Chlamydia pneumoniae reactive T lymphocytes in the walls of abdominal aortic aneurysms

Human abdominal aortic aneurysm (AAA): Evidence for an autoimmune antigen-driven disease

Abdominal aortic aneurism (AAA) is a complex immunological disease with a strong genetic component, and one of the ten leading causes of death of individuals 55-74 years old worldwide. Strong evidence has been accumulated suggesting that AAA is an autoimmune specific antigen-driven disease. Mononuclear cells infiltrating AAA lesions comprised of T and B lymphocytes and other cells expressing early-, intermediate- and late-activation antigens, and the presence of antigen-presenting cells have been documented, demonstrating an ongoing immune response. The three components of the trimolecular complex, T-cell receptor (TCR)/peptide (antigen)/HLA have been identified in AAA, and specifically: (i) clonal expansions of T-cell clones in AAA lesions; (ii) the association of AAA with particular HLA Class I and Class II; and (iii) self or nonself putative AAA-associated antigens. IgG autoantibodies recognizing proteins present in normal aortic tissue have been reported in patients with AAA. Molecular mimicry, defined as the sharing of antigenic epitopes between microorganisms (bacteria, viruses) and self antigens, maybe is responsible for T-cell responses and antibody production in AAA. Also, the frequency and the suppressor activity of CD4 + CD25 + FOXP3+ Tregs and the expression of FOXP3 transcripts and protein have been reported to be significantly impaired in AAA patients vs normal donors.

Blood Biomarkers and Serologic Immunological Profiles Related to Periodontitis in Abdominal Aortic Aneurysm Patients

Background

Periodontitis is a chronic inflammatory gum disease associated with systemic diseases such as cardiovascular diseases.

Aim

To investigate the association of systemic blood biomarkers, C-reactive protein (CRP), levels of lipopolysaccharide (LPS), and IgG levels against periodontal pathogens Aggregatibacter actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg) with the stability, based on the aortic diameter, the growth rate and the eligibility for surgical intervention, of patients with abdominal aortic aneurysm (AAA).

Methods

Patients with stable AAA (n = 30) and unstable AAA (n = 31) were recruited. The anti-A. actinomycetemcomitans and anti-P. gingivalis IgG levels were analyzed by ELISA, the LPS analysis was performed by using the limulus amebocyte lysate (LAL) test, and plasma levels of CRP were determined using an immune turbidimetric method. The association between these blood systemic biomarkers, AAA features, periodontal clinical parameters and oral microbial profiles were explored. Regression models were used to test the relationship between variables.

Results

The presence of antibodies against Pg and Aa, LPS and high CRP concentrations were found in all AAA patients. The IgG levels were similar in patients with stable and unstable AAA (both for Aa and Pg). Among investigated blood biomarkers, only CRP was associated with AAA stability. The amount of LPS in saliva, supra, and subgingival plaque were significantly associated with the systemic LPS (p <0.05).

Conclusions

This post-hoc study emphasizes the presence of antibodies against Pg and Aa, LPS and high CRP concentrations in all AAA patients. The presence of Pg in saliva and subgingival plaque was significantly associated with the blood LPS levels. For further studies investigating periodontitis and systemic diseases, specific predictive blood biomarkers should be considered instead of the use of antibodies alone.

AAA Revisited: A Comprehensive Review of Risk Factors, Management, and Hallmarks of Pathogenesis

Despite declining incidence and mortality rates in many countries, the abdominal aortic aneurysm (AAA) continues to represent a life-threatening cardiovascular condition with an overall prevalence of about 2-3% in the industrialized world. While the risk of AAA development is considerably higher for men of advanced age with a history of smoking, screening programs serve to detect the often asymptomatic condition and prevent aortic rupture with an associated death rate of up to 80%. This review summarizes the current knowledge on identified risk factors, the multifactorial process of pathogenesis, as well as the latest advances in medical treatment and surgical repair to provide a perspective for AAA management.

Further evidence on the relationship between abdominal aortic aneurysm and periodontitis: A cross-sectional study

BACKGROUND

Periodontitis is a chronic inflammatory disease characterized by Gram-negative bacteria responsible for the degradation of tissues surrounding tooth. Moreover, periopathogens can invade the bloodstream, disseminate and promote cardiovascular disease, such as the link between Porphyromonas gingivalis and atherosclerosis. The aim of this study was to explore the relationship between the severity of periodontitis and of abdominal aortic aneurysm (AAA).

METHODS

This cross-sectional study compared patients with stable AAA (n = 30) and patients with unstable AAA (n = 31) based on aortic diameter, growth rate, and eligibility for surgical intervention. Periodontal clinical parameters were recorded as well as the Periodontal Inflamed Surface Area and the Periodontal Index for Risk of Infectiousness (PIRI). Microbiological analyses were performed on saliva and supragingival and subgingival plaque. Quantification of Tannerella forsythia (Tf), Porphyromonas gingivalis (Pg), Aggregatibacter actinomycetemcomitans (Aa), Fusobacterium nucleatum (Fn), and Prevotella intermedia (Pi) was done by quantitative polymerase chain reaction.

RESULTS

The two AAA groups were homogeneous for age, sex, and most risk factors except hypertension and chronic obstructive pulmonary disease. Periodontal parameters were comparable but the proportion of patients with high PIRI scores was greater in those with unstable AAA (51.6% versus 23.3%). The probing depth (PD) and the proportion of PD >6 mm were positively correlated with AAA size and thrombus volume. Several associations were found between periopathogens such as Pg and AAA diameters and volumes, but no difference could be evidenced between stable and unstable AAA groups.

CONCLUSIONS

Periodontitis was highly prevalent in both stable and unstable AAA patients. Severe and progressive periodontitis (stage IV and grade C) tended to be more frequent in the group of patients with unstable AAA. Moreover, Pg was observed in all the samples (saliva, supragingival, and subgingival plaque) and was correlated with AAA diameters and volumes. The study evidenced potential relationships between periodontitis severity and size of AAA.

Clonally expanded alpha-chain T-cell receptor (TCR) transcripts are present in aneurysmal lesions of patients with Abdominal Aortic Aneurysm (AAA)

Abdominal aortic aneurysm (AAA) is a life-threatening immunological disease responsible for 1 to 2% of all deaths in 65 year old or older individuals. Although mononuclear cell infiltrates have been demonstrated in AAA lesions and autoimmunity may be responsible for the initiation and account for the propagation of the disease, the information available about the pathogenesis of AAA is limited. To examine whether AAA lesions from patients with AAA contain clonally expanded α-chain TCR transcripts, we amplified by the non-palindromic adaptor-PCR (NPA-PCR)/Vα-specific PCR and/or the Vα-specific PCR these α-chain TCR transcripts. The amplified transcripts were cloned and sequenced. Substantial proportions of identical α-chain TCR transcripts were identified in AAA lesions of 4 of 5 patients, demonstrating that clonally expanded T cells are present in these AAA lesions. These results were statistically significant by the bimodal distribution. Three of 5 of these patients were typed by DNA-based HLA-typing and all three expressed DRB1 alleles containing the DRβGln70 amino acid residue that has been demonstrated to be associated with AAA. All three patients exhibited clonally expanded T cells in AAA lesions. Four of the 5 patients with AAA who exhibited clonal expansions of α-chain TCR transcripts, also exhibited clonal expansions of β-chain TCR transcripts in AAA lesions, as we have demonstrated previously (J Immunol 192:4897, 2014). αβ TCR-expressing T cells infiltrating AAA lesions contain T-cell clones which have undergone proliferation and clonal expansion in vivo in response to as yet unidentified specific antigens that may be self or nonself. These results provide additional evidence supporting the hypothesis that AAA is a specific antigen-driven T-cell autoimmune disease.

Pathophisiology of abdominal aortic aneurysm: biomarkers and novel therapeutic targets

Abdominal aortic aneurysm (AAA) is a vascular pathology with a high rate of morbidity and mortality and a prevalence that, in men over 65 years, can reach around 8%. In this disease, usually asymptomatic, there is a progressive dilatation of the vascular wall that can lead to its rupture, a fatal phenomenon in more than 80% of cases. The treatment of patients with asymptomatic aneurysms is limited to periodic monitoring with imaging tests, control of cardiovascular risk factors and treatment with statins and antiplatelet therapy. There is no effective pharmacological treatment capable of limiting AAA progression or avoiding their rupture. At present, the aortic diameter is the only marker of risk of rupture and determines the need for surgical repair when it reaches values greater than 5.5cm. This review addresses the main aspects related to epidemiology, risk factors, diagnosis and clinical management of AAA, exposes the difficulties to have good biomarkers of this pathology and describes the strategies for the identification of new therapeutic targets and biomarkers in AAA.

Exploring autoimmunity in the pathogenesis of abdominal aortic aneurysms

The abdominal aortic aneurysm (AAA) is a disease process that carries significant morbidity and mortality in the absence of early identification and treatment. While current management includes surveillance and surgical treatment of low- and high-risk aneurysms, respectively, our narrow understanding of the pathophysiology of AAAs limits our ability to more effectively manage and perhaps even prevent the occurrence of this highly morbid disease. Over the past couple of decades, there has been considerable interest in exploring the role of autoimmunity as an etiological component of AAA. This review covers the current literature pertaining to this immunological process, focusing on research that highlights the local and systemic immune components found in both human patients and murine models. A better understanding of the autoimmune mechanisms in the pathogenesis of AAAs can pave the way to novel and improved treatment strategies in this patient population.

Chlamydia pneumoniae infection of lungs and macrophages indirectly stimulates the phenotypic conversion of smooth muscle cells and mesenchymal stem cells: potential roles in vascular calcification and fibrosis

Two hallmarks of advanced atherosclerosis are calcification and fibrosis. We hypothesized that Chlamydia pneumoniae infection may contribute to atherosclerosis by inducing the conversion of vascular smooth muscle cells to calcifying cells or by converting mesenchymal stem cells to osteochondrocytic or fibroblastic phenotypes. In this study, direct infection of bovine aortic smooth muscle cells (BSMCs) did not induce the expression of alkaline phosphatase or the deposition of extracellular calcium phosphate. However, conditioned media from C. pneumoniae-infected macrophages accelerated conversion of BSMCs to a calcifying phenotype. Treatment of the conditioned media with an anti-TNF-alpha blocking antibody abrogated this stimulatory effect. Treatment of perivascular Sca-1+, CD31-, CD45- cells from apoE-/- mouse aortas with the conditioned media from infected macrophages induced the Sca-1+ cells to produce collagen II, an additional marker of an osteochondrocytic phenotype. Treatment of mouse coronary perivascular Sca-1+, CD31-, CD45- cells with the supernatant from homogenates of C. pneumoniae-infected mouse lungs as compared to noninfected lungs induced expression of the Collagen 1α1 gene and deposition of collagen. Therefore, an increase in plasma cytokines or other factors in response to respiratory infection with C. pneumoniae or infection of macrophages within the blood vessel could contribute to both calcification and fibrosis of advanced atherosclerotic lesions.

Aneurysmal lesions of patients with abdominal aortic aneurysm contain clonally expanded T cells

Abdominal aortic aneurysm (AAA) is a common disease with often life-threatening consequences. This vascular disorder is responsible for 1-2% of all deaths in men aged 65 years or older. Autoimmunity may be responsible for the pathogenesis of AAA. Although it is well documented that infiltrating T cells are essentially always present in AAA lesions, little is known about their role in the initiation and/or progression of the disease. To determine whether T cells infiltrating AAA lesions contain clonally expanded populations of T cells, we amplified β-chain TCR transcripts by the nonpalindromic adaptor-PCR/Vβ-specific PCR and/or Vβ-specific PCR, followed by cloning and sequencing. We report in this article that aortic abdominal aneurysmal lesions from 8 of 10 patients with AAA contained oligoclonal populations of T cells. Multiple identical copies of β-chain TCR transcripts were identified in these patients. These clonal expansions are statistically significant. These results demonstrate that αβ TCR(+) T lymphocytes infiltrating aneurysmal lesions of patients with AAA have undergone proliferation and clonal expansion in vivo at the site of the aneurysmal lesion, in response to unidentified self- or nonself Ags. This evidence supports the hypothesis that AAA is a specific Ag-driven T cell disease.

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.

Intermittent Roxithromycin for Preventing Progression of Small Abdominal Aortic Aneurysms: Long-Term Results of a Small Clinical Trial

Background: Antibodies against Chlamydia pneumoniae are associated with an increased rate of expansion of small abdominal aortic aneurysms (AAAs). Short-term follow-up trials have shown a transient reduction AAA growth rate, in macrolide treated compared with placebo. Therefore we analysed the influence of intermittent, long-term roxithromycin treatment on AAA expansion and referral for surgery. Methods: Eighty-four patients with small AAAs were randomized to either an annual 4 weeks’ treatment with roxithromycin or placebo, and followed prospectively. Results: Intermittent, long-term Roxithromycin-treatment reduced mean annual growth rate by 36% compared with placebo after adjustment for potential confounders. Long-term roxithromycin-treated patients had a 29% lower risk of being referred for surgical evaluation, increasing to 57% after adjusting for potential confounders. Conclusion: Annual 4 week treatment with 300 mg roxithromycin daily may reduce the progression of small AAAs, and later need for surgical repair. However, more robust studies are needed for confirmation.

[Chlamydophila pneumoniae: from its proteomics to arteriosclerosis]

Chlamydophila pneumoniae is a highly prevalent intracellular human pathogen with a unique biphasic life cycle. It is a common cause of upper respiratory infection and pneumonia, and is currently being studied as a potential risk factor for the development of atherosclerotic cardiovascular disease. The outer membrane surface antigens of C. pneumoniae are highly complex: some, such as the major outer membrane protein, are specific, but poorly immunodominant, whereas others have stronger immunogenicity, but are cross-reactive among Chlamydia species. Therefore, new, highly immunodominant, species-specific antigens should be sought. In this regard, the polymorphic membrane proteins (PMPs) are a) unique to Chlamydiae, b) often exposed on the surface of the bacteria, and c) highly immunogenic; these factors make them potential candidates for application in laboratory assays. Other chlamydial antigens, such as heat shock protein (HSP) 60, have been associated with atherosclerotic lesions because of their ability to induce an immunological attack on the endothelial wall. Over the last decade, several studies have suggested a potential role of chronic C. pneumoniae infection in human atherosclerosis. Nevertheless, prospective studies with sufficiently large samples and a healthy comparison group, using a combination of direct and indirect microbiological techniques in the same subject and sample, are needed to establish a relationship between the infection and disease activity.

Role of CD8(+)T cells in the host response to Chlamydia

Chlamydia infections constitute a major public health problem. Although multiple arms of the immune system participate in the control of Chlamydia in infected hosts, T lymphocytes are essential. This review focuses on the roles that CD8(+)T cells may play in immunoprotection and immunopathology following recognition of Chlamydia-infected cells.

The efficacy of pharmacotherapy for decreasing the expansion rate of abdominal aortic aneurysms: a systematic review and meta-analysis

Background

Pharmacotherapy may represent a potential means to limit the expansion rate of abdominal aortic aneurysms (AAAs). Studies evaluating the efficacy of different pharmacological agents to slow down human AAA-expansion rates have been performed, but they have never been systematically reviewed or summarized.

Methods and Findings

Two independent reviewers identified studies and selected randomized trials and prospective cohort studies comparing the growth rate of AAA in patients with pharmacotherapy vs. no pharmacotherapy. We extracted information on study interventions, baseline characteristics, methodological quality, and AAA growth rate differences (in mm/year). Fourteen prospective studies met eligibility criteria. Five cohort studies raised the possibility of benefit of beta-blockers [pooled growth rate difference: −0.62 mm/year, (95%CI, −1.00 to −0.24)], but this was not confirmed in three beta-blocker RCTs [pooled RCT growth rate difference: −0.05 mm/year (−0.16 to 0.05)]. Statins have been evaluated in two cohort studies that yield a pooled growth rate difference of −2.97 (−5.83 to −0.11). Doxycycline and roxithromycin have been evaluated in two RCTs that suggest possible benefit [pooled RCT growth rate difference: −1.32 mm/year (−2.89 to 0.25)]. Studies assessing NSAIDs, diuretics, calcium channel blockers and ACE inhibitors, meanwhile, did not find statistically significant differences.

Conclusions

Beta-blockers do not appear to significantly reduce the growth rate of AAAs. Statins and other anti-inflammatory agents appear to hold promise for decreasing the expansion rate of AAA, but need further evaluation before definitive recommendations can be made.

Abdominal aortic aneurysm is a specific antigen-driven T cell disease

To determine whether monoclonal/oligoclonal T cells are present in abdominal aortic aneurysm (AAA) lesions, we amplified beta-chain T cell receptor (TCR) transcripts from these lesions by the nonpalindromic adaptor (NPA)-polymerase chain reaction (PCR)/V-beta-specific PCR followed by cloning and sequencing. Sequence analysis revealed the presence of substantial proportions of identical beta-chain TCR transcripts in AAA lesions in 9 of 10 patients examined, strongly suggesting the presence of oligoclonal populations of alphabeta TCR+ T cells. We have also shown the presence of oligoclonal populations of gammadelta TCR+ T cells in AAA lesions. Sequence analysis after appropriate PCR amplification and cloning revealed the presence of substantial proportions of identical VgammaI and VgammaII TCR transcripts in 15 of 15 patients examined, and of Vdelta1 and Vdelta2 TCR transcripts in 12 of 12 patients. These clonal expansions were very strong. All these clonal expansions were statistically significant by the binomial distribution. In other studies, we determined that mononuclear cells infiltrating AAA lesions express early- (CD69), intermediate- (CD25, CD38), and late- (CD45RO, HLA class II) activation antigens. These findings suggest that active ongoing inflammation is present in the aortic wall of patients with AAA. These results demonstrate that oligoclonal alphabeta TCR+ and gammadelta TCR+T cells are present in AAA lesions. These oligoclonal T cells have been clonally expanded in vivo in response to yet unidentified antigens. Although the antigenic specificity of these T cells remains to be determined, these T cells may play a significant role in the initiation and/or the propagation of the AAA. It appears that AAA is a specific antigen-driven T cell disease.

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.

Overexpression of transforming growth factor-beta1 stabilizes already-formed aortic aneurysms: a first approach to induction of functional healing by endovascular gene therapy

BACKGROUND

The cell response to transforming growth factor-beta1 (TGF-beta1), a multipotent cytokine with healing potential, varies according to tissue context. We have evaluated the ability of TGF-beta1 overexpression by endovascular gene therapy to stabilize abdominal aortic aneurysms (AAAs) already injured by inflammation and proteolysis.

METHODS AND RESULTS

Active TGF-beta1 overexpression was obtained in already-developed experimental AAAs in rats after endovascular delivery of an adenoviral construct encoding for a mutated form of active simian TGF-beta1 and in an explant model using human atherosclerotic AAA fragments incubated with recombinant active TGF-beta1. Transient exogenous TGF-beta1 overexpression by endovascular gene delivery was followed by induction of endogenous rat TGF-beta1. Overexpression of active TGF-beta1 in experimental AAAs was associated with diameter stabilization, preservation of medial elastin, decreased infiltration of monocyte-macrophages and T lymphocytes, and a decrease in matrix metalloproteinase-2 and -9, which was also observed in the explant model, in both thrombus and wall. In parallel with downregulation of the destructive process, active TGF-beta1 overexpression triggered endoluminal reconstruction, replacing the thrombus by a vascular smooth muscle cell-, collagen-, and elastin-rich intima.

CONCLUSIONS

Local TGF-beta1 self-induction after transient exogenous overexpression reprograms dilated aortas altered by inflammation and proteolysis and restores their ability to withstand arterial pressure without further dilation. This first demonstration of stabilization of expanding AAAs by delivery of a single multipotent self-promoting gene supports the view that endovascular gene therapy should be considered for treatment of aneurysms.

Functional characterization of T cells in abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) exhibit features of a chronic inflammatory disorder. The functional attributes of the T cells in AAA tissue are unclear, with little quantitative or functional data. Using a novel, non-enzymatic method to isolate viable cells from AAA tissue, functional properties of AAA T cells were investigated for the first time. Composition and phenotype of AAA T cells was determined by flow cytometry and verified by immunohistochemistry. Tissue mononuclear cells (MNCs) were cultured in the presence of T-cell mitogens, and cell cycle analysis and cytokine production assessed. Typical cell yield was 4.5 x 10(6) cells per gram of AAA tissue. The majority (58.1+/-5.3%) of haematopoietic (CD45+) cells recovered were CD3+ T cells, B cells comprised 41.1+/-5.7%, natural killer cells 7.3+/-2.5%, and macrophages 2%. Freshly isolated T cells were in resting (G1) state, with 25% expressing the activation-associated cell surface antigens major histocompatibility complex II and CD25. When stimulated in vitro, a significant proportion entered S and G2 phase of the cell cycle, up-regulated CD25, and secreted tumour necrosis factor-alpha, interferon-gamma, interleukin (IL)-5 and IL-6. Despite patient differences, the composition of the AAA inflammatory infiltrate was remarkably consistent, and when re-stimulated ex-vivo T cells produced a stereotypical cytokine response, consistent with the hypothesis that AAA T cells can promote tissue inflammation by secretion of proinflammatory cytokines, and in addition provide signals for B-cell help.

Chlamydia pneumoniae Infection as a Risk Factor for Subarachnoid Hemorrhage

Many risk factors for subarachnoid hemorrhage (SAH), such as hypertension and recent infection, have already been established. Chlamydia pneumoniae is a common respiratory pathogen that has been implicated as a potential risk factor for hypertension and atherosclerotic diseases. The purpose of the case-control study presented here was to examine the causative relationship between C. pneumoniae infection and SAH. Serum C. pneumoniae IgG and IgA antibodies were measured using an enzyme-linked immunosorbent assay in 52 patients with SAH and in 104 healthy age-matched control subjects. Multivariate analysis revealed a significant association between SAH and both a strong seropositivity for IgG and/or IgA antibodies against C. pneumoniae (odds ratio, OR, 3.62; 95% confidence intervals, CI, 1.06-12.39; p = 0.040), which indicates the presence of acute C. pneumoniae infection, and hypertension (OR, 2.91; 95% CI, 1.42-5.96; p = 0.0035). These results provide evidence that infection with C. pneumoniae may be a risk factor for SAH from a ruptured intracranial aneurysm.

The Role of Chlamydia Pneumoniae in Human Aortic Disease—A Hypothesis Revisited

BACKGROUND

The role of Chlamydia pneumoniae in the pathogenesis of aortic aneurysm is controversial. We investigated the presence of C. pneumoniae in tissue samples excised from patients and controls.

METHODS

Aortic wall specimens were obtained from 17 patients with acute Stanford type A aortic dissection, 25 patients with thoracic aortic aneurysms (TAA) and 23 patients with abdominal aortic aneurysms (AAA). Eighty-three tissue samples of 73 control patients free of aortic disease were obtained either at surgery or autopsy. The presence of Chlamydia subspecies DNA (sequences specific for all known Chlamydiaceae) and DNA of C. pneumoniae, C. trachomatis and C. psittaci were assessed by a validated highly sensitive and specific real time polymerase chain reaction (PCR) analysis. Atherosclerotic risk factors were assessed in all patients.

RESULTS

We failed to detect C. pneumoniae and C. psittaci-DNA in any of the 148 vessel specimens. C. trachomatis-DNA was detected in 1/65 patients and in none of 83 controls (P=0.43). Chlamydia subspecies DNA was found in samples of eight cases and in one control (P=0.01), however, no significant differences were found between the subgroups aortic dissection (P=0.09), TAA (P=0.99) and AAA (P=0.15) and respective controls.

CONCLUSIONS

C. pneumoniae does not play a clinically relevant role in acute and chronic aortic disease. The impact of other organisms of the family Chlamydiaceae needs further evaluation.

Adaptive cellular immunity in aortic aneurysms: cause, consequence, or context?

Abdominal aortic aneurysms are common and life threatening. Although CD4(+) T cells are abundant in aneurysm tissue, their role in disease progression remains unclear. A new study shows that mouse aortic allografts placed in animals lacking IFN-gamma receptors develop a Th2 inflammatory response with aortic aneurysms, whereas Th1 responses promote intimal hyperplasia. It is expected that these surprising findings will stimulate further efforts to clarify whether adaptive cellular immunity in aneurysm disease is detrimental or potentially beneficial.

The detection of Chlamydia pneumoniae in aneurysm of abdominal aorta and in normal aortic wall of organ donors

Sixty patients underwent surgery due to abdominal aortic aneurysms; the group included 30 patients with asymptomatic aneurysm and 30 with ruptured aneurysm. A control group comprised 30 organ donors. Surgical specimens derived from aneurysm or aorta fragments were investigated for Chlamydia pneumoniae DNA using PCR. In asymptomatic aneurysms, DNA was found in 9 cases (29%), and in ruptured aneurysms in 14 cases (49%). In the control group, C. pneumoniae DNA was not detected in an aortic wall. These results suggest that healthy aortic wall is not susceptible to chlamydial infection. A large number of aneurysm infections implies C. pneumoniae role in proteolysis and degradation of the aneurysm wall. The biological effect of this process may cause an enlargement of the aneurysm.

Chlamydia pneumoniae and atherosclerosis

Exposure to Chlamydia pneumoniae is extremely common, and respiratory infections occur repeatedly among most people. Strong associations exist between C. pneumoniae infection and atherosclerosis as demonstrated by: (i) sero-epidemiological studies showing that patients with cardiovascular disease have higher titres of anti-C. pneumoniae antibodies compared with control patients; (ii) detection of the organism within atherosclerotic lesions, but not in adjacent normal tissue by immunohistochemistry, polymerase chain reaction and electron microscopy and by culturing the organism from lesions; and (iii) showing that C. pneumoniae can either initiate lesion development or cause exacerbation of lesions in rabbit and mouse animal models respectively. The association of this organism with atherosclerosis has also provided sufficient impetus to conduct a variety of human secondary prevention antibiotic treatment trials. The results of these studies have been mixed and, thus far, no clear long-lasting benefit has emerged from these types of investigations. Studies of C. pneumoniae pathogenesis have shown that the organism can infect many cell types associated with both respiratory and cardiovascular sites, including lung epithelium and resident alveolar macrophages, circulating monocytes, arterial smooth muscle cells and vascular endothelium. Infected cells have been shown to exhibit characteristics associated with the development of cardiovascular disease (e.g. secretion of proinflammatory cytokines and procoagulants by infected endothelial cells and foam cell formation by infected macrophages). More detailed analysis of C. pneumoniae pathogenesis has been aided by the availability of genomic sequence information. Genomic and proteomic analyses of C. pneumoniae infections in relevant cell types will help to define the pathogenic potential of the organism in both respiratory and cardiovascular disease.

Prospects for the medical management of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are a chronic degenerative disease with life-threatening implications. While AAAs are thought to arise through a localized form of arterial wall injury superimposed on various predisposing factors, their natural history is one of progressive structural deterioration, gradual expansion, and eventual rupture. Pathologic processes contributing to the changes observed in AAAs include chronic inflammation, destructive remodeling of the extracellular matrix, and depletion of vascular smooth muscle cells. These changes result in progressive aortic dilatation accompanied by alterations in vessel geometry, redistribution of hemodynamic wall stresses, and diminished tensile strength. As outlined in this review, better understanding of the biological mechanisms underlying these changes will allow design of novel therapeutic strategies to suppress the process of aneurysmal degeneration.

Chlamydia pneumoniae in patients undergoing surgery for thoracic aortic disease

OBJECTIVE

To investigate if Chlamydia pneumoniae is present in the wall of the thoracic aorta in patients operated on for aneurysm or aortic dissection.

DESIGN

Consecutive patients undergoing surgery for thoracic aortic aneurysm (TAA, 32 patients) and for aortic dissection (6 patients) were included in this prospective study. Tissue samples from the aorta were analysed for the presence of C. pneumoniae by polymerase chain reaction (PCR), histopathology, immunohistochemistry and in one aortic tissue sample C. pneumoniae was verified by electron microscopy and immunogold labelling technique. Cultured Hep 2 cells infected with C. pneumoniae were used as a positive control for electron microscopy. Sera for microimmunofluorescence were obtained in 36/38 and throat swabs for C. pneumoniae PCR in 17/38 patients.

RESULTS

Chlamydia pneumoniae was detected by PCR in 4 of 32 TAA tissue samples (12%) and in 0 of 6 patients operated on for aortic dissection. Chlamydia pneumoniae inclusion bodies in one of the PCR positive tissue samples were verified by electron microscopy. IgG antibodies to C. pneumoniae were present in 17/31 (55%) and IgA in 15/31 (48%) of the TAA patients and in none of five tested patients with dissection. None of the tested throat swabs was positive.

CONCLUSION

In this study we report the presence of C. pneumoniae by PCR and electron microscopy in the wall of TAA. A high prevalence of serum IgA antibodies to C. pneumoniae was found in TAA patients. In contrast no signs of C. pneumoniae were detected in patients with thoracic aortic dissection.

Presence of Chlamydia pneumoniae in abdominal aortic aneurysms is not associated with increased activity of matrix metalloproteinases

OBJECTIVE

to test the hypothesis that the presence of Chlamydia pneumoniae (C. pneumoniae) in the wall of abdominal aortic aneurysms (AAA) is associated with increased activity of matrix metalloproteinase (MMP)-2 and/or MMP-9.

DESIGN

case-control study.

MATERIAL AND METHODS

in a series of 40 patients with AAA > or =5cm in maximal cross-sectional diameter, C. pneumoniae-DNA was identified in the aneurysm wall by nested PCR in 14 (35%) patients. Another 14 C. pneumoniae-DNA-negative AAA patients from the same series, matched for gender and aneurysm diameter, were used as controls. In each group there were 7 asymptomatic (aAAA) and 7 ruptured (rAAA) aneurysms. MMP-2 and -9 activity was estimated in AAA wall biopsies by gelatin zymography.

RESULTS

patients with a C. pneumoniae-DNA-positive aneurysm wall specimen showed an over-all lower activity of MMP-2 and MMP-9 (pro- and active enzyme) compared to the C. pneumoniae-DNA negative patients. However, there were no statistically significant differences in MMP activity between the two groups of patients with aAAA. Among patients with rAAA both pro-MMP-9 (p=0,026) and active-MMP-9 (p=0.007) were significantly lower in C. pneumoniae-DNA-positive patients compared to C. pneumoniae-DNA-negative patients, whereas there were no significant differences in pro-MMP-2 or active-MMP-2.

CONCLUSION

this preliminary study does not support the hypothesis that the presence of C. pneumoniae in the AAA wall is associated with increased activity of MMP-2 and MMP-9.

Cerebral aneurysms in a child with acquired immune deficiency syndrome during rapid immune reconstitution

A 12-year-old boy with perinatally acquired human immunodeficiency virus infection an d Centers for Disease Control and Prevention class C3 disease presented with acute onset of confusion and a right-sided movement disorder 5 months after beginning a new antiretroviral regimen. His CD4 count had been below 50 cells/microL for 4 years but had abruptly risen to more than 250 cells/microL. Computed tomographic and magnetic resonance imaging scans showed cerebral aneurysms and new cerebral lesions consistent with ischemic strokes. The presentation during immune reconstitution suggests that cerebral aneurysms in pediatric patients with acquired immune deficiency syndrome can result from an immune-mediated response to chronic vascular infection.

In vitro degradation of aortic elastin by Chlamydia pneumoniae

OBJECTIVES

to investigate whether Chlamydia pneumoniae (C. pneumoniae) may increase elastin degradation in the aortic wall.

MATERIALS AND METHODS

eighteen full thickness aortic wall samples from non-aneurysmal infrarenal abdominal aortas were collected from autopsies. Two adjacent and equally large pieces were cut out of each aortic sample. From each sample, one piece was incubated in a HEp-2 cell culture infected with C. pneumoniae and the other piece was incubated in an uninfected HEp-2 cell culture. The incubation time was one week at 35 degrees C. The concentration of elastin-derived peptides (EDP) (ng/ml) in the medium of each cell culture was measured in duplicate. For each paired sample, delta-EDP (EDP in HEp-2 cell culture infected with C. pneumoniae- EDP in uninfected HEp-2 cell culture) was calculated.

RESULT

there was a significantly increased degradation of aortic elastin, estimated by EDP concentrations in cell culture conditioned medium, when aortic wall samples were incubated in C. pneumoniae cultures compared with uninfected cultures (p=0.025, Wilcoxon signed ranks test).

CONCLUSION

these results indicate that there is a relationship between the presence of C. pneumoniae and increased elastin degradation in the aortic wall in vitro. This suggests C. pneumoniae in the aortic wall directly or indirectly leads to the degradation of aortic elastin.

Use of doxycycline to decrease the growth rate of abdominal aortic aneurysms: a randomized, double-blind, placebo-controlled pilot study

OBJECTIVE

Eradication of Chlamydia pneumoniae infection and inhibition of elastolytic matrix metalloproteinases with doxycycline have been suggested to reduce the growth rates of small abdominal aortic aneurysms (AAA). We designed a study to investigate the efficacy of doxycycline in reducing the expansion of small AAAs.

SUBJECTS AND METHODS

This was a prospective, double-blind, randomized, placebo-controlled study that was set in a university referral hospital. The study group consisted of 32 of 34 initially eligible patients who had an AAA diameter perpendicular to the aortic axis of 30 mm or more in size or a ratio of infrarenal to suprarenal aortic diameter of 1.2 or more and a diameter less than 55 mm. Patients were randomly assigned to receive either doxycycline (150 mg daily) or placebo during a 3-month period and underwent ultrasound surveillance during an 18-month period. Outcome measures included aneurysm expansion rates, the number of patients who had AAA rupture or repair, C pneumoniae antibody titers, and serum concentrations of C-reactive protein.

RESULTS

The aneurysm expansion rate in the doxycycline group was significantly lower than that in the placebo group during the 6- to 12-month (P = .01) and the 12- to 18-month periods (P =.01). Five patients (41%) in the placebo group and 1 patient (7%) in the doxycycline group had an overall expansion of the aneurysm of 5 mm or more during the 18-month follow-up. Among the placebo group patients, a higher expansion rate was observed in those with enhanced C pneumoniae immunoglobulin G antibody titers (> 128) than in those with lower titers (P = .03). Doxycycline treatment had no clear effect on antibody titers. However, at 6-month follow-up, C-reactive protein levels in the doxycycline group were significantly lower than the baseline levels (P = .01).

CONCLUSIONS

The results of this small pilot study suggest that doxycycline may favorably alter the outcome of patients with small AAA. However, because of the small size of this randomized study and of the potentially confounding effect of pretreatment risk factors, doxycycline-based treatment cannot be justified only on the ground of the current results. Because of the high prevalence of this disorder and its clinical, social, and economic relevance, a multicenter study should be performed to further investigate whether there is any place for medical treatment of small AAAs.

Antibodies against Chlamydia pneumoniae predict the need for elective surgical intervention on small abdominal aortic aneurysms

OBJECTIVE

to compare the ability of two independent Chlamydia pneumoniae antibody tests to predict need for small abdominal aortic aneurysm (AAA) repair.

PATIENTS AND METHODS

annual scans were offered to 149 screening diagnosed small AAA (<5 cm). Serum samples were collected for measuring IgA and IgG-antibodies to C. pneumoniae by microimmunofluorescence (MIF) test and the new ELISA (Labsystems).

RESULTS

a significant concordance was found between MIF and ELISA titres with Kappa values of 0.29 for S-IgA and 0.42 for S-IgG. IgG antibodies measured by ELISA were most predictive for cases expanding operation recommendable sizes with a sensitivity and specificity of 80% and 66%, respectively.

CONCLUSION

the simpler EIA has a high correlation with the MIF test and both were predictive for the natural history of AAA. Chlamydia antibody test may be used to identify individuals who might benefit from follow-up and anti-chlamydia treatment.

The role of inflammation and infection in coronary artery disease

New insights into atherosclerosis, the most common disease affecting coronary arteries, may change therapeutic strategies from largely symptomatic to causal. Atherosclerotic plaques contain a lipid-related, immune-mediated inflammation, with release of secretory products capable of changing plaque morphology. Plaques prone to complications contain large numbers of inflammatory cells; stable plaques contain little inflammation. Similarly, atherectomy specimens from patients with coronary syndromes revealed more inflammatory cells in unstable than in stable patients. These observations, and the fact that acute coronary syndromes are associated with increased blood levels of inflammatory markers, have renewed interest in the possible relationship between infection and atherogenesis. Of all potential candidate antigens, Chlamydia pneumoniae presently is considered the most likely because a substantial number of patients with unstable syndromes contain C. pneumoniae-reactive T cells, both in blood and within the atherosclerotic plaque, suggesting enhancement of intraplaque inflammation.

The evolving relationship between Chlamydia pneumoniae and atherosclerosis

A body of evidence supports an association between Chlamydia pneumoniae and atherosclerosis. Recent prospective, seroepidemiologic studies have refined estimations of relative risk. Advances in diagnostic testing with the polymerase chain reaction have created a potential opportunity to screen for infected individuals. New insights into the pathogenesis of infection with C. pneumoniae have been reported, many of which are relevant to the development of atherosclerotic plaque. Clinical trials have now been initiated and should provide guidance as to the utility of antibiotics in the treatment or prevention of coronary artery disease.

T lymphocyte lines isolated from atheromatous plaque contain cells capable of responding to Chlamydia antigens

Chlamydia pneumoniae infection is associated with atherosclerosis and the organism has been identified in arterial lesions. To determine whether T lymphocyte-mediated immune responses to Chlamydia antigens within plaque could contribute to pathogenesis, we have derived T cell lines from atherosclerotic plaques of 32 patients. Culture with IL-2 alone proved insufficient for cellular activation and expansion, but additional stimulation with phytohaemagglutinin (PHA) or recall antigens allowed consistent establishment of T cell lines. Furthermore, in cultures of approx. 500 tissue fragments, Chlamydia organisms proved as effective as other recall antigens in producing outgrowth of arterial T cells (20-25% wells produced T cell lines). Testing the antigen responsiveness of T cell lines showed that those derived using Chlamydia organisms were more likely to respond to Chlamydia (5/29+) than those isolated using other stimuli (6/69+ for PHA; 5/57+ for PPD and tetanus toxoid (TT)). However, lines responsive to each of the recall antigens were observed. Using recombinant Chlamydia antigens, some Chlamydia-specific T cell lines were shown to respond to OMP2 and/or hsp60. Those recognizing Chlamydia hsp60 did not cross-react with human hsp60, but human hsp60-responsive lines were also observed. Thus, atherosclerotic plaque tissue contains a variety of memory T lymphocytes, and amongst these are cells capable of recognizing Chlamydia antigens. In a C. pneumoniae-infected plaque, such T cells may be activated by local antigen and could contribute to the inflammatory process in the arterial wall through CD40 ligand expression and cytokine secretion.

Chlamydia trachomatis reactive T lymphocytes from upper genital tract tissue specimens

Chlamydia trachomatis infection is associated with pelvic inflammatory disease (PID) and tubal factor infertility (TFI). We investigated the role of C. trachomatis as a target antigen of endometrial and salpingeal tissue lymphocytes derived from PID and TFI patients. Antigen specificity of the tissue originated T lymphocyte lines (TLL) was tested against C. trachomatis elementary bodies and chlamydial heat shock protein 60 (CHSP60). C. trachomatis antigen stimulated proliferation in two out of eight endometrial TLL derived from PID patients and three out of four TLL derived from TFI patients. All (n = 4) TLL derived from the salpingeal specimens responded to CHSP60 compared with only one out of 12 TLL derived from the endometrial specimens. In-vivo expression of interferon-gamma (IFN-gamma) mRNA revealed that it was present in nine of 13 specimens obtained from PID patients. The dominant activity of type-1 T lymphocytes was confirmed by the in-vitro production of IFN-gamma (median 1007 pg/ml) from all (n = 5) C. trachomatis specific TLL while IL-5 secretion was lower (median 779 pg/ml). In conclusion, C. trachomatis reactive TLL were established from in-vivo activated lymphocytes from the upper genital tract tissue of PID and TFI patients. The reactivity of the salpingeal TLL to CHSP60 provided further evidence that immunoreactivity to CHSP60 is a predominant response in patients with tubal damage.

Detection of Chlamydia pneumoniae-reactive T lymphocytes in human atherosclerotic plaques of carotid artery

Linkage between Chlamydia pneumoniae infection and atherosclerosis has been confirmed in several studies, but the precise role of this organism in the disease process is not known. We investigated the relation and reactivity of T lymphocytes of human carotid plaques to C pneumoniae antigens. Tissue specimens were obtained from 17 patients who underwent carotid endarterectomy. Immunohistological staining and/or in situ hybridization revealed the presence of C pneumoniae in 11 (64%) of the 17 of the cases. Inflammatory infiltration seen in the vessel walls consisted primarily of CD45RO+ T-memory lymphocytes (median 80%, range 50% to 90%), whereas CD20+ B cells and monocytes were in minor proportion. In vivo activated T lymphocytes were propagated from the specimens with interleukin-2, and the antigen specificity of the established T-cell lines (TLLs) was analyzed against C pneumoniae elementary body antigen. TLLs were established from all 17 carotid tissues but none from the control specimens of ascending aorta. C pneumoniae was recognized as a specific T-cell-stimulating antigen in 7 (41%) of 17 cases. Further analyses of the C pneumoniae-reactive TLLs showed that chlamydial 60-kDa heat-shock protein induced specific proliferation in 5 (71%) of 7 cases and revealed 2 haplotype (DRB1*1502 and DQB1*06) binding motifs in human 60-kDa heat-shock protein. C pneumoniae was identified as a specific microbial antigen recognized by 41% of TLLs propagated from in vivo activated plaque T cells. Our results suggests that cell-mediated immunity to C pneumoniae plays a role in the atherosclerotic process and that this response may involve autoimmunity.

Atherosclerosis, inflammation, and infection

In recent years, it has been shown that inflammation plays an important role in the pathogenesis of atherosclerosis. Activated macrophages, T lymphocytes, and mast cells are present in atherosclerotic plaques, which has led to the notion that the inflammatory response is an immune-mediated process. Complicated lesions, moreover, appear to be associated with an increase in the amount of the inflammatory response and in these patients, increased levels of acute phase proteins are present. The appreciation that atherosclerosis is an immune-mediated inflammatory disease has also led to renewed interest in the potential role of infectious agents in initiating or modulating atherosclerosis. Seroepidemiological studies have shown raised antibody titres against several micro-organisms. However, as yet, there are hardly any data available that provide a sound scientific basis for an infectious origin. Of all potential candidate organisms, Chlamydia pneumoniae appears as the one most likely involved in atherogenesis. C. pneumoniae has been retrieved from atherosclerotic tissues; the level of raised plasma titres correlates with the severity of symptomatic atherosclerotic disease; and the incidence of C. pneumoniae-responsive T cells in peripheral blood is increased in patients with coronary heart disease. It also appears that in some patients T cells generated from atherosclerotic plaques respond to C. pneumoniae. At the present state of knowledge, however, it is fair to state that the relationship between infection, intraplaque inflammation, and atherosclerosis still remains hypothetical, despite the increasing evidence that such a relationship could exist.