs. 1.50 ± 0.20 mm; duplex ultrasound, 1.90 ± 0.10 mm vs. 1.70 ± 0.30 mm; p > 0.05). Transplanted EPCs were tracked positively only in group 1. Pathologic analysis demonstrated neointimal hyperplasia thickness of 0.21 ± 0.09 mm in group 1 vs. 0.11 ± 0.07 mm in group 2 (p < 0.05)., Conclusion: Endothelial progenitor cell capture stent placement plus local EPC transplant decreases the ISR rate through thrombosis reduction rather than through neointimal hyperplasia inhibition.

Porcine circovirus-associated disease is caused by porcine circovirus type 2 (PCV2) infection, which targets iliac artery endothelial cells (PIECs); it leads to severe immunopathologies and is associated with major economic losses in the porcine industry. Here, we report that in vitro PCV2 infection of PIECs causes cell injury, which affects DC function as well as adaptive immunity. Specifically, PCV2 infection downregulated PIEC antigen-presenting molecule expression, upregulated cytokines involved in the immune and inflammatory response causing cell damage and repair, and altered the migratory capacity of PIECs. In addition, PCV2-infected PIECs inhibited DC maturation, enhanced the endocytic ability of DCs, and weakened the stimulatory effect of DCs on T lymphocytes. Together, these findings indicate that profound functional impairment of DCs in the presence of PCV2-infected PIECs may be a potential pathogenic mechanism associated with PCV2-induced porcine disease.

Introduction: The viability and immunological response induced by cryopreserved arterial allografts remain unclear. This study examines the post-graft behaviour of this type of vessel substitute., Materials and Methods: Both iliac arteries were extracted from Lewis rats (donors) and used to establish groups of allogeneic fresh (group I) or cryopreserved (group II) grafts in Fisher-344 rats (recipients). Cryopreserved segments for grafting were prepared by automated controlled freezing at a cooling rate of 1°C/min followed by storage in liquid nitrogen vapour at -145°C for 30 days. Before grafting, the vessels were slowly thawed. Animals were sacrificed at 14, 30, 90 and 180 days post-surgery when graft specimens were obtained for light and electron microscopy and immunohistochemical detection of inflammatory cells (CD45, ED1, CD4, CD8)., Results: After surgery, 85.71% of the grafts in group I and 82.14% in group II were patent. Following long-term implant, both the fresh and cryopreserved allografts showed complete loss of the muscle compartment of the media. Inflammatory or CD45-positive cells (mainly macrophages and CD8 T-lymphocytes) were detected at earlier time points in suture zones and adventitia. In the fresh allografts, the number of immunolabelled cells steadily increased until they were seen to occupy the entire adventitia at 90 days, with high numbers persisting at 6 months. In the cryopreserved allografts, this adventitial inflammatory infiltrate was significantly reduced., Conclusions: The cryopreservation/slow thawing protocol used diminished the immune response induced by fresh arterial allografts improving their behaviour after grafting.

Background: To enable intravascular detection of inflammation in atherosclerosis, we developed a near-infrared fluorescence (NIRF) catheter-based strategy to sense cysteine protease activity during vascular catheterization., Methods and Results: The NIRF catheter design was based on a clinical coronary artery guidewire. In phantom studies of NIRF plaques, blood produced only a mild (<30%) attenuation of the fluorescence signal compared with saline, affirming the favorable optical properties of the NIR window. Catheter evaluation in vivo used atherosclerotic rabbits (n=11). Rabbits received an injection of a cysteine protease-activatable NIRF imaging agent (Prosense750; excitation/emission, 750/770 nm) or saline. Catheter pullbacks through the blood-filled iliac artery detected NIRF signals 24 hours after injection of the probe. In the protease agent group, the in vivo peak plaque target-to-, Background: <0.05). Ex vivo fluorescence reflectance imaging corroborated these results (target-to-, Background: <0.01). In the protease group only, saline flush-modulated NIRF signal profiles further distinguished atheromata from normal segments in vivo (P<0.01). Good correlation between the in vivo and ex vivo plaque target-to-, Background: =0.82, P<0.01). Histopathological analyses demonstrated strong NIRF signal in plaques only from the protease agent group. NIRF signals colocalized with immunoreactive macrophages and the cysteine protease cathepsin B., Conclusions: An intravascular fluorescence catheter can detect cysteine protease activity in vessels the size of human coronary arteries in real time with an activatable NIRF agent. This strategy could aid in the detection of inflammation and high-risk plaques in small arteries.

Background: Inflammation is important to vascular repair following injury, modulating neointimal proliferation and remodeling. Previously, we have shown that a low-intensity inflammatory response aggravates neointimal formation following balloon and stent injury. The present study examined whether modulation of the extent and timing of nonspecific inflammation mediates the local vascular response in an additive unidirectional or rather a bidirectional fashion., Methods and Results: Rabbits subjected to denudation and balloon injury of the iliac artery were treated with low (1 microg/kg) or high (100 microg/kg) doses of bacterial endotoxin (LPS) immediately after injury, or with early high-dose LPS administered 3 days prior to injury (preconditioning). Neointimal formation at 28 days was significantly increased in the low-dose group (0.537+/-0.059 mm(2)) as compared with controls (0.3+/-0.03 mm(2)). High-dose LPS did not significantly affect neointimal formation while early high dose significantly reduced neointima (0.296+/-0.033 and 0.194+/-0.025 mm(2), respectively, n=12-14/group). Arterial wall and systemically circulating interleukin-1 beta levels, and monocyte CD14 activation correlated with neointimal formation. Vascular remodeling was accelerated in animals treated with low- or high-dose LPS while not affected in the preconditioned group. Remodeling index inversely correlated with arterial matrix metalloproteinase-2 levels 6 days after injury., Conclusions: The extent and timing of nonspecific inflammation that is concurrent with vascular injury can determine different and opposite vascular repair patterns.

Background: Neointimal hyperplasia is strikingly suppressed in an endothelium injury model in mice deficient in the growth factor midkine. Knockdown of midkine expression by means of antisense oligonucleotide or small interfering RNA has been shown to lead to suppression of neointimal hyperplasia in a balloon injury model and a rabbit vein graft model; therefore, midkine is an essential factor for neointimal hyperplasia. These findings, however, do not necessarily apply to the function of midkine in vascular stenoses such as in-stent restenosis, because human vascular stenosis is often accompanied by atherosclerosis., Methods: We investigated midkine expression in the neointima induced by implantation of a bare metal stent in the atheromatous lesions of hypercholesterolemic rabbits. We analyzed midkine expression during a THP-1 cell differentiation and in peritoneal macrophages exposed to low-density lipoprotein or oxidized low-density lipoprotein., Results: Midkine expression reached the maximum level within 7 days after stenting and was detected in infiltrating macrophages. Differentiation of THP-1 cells to macrophage-like cells did not trigger midkine expression. Neither low-density lipoprotein nor oxidized low-density lipoprotein enhanced midkine expression in peritoneal macrophages that had been activated by thioglycollate, although these cells expressed a significant amount of midkine., Conclusion: The results indicate that macrophages are the major source of midkine in the atherosclerotic neointima. The amount of midkine expressed in macrophages may be sufficient (ie, further enhancement of the expression is not necessary) for the pathogenesis, because oxidized low-density lipoprotein stimulation did not induce the midkine expression., Clinical Relevance: The growth factor midkine is induced during vascular stenosis in mouse and rat models with normal diet. Knockdown of midkine expression suppresses neointimal hyperplasia. The vascular response after stenting differs from that after balloon injury in that the inflammation is more prolonged and the accumulation of macrophages is more abundant in stent-injured vessel. We found here that macrophages are the major source of midkine in the atherosclerotic neointima of in-stent restenosis in hypercholesterolemic rabbits. Our data suggest that midkine has an important role in in-stent restenosis of atherosclerotic vessels and is a candidate molecular target to prevent in-stent restenosis.

Vascular endothelial cells (ECs) can be injured in a variety of pathologic processes that involve activated complement. We reported previously that porcine ECs incubated with exogenous IL-4 or IL-13 are protected from cytotoxicity by human complement and also from apoptosis by TNF-alpha. The resistance to complement consists of an intrinsic mechanism that is lost a few days after cytokine removal. In our current study, we investigated whether transfer of the IL-4 gene into porcine ECs in vitro and into porcine vascular tissues in vivo would induce efficient and durable protection from human complement. We found that ECs transduced with adenoIL-4 or adenoIL-13 exhibited continuous production of the cytokine and prolonged protection from complement-mediated killing. IL-4 also protected ECs from activation: ECs incubated with IL-4 did not develop cell retraction and intercellular gaps upon stimulation with sublytic complement. The endothelium and subendothelium of pig iliac arteries that were transduced with the IL-4 gene were effectively protected from complement-dependent immediate injury after perfusion with human blood. However, after similar perfusion, the endothelium was immediately lost from arteries that were transduced with a control adenovirus. The protection was not due to up-regulation of the complement regulators decay accelerating factor, membrane cofactor protein, and CD59, or to reduced complement activation, but required the participation of Akt. Although our studies model protection in pig-to-primate xenotransplantation, our findings of IL-4 induction of Akt-mediated protection may be more broadly applicable to EC injury as manifested in ischemia-reperfusion, allotransplantation, and various vascular diseases.

Objective: Inflammatory responses of large vein endothelium are of importance in pathological processes such as venous thrombosis, chronic venous congestion, and vein graft atherosclerosis. However, the inflammatory properties of large vein endothelium are unclear., Methods and Results: In this study, we used several microscopy techniques to investigate the inflammatory properties of large vein endothelium in vivo. We show that the endothelium in the mouse inferior vena cava (IVC) possesses powerful inflammatory properties that are distinct from the less inflammatory reactive aortic endothelium and virtually identical to endothelial responses in postcapillary venules. Inflammatory stimulation with tumor necrosis factor-alpha induced strong expression of cell adhesion molecules (CAMs) in the IVC. These CAMs promoted recruitment of leukocytes, platelets, and erythrocytes to the vein wall. The inflammatory responses altered endothelial structure and increased endothelial permeability in the IVC. Accumulation of blood cells and endothelial damage were markedly reduced in mice deficient in the endothelial leukocyte recruitment molecules E-selectin and P-selectin, indicating a central role for these molecules in driving structural and functional changes of IVC endothelium., Conclusions: These findings provide the first comprehensive demonstration of the inflammatory capacity of large vein endothelium and emphasize the actions of endothelial cells as targets in large vein disease.

Unlabelled: Inflammation plays a central role in restenosis following coronary intervention. Recent human and animal data suggest important differences between the inflammatory responses to simple balloon angioplasty compared with stent implantation. To investigate the mechanisms of these differences, New Zealand white rabbits underwent bilateral iliac artery balloon denudation. Half received intravascular stents. Arteries were harvested at three, seven and 14 days for immunohistochemistry, and 4 hours, 8 hours and 14 days for chemokine mRNA analysis. Leukocyte content was quantified utilizing immunohistochemistry (RPN357, monoclonal antibody (mAb) against rabbit neutrophil; RAM-11, mAb against rabbit macrophage). We analyzed the mRNA levels of the chemokines monocyte chemoattractant protein 1 (MCP-1) and interleukin 8 (IL-8) through semi-quantitative polymerase chain reaction. We demonstrated the spatial pattern of MCP-1 mRNA levels through in situ mRNA hybridization. In balloon-injured arteries, leukocyte recruitment was confined to early neutrophil infiltration. IL-8 and MCP-1 mRNA levels peaked within hours and were undetectable at 14 days. In contrast, in stented arteries, early neutrophil recruitment was followed by prolonged macrophage accumulation. IL-8 and MCP-1 mRNA levels peaked within hours but were still detectable 14 days post injury., Conclusions: In contrast to balloon injury, stent-induced injury results in sustained chemokine expression and leukocyte recruitment. These data may have important implications for antirestenotic strategies.

Background: The activation of platelets or leukocytes plays an important role in development of intimal hyperplasia. We investigated whether the local blood serotonin and soluble P-selectin levels changed during endovascular therapy of the iliac artery., Methods: Blood samples were obtained from the iliac artery of 18 lower limbs undergoing percutaneous balloon angioplasty alone (8 limbs, group I) or percutaneous balloon angioplasty and primary stenting (10 limbs, group II). The serotonin levels in platelet-poor plasma were measured in all limbs. In group I the urinary level of the serotonin metabolite 5-hydroxyindoleacetic acid was also measured 24 hours before and 24 hours after the procedures. The soluble P-selectin levels were measured in the 6 patients in group II., Results: Before angioplasty the mean (+/- SEM) serotonin concentrations were 1.2 +/- 0.2, 1.2 +/- 0.4, and 1.2 +/- 0.3 ng/mL in all cases, group I, and group II, respectively. After angioplasty these values changed to 1.7 +/- 0.4 (P =.0750), 1.2 +/- 0.4 (P =.8001), and 2.1 +/- 0.6 ng/mL (P =.0529), respectively. In group I urinary 5-hydroxyindoleacetic acid concentrations 24 hours before and 24 hours after the procedures were 0.0026 +/- 0.0004 and 0.0031 +/- 0.0006 mg/mg creatinine, respectively (P =.2566). In group II the soluble P-selectin levels significantly increased after intervention, from 26.0 +/- 5.7 to 33.9 +/- 5.3 ng/mL (P =.0296)., Conclusions: Although the serotonin levels did not change significantly, the soluble P-selectin levels increased significantly after intervention. Leukocyte activation may therefore contribute to the progression of restenosis after peripheral endovascular therapy.

CD40-CD154-mediated signaling has recently been described as playing a role in cellular functions involved in atherosclerotic processes. CD40 is expressed in macrophages, lymphocytes, endothelial cells, and vascular smooth muscle cells. However, cross-sectional studies investigating the expression of CD40 in atherosclerotic lesions are lacking. In the present study the expression of CD40 was studied in atherosclerotic lesions from 43 patients classified according to the World Health Organization criteria. Serial immunohistologic stainings of human iliac arteries from 43 patients were performed using monoclonal antibodies. Lesions were classified according to World Health Organization criteria, and CD40 expression was analyzed with regard to cell morphology and cellular markers by 2 independent observers. Human atherosclerotic lesions revealed a significant increase in intimal thickness, number of inflammatory infiltrates, and CD40-positive macrophages and vascular smooth muscle cells with progression of the lesions. This increase was most prominent from stage 0 to stage I. A significant correlation between intimal thickness and CD40-positive macrophages (r = 0.75, p <0.0005) and CD40-positive vascular smooth muscle cells (r = 0.81, p <0.0005) was observed. Ligation of the cellular CD40 receptor contributes to inflammatory cellular events in human vascular smooth muscle cells. These data suggest a direct association of CD40 expression in atherosclerotic lesions with early plaque development.

Macrophages are abundant after stent-induced arterial injury. Inhibition of macrophage recruitment blocks neointimal growth in this model. In contrast, after superficial injury from balloon endothelial denudation, macrophages are sparse. However, many anti-inflammatory therapies remain effective against neointimal growth after balloon injury. To investigate further the role of leukocytes after injury, 41 New Zealand White rabbits underwent iliac artery balloon denudation. In 18, subcutaneous pumps were placed to deliver intravenous heparin (0.3 mg/kg per hour). Arteries were harvested at 6 hours and at 3, 7, and 14 days. In 8 animals, either M1/70 (a monoclonal antibody [mAb] against adhesion molecule Mac-1) or a nonspecific IgG was given (5 mg/kg IV bolus and then 1 mg/kg SC QOD), and arteries were harvested at 6 hours and 3 days. Computer-aided morphometry was performed as was immunohistochemistry to assess smooth muscle cell (SMC) proliferation (bromodeoxyuridine-positive cells), neutrophil content (RPN357, mAb against rabbit neutrophil/thymocyte), and macrophage content (RAM-11, mAb against rabbit macrophage). Heparin inhibited neointimal growth at 7 and 14 days (64% and 32.5% reduction, respectively; P:<0.05). Neutrophils were observed in the media early after balloon injury, and heparin and M1/70 inhibited this infiltration (82% and 83% reduction, respectively; P:<0.05 each) with a coincident inhibition of medial SMC proliferation at 3 days (49% and 84% reduction, respectively; P:<0.05 each). Macrophages were absent at all time points. Neutrophil, but not macrophage, infiltration occurs early after endothelial denudation. Inhibition of this process is associated with a reduction in medial SMC proliferation. These data suggest a central role for neutrophils in restenosis and help to explain prior reports of an inhibitory effect of anti-inflammatory therapies on neointimal growth after balloon injury.

Leukocytes are recruited early and abundantly to experimentally injured vessels, in direct proportion to cell proliferation and intimal growth. Activated circulating leukocytes and Mac-1 (CD11b/CD18, alphaMbeta2) expression are markers of restenosis risk in patients undergoing angioplasty. As angioplastied vessels lack endothelium but have extensive fibrin(ogen) and platelet deposition, we hypothesized that Mac-1-dependent adhesion to fibrin(ogen) is an important determinant of leukocyte recruitment and function, which may in turn promote intimal growth. To study this hypothesis we administered M1/70, an anti-CD11b blocking mAb, to rabbits (1 mg/kg i.v.) immediately before, and every 48 hr for 3, 6, or 14 days after, iliac artery balloon denudation or deeper stent-induced injury. M1/70, which bound to isolated rabbit monocytes and dose-dependently inhibited Mac-1-mediated fibrinogen binding in vitro, reduced leukocyte recruitment more than 2-fold 3, 6, and 14 days after injury. Neointimal growth 14 days after injury was markedly attenuated by treatment with M1/70 (intimal area after balloon injury, 0.12 +/- 0.09 mm2, compared with 0.32 +/- 0.08 mm2 in vehicle-treated controls, P < 0.01, and 0.38 +/- 0.08 mm2 in IgG-treated controls, P < 0.005; intimal area after stent injury, 0. 56 +/- 0.16 mm2, compared with 0.84 +/- 0.13 mm2 in vehicle-treated controls, P < 0.05, and 0.90 +/- 0.15 mm2 in IgG-treated controls, P < 0.02). Mac-1 blockade reduces experimental neointimal thickening, suggesting that leukocyte recruitment to and infiltration of injured arteries may be a valid target for preventing intimal hyperplasia.

Transabdominal aortic replacement is the most widely accepted approach for aortic surgery. Several controlled studies report a more favorable outcome after an extraperitoneal incision, yet there are an equal number of papers with contradictory results. The aim of our study was to assess operative trauma after aortic surgery, depending on whether transperitoneal or extraperitoneal access was used. As a parameter for the extent of the surgical trauma the concentration of Interleukin 6 and acute phase proteins (CRP) was measured pre-, 6 h and 24 h after aortic surgery. One group consisted of 34 patients scheduled for aortic surgery for exclusion of an abdominal aortic aneurysm. The second group consisted of 26 patients who were operated on for aorto-iliac occlusive disease. Each group was subdivided into an equal group of patients operated on either extra- or transperitoneally. In the retroperitoneal aneurysm patients, a posterolateral access was favored, and in patients with occlusive disease an extraperitoneal anterolateral approach was chosen. As a result patients with an extraperitoneal incision and aorto-iliac occlusive disease required less postoperative respiratory support than those operated on transperitoneally. In this subgroup of patients there was a significantly reduced synthesis of Interleukin 6 and CRP. When a retroperitoneal posterolateral approach was required in aneurysm patients, there was no difference between groups. We conclude from our data that only patients with limited infrarenal aortic access can benefit, from the retroperitoneal incision in terms of a reduced immunological reaction.

A 63-year-old woman showed positive perinuclear antineutrophil cytoplasmic antibodies (pANCA) and presented with an interesting CT finding of a periaortic soft-tissue structure seen as a rind of tissue surrounding the aorta, extending longitudinally from descending thoracic aorta to bilateral common iliac arteries which was compatible with an early stage of retroperitoneal fibrosis (RPF). Both pANCA titers and a periaortic mass volume were reduced following corticosteroid treatment. No cases of RPF with a periaortic mass associated with pANCA have been described. Our findings of RPF with pANCA positivity may enlarge the groups of ANCA-associated diseases.

The etiology and pathogenesis of Kawasaki syndrome (KS) remain unknown. Clinical and epidemiologic features of KS are consistent with an infectious cause. To search for an etiologic agent of KS, a phage cDNA expression library was constructed from the aorto-iliac junction of a patient with fatal acute KS and screened with convalescent KS serum followed by anti-human Ig. Unexpectedly, 0.1% of the clones in the library react with anti-human Ig, indicating the presence of many Ig-producing B lymphocytes in the vasculitic tissue. To confirm this finding and to determine the isotypes produced, frozen vascular tissue sections from the patient and paraffin sections from coronary arteries from six additional patients with fatal acute or subacute KS were incubated with Abs to Ig isotypes. Histopathology of the tissues revealed the presence of many plasma cells in the inflammatory infiltrate. IgA was the predominant isotype produced in vascular tissue in all seven KS patients. IgM- and IgG-producing cells were less often detected. We conclude that there is a marked plasma cell response within the vasculitic tissue in KS, with unusual IgA production locally in this nonlymphoid, nonmucosal tissue. We suggest that the prominence of IgA plasma cells in the vascular infiltrate in the early, acute, and subacute stages of KS indicates an Ag-driven immune response to an etiologic agent with a respiratory or gastrointestinal portal of entry and speculate that this unusual immune response is integral to the pathogenesis of the illness.

Fibrous plaques and intimal thickenings of 5 femoral and 5 iliac human arteries obtained at surgery were processed for indirect and double-labeling immunoelectron microscopy using an affinity purified rabbit IgG anti-C5b-9 neoantigen and the EBM 11 monoclonal antibody anti-human macrophages. The C5b-9 complexes were localized in intact cells, disintegrated cells and cell debris enmeshed in the connective tissue matrix. Some of the cell debris bearing C5b-9 deposits was found to be of macrophage origin. Endocyted or exocyted pieces of membrane with pore-forming C5b-9 complexes were also identified. Damage of cells by complement in atherosclerotic lesions may contribute to atherogenesis.

Endothelial injury is associated with an intracellular accumulation of IgG. Fluorescent antibodies were used to detect IgG and complement factor C3 in biopsies of human arteries. Both proteins were found in endothelial cells with signs of injury, in normal and atherosclerotic arteries. Rhodamine-conjugated anti-IgG and FITC-conjugated anti-C3 were used to count the number of IgG- and C3-containing endothelial cells in non-atherosclerotic cystic arteries. IgG was found in 26% of the cells, with C3 in 38% of the IgG-containing cells. Both IgG and C3 were also observed in the subendothelial intima of cystic arteries and in atherosclerotic lesions of iliac and femoral arteries. The accumulation of IgG and C3 in injured endothelium and in atherosclerotic lesions could be of importance for complement-mediated tissue destruction and for the attraction and activation of white blood cells.

The assembly of the terminal C5b-9 complement complex is a prime mechanism of complement-induced membrane damage followed by inflammatory response mediation and subsequent extensive tissue damage. In the assembly process the terminal complement components expose neoantigenic determinants which can be recognized by specific antibodies. Using such a specific antibody, affinity-purified rabbit IgG and by means of immunoelectron microscopy, the C5b-9 neoantigens were localized on the structures of the human fibrous plaque from 3 iliac and 3 femoral arteries obtained at surgery. The immunoelectron-dense deposits were localized on the cell debris, enmeshed in the connective tissue matrix, consisting of irregular particles that frequently had the shape and size of intracellular organelles or vesicles with concentric osmiophilic lamellae. No deposits could be found on the intact cells, on the connective tissue matrix or on cholesterol and lipid deposits. The presence of C5b-9 neoantigens deposits in the fibrous plaques frequently associated with other immune-related proteins indicates that complement activation has occurred in situ and could be related to the chronic progression of the atherosclerotic lesion.