Melanoma growth stimulatory activity (MGSA/GRO-alpha) chemokine genes incorporated into an African green monkey simian cytomegalovirus-derived stealth virus

Patterns of divergence in the vCXCL and vGPCR gene clusters in primate cytomegalovirus genomes

Primate cytomegalovirus (CMV) genomes contain tandemly repeated gene clusters putatively encoding divergent CXC chemokine ligand-like proteins (vCXCLs) and G protein-coupled receptor-like proteins (vGPCRs). In human, chimpanzee and rhesus CMVs, respectively, the vCXCL cluster contains two, three and six genes, and the vGPCR cluster contains two, two and five genes. We report that (i) green monkey CMV strains fall into two groups, containing either eight and five genes or seven and six genes in the respective clusters, and (ii) owl monkey CMV has two and zero genes. Phylogenetic analysis suggested that the vCXCL cluster evolved from a CXCL chemokine gene (probably GRO-alpha) that was captured in an incompletely spliced form by an ancestor of Old and New World primate CMVs, and that the vGPCR cluster evolved from a GPCR gene captured by an Old World primate CMV. Both clusters appear to have evolved via complex duplication and deletion events.

Alternative cellular energy pigments from bacteria of stealth virus infected individuals

Bacteria isolated from patients infected with stealth-adapted viruses can produce complex solid and thread-like structures similar to the alternative cellular energy pigments (ACE pigments) seen in cultures of stealth-adapted virus infected patients. Bacteria replication of stealth-adapted viruses can explain why certain patients diagnosed as having delusional parasitosis insist that the particles that they believe are parasitic, increase in number even when outside of the body. Bacterial production of ACE pigments may also be contributing to the ACE pigments that can be isolated from the hair, sweat, and urine of such patients. The term viteria has been applied to stealth-adapted viruses that have acquired bacterial sequences. Viteria infected bacteria clearly pose an important public health problem and may lead to a wider dissemination of stealth-adapted viruses.

Consequences of human cytomegalovirus mimicry

The HCMV genome has evolved with its host by incorporating a series of genes that are homologous to, or functionally mimic, cellular genes. Some are designed to counteract the stress of infection on the host cell, notably the viral antiapoptotic proteins (vICA, vMIA). Others potentially help the infected cell maintain a low immunologic profile. These include virus-encoded chemokine receptors (UL33, UL78, US27, US28), FcRs (gp TRL11/IRL11, gp UL119-118), and proteins that directly or indirectly thwart natural killer cell activity (UL16, gpUL40). In addition, some viral proteins may play a role in immunopathology because of fortuitous cross-reactivity with host cell proteins. This overview discusses how these proteins affect the life of the host cell and its immediate neighbors.

Subversion of the chemokine world by microbial pathogens

It is well known that microbial pathogens are able to subvert the host immune system in order to increase microbial replication and propagation. Recent research indicates that another arm of the immune response, that of the chemokine system, is also subject to this sabotage, and is undermined by a range of microbial pathogens, including viruses, bacteria, and parasites. Currently, it is known that the chemokine system is being challenged by a number of mechanisms, and still more are likely to be discovered with further research. Here we first review the general mechanisms by which microbial pathogens bypass mammalian chemokine defences. Broadly, these can be grouped as viral chemokine interacting proteins, microbial manipulation of host chemokine and chemokine receptor expression, microbial blockade of host chemokine receptor signalling, and the largely hypothetical mechanisms of microbial enhancement of host anti-chemokine networks (including digestion, antagonism, and neutralisation of host chemokines and chemokine receptors). We then discuss the potential results of these interactions in terms of outcome of infection.

Fatal attraction: cytomegalovirus-encoded chemokine homologs

Members of the cytomegalovirus (CMV) subfamily of betaherpesviruses infecting primates and rodents encode divergent proteins with sequence characteristics and activities of chemokines, a class of small, secreted proteins that control leukocyte migration and trafficking behavior. Human CMV genes UL146 and UL147 encode proteins with sequence characteristics of CXC chemokines, whereas, murine CMV encodes a CC chemokine homolog (MCK-2). Human CMV UL146 encodes a neutrophil-attracting chemokine denoted viral CXC chemokine-1 (vCXCL1) that is as potent as host IL-8 and functions via the CXCR2 receptor, one of two human IL-8 receptors. Murine CMV MCK-2 is composed of a chemokine domain derived from open reading frame (ORF) m131 (and denoted MCK-1) as well as a domain derived from m129 that does not have sequence similarity to any known class of proteins. A synthetic version of murine CMV m131 (MCK-1) protein carries out many of the activities of a positive-acting chemokine, including transient release of intracellular calcium stores and cell adhesion of peritoneal macrophage populations. In the context of the viral genome and infection of the mouse host, the m131-m129 (MCK-2) gene product confers increased inflammation, higher levels of viremia, and higher titers of virus in salivary glands, consistent with a role in promoting dissemination by attracting an important mononuclear leukocyte population. Other characterized primate CMVs, but not other primate betaherpesviruses, encode gene products similar to human UL146 and UL147. Other characterized rodent CMVs encode a gene product similar to the murine CMV chemokine homolog, although not as a spliced gene product. Thus chemokines, like viral proteins that downmodulate MHC class I expression or have sequence homology to host MHC class I proteins, have evolved in primate and rodent CMVs to carry out an analogous set of immunomodulatory functions during infection of the host even though they arise from distinct origins.

Viral exploitation and subversion of the immune system through chemokine mimicry

The chemokine superfamily of leukocyte chemoattractants coordinates development and deployment of the immune system by signaling through a family of G protein-coupled receptors. The importance of this system to antimicrobial host defense has been supported by the discovery of numerous herpesviruses and poxviruses that encode chemokine mimics able to block chemokine action. However, specific herpesviruses and lentiviruses can also exploit the immune system through chemokine mimicry, for example, to facilitate viral dissemination or, as in the case of HIV-1, to directly infect leukocyte target cells. The study of viral mimicry of chemokines and chemokine receptors is providing important new concepts in viral immunopathogenesis, new anti-inflammatory drug leads and new targets and concepts for antiviral drug and vaccine development.

Chemokine receptor-related genetic sequences in an african green monkey simian cytomegalovirus-derived stealth virus

The US28 gene of human cytomegalovirus (HCMV) codes a cell surface receptor for both beta chemokine and fractalkine molecules. This receptor facilitates HCMV-induced cell fusion and virus dissemination and influences susceptibility to infection with other viruses, including the human immunodeficiency virus. Five adjacent but divergent open reading frames that potentially code for molecules related to the US28 protein of HCMV are present in an African green monkey simian cytomegalovirus-derived stealth virus. This finding implies a role for chemokines in the pathogenicity of at least some stealth-adapted viruses. It may also help explain the apparent therapeutic benefit achieved in certain stealth virus-infected patients treated with agents that downregulate chemokine production.

Modulating chemokines: more lessons from viruses

Chemokines are crucial effector molecules involved in orchestrating the host inflammatory response against invading pathogens. Viruses have devised several strategies for exploiting or neutralizing chemokines or their receptors to further their own propagation or elude host defenses. Insight into strategies used by viruses to modulate chemokines might help generate novel approaches for treating viral diseases and chemokine-mediated inflammatory disorders.

Evasion and exploitation of chemokines by viruses

Chemokines and chemokine receptors play a critical role in the host defense against viruses by mobilizing leukocytes to sites of infection, injury and inflammation. In order to replicate successfully within their host organisms, viruses have devised novel strategies for exploiting or subverting chemokine networks. This review summarizes various mechanisms that are currently known to be used by viruses for modulating chemokine activities including viral homologs of chemokines and chemokine receptors and soluble viral chemokine binding proteins. Insight into these strategies is providing a wealth of information on viral-host interactions, the function of chemokines in host defense and may help to generate novel anti-chemokine agents for treating against viral diseases or inflammatory disorders.

Stealth virus epidemic in the Mohave Valley: severe vacuolating encephalopathy in a child presenting with a behavioral disorder

An infectious illness, attributed to atypically structured cytopathic "stealth" viruses, occurred in 1996 in the Mohave Valley region of the United States. A stealth virus-infected child from this region has developed a severe noninflammatory, vacuolating (spongiform) en cephalopathy. The illness initially presented as a behavioral problem without overt neurological signs. Extensive investigations, including repeated magnetic resonance imaging, two brain biopsies, and stealth virus cultures, have helped define the disease process occurring in this child. Significant clinical benefit with apparent retardation of disease progression occurred during a 6-week course of ganciclovir therapy. The potential contributing role of stealth virus infections in children presenting with behavioral problems needs to be addressed.