Chronic infection and frailty: surrogate markers, associations, and causality

Molecular Determinants and the Regulation of Human Cytomegalovirus Latency and Reactivation

Human cytomegalovirus (HCMV) is a beta herpesvirus that establishes a life-long persistence in the host, like all herpesviruses, by way of a latent infection. During latency, viral genomes are maintained in a quieted state. Virus replication can be reactivated from latency in response to changes in cellular signaling caused by stress or differentiation. The past decade has brought great insights into the molecular basis of HCMV latency. Here, we review the complex persistence of HCMV with consideration of latent reservoirs, viral determinants and their host interactions, and host signaling and the control of cellular and viral gene expression that contributes to the establishment of and reactivation from latency.

Complex expression of the UL136 gene of human cytomegalovirus results in multiple protein isoforms with unique roles in replication

Human cytomegalovirus (HCMV) is a complex DNA virus with a 230-kb genome encoding 170 and up to 750 proteins. The upper limit of this coding capacity suggests the evolution of complex mechanisms to substantially increase the coding potential from the 230-kb genome. Our work examines the complexity of one gene, UL136, encoded within the ULb' region of the genome that is lost during serial passage of HCMV in cultured fibroblasts. UL136 is expressed as five protein isoforms. We mapped these isoforms and demonstrate that they originate from both a complex transcriptional profile and, possibly, the usage of multiple translation initiation sites. Intriguingly, the pUL136 isoforms exhibited distinct subcellular distributions with varying association with the Golgi apparatus. The subcellular localization of membrane-bound isoforms of UL136 differed between when they were expressed exogenously and when they were expressed in the context of viral infection, suggesting that the trafficking of these isoforms is mediated by infection-specific factors. While UL136, like most ULb' genes, was dispensable for replication in fibroblasts, the soluble 23- and 19-kDa isoforms suppressed virus replication. In CD34(+) hematopoietic progenitor cells (HPCs) infected in vitro, disruption of the 23- and 19-kDa isoforms resulted in increased replication and a loss of the latency phenotype, similar to the effects of the UL138 latency determinant encoded within the same genetic locus. Our work suggests a complex interplay between the UL136 isoforms which balances viral replication in multiple cell types and likely contributes to the cell type-dependent phenotypes of the UL133/8 locus and the outcome of HCMV infection.

IMPORTANCE

HCMV is a significant cause of morbidity in immunocompromised individuals, including transplant patients. The lifelong persistence of the virus results in a high seroprevalence worldwide and may contribute to age-related pathologies, such as atherosclerosis. The mechanisms of viral persistence are poorly understood; however, understanding the molecular basis of persistence is imperative for the development of new treatments. In this work, we characterize a complex HCMV gene, UL136, which is expressed as five protein isoforms. These isoforms arise predominantly from complex transcriptional mechanisms, which contribute to an increased coding capacity of the virus. Further, the UL136 isoforms oppose the activity of one another to balance HCMV replication in multiple cell types. We identify soluble isoforms of UL136 that function to suppress virus replication in fibroblasts and in CD34(+) HPCs for latency.

Antagonistic determinants controlling replicative and latent states of human cytomegalovirus infection

The mechanisms by which viruses persist and particularly those by which viruses actively contribute to their own latency have been elusive. Here we report the existence of opposing functions encoded by genes within a polycistronic locus of the human cytomegalovirus (HCMV) genome that regulate cell type-dependent viral fates: replication and latency. The locus, referred to as the UL133-UL138 (UL133/8) locus, encodes four proteins, pUL133, pUL135, pUL136, and pUL138. As part of the ULb' region of the genome, the UL133/8 locus is lost upon serial passage of clinical strains of HCMV in cultured fibroblasts and is therefore considered dispensable for replication in this context. Strikingly, we could not reconstitute infection in permissive fibroblasts from bacterial artificial chromosome clones of the HCMV genome where UL135 alone was disrupted. The loss of UL135 resulted in complex phenotypes and could ultimately be overcome by infection at high multiplicities. The requirement for UL135 but not the entire locus led us to hypothesize that another gene in this locus suppressed virus replication in the absence of UL135. The defect associated with the loss of UL135 was largely rescued by the additional disruption of the UL138 latency determinant, indicating a requirement for UL135 for virus replication when UL138 is expressed. In the CD34(+) hematopoietic progenitor model of latency, viruses lacking only UL135 were defective for viral genome amplification and reactivation. Taken together, these data indicate that UL135 and UL138 comprise a molecular switch whereby UL135 is required to overcome UL138-mediated suppression of virus replication to balance states of latency and reactivation.

IMPORTANCE

Mechanisms by which viruses persist in their host remain one of the most poorly understood phenomena in virology. Herpesviruses, including HCMV, persist in an incurable, latent state that has profound implications for immunocompromised individuals, including transplant patients. Further, the latent coexistence of HCMV may increase the risk of age-related pathologies, including vascular disease. The key to controlling or eradicating HCMV lies in understanding the molecular basis for latency. In this work, we describe the complex interplay between two viral proteins, pUL135 and pUL138, which antagonize one another in infection to promote viral replication or latency, respectively. We previously described the role of pUL138 in suppressing virus replication for latency. Here we demonstrate a role of pUL135 in overcoming pUL138-mediated suppression for viral reactivation. From this work, we propose that pUL135 and pUL138 constitute a molecular switch balancing states of latency and reactivation.

Incidence and economical effects of pneumonia in the older population living in French nursing homes: design and methods of the INCUR study

Background

Among the most burdensome clinical conditions occurring in older persons, respiratory infections are particularly relevant. In fact, the onset of pneumonias is associated with a significant worsening of the individual’s global health status and significant increase of healthcare costs. The clinical and economical negative consequences of pneumonia may be particularly evident among the frailest groups of elders, in particular those living in nursing home. Nevertheless, specific research on incidence and economical effects of pneumonia in nursing homes residents is still scarce. In the present article, we present the rationale, the design and the methods of the “Incidence of pNeumonia and related ConseqUences in nursing home Resident (INCUR) study, specifically aimed at filling some of the gaps currently present in the field.

Methods/design

INCUR is an observational longitudinal study recruiting 800 residents across 13 randomly selected nursing homes in France. Multidimensional evaluations of participants are conducted at the baseline, mid-term (at 6 months), and end of the study (at 12 months) visits in order to measure and follow-up their physical function, nutrition, cognition, depression, quality of life, and healthcare costs. Incident pneumonia as well as the onset/recurrence of other major health-related events are monitored during the study follow-up.

Discussion

The INCUR study will provide valuable information about older persons living in nursing homes. Results from INCUR study may constitute the basis for the development of future preventive campaigns against pneumonia and its consequences.

A novel human cytomegalovirus locus modulates cell type-specific outcomes of infection

Clinical strains of HCMV encode 20 putative ORFs within a region of the genome termed ULb' that are postulated to encode functions related to persistence or immune evasion. We have previously identified ULb'-encoded pUL138 as necessary, but not sufficient, for HCMV latency in CD34+ hematopoietic progenitor cells (HPCs) infected in vitro. pUL138 is encoded on polycistronic transcripts that also encode 3 additional proteins, pUL133, pUL135, and pUL136, collectively comprising the UL133-UL138 locus. This work represents the first characterization of these proteins and identifies a role for this locus in infection. Similar to pUL138, pUL133, pUL135, and pUL136 are integral membrane proteins that partially co-localized with pUL138 in the Golgi during productive infection in fibroblasts. As expected of ULb' sequences, the UL133-UL138 locus was dispensable for replication in cultured fibroblasts. In CD34+ HPCs, this locus suppressed viral replication in HPCs, an activity attributable to both pUL133 and pUL138. Strikingly, the UL133-UL138 locus was required for efficient replication in endothelial cells. The association of this locus with three context-dependent phenotypes suggests an exciting role for the UL133-UL138 locus in modulating the outcome of viral infection in different contexts of infection. Differential profiles of protein expression from the UL133-UL138 locus correlated with the cell-type dependent phenotypes associated with this locus. We extended our in vitro findings to analyze viral replication and dissemination in a NOD-scid IL2Rγ(c) (null)-humanized mouse model. The UL133-UL138(NULL) virus exhibited an increased capacity for replication and/or dissemination following stem cell mobilization relative to the wild-type virus, suggesting an important role in viral persistence and spread in the host. As pUL133, pUL135, pUL136, and pUL138 are conserved in virus strains infecting higher order primates, but not lower order mammals, the functions encoded likely represent host-specific viral adaptations.

Seroprevalence of cytomegalovirus among some voluntary blood donors at the 37 military hospital, accra, ghana

SUMMARY BACKGROUND

Cytomegalovirus (CMV) is one of the most significant pathogens infecting immunosuppressed individuals. CMV is transmissible through transfusion of blood components.

AIM

The goal of this study was to determine the seroprevalence of antibodies to CMV among blood donors seen at the 37 Military Hospital Blood Transfusion Unit, (MHBTU) Accra, Ghana.

METHODS

The seroprevalence of antibodies specific for CMV was tested using CMV IgG/IgM particle agglutination test kit and ELISA.

RESULTS

Of the 264 blood donors, 18 were negative and 246 were positive for CMV IgG antibodies, giving an overall CMV prevalence rate of 93.2%. None of the 264 blood donors was positive for CMV IgM antibodies. About 96% of the donors aged between 30 to 39 years were seropositive for CMV, as against 91.9% in those aged 20-29 years, 88.6% in 40 to 49 years, 75.0% (3 out of 4) in 50 to 59 years, and 100% (1 out 1) in 60-69 years. There was no statistically significant difference (P>0.05) in the CMV IgG status in different age groups. The blood donors comprised largely of male donors (236 out of 264), making sex comparisons statistically undesirable. However, all the female (n=28) donors were positive for CMV IgG.

CONCLUSION

Since about 93% of blood donors at the MHBTU are seropositive for CMV, it would be very useful to screen blood donors in Ghana for CMV to identify the very few CMV-seronegative blood donors, and maintain an inventory of them for use as donors.

Inflammation, genetic background and longevity

Ageing is an inexorable intrinsic process that affects all cells, tissues, organs and individuals. Due to a diminished homeostasis and increased organism frailty, ageing causes a reduction of the response to environmental stimuli and, in general, is associated to an increased predisposition to illness and death. Actually, it is characterized by a state of reduced ability to maintain health and general homeodynamics of the organism. A large part of the ageing phenotype is explained by an imbalance between inflammatory and anti-inflammatory networks, which results in the low grade chronic pro-inflammatory status of ageing, "inflamm-ageing". It is strictly linked to immunosenescence, and on the whole they are the major contributory factors to the increased frequency of morbidity and mortality among elderly. Inflamm-ageing is compatible with longevity; even if centenarians have an increased level of inflammatory mediators in comparison to old subjects and they are very frail, they also have high level of anti-inflammatory cytokines together with protective genotypes. Actually, data on case control studies performed in Italian centenarians suggest that a pro-inflammatory genotype is unfavourable to reach extreme longevity in good health and likely favours the onset of age-related diseases such as cardiovascular diseases and Alzheimer's disease, the leading causes of mortality and disability in the elderly. However, many associations between gene variants and longevity have been found only in Italian population. This should not be unexpected, since ageing and longevity are complex traits resulting not only and not exclusively from genetics, but rather from the interactions between genetics, environment and chance.

Intense antiextracellular adaptive immune response to human cytomegalovirus in very old subjects with impaired health and cognitive and functional status

Human aging is characterized by expanded and altered adaptive immune responses to human CMV (HCMV). It is unclear whether this expansion has its origins in age-related homeostatic disturbances or viral reactivation, whether anti-CMV immune surveillance may still be effective, and what are the consequences of this expanded immune response for health and longevity. We conducted an observational cross-sectional study in groups of HCMV-seropositive subjects aged >or=65 y of variable health status to compare the intensity of Ab responses against HCMV with those against EBV and with CD4(+) and CD8(+) T cell proinflammatory effector responses directed to HCMV-derived pp65 and immediate-early protein 1 synthetic peptides. Ab responses to HCMV, but not to EBV, and anti-HCMV CD4(+), but not CD8(+), T cell responses were more intense in elderly subjects aged >or=85 y in poor health and were inversely correlated with markers of functional activity and cognitive function. Therefore, humoral and CD4(+) T cell anti-HCMV responses were specifically intensified in advanced aging associated with comorbidity and cognitive and functional impairments. Such a distinctive pattern of adaptive immunity indicates that immune responses targeting the extracellular phase of HCMV are increased in these elderly subjects and could represent an indirect effect of localized and undetectable HCMV reactivation. This study demonstrates that the oldest subjects in poor health with physical and mental impairment express intense functional immune responses to extracellular HCMV and suggests that they may be at risk for direct pathogenic effects by HCMV reactivation as well as indirect pathogenic effects linked to proinflammatory anti-HCMV effector responses.

High innate production capacity of tumor necrosis factor-α and decline of handgrip strength in old age

Increased signaling of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) elicits apoptosis of skeletal muscle cells in various animal models. Within a population-based prospective follow up study of elderly people aged 85 years we show that a high innate production capacity of TNF-alpha precedes a steeper decline in muscle strength over time.