Autoimmunity in the Abdominal Aortic Aneurysm and its Association with Smoking.

Smoking increases the risk of abdominal aortic aneurysm (AAA) in both humans and mice, although the underlying mechanisms are not completely understood. An adventitial aortic antigen, AAAP-40, has been partially sequenced. It has motifs with similarities to all three fibrinogen chains and appears to be connected in evolution to a large family of proteins called fibrinogen-related proteins. Fibrinogen may undergo non-enzymatic nitration, which may result from exposure to nitric oxide in cigarette smoke. Nitration of proteins renders them more immunogenic. It has recently been reported that anti-fibrinogen antibody promotes AAA development in mice. Also, anti-fibrinogen antibodies are present in patients with AAA. These matters are reviewed in the overall context of autoimmunity in AAA. The evidence suggests that smoking amplifies an auto-immune reaction that is critical to the pathogenesis of AAA.

Pulse wave imaging of normal and aneurysmal abdominal aortas in vivo.

The abdominal aortic aneurysm (AAA) is a common vascular disease. The current clinical criterion for treating AAAs is an increased diameter above a critical value. However, the maximum diameter does not correlate well with aortic rupture, the main cause of death from AAA disease. AAA disease leads to changes in the aortic wall mechanical properties. The pulse-wave velocity (PWV) may indicate such a change. Because of limitations in temporal and spatial resolution, the widely used foot-to-foot method measures the global, instead of regional, PWV between two points at a certain distance in the circulation. However, mechanical properties are nonuniform along the normal and pathological (e.g., the AAA and atherosclerosis) arteries; thus, such changes are typically regional. Pulse-wave imaging (PWI) has been developed by our group to map the pulse-wave propagation along the abdominal aorta in mice in vivo. By using a retrospective electrocardiogram (ECG) gating technique, the radio-frequency (RF) signals over one cardiac cycle were obtained in murine aortas at the extremely high frame rate of 8 kHz and with a field-of-view (FOV) of 12 x 12 mm(2). The velocities of the aortic wall were estimated using an RF-based speckle tracking method. An Angiotensin II (AngII) infusion-based AAA model was used to simulate the human AAA case. Sequences of wall velocity images can noninvasively and quantitatively map the propagation of the pulse wave along the aortic wall. In the normal and sham aortas, the propagation of the pulse wave was relatively uniform along the wall, while in the AngII-treated aortas, the propagation was shown to be nonuniform. There was no significant difference ( p > 0.05) in the PWV between sham (4.67 +/- 1.15 m/s, n=5) and AngII-treated (4.34 +/- 1.48 m/s, n=17) aortas. The correlation coefficient of the linear regression was significantly higher ( p < 0.005) in the sham aortas (0.89 +/- 0.03, n=5 ) than in the AngII-treated ones (0.61 +/- 0.15, n=17). The wall velocities induced by the pulse wave were lower and the pulse wave moved nonuniformly along the AngII-treated aorta ( p < 0.005), with the lowest velocities at the aneurysmal regions. The discrepancy in the regional wall velocity and the nonuniform pulse-wave propagation along the AngII-treated aorta indicated the inhomogeneities in the aortic wall properties, and the reduced wall velocities indicated stiffening of the aneurysmal wall. This novel technique may thus constitute an early detection tool of vascular degeneration as well as serve as a suitable predictor of AAA rupture, complementary to the current clinical screening practice.

The lymphocytic infiltration in calcific aortic stenosis predominantly consists of clonally expanded T cells.

Valve lesions in degenerative calcific aortic stenosis (CAS), a disorder affecting 3% of those older than 75 years, are infiltrated by T lymphocytes. We sought to determine whether the alphabeta TCR repertoire of these valve-infiltrating lymphocytes exhibited features either of a polyclonal nonselective response to inflammation or contained expanded clones suggesting a more specific immune process. TCR beta-chain CDR3-length distribution analysis using PCR primers specific for 23 Vbeta families performed in eight individuals with CAS affecting tri- or bileaflet aortic valves revealed considerable oligoclonal T cell expansion. In five cases, beta-chain nucleotide sequencing in five selected Vbeta families showed that an average of 92% of the valve-infiltrating T cell repertoire consisted of expanded T cell clones, differing markedly in composition from the relatively more polyclonal peripheral CD8 or CD4 T cell subsets found even in this elderly population. Twenty-four of the valve-infiltrating T cell clones also had the same clone identified in blood, some of which were highly expanded. Interestingly, 22 of these 24 shared clones were CD8 in lineage (p = 1.5 x 10(-12)), suggesting a possible relationship to the expanded CD8(+)CD28(-) T cell clones frequently present in the elderly. Additionally, the sequences of several TCR beta-chain CDR3 regions were homologous to TCR beta-chains identified previously in allograft arteriosclerosis. We infer that these findings are inconsistent with a nonselective secondary response of T cells to inflammation and instead suggest that clonally expanded alphabeta T cells are implicated in mediating a component of the valvular injury responsible for CAS.

The candidate gene approach to susceptibility for abdominal aortic aneurysm: TIMP1, HLA-DR-15, ferritin light chain, and collagen XI-Alpha-1.

There are two approaches to gene discovery for diseases when genetic susceptibility has been implicated by clinical genetic or case-control studies: (1) genome-wide screening and (2) evaluation of candidate genes. Each has specific advantages and disadvantages. The principal advantage of genome-wide screening is that it is impeccably objective in as much as it proceeds without any presuppositions regarding the importance of specific pathobiological features of the disease process. The principal disadvantage is that such a study is expensive and resource intensive. A large population of enrolled patients and multidisciplinary teams of investigators cooperating from several institutions are usually required. The alternative approach of evaluating candidate genes can be pursued by a small independent laboratory with limited funding and resources, a small collection of clinical specimens, and a small number of team players. The disadvantage is that it is by necessity highly subjective in the process of selecting specific candidates among many reasonable possibilities. There is no a priori assurance that effort will not be expended on one or more candidates that turn out in the end to be failures. This report reviews efforts in our laboratory to evaluate four genes as candidates. One of these tissue inhibitor of metalloprotease 1(TIMP1) led to the description of a polymorphism, but not a conclusive mutation. The other three (HLA-DR-15, ferritin light chain (FTL), and collagen XI-alpha-1 (COL11A1) are subjects of continuing interest.

Ongoing angiogenesis in blood vessels of the abdominal aortic aneurysm.

Pathogenesis of the abdominal aortic aneurysm has been attributed to neovascularization of the aortic wall. However, it is not clear whether angiogenesis persists in the aneurysm. In sections of aneurysms, we determined the immunohistochemical distributions of the avb3 integrin, tenascin and endothelial nitric oxide synthase (eNOS), which are markers respectively, of angiogenesis, matrix remodeling and vasoregulatory function. In addition, we used reverse transcription followed by in situ PCR, to determine the distribution of av mRNA. All aneurysm specimens exhibited extensive increases of wall vascularization as compared with the control aortic wall, and showed the presence of perivascular inflammatory exudates containing macrophages and lymphocytes. The neovascularization consisted of thick-walled vessels in the media and adventitia, and capillaries in the subintima. The majority of vessels stained positively for the avb3 antigen and eNOS. Tenascin was deposited as bands that circumscribed thick-walled vessels. The distribution of av mRNA was extensive and was positive even in those vessels that failed to stain for the avb3 protein. No staining was evident in control aortas for the avb3 antigen, tenascin or av mRNA. The upregulation of av mRNA and the avb3 integrin in blood vessels surrounded by a matrix expressing tenascin, indicates that angiogenesis is an ongoing process in the mature aortic aneurysm.

The role of a putative microfibrillar protein (80 kDa) in abdominal aortic aneurysm disease.

BACKGROUND: We previously have reported the partial amino acid sequence of a putative aortic autoantigen in patients with abdominal aortic aneurysm (AAA) disease that has homologies with an elastin-associated microfibrillar protein found in aorta of pigs. This study was conducted to further define the role that microfibrillar proteins may play as autoantigens in AAA disease. MATERIALS AND METHODS: An extraction procedure was performed on AAA tissue using high concentrations of guanidinium hydrochloride (GuHCl) under reducing conditions. The microfibrillar extract was then probed with immunoglobulin (Ig) G isolated with Protein A from phosphate-buffered saline (PBS) extracts of 10 AAA specimens and 6 atherosclerotic, nonaneurysmal aortas. Immunoblotting was also performed with serum IgG from 9 AAA patients and 9 normal control patients. Immunohistochemistry using goat anti-human IgG (Fc-specific) on AAA tissue and AAA wall IgG on normal aorta were also performed. RESULTS: Eight of 10 AAA wall IgG reacted with an 80-kDa protein from the aortic microfibrillar extract, compared to 0 out of 6 atherosclerotic wall IgG (P = 0.0035, Fischer's Exact Test). Staining of the 80-kDa band appeared to increase with progressive additions of GuHCl, up to extract SKGCGC. Immunoblotting using serum IgG from 9 AAA patients and 9 normal control patients on the aneurysm microfibrillar extracts revealed no reactive bands. Immunohistochemistry using IgG from AAA wall showed the localization of the antibodies to the adventitial connective tissue matrix, mainly collagen fibers. CONCLUSIONS: These observations suggest that a collagen-associated protein, extractable by a microfibrillar extraction procedure from aortic aneurysm tissue, may be among the targets of an autoimmune response in AAA disease.