Cytomegalovirus is involved in vascular pathology

A novel cytomegalovirus-induced regulatory-type T-cell subset increases in size during older life and links virus-specific immunity to vascular pathology

Background. Cytomegalovirus (CMV) infection directly targets vascular endothelium and smooth muscle and at older ages is associated with accelerated vascular pathology and mortality. CMV-specific cellular immunity might directly contribute to this process.

Methods. Conventional ex vivo activation–induced T-cell responses to 19 dominant CMV antigens, along with CMV-specific inducible regulatory-type CD4⁺ T cells (iTregs), were measured in healthy older people, using a novel protocol that included classic Treg markers alongside the activation marker CD134. Measurements were correlated with diastolic, systolic, and mean arterial blood pressure, a surrogate marker for arterial stiffness.

Results. CMV-specific iTregs recognized the same antigens as conventional CD4⁺ T cells and were significantly more frequent at older ages. They suppressed antigen-specific and nonspecific proliferation and in large part expressed Foxp3. Frequencies of CMV-specific iTregs and CD8⁺ T cells (summated response) were significantly associated with diastolic and mean arterial pressures. Confounders, including age, body mass index, smoking, antihypertensive medication use, or C-reactive protein levels, did not explain these observations.

Conclusions. A novel CMV-induced regulatory-type CD4⁺ T-cell subset is readily detectable in CMV-infected people and, like the aggregate CD8⁺ T-cell response to the most dominant CMV antigens, is quantitatively associated with arterial stiffness in older life. Whereas CD8⁺ effector T cells might directly cause vascular injury, iTregs may attenuate this response.

Does cytomegalovirus play a causative role in the development of various inflammatory diseases and cancer?

Human cytomegalovirus (HCMV) is a herpes virus that infects and is carried by 70-100% of the world's population. During its evolution, this virus has developed mechanisms that allow it to survive in an immunocompetent host. For many years, HCMV was not considered to be a major human pathogen, as it appeared to cause only rare cases of HCMV inclusion disease in neonates. However, HCMV is poorly adapted for survival in the immunosuppressed host and has emerged as an important human pathogen in AIDS patients and in patients undergoing immunosuppressive therapy following organ or bone marrow transplantation. HCMV-mediated disease in such patients has highlighted the possible role of this virus in the development of other diseases, in particular inflammatory diseases such as vascular diseases, autoimmune diseases and, more recently, with certain forms of cancers. Current research is focused on determining whether HCMV plays a causative role in these diseases or is merely an epiphenomenon of inflammation. Inflammation plays a central role in the pathogenesis of HCMV. This virus has developed a number of mechanisms that enable it to hide from the cells of the immune system and, at the same time, reactivation of a latent infection requires immune activation. Numerous products of the HCMV genome are devoted to control central functions of the innate and adaptive immune responses. By influencing the regulation of various cellular processes including the cell cycle, apoptosis and migration as well as tumour invasiveness and angiogenesis, HCMV may participate in disease development. Thus, the various drugs now available for treatment of HCMV disease (e.g. ganciclovir, acyclovir and foscarnet), may also prove to be useful in the treatment of other, more widespread diseases.

Prolonged activation of NF-kappaB by human cytomegalovirus promotes efficient viral replication and late gene expression

Infection of fibroblasts by human cytomegalovirus (HCMV) rapidly activates the NF-kappaB signaling pathway, which we documented promotes efficient transactivation of the major immediate-early promoter (DeMeritt, I.B., Milford, L.E., Yurochko, A.D. (2004). Activation of the NF-kappaB pathway in human cytomegalovirus-infected cells is necessary for efficient transactivation of the major immediate-early promoter. J. Virol. 78, 4498-4507). Because a second, sustained increase in NF-kappaB activity following the initial phase of NF-kappaB activation was also observed, we investigated the role that this prolonged NF-kappaB activation played in viral replication and late gene expression. We first investigated HCMV replication in cells in which NF-kappaB activation was blocked by pretreatment with NF-kappaB inhibitors: HCMV replication was significantly decreased in these cultures. A decrease in replication was also observed when NF-kappaB was inhibited up to 48 h post-infection, suggesting a previously unidentified role for NF-kappaB in the regulation of the later class of viral genes.

The association of infection and coronary artery disease: an update

Numerous studies have reported an association of coronary atherosclerosis and restenosis with certain bacterial and viral infections. This article reviews the pathophysiology of atherosclerosis, the role of infectious agents (cytomegalovirus, Chlamydia pneumoniae and Helicobacter pylori) in atherogenesis and studies supporting the potential beneficial effects of antibiotics or antiviral agents in the management of atherosclerotic disease. The interactions of cytomegalovirus and the arterial wall have been extensively studied. However, despite the successful preliminary therapeutic trials with the use of macrolides in augmenting possible C. pneumoniae-induced cardiovascular events, the exact mechanisms of how C. pneumoniae enters the arterial wall remains unknown at this point. For H. pylori, regardless of the large number of studies performed to assess the association between H. pylori and coronary artery disease, no definitive conclusion could be made at this time, due to contradictory results. Before one can widely adopt the use of antibiotics or antiviral agents as treatment for atherosclerosis, further studies must be designed to address some important issues. In vivo animal models need to be established to further examine the various hypotheses regarding the interaction of infectious agents and atherosclerosis and restenosis. Large-scale prospective cohort studies should be designed to relate evidence of infection to future risk of cardiovascular diseases. Confounding variables, such as other cardiovascular risk factors and socio-economic status, should be controlled in order to strengthen the association. Further interventional studies are also required to establish the best antibiotic or antiviral regimen to maximise efficacy and minimise side effects.