Detection of C. pneumoniae by polymerase chain reaction-enzyme immunoassay in abdominal aortic aneurysm walls and its association with rupture

Presence of Borrelia burgdorferi sensu lato antibodies in the serum of patients with abdominal aortic aneurysms

Infectious agents are likely to play a role in the pathogenesis of chronic inflammatory diseases, including abdominal aortic aneurysms (AAAs). The goal of this study was to determine if Borrelia burgdorferi sensu lato (sl), a microorganism responsible for Lyme disease, is involved in the etiology of AAAs. The presence of serum antibodies against B. burgdorferi sl was measured with enzyme-linked immunosorbent assay (ELISA) and confirmed by Western blotting in 96 AAA and 108 peripheral artery disease (PAD) patients. Polymerase chain reaction (PCR) was used for the detection of Borrelia-specific DNA in the aneurysm wall. Among AAA patients 34% and among PAD patients 16% were seropositive for B. burgdorferi sl antibodies (Fisher's exact test, p = 0.003; odds ratio [OR] 2.79; 95% confidence interval [CI] 1.37-5.85). In the German general population, 3-17% are seropositive for Borrelia antibodies. No Borrelia DNA was detected in the aneurysm wall. Our findings suggest a relationship between AAAs and B. burgdorferi sl. We hypothesize that the underlying mechanism for B. burgdorferi sl in AAA formation is similar to that by the spirochete Treponema pallidum; alternatively, AAAs could develop due to induced autoimmunity via molecular mimicry due to similarities between some of the B. burgdorferi sl proteins and aortic proteins.

Quantification and location of Chlamydia pneumoniae-specific antigen in the walls of abdominal aortic aneurysms

BACKGROUND

To evaluate the prevalence and quantity of Chlamydia pneumoniae-specific antigen in the three layers (intima, media, and adventitia) of abdominal aortic aneurysms (AAAs), so as to further investigate the pathogenesis of AAAs.

METHODS

Aortic walls were collected from 20 patients with AAA and 11 healthy organ donors. Immunohistochemistry was used to identify the C pneumoniae-specific antigen, and image analysis system was used to quantify and locate it.

RESULTS

The positive rate of C pneumoniae-specific antigen was higher in the AAA group than in the control group (100% vs. 54.54%, p = 0.003), positive intensity decreased from the tunica intima to the adventitia in the AAA group (16.32% ± 2.13%, 14.84% ± 1.80%, and 14.25% ± 1.67%, respectively, p = 0.003). In the control group, positive cells were mainly found in focal lesion areas.

CONCLUSION

We have demonstrated the presence and differentiation of C pneumoniae-specific antigen in the three layers of AAAs, which are in accordance with pathology, thus suggesting a pathogenic role of the antigen.

Novel aspects of the pathogenesis of aneurysms of the abdominal aorta in humans

Aneurysm of the abdominal aorta (AAA) is a particular, specifically localized form of atherothrombosis, providing a unique human model of this disease. The pathogenesis of AAA is characterized by a breakdown of the extracellular matrix due to an excessive proteolytic activity, leading to potential arterial wall rupture. The roles of matrix metalloproteinases and plasmin generation in progression of AAA have been demonstrated both in animal models and in clinical studies. In the present review, we highlight recent studies addressing the role of the haemoglobin-rich, intraluminal thrombus and the adventitial response in the development of human AAA. The intraluminal thrombus exerts its pathogenic effect through platelet activation, fibrin formation, binding of plasminogen and its activators, and trapping of erythrocytes and neutrophils, leading to oxidative and proteolytic injury of the arterial wall. These events occur mainly at the intraluminal thrombus-circulating blood interface, and pathological mediators are conveyed outwards, where they promote matrix degradation of the arterial wall. In response, neo-angiogenesis, phagocytosis by mononuclear cells, and a shift from innate to adaptive immunity in the adventitia are observed. Abdominal aortic aneurysm thus represents an accessible spatiotemporal model of human atherothrombotic progression towards clinical events, the study of which should allow further understanding of its pathogenesis and the translation of pathogenic biological activities into diagnostic and therapeutic applications.

Can local secretion of prostaglandin E2, thromboxane B2, and interleukin-6 play a role in ruptured abdominal aortic aneurysm?

BACKGROUND

Our laboratory has previously shown that the levels of secreted prostaglandin E(2) (PGE(2)), Thromboxane B(2) (TxB(2)), and interleukin-6 (IL-6) by aortic explant cultures were high in patients with ruptured abdominal aortic aneurysm (AAA). In the present study, we sought to examine the secretory levels of these inflammatory mediators in aortic explant cultured from a group of AAAs rupturing at a certain size and a group that did not rupture at that size. It was thought that such a comparison might reveal the contribution of those inflammatory mediators to the risk of AAA rupture.

MATERIALS AND METHODS

All subjects had abdominal computed tomography (CT) scans to determine the size of the aneurysm, and surgical aortic tissue was collected from both nonruptured AAAs (18 with a mean size of 6 + 0.5 cm [range: 5-7 cm] and 12 with a mean size of 8 + 0.1 cm [range: 7.01-10 cm]) and ruptured AAAs (10 with a mean size of 5.8 + 0.3 cm [range: 5-7 cm] and 10 with a mean size of 7.8 + 0.1 cm [range: 7.01-10 cm]). Aortic explant cultures from different sizes of aneurysms were immediately established and the culture media were collected 72 h later.

RESULTS

The levels of PGE(2), TxB(2), and IL-6 secreted in the cultured medium were quantified by specific enzyme-linked immunosorbent assays (ELISA). The secretary levels of PGE(2), TxB(2), and IL-6 were significantly higher in ruptured AAAs than in nonruptured AAAs of similar diameter. However, there was no correlation between these three inflammatory mediators and the size of AAA.

CONCLUSIONS

This study shows that these inflammatory mediators may play a role in the progression toward rupture but may not be responsible for the expansion of AAA.

Chlamydia pneumoniae and vascular disease: an update

Exposure to Chlamydia pneumoniae is extremely common, and its incidence increases with age. C pneumoniae infection is strongly associated with coronary artery disease, as well as with atherosclerosis of the carotid artery, aorta, and peripheral arteries. This association has been shown in seroepidemiologic studies and by direct detection of the organism in atherosclerotic lesions by immunohistochemistry, polymerase chain reaction, electron microscopy, and tissue culture. Animal models of atherosclerosis have been used to study the role of C pneumoniae in the initiation and progression of atherosclerotic disease. The association of this organism with cardiovascular complications has inspired many human trials of antibiotics for the secondary prevention of atherosclerosis. C pneumoniae can infect several types of cells, including circulating macrophages, arterial smooth muscle cells, and vascular endothelial cells, causing the secretion of proinflammatory cytokines and procoagulants by endothelial cells and foam cell formation by infected macrophages. This report reviews the role of C pneumoniae in atherogenesis in light of recent, large antibiotic treatment trials, animal studies, and in vitro studies. The role of Chlamydia heat shock protein as a potential mediator of this harmful effect is also reviewed.

Chronic Inflammation, Immune Response, and Infection in Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAA) are associated with atherosclerosis, transmural degenerative processes, neovascularization, decrease in content of vascular smooth muscle cells, and a chronic infiltration, mainly located in the outer aortic wall. The chronic infiltration consists mainly of macrophages, lymphocytes, and plasma cells. The dominant cells are Th2 restricted CD3+ lymphocytes expressing interleukine 4, 5, 8, and 10, and tumor necrosis factor-alpha for regulation of the local immune response. They also produce interferon-gamma and CD40 ligand to stimulate surrounding cells to produce matrix metalloproteases and cysteine proteases for aortic matrix remodeling. The lymphocyte activation may be mediated by microorganisms as well as autoantigens generated from vascular structural proteins, perhaps through molecular mimicry. As in autoimmune diseases, the risk of AAA is increased by certain genotypes concerning human leucocyte antigen class II. These types are also associated with increased aneurysmal inflammation indicating a genetic susceptibility to aortic inflammation. Chlamydia pneumoniae is often detected in AAA but the validity of the methods can be questioned, and two small antibiotic trials have been disappointing. However, serum antibodies against C. pneumoniae have been associated with AAA growth and cross-react with AAA wall proteins. Thus, immune responses mediated by microorganisms and autoantigens may play a pivotal role in AAA pathogenesis.