Discordant detection of Chlamydia pneumoniae in patients with carotid artery disease using polymerase chain reaction, immunofluorescence microscopy and serological methods

Evolution to a chronic disease niche correlates with increased sensitivity to tryptophan availability for the obligate intracellular bacterium Chlamydia pneumoniae

The chlamydiae are obligate intracellular parasites that have evolved specific interactions with their various hosts and host cell types to ensure their successful survival and consequential pathogenesis. The species Chlamydia pneumoniae is ubiquitous, with serological studies showing that most humans are infected at some stage in their lifetime. While most human infections are asymptomatic, C. pneumoniae can cause more-severe respiratory disease and pneumonia and has been linked to chronic diseases such as asthma, atherosclerosis, and even Alzheimer's disease. The widely dispersed animal-adapted C. pneumoniae strains cause an equally wide range of diseases in their hosts. It is emerging that the ability of C. pneumoniae to survive inside its target cells, including evasion of the host's immune attack mechanisms, is linked to the acquisition of key metabolites. Tryptophan and arginine are key checkpoint compounds in this host-parasite battle. Interestingly, the animal strains of C. pneumoniae have a slightly larger genome, enabling them to cope better with metabolite restrictions. It therefore appears that as the evolutionarily more ancient animal strains have evolved to infect humans, they have selectively become more "susceptible" to the levels of key metabolites, such as tryptophan. While this might initially appear to be a weakness, it allows these human C. pneumoniae strains to exquisitely sense host immune attack and respond by rapidly reverting to a persistent phase. During persistence, they reduce their metabolic levels, halting progression of their developmental cycle, waiting until the hostile external conditions have passed before they reemerge.

Why should a doctor be interested in oral disease?

Oral health has been implicated in systemic disease throughout the ages; however, the understanding of the relationship between oral disease and systemic diseases such as cardiovascular disease and Type 2 diabetes mellitus is still emerging today. Chronic periodontal disease is widespread in the general population and a significant proportion of adults suffer from the most severe form of the disease. Dental plaque biofilm is necessary for the development of chronic periodontal disease with genetic and environmental factors contributing towards the pathogenesis. The putative biological mechanisms of the association between oral disease and atherogenesis are discussed, although there is insufficient evidence to establish causality at this time. Regardless of a direct causal relationship between oral disease and cardiovascular disease, treatment of oral disease leads to both a reduction in the systemic inflammatory burden as reflected in inflammatory markers and an improvement in endothelial function and hence improved overall health outcomes. A brief overview of periodontal disease including etiology, pathogenesis, screening and therapeutic implications is presented.

cIAP-1 controls innate immunity to C. pneumoniae pulmonary infection

The resistance of epithelial cells infected with Chlamydophila pneumoniae for apoptosis has been attributed to the induced expression and increased stability of anti-apoptotic proteins called inhibitor of apoptosis proteins (IAPs). The significance of cellular inhibitor of apoptosis protein-1 (cIAP-1) in C. pneumoniae pulmonary infection and innate immune response was investigated in cIAP-1 knockout (KO) mice using a novel non-invasive intra-tracheal infection method. In contrast to wildtype, cIAP-1 knockout mice failed to clear the infection from their lungs. Wildtype mice responded to infection with a strong inflammatory response in the lung. In contrast, the recruitment of macrophages was reduced in cIAP-1 KO mice compared to wildtype mice. The concentration of Interferon gamma (IFN-γ) was increased whereas that of Tumor Necrosis Factor (TNF-α) was reduced in the lungs of infected cIAP-1 KO mice compared to infected wildtype mice. Ex vivo experiments on mouse peritoneal macrophages and splenocytes revealed that cIAP-1 is required for innate immune responses of these cells. Our findings thus suggest a new immunoregulatory role of cIAP-1 in the course of bacterial infection.

Chlamydia pneumoniae and atherosclerosis: current state and future prospectives

Chlamydia pneumoniae, an intracellular bacterial pathogen, is known as a leading cause of human respiratory tract infections worldwide. Over the last decade, several reports in the literature have suggested that infection with C. pneumoniae may contribute to the pathogenesis of atherosclerosis. In order to play a causative role in chronic disease, C. pneumoniae would need to persist within infected tissue for extended periods of time, thereby stimulating a chronic inflammatory response. C. pneumoniae has been shown to disseminate systemically from the lungs through infected peripheral blood mononuclear cells and to localize in arteries where it may infect endothelial cells, vascular smooth muscle cells, monocytes/macrophages and promote inflammatory atherogenous process. The involvement of C. pneumoniae in atherosclerosis was investigated by seroepidemiological and pathological studies, in vivo and in vitro studies, and in clinical antibiotic treatment trials. This review will provide an update on the role of C. pneumoniae in atherosclerosis focusing on the recent insights and suggesting areas for future research.

Role of Chlamydia pneumoniae in atherosclerosis

Cardiovascular disease, resulting from atherosclerosis, is a leading cause of global morbidity and mortality. Genetic predisposition and classical environmental risk factors explain much of the attributable risk for cardiovascular events in populations, but other risk factors for the development and progression of atherosclerosis, which can be identified and modified, may be important therapeutic targets. Infectious agents, such as Chlamydia pneumoniae, have been proposed as contributory factors in the pathogenesis of atherosclerosis. In the present review, we consider the experimental evidence that has accumulated over the last 20 years evaluating the role of C. pneumoniae in atherosclerosis and suggest areas for future research in this field.

Severity of carotid atherosclerosis unrelated to Chlamydia pneumoniae infection in acute ischemic stroke patients: a clinicopathological study

BACKGROUND

Both clinical and pathological alterations of the carotid arteries were correlated with Chlamydia pneumoniae infection in 67 acute ischemic stroke patients with severe neurological symptoms.

METHODS

In the clinical study, intima-media thickness (IMT) of the common carotid arteries was determined in vivo by B-mode ultrasound measurement and C. pneumoniae-specific IgG and IgA responses were detected. In the pathological study, the absolute wall thickness of the common, internal and external carotid arteries was measured postmortem in specimens obtained at the autopsy of patients who died due to complications of acute stroke. In the atherosclerotic plaques of the autopsy specimens, C. pneumoniae genomic DNA was detected by polymerase chain reaction amplification.

RESULTS

The Spearman's rho correlation coefficient of IMT with the average wall thickness of the common, internal and external carotid arteries was 0.51 (p = 0.002), 0.34 (p = 0.052) and 0.58 (p < 0.001), respectively. Anti-C. pneumoniae IgG and IgA antibodies were detected in 43 (73%) and 29 (49%) patients, but neither antibody marker correlated with IMT (median: 0.91 mm in IgG positives vs. 0.90 mm in IgG negatives, p = 0.86; 0.88 mm in IgA positives vs. 0.90 mm in IgA negatives, p = 0.53). The presence of C. pneumoniae DNA was detected in the carotid plaques of 21 (54%) of the 39 tested patients, independently of either IMT values or the average wall thickness of all carotid arteries.

CONCLUSIONS

In acute ischemic stroke patients, C. pneumoniae infection was frequently detected in the arteriosclerotic plaques of the carotid arteries but it did not correlate with the severity of carotid arteriosclerosis.

Presence of Chlamydia pneumoniae in patients with and without atherosclerosis

Data published over the past decade show that Chlamydia pneumoniae is likely associated with the development of atherosclerosis. The aim of this study was to ascertain whether C. pneumoniae infections occur more frequently in patients with atherosclerosis than in healthy subjects. A total of 517 persons were studied. Serum samples, leukocytes, and tissue samples were assayed for the presence of C. pneumoniae-specific IgG and IgA antibodies and C. pneumoniae DNA. C. pneumoniae DNA was found in renal, iliac, and brachial vessels, but it was not detected in radial arteries. C. pneumoniae DNA was found most often in directional coronary atherectomy tissue specimens (11/41, 26.8%), but it was also found in the leukocytes of 14.9% (28/188) of patients with atherosclerosis and 24.6% (28/114) of patients without atheroma changes in vessels. Specific IgG and IgA antibodies were present in 63.8 and 49.9% of atheroma patients, respectively. The prevalence of C. pneumoniae antibodies differs significantly in patients with and without atherosclerosis (for IgG, p=0.002, and for IgA, p=0.006). The identification of persons with chlamydial infection of atherosclerotic arteries necessitates the examination of vascular tissues obtained during revascularization procedures. Serological investigation alone cannot identify individuals with vascular chlamydial infections. Detection of C. pneumoniae DNA in peripheral blood mononuclear cells does not seem to be the exclusive marker of persistent vascular infection. A more easily accessible parameter that allows prediction of chlamydial vascular infection is required.