Aortic Fatty Streak Research Articles

Apolipoprotein A-I-containing particles and reverse cholesterol transport: Evidence for connection between cholesterol efflux and atherosclerosis risk

It is now clearly established that apo A-I-containing lipoproteins exist as two major families, those containing apo A-I and apo A-II (LpA-I:A-II) and those containing apo A-I but free of apo A-II (LpA-I). Metabolic studies utilizing radiolabeled lipoprotein particles suggested that there is a kinetic difference between LpA-I and LpA-I:A-II family and support the concept that there may be important functional differences between the lipoprotein particles present within HDL. Of considerable significance was the finding that proteins stimulating reverse cholesterol transport (lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP)) are mainly present in LpA-I and not in LpA-I:A-II family. Cholesterol efflux mediated by A-I-containing particles has been studied in different cells. Long term exposure to LpA-I family promoted cholesterol efflux whereas less efflux was observed in the presence of LpA-I:A-II family. The fact that LpA-I:A-II family can inhibit the LpA-I promoted cholesterol efflux strongly supports the role of apo A-II as an antagonist in the production of cholesterol efflux. These results which emphasize that LpA-I and LpA-I:A-II families behave as distinct entities have been confirmed in other studies showing that they have different clinical significance. The results in mice transgenic for apo A-I indicate that overexpression of apo A-I induces more cholesterol efflux and protects C57BL/6 mice from atherosclerosis. Increased expression of apo A-II in mice appears to decrease cholesterol efflux and to promote rather than retard aortic fatty streak development. Using natural variants of human apo A-I and an immunochemical approach with mapped monoclonal antibodies, we suggest that the region around residue 165 is involved in the interaction of apo A-I with cells. The use of a synthetic tetrameric peptide that mimics properties of apo A-I allowed us to confirm the importance of this particular region in the biological role of apo A-I.

Genetic evidence for a common pathway mediating oxidative stress, inflammatory gene induction, and aortic fatty streak formation in mice.

In a previous survey of inbred mouse strains on an atherogenic diet, we observed that the susceptibility to aortic atherosclerotic lesion formation was associated with the accumulation of lipid peroxidation products, induction of inflammatory genes, and the activation of NF-kB-like transcription factors (Liao, F., A. Andalibi, F. C. deBeer, A. M. Fogelman, and A.J. Lusis. 1993. J. Clin. Invest. 91:2572-2579). We hypothesized that the inflammation-related processes were stimulated by oxidized lipids, since injection of minimally oxidized LDL (MM-LDL) activated the same set of genes. We now report that the induction of inflammatory genes and activation of NF-kB-like transcription factors cosegregate with aortic atherosclerotic lesion formation in BXH recombinant inbred strains derived from parental C57BL/6J (susceptible) and C3H/HeJ (resistant) mice. In addition, the accumulation of hepatic conjugated dienes exhibited a significant correlation with inflammatory gene activation. These results provide strong evidence for the role of inflammatory mediators inducible by oxidative stress in atherogenesis. They also suggest that a major gene contributing to aortic lesion development in this mouse model, designated Ath-1, may control either the accumulation of lipid peroxides in tissues or the cellular responses to such lipid peroxides.

Identification of apolipoprotein B-100 low density lipoproteins, apolipoprotein B-48 remnants, and apolipoprotein E-rich high density lipoproteins in the mouse.

Plasma lipoprotein fractions from inbred C57BL/6J mice and outbred ICR mice were prepared by sequential density ultracentrifugation using density ranges that were optimized for separating mouse lipoproteins, or by Superose 6 HR10/30 fast performance liquid chromatography (FPLC). The lipoproteins were characterized by migration behavior in agarose, apolipoprotein (apo) composition, lipid composition, and particle size distribution. Both sequential density ultracentrifugation and Superose 6 FPLC were adapted for the separation of lipoproteins from a single mouse. In the plasma of ICR and C57BL/6J mice, in contrast to human plasma, alpha-migrating high density lipoproteins (HDL) and beta-migrating low density lipoproteins (LDL) had overlapping density ranges. For example, beta-migrating apoB-100 LDL, slow pre-beta-migrating apoB-48 remnants, and alpha-migrating HDL1 were found together in the d 1.02-1.04 g/ml fraction. The d 1.04-1.06 g/ml fraction contained beta-migrating apoB-100 LDL and alpha-migrating HDL1. Large HDL1 that were found at d 1.02-1.06 g/ml were apoE-rich HDL1, characteristic of cholesteryl ester transfer protein-deficient mammals. The d 1.10-1.21 g/ml fraction, in addition to alpha-migrating HDL, included unique slow beta-migrating particles that contained apoE and apoA-I but was deficient in neutral lipids. These slow beta-HDL eluted in the same FPLC fractions as dense alpha-migrating HDL. Compared to ICR mouse plasma, C57BL/6J mouse plasma contained more LDL and less HDL1, which might contribute to the susceptibility of C57BL/6J and the resistance of ICR mice to the development of aortic fatty streak lesions when challenged with an atherogenic diet.

Involvement of the tyrosinase gene in the deposition of cardiac lipofuscin in mice. Association with aortic fatty streak development.

Lipofuscin pigment, a terminal oxidation product, accumulates within cells during the normal aging process and under certain pathological conditions. We have analyzed a genetic cross between two inbred mouse strains, BALB/cJ and a subline of C57BL/6J, which differ in lipofuscin deposition. A comparison of the segregation pattern of cardiac lipofuscin with the albino locus (c) on mouse chromosome 7 revealed complete concordance. Analysis of spontaneous mutants of the tyrosinase gene, encoded by the albino locus, confirmed that the tyrosinase gene itself controls lipofuscin formation. Genetic analysis of other strains indicated that one or more additional genes cab contribute to the inheritance of lipofuscin. We also present evidence for an association between cardiac lipofuscin deposition and aortic fatty streak development in the mouse.

Increased prevalence of aortic fatty streaks in cholesterol-fed rabbits administered intravenous cocaine: the role of vascular endothelium.

Several recent postmortem studies suggest an increased prevalence of atherosclerosis in young habitual cocaine abusers. However, little is known about the effects of cocaine abuse on the vascular endothelium and its relationship to atherosclerosis. Therefore, the consequence of chronic administration of intravenous cocaine on the induction of aortic sudanophilia was examined. Male New Zealand White rabbits were fed a 0.5% cholesterol diet for 10 wk. During this period, animals were randomized to receive either cocaine-hydrochloride (0.25 mg/kg) intravenously (n = 17) twice daily; or an equivalent volume of 0.9% physiologic saline, control group (n = 16). Mean values for total circulating leukocytes and platelets and total plasma cholesterol and triglycerides were similar in both groups throughout the protocol. At the completion of the study, aortic sudanophilia was measured and expressed as a percentage of regional involvement (R1 = proximal 4 cm, R2 = middle 6 cm, and R3 = distal 10 cm). Statistical significance among groups was achieved in the proximal thoracic aorta (p = 0.057). No significant differences in sudanophilia were noted in the middle and distal segments. When animals were placed in subgroups according to percent total plaque involvement, there was a significant increased distribution of rabbits with a greater extent of sudanophilia in the cocaine-treated group as compared with control (p = 0.01, chi-square analysis). Immunocytochemical studies using the macrophage-specific and muscle actin-specific monoclonal antibodies demonstrated that sudanophilic areas in both groups were predominantly composed of macrophage-derived foam cells. Evaluation of plaque morphology showed an increase in intimal plaque thickness and in the number of macrophages and smooth muscle cells in cocaine-treated animals; however, group differences were not statistically significant. Because no significant differences were found in the cellular composition of atherosclerotic plaques between groups, further studies were performed to assess the effects of cocaine on the permeability function of cultured endothelial cell monolayers as a possible mechanism of increased sudanophilia. Cocaine (100 microM)-treated endothelial cell monolayers demonstrated an increased permeability to horseradish peroxidase during all time intervals studied (0-6 hr). Permeability differences were statistically significant at 30 min and 1 hr (p = 0.003 and 0.02, respectively). Collectively, these observations suggest that administration of cocaine to cholesterol-fed rabbits increases the prevalence of aortic sudanophilia via at least one possible mechanism involving enhanced vascular permeability.

The distribution of adhesion molecules in human atherosclerosis.

Chronic inflammatory cells are a recognized component of atherosclerotic plaques at all stages of development. As adhesion molecules play a fundamental role in inflammatory processes, we have carried out an immunohistochemical investigation of the distribution of endothelial leucocyte adhesion molecule-1 (ELAM-1)*, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in human atherosclerotic lesions. Autopsy specimens from abdominal aorta and coronary arteries were obtained from 21 cases within 24 h of death. ELAM-1 and ICAM-1 were consistently expressed by the entire intimal endothelium of normal coronary arteries and also by the intimal endothelium overlying aortic fatty streaks. Both coronary artery and aortic lesions showed strong staining for ICAM-1 on and around macrophages. VCAM-1 was not detected on intimal endothelial cells, but strong staining of adventitial lymphoid aggregates for this molecule was seen. This work suggests a role for ELAM-1 and ICAM-1 in mononuclear cell recruitment during atherogenesis.

Influence of the apoA-II gene locus on HDL levels and fatty streak development in mice.

Previous studies have shown that distal mouse chromosome 1 contains the apolipoprotein AII (apoAII) gene, encoding the second most abundant apolipoprotein in high density lipoproteins (HDLs), as well as a gene termed Ath-1 that controls aortic fatty streak development and HDL cholesterol levels in response to a high-fat, high-cholesterol diet. We report genetic studies confirming that the genes are distinct. Using molecular markers for mouse chromosome 1, we have further mapped the two genes, and our results indicate that they are separated by a minimum of 2 cM. We also report evidence that in mice on a low-fat chow diet, the apoAII gene locus influences HDL cholesterol levels. Thus, statistical analysis of two sets of recombinant inbred strains revealed concordant segregation patterns of HDL cholesterol levels and the apoAII gene locus. The effect of apoAII expression on HDL cholesterol levels was further tested by using a congenic strain that exhibits increased apoAII synthesis in comparison to the background strain. The results support the concept that increased synthesis of apoAII results in increased HDL cholesterol levels. Unexpectedly, increased expression of apoAII appeared to promote rather than retard aortic fatty streak development.

EM of human atherosclerosis: Aortic fatty streaks with transitional lesion features

The earliest distinctive lesions in human atherosclerosis are fatty streaks (FS), characterized initially by lipid-laden foam cell formation. Fibrous plaques (FP), the clinically significant lesions, differ from FS in several respects. In addition to foam cells, the FP also exhibit fibromuscular proliferation and a necrotic core region rich in extracellular lipid. The possible transition of FS into mature FP has long been debated, however. A subset of FS described by Katz etal., was intermediate in lipid composition between ordinary FS and FP. We investigated this hypothesis by electron microscopic cytochemistry by employing a tissue processing technique previously described by our laboratory. Osmium-tannic acid-paraphenylenediamine (OTAP) tissue preparation enabled ultrastructural analysis of lipid deposits to discern features characteristic of mature fibrous plaques.

Antiatherosclerotic effects of antioxidants are lesion-specific when evaluated in hypercholesterolemic New Zealand White rabbits

Oxidative modification of LDL may represent an initiating event in the formation of monocyte-macrophage foam cells, a major cell present in fatty streaks and atherosclerotic fibrous plaques. Therefore, we studied the effect of such antioxidants as probucol (500 mg/kg) and vitamins E and C (500 mg/kg each) on the regression of induced iliac-femoral lesions and progression of naturally occurring thoracic aortic fatty streak lesions in hypercholesterolemic New Zealand White rabbits. Following an initial 9-week lesion induction phase, both therapies were evaluated for 8 weeks. Probucol lowered plasma cholesterol 47% while vitamins E and C had no effect on plasma cholesterol. Probucol decreased the cholesteryl ester (CE) content of the thoracic aorta by 31% without changing the thoracic aortic lesion coverage. Vitamins E and C decreased thoracic aortic CE content by 40% and lesion coverage by 46%. Neither probucol nor vitamins E and C altered the CE content, lesion size, or macrophage/lesion ratio of the iliac-femoral artery. Thus, we conclude that the effects of antioxidants are specific to the stage of atherosclerotic lesion development. Antioxidant therapy alters the progression and cholesteryl ester enrichment of diet-induced thoracic aortic fatty streaks but has no effect on the progression and/or regression of more complicated injury-induced iliac-femoral lesions.

Early lesions of atherosclerosis in childhood and youth: natural history and risk factors.

This paper traces the development of knowledge concerning early lesions of atherosclerosis and the relationship to risk factors in children, youth, and young adults. Autopsy studies have shown that atherosclerosis begins in childhood with the appearance of aortic fatty streaks. Aortic fatty streaks of some degree are present in practically all individuals from every human population. Coronary fatty streaks begin to form in adolescence. Most persons 20-29 years of age have coronary fatty streaks of some degree, regardless of sex, race, or national origin. While fatty streaking is clinically harmless and potentially reversible, progression to fibrous plaques and more advanced lesions often leads to a critical stage of atherosclerosis in which clinical disease develops. Development of fibrous plaques begins in the 20s. The most recent studies of atherosclerosis in youth and young adults provide additional details to establish the relationship of these lesions to serum lipids and lipoproteins and other identified risk factors for atherosclerosis and coronary heart disease in adults. One report shows that microscopic counterparts of fatty streaks occur in the left anterior descending coronary artery in the majority of children 10-14 years of age. Over 5% have more advanced microscopic lesions at this age. Autopsy studies of youth have shown that serum total cholesterol and low-density lipoprotein cholesterol levels are strongly related to aortic fatty streaks and the very-low-density lipoprotein cholesterol levels are positively correlated to coronary artery fatty streaks. Finally, a definitive report indicates that serum lipoprotein cholesterol concentrations and smoking are important determinants of the early stages of atherosclerosis in adolescents and young adults.

Effect of clentiazem on lipid profile, lipoprotein composition and aortic fatty streaks in cholesterol-fed rabbits

Numerous experimental studies have reported that common antihypertensive drugs such as diuretics, beta-blockes, and methyldopa have adverse effects on plasma lipids and lipoproteins. The present study was designed to define the effect of clentiazem (10 mg/kg/day) an antihypertensive drug, on hyperlipidemia in rabbits on a cholesterol-rich diet (1%) for 12 weeks. Compared with controls, clentiazem treated rabbits had lower plasma concentrations of triglycerides (55%), total cholesterol (24%), free cholesterol (27%), esterified cholesterol (23%) and phospholipids (24%). The decrease in cholesterol was accounted for by a reduction of VLDL-cholesterol (13%), IDL-cholesterol (24%) and primarily LDL-cholesterol (45%). Neither HDL-cholesterol nor chemical composition of VLDL, IDL, LDL and HDL was altered. When the aortic atherosclerotic involvement was evaluated by computerized planimetry, a 24% reduction of lesions was noted in clentiazem treated animals ( P < 0.05). Similarly, cholesterol content extracted from aortic wall was decreased. Our data therefore demonstrated that clentiazem is a potential antiatherosclerotic agent capable of decreasing plasma lipids and atherogenic lipoproteins as well as aortic fatty streaks.

Immunology of atherosclerosis: Cellular composition and major histocompatibility complex class II antigen expression in aortic intima, fatty streaks, and atherosclerotic plaques in young and aged human specimens

There is evidence that fatty streaks in arteries can transform into atherosclerotic plaques. Mononuclear cells, including both monocytes and lymphocytes, are among the first cells participating in the development of atherosclerosis of experimental animals. To investigate the celes of different cell types in human atherosclerosis, we enumerated and compared the cellular compositions of normal intima, the transition zone (the area between the normal intima and the core of fatty streaks), fatty streaks, and plaques in young (age 16–30 years) and aged (over 60 years) human specimens using double-staining immunofluorescence with a series of monoclonal and polyclonal antibodies. T lymphocytes, both T helper/inducer (70% of T cells) and T suppressor/cytotoxic (30%) pheno-types, were found in every stage of atherosclerosis, constituting 30 to 40% of total cells in fatty streaks and transition zones of young subjects, and occasionally even in normal intima. Seventy percent of these T cells were HLA-DR positive, which indicated that most of them were activated. Macrophages were most frequent in fatty streaks and around the necrotic core of plaques. Smooth muscle cells, increasing from 5 to 30% with lesion progression, were HLA-DR positive where activated T helper cells occurred in the vicinity. The intracellular presence of the invariant γ chain confirmed that HLA-DR was actually synthesized by these smooth muscle cells. Endothelial cells were HLA-DR positive above those regions of the lesions where HLA-DR-positive cells had accumulated, but not in normal intima, again suggesting induction of HLA-DR expression by T-cell-derived γ-interferon. Furthermore, most HLA-DR-positive cells were also identified as HLA-DP and HLA-DQ positive. This aberrant major histocompatibility complex class II antigen expression in smooth muscle and endothelial cells may participate in the perpetuation of the atherogenetic autoimmune reaction.

Regression of atherosclerotic lesions by high density lipoprotein plasma fraction in the cholesterol-fed rabbit.

The effects of homologous plasma HDL and VHDL fractions on established atherosclerotic lesions were studied in cholesterol-fed rabbits. Atherosclerosis was induced by feeding the animals a 0.5% cholesterol-rich diet for 60 d (group 1). Another group of animals were maintained on the same diet for 90 d (group 2). A third group was also fed the same diet for 90 d but received 50 mg HDL-VHDL protein per wk (isolated from normolipemic rabbit plasma) during the last 30 d (group 3). Aortic atherosclerotic involvement at the completion of the study was 34 +/- 4% in group 1, 38.8 +/- 5% in group 2, and 17.8 +/- 4% in group 3 (P less than 0.005). Aortic lipid deposition was also significantly reduced in group 3 compared with group 1 (studied at only 60 d) and group 2. This is the first in vivo, prospective evidence of the antiatherogenic effect of HDL-VHDL against preexisting atherosclerosis. Our results showed that HDL plasma fractions were able to induce regression of established aortic fatty streaks and lipid deposits. Our results suggest that it may be possible not only to inhibit progression but even to reduce established atherosclerotic lesions by HDL administration.

Lipoprotein metabolism of human and rabbit arterial cells in primary culture

The early atherosclerotic lesion, the fatty streak, consists of cholesteryl ester-containing foam cells originating mainly from monocyte-macrophages and to a lesser extent from smooth muscle cells. In this study, we describe lipoprotein uptake and cholesterol accumulation into enzyme-dispersed primary cell cultures from cholesterol-fed rabbit aortas and human aortic fatty streaks. Uptake of fluorescently labelled acetylated low density lipoprotein (acetyl-LDL) was demonstrable in macrophage-derived foam cells and in many smooth muscle cells in early primary cultures. The uptake of acetyl-LDL led to significantly enhanced cellular esterification of cholesterol. Fluorescent beta-migrating very low density lipoprotein (beta-VLDL) was internalized by a considerable number of lesion macrophages and also by smooth muscle cells. Also beta-VLDL uptake stimulated cholesterol esterification, although the effect was milder than that of acetyl-LDL. These findings lend support to the assumption that, during atherogenesis, arterial macrophages are capable of accumulating cholesteryl esters by receptor-mediated uptake of beta-VLDL and modified LDL. The internalization of modified LDL by smooth muscle cells represents a mechanism potentially contributing to the formation of foam cells in the atherosclerotic lesion.

Macrophage foam cells from human aortic fatty streaks take up beta-VLDL and acetylated LDL in primary culture.

Intimal cells from human aortic fatty streak lesions were isolated with collagenase-elastase digestion and the cellular uptake of lipoproteins fluorescently labeled with 3,3'-dioctadecylindocarbocyanine (DiI) was studied in primary culture. The majority of the cells in primary culture contained lipid droplets and the foam cells consisted of both macrophages and smooth muscle cells (SMC), identified with electron microscopy and the macrophages also using the monoclonal anti-Leu-M3 antibody. The lipid inclusions contained cholesteryl ester, as visualized with filipin staining. Arterial macrophages took up DiI-labeled acetylated low density lipoprotein (DiI-acetyl-LDL) in the same way as did monocyte-macrophages isolated from blood. DiI-labeled beta-very low density lipoprotein (DiI-beta-VLDL) isolated from cholesterol-fed rabbits, was taken up by both macrophages and SMCs. In macrophages DiI-beta-VLDL was internalized also in the presence of excess unlabeled low density lipoprotein (LDL), whereas in SMCs the uptake was partially prevented. DiI-LDL uptake was only seen in SMCs free of lipid inclusions and especially during cell growth. The present results show that, in human aortic fatty streaks, (a) both macrophages and SMCs accumulate cholesteryl ester, (b) macrophage foam cells possess active scavenger receptors capable of mediating the uptake of acetyl-LDL, and (c) macrophages are also capable of accumulating cholesteryl ester by receptor-mediated uptake of beta-VLDL.

Dehydroepiandrosterone feeding prevents aortic fatty streak formation and cholesterol accumulation in cholesterol-fed rabbit.

The concentration of dehydroepiandrosterone sulfate (DHEA-S) in human plasma is higher than any other steroid. Recent evidence has suggested an inverse relationship between plasma DHEA levels and the development of coronary atherosclerosis in humans. We used the cholesterol-fed rabbit model to investigate whether DHEA feeding would diminish aortic fatty streak formation in this model. Fifteen New Zealand White rabbits were fed rabbit chow supplemented with 0.5% cholesterol (wt/wt). Seven animals were, in addition, fed DHEA, 0.5% of diet (wt/wt). Animals were sacrificed after 2 months, and the aortic involvement with fatty streaks was evaluated by computerized planimetry of Sudan IV-stained aortas and by chemical analysis of aortic wall lipids. Compared to controls, DHEA-fed animals had similar plasma levels of total, very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL) cholesterol, corticoids, and estrogens. DHEA-fed animals had higher plasma levels of total, VLDL, and LDL triglycerides and lower HDL triglycerides than did controls. DHEA feeding resulted in 30% and 40%, respectively, inhibition of fatty streak formation by chemical analysis and planimetry. We conclude that DHEA feeding inhibits the development of aortic fatty streaks in cholesterol-fed rabbits, independent of changes in plasma total and LDL cholesterol levels of DHEA conversion to estrogens or corticoids.

Analysis of solid phase debris from laser angioplasty: Potential risks of atheroembolism

Laser energy can vaporize biologic tissues, and this unique method of ablation has been considered for the disobstruction of the occlusive lesion in atherosclerotic disease. To assess the potential embolic sequelae from laser angioplasty, solid phase debris (SPD) was analyzed. Specimens of human cadaver aorta were subjected to standardized argon laser injury, and SPD was quantified by weight in four types of ablated tissue: normal aortic intima, fatty streaks, fibrous plaque, and calcified plaque (CP). The debris by weight of tissue ablated was significantly higher for CP (p < 0.05), measuring 7.9%, whereas normal aortic intima, fatty streaks, and fibrous plaque yielded 3.2%, 2.7%, and 3.7%, respectively. Likewise, the amount of debris liberated per unit volume of albated tissue was greatest for CP averaging 156 mg/cc. Light and scanning electron microscopy of SPD revealed carbonized tissue particles up to 350 μm from all classes and cholesterol crystals up to 250 μm from CP. SPD from CP was infused into renal arteries of rats at two dosages, 4 and 16 mg, to observe effects on end-organ tissue. At 10 days, all kidneys demonstrated focal ischemic atrophy and recovering acute tubular necrosis in a dose-dependent fashion (p < 0.05). Control rats showed no disease. Kidneys embolized with SPD also displayed foreign body granulomas (9 of 12), periarterial inflammation (11 of 12), and cortical wedge infarcts (10 of 12). Argon laser energy that ablates tissue predominantly by thermal mechanisms liquified or vaporized 96% to 97% of noncalcified atheromatous material. Laser ablation of CP, however, liberated significantly more SPD. The ischemic and inflammatory injuries caused by embolization of SPD were identical with the classic descriptions of atheroembolism.

Activation of the human terminal complement pathway in atherosclerosis

The presence of the terminal C5b-9 complement complex in tissues indicates that complement activation has occurred in situ with subsequent membrane damage, tissue injury, and inflammatory response mediation. The terminal C5b-9 neoantigens of the complement system, S protein, C3d, C3d, and apolipoprotein B deposits were localized in 20 aortic fibrous plaques, 12 aortic intimal thickenings, 8 aortic fatty streak intimae, 14 coronary fibrous plaques, 5 coronary intimal thickenings, and 8 femoral fibrous plaques, using an indirect and double-staining immunoperoxidase technique. The specific granular deposits were present from the early to the advanced stages of atherosclerosis in relation to the degree of fibrosis and necrosis. The different double-staining localization of C5b-9 and S protein may suggest local assembly of the complex as a consequence of complement activation and may sustain its role in the chronic progression of atherosclerosis.

An immunohistochemical analysis of human aortic fatty streaks

Recent studies have shown both macrophages and lymphocytes in very early intimal lesions of experimental aortic atherosclerosis. The authors obtained fresh samples of human aortic wall, which had been removed in the course of aortocoronary bypass graft surgery. Intimal fatty streaks were identified macroscopically and six were studied immunohistochemically. The fatty streaks contained foam cells that were virtually all labeled by antibodies directed against members of the mononuclear phagocyte series (RFD-2 and RFD-7). Macrophages demonstrated acid phosphatase activity and marked expression of HLA-DR, suggesting activation. Other monoclonal antibodies (UCHT-1, OKT-4, and RFT-8) identified T lymphocytes, of both helper and suppressor phenotypes, within the fatty streaks. T lymphocytes of suppressor phenotype appeared to predominate over helper cells. B lymphocytes were not detected. The presence of activated macrophages and T lymphocytes in the fatty streaks indicates that components of a cell-mediated immune response are present. Such an immune process may be important in the pathogenesis of human atherosclerosis.

Endothelial cilia in human aortic atherosclerotic lesions.

"Primary" cilia were present in the endothelial cells of human aortic fatty dots and streaks but not in those of normal intima. They had the features of cilia of the "9 + 0" axonemal configuration observed in many other cells. A lateral foot process and transitional fibers "anchored" the ciliary basal body in the cytoplasm, but rootlets were not identified in material examine. Ladder-like configurations interconnected the two centrioles (= diplosome) of control endothelium. The "primary" cilia of endothelium differed from those of the rudimentary type observed in smooth muscle cells in similar lesions of man, but shared many features with cilia of those present in experimental atherosclerosis in rabbit. Cilia were rarely described in vascular endothelium. It is believed that, to date, they were not reported to occur in normal or pathological arteries in man. It is being stressed that whereas the significance of these unusual organelles remains uncertain, their widespread occurrence may indicate that their role is more important than was believed previously, and they should cease being a curiosity only.