Characterization of specific antibodies against cytomegalovirus (CMV)-encoded interleukin 10 produced by 28% of CMV-seropositive blood donors

Cytokine Autoantibodies Alter Gene Expression Profiles of Healthy Donors

Autoantibodies against cytokines (c-aAb) have been implicated in the pathophysiology of autoimmune diseases, and a variety of infections. In addition, several independent studies have detected elevated titers of c-aAb in the circulation of healthy individuals. To further understand their impact on immune responses, we measured c-aAb against IFN-α, IFN-γ, CSF2, IL-1α, IL-6, and IL-10 in the plasma of 1000 healthy individuals of the Milieu Intérieur (MI) cohort. Focusing on donors above a defined positive cut-off we observed significant age effects for c-aAb against IL-1α, but no major environmental or lifestyle associated factors were identified. Using TruCulture stimulation data from the MI cohort, we observed a strong association between induced IL-1α and c-aAb levels after LPS stimulation. For several other stimuli, c-aAb against IL-1α and IL-10 were associated with decreased or increased proinflammatory gene expression, respectively. Finally, TruCulture assays supplemented with plasma containing high-titer c-aAb showed a strong influence of anti-IFN-α and anti-IL-6 c-aAb on both baseline and induced gene expression. In summary, this study shows a widespread prevalence of anti-cytokine autoantibodies in healthy donors with impacts on diverse immune responses, suggesting a significant contribution of c-aAb to interindividual immune heterogeneity.

Herpesviral capture of immunomodulatory host genes

Herpesviruses have acquired numerous genes from their hosts. Although these homologs are not essential for viral replication, they often have important immunomodulatory functions that ensure viral persistence in the host. Some of these viral molecules are called virokines as they mimic cellular cytokines of their host such as interleukin-10 (cIL-10). In recent years, many viral homologs of IL-10 (vIL-10s) have been discovered in the genome of members of the order Herpesvirales. For some, gene and protein structure as well as biological activity and potential use in the clinical context have been explored. Besides virokines, herpesviruses have also captured genes encoding membrane-bound host immunomodulatory proteins such as major histocompatibility complex (MHC) molecules. These viral MHC mimics also retain many of the functions of the cellular genes, in particular directly or indirectly modulating the activity of natural killer cells. The mechanisms underlying capture of cellular genes by large DNA viruses are still enigmatic. In this review, we provide an update of the advances in the field of herpesviral gene piracy and discuss possible scenarios that could explain how the gene transfer from host to viral genome was achieved.

Modulation of the Host Environment by Human Cytomegalovirus with Viral Interleukin 10 in Peripheral Blood

Background

Human cytomegalovirus (HCMV) is a herpesvirus with both lytic and latent life cycles. Human cytomegalovirus encodes 2 viral cytokines that are orthologs of human cellular interleukin 10 (cIL-10). Both cytomegalovirus interleukin 10 (cmvIL-10) and Latency-associated cytomegalovirus interleukin 10 (LAcmvIL-10) (collectively vIL-10) are expressed during lytic infection and cause immunosuppressive effects that impede virus clearance. LAcmvIL-10 is also expressed during latent infection of myeloid progenitor cells and monocytes and facilitates persistence. Here, we investigated whether vIL-10 could be detected during natural infection.

Methods

Plasma from healthy blood donors was tested by enzyme-linked immunosorbent assay for anti-HCMV immunoglobulin G and immunoglobulin M and for cIL-10 and vIL-10 levels using a novel vIL-10 assay that detects cmvIL-10 and LAcmvIL-10, with no cross-reactivity to cIL-10.

Results

vIL-10 was evident in HCMV+ donors (n = 19 of 26), at levels ranging 31-547 pg/mL. By comparison, cIL-10 was detected at lower levels ranging 3-69 pg/mL. There was a strong correlation between vIL-10 and cIL-10 levels (P = .01). Antibodies against vIL-10 were also detected and neutralized vIL-10 activity.

Conclusions

vIL-10 was detected in peripheral blood of healthy blood donors. These findings suggest that vIL-10 may play a key role in sensing or modifying the host environment during latency and, therefore, may be a potential target for intervention strategies.

Exploiting viral natural history for vaccine development

The partial successes of the Phase 2 gB-based vaccine trials for HCMV highlight the very real likelihood that vaccine-mediated induction of antibodies that neutralize the fusion pathway of fibroblast infection is not sufficient as a singular strategy to confer protective efficacy against primary HCMV infection. Alternative strategies that serve as adjuncts to gB-based vaccines are likely required to target different aspects of the complex lifecycle of HCMV infection. There has been considerable recent interest in targeting the gH/gL/UL128/UL130/UL131 pentamer complex (gH/gL-PC) to neutralize the endocytic pathway of HCMV infection of epithelial and endothelial cells. Since both cell types are critical during primary mucosal infection, intrahost spread, and shedding of HCMV in an infected host, the gH/gL-PC represents a high-value target for vaccination to interrupt the HCMV lifecycle. The natural history of HCMV is exceedingly complex and incompletely resolved, and the protective efficacy generated by gH/gL-PC remains to be validated in clinical trials. Yet, there are salient aspects of its lifecycle that offer clues about how other novel vaccine strategies can be targeted to especially susceptible parts of the viral proteome to significantly disrupt HCMV's ability to infect susceptible hosts. In particular, the protracted evolution of Herpesvirales has endowed HCMV with two remarkable properties of its natural history: (1) lifelong persistence within immune hosts that develop extraordinarily large antiviral immune responses and (2) the ability to reinfect those with prior immunity. The latter phenotype strongly implies that, if HCMV can overcome prior immunity to initiate a new infection, it is likely irrelevant whether prior immunity derives from prior infection or prior vaccination. Both phenotypes are unified by the extensive devotion of the HCMV coding repertoire (~50%) to viral proteins that modulate host cell signaling, trafficking, activation, antigen presentation, and resistance to apoptosis. Collectively, these viral proteins are the likely reason for the high barrier to success for the 4-decade effort to design an HCMV vaccine, and they represent the viral proteins that make HCMV be the virus that it is. James Hanshaw wrote in 1971 that, based on a 15-year retrospective of congenital HCMV cases, "… any thoughtful program designed at prevention or treatment deserves consideration". Drawing upon natural history data from the nonhuman primate model of HCMV persistence and pathogenesis, a "thoughtful program" is put forth that HCMV immune-modulating proteins should be considered as vaccine candidates.

Expression of immune-related genes of common carp during cyprinid herpesvirus 3 infection

Fish herpesviruses and their hosts may have coevolved for 400 to 450 million yr. During this coexistence, the hosts have equipped themselves with an elaborate immune system to defend themselves from invading viruses, whereas the viruses have developed strategies to evade host immunity, including the expression of cytokine genes that have been captured from the host. Taking advantage of our experimental model for cyprinid herpesvirus 3 (CyHV-3) persistence in carp, we studied the gene expression of host and virus immune-related genes in each stage of infection: acute, persistent and reactivation phases. IFNγ-1, IFNγ-2, IL-12 and IL-10 host genes, and the CyHV-3 vIL-10 gene (khvIL-10) were highly significantly up-regulated in different phases of CyHV-3 infection. Similarly, host IL-1β was up-regulated in the acute phase of CyHV-3 infection. There was no significant difference in the expression of host TNFα-1 and MHC-II genes during all phases of CyHV-3 infection. Based on the expression profile of carp immune-related genes in each stage of CyHV-3 infection, we propose a possible interaction between carp IL-12, carp IL-10 and khvIL-10 during the course of viral infection. To our knowledge, this is the first report on the expression of cytokine genes during all phases (acute, persistent and reactivation) of CyHV-3 infection.

Mimicry of cytokine pathways by human herpesviruses

ABSTRACT 

Viruses have evolved to subvert host cell pathways to enable their replication and persistence. In particular, virus-encoded gene products target the host's immune system to evade elimination by antiviral immune defenses. Cytokines are soluble, secreted proteins, which regulate many aspects of immune responses, by providing signals through cell surface receptors on target cells. Cytokine pathways are therefore attractive targets for modulation by viruses during their replication cycle. This review deals with modulation of cytokine pathways by the human herpesvirus, a family of viruses that are capable of life-long persistence in the host and cause severe disease particularly in immunocompromised individuals.

Modulation of dendritic cell functions by viral IL-10 encoded by human cytomegalovirus

Human cytomegalovirus (HCMV), a clinically important β-herpesvirus, is a master of evasion and modulation of the host immune system, including inhibition of a number of dendritic cell (DC) functions. DCs play a central role in co-ordination of the immune response against pathogens and any disturbance of DCs functions can result in a cascade effect on a range of immune cells. Recently, the HCMV gene UL111A, which encodes viral homologs of human interleukin 10, has been identified as a strong suppressor of a number of DCs functions. In this mini review, we focus on HCMV-encoded viral IL-10-mediated inhibitory effects on DCs and implications for the development of an effective HCMV vaccine.

Using the nonhuman primate model of HCMV to guide vaccine development

The natural history of human cytomegalovirus (HCMV) is inextricably associated with mucosal surfaces. The vast preponderance of primary infections occur following mucosal exposure to infectious virions, and the high seroprevalence of HCMV throughout the world is due to long-term excretion of HCMV in bodily fluids from multiple mucosal sites. Accumulating evidence presents a model where the earliest virus-host interactions following infection dictate the long-term pattern of infection, alter innate immune responses that skew adaptive responses to enable persistence within an immune host, and are essential for reinfection of a host with prior immunity. HCMV has evolved a complex repertoire of viral functions fine-tuned to manipulate the immune environment both locally at the sites of infection and systemically within an infected host. Collectively, viral immune modulation represents a significant impediment for an HCMV vaccine. As HCMV can disseminate beyond mucosal surfaces to reinfect immune hosts, it may not matter whether prior immunity results from prior infection or immunization. A better understanding of the earliest virus-hosts interactions at mucosal surfaces may identify elements of the viral proteome that are especially susceptible to vaccine-mediated disruption and prevent challenge virus from disseminating to distal sites, particularly the maternal-fetal interface.

Pathogen manipulation of cIL-10 signaling pathways: opportunities for vaccine development?

Interleukin-10 (IL-10) is a tightly regulated, pleiotropic cytokine that has profound effects on all facets of the immune system, eliciting cell-type-specific responses within cells expressing the IL-10 receptor (IL-10R). It is considered a master immune regulator, and imbalances in IL-10 expression, resulting from either inherent or infectious etiologies, have far reaching clinical ramifications. Regarding infectious diseases, there has been accumulating recognition that many pathogens, particularly those that establish lifelong persistence, share a commonality of their natural histories: manipulation of IL-10-mediated signaling pathways. Multiple viral, bacterial, protozoal, and fungal pathogens appear to have evolved mechanisms to co-opt normal immune functions, including those involving IL-10R-mediated signaling, and immune effector pathways away from immune-mediated protection toward environments of immune evasion, suppression, and tolerance. As a result, pathogens can persist for the life of the infected host, many of whom possess otherwise competent immune systems. Because of pathogenic avoidance of immune clearance, persistent infections can exact incalculable physical and financial costs, and represent some of the most vexing challenges for improvements in human health. Enormous benefits could be gained by the development of efficient prevention and/or therapeutic strategies that block primary infection, or clear the infection. There are now precedents that indicate that modalities focusing on pathogen-mediated manipulation of IL-10 signaling may have clinical benefit.

IL-10 encoded by viruses: a remarkable example of independent acquisition of a cellular gene by viruses and its subsequent evolution in the viral genome

Many viruses have evolved strategies to deregulate the host immune system. These strategies include mechanisms to subvert or recruit the host cytokine network. IL-10 is a pleiotropic cytokine that has both immunostimulatory and immunosuppressive properties. However, its key features relate mainly to its capacity to exert potent immunosuppressive effects. Several viruses have been shown to upregulate the expression of cellular IL-10 (cIL-10) with, in some cases, enhancement of infection by suppression of immune functions. Other viruses encode functional orthologues of cIL-10, called viral IL-10s (vIL-10s). The present review is devoted to these virokines. To date, vIL-10 orthologues have been reported for 12 members of the family Herpesviridae, two members of the family Alloherpesviridae and seven members of the family Poxviridae. Study of vIL-10s demonstrated several interesting aspects on the origin and the evolution of these viral genes, e.g. the existence of multiple (potentially up to nine) independent gene acquisition events at different times during evolution, viral gene acquisition resulting from recombination with cellular genomic DNA or cDNA derived from cellular mRNA and the evolution of cellular sequence in the viral genome to restrict the biological activities of the viral orthologues to those beneficial for the virus life cycle. Here, various aspects of the vIL-10s described to date are reviewed, including their genetic organization, protein structure, origin, evolution, biological properties and potential in applied research.

Human cytomegalovirus encoded homologs of cytokines, chemokines and their receptors: roles in immunomodulation

Human cytomegalovirus (HCMV), the largest human herpesvirus, infects a majority of the world’s population. Like all herpesviruses, following primary productive infection, HCMV establishes a life-long latent infection, from which it can reactivate years later to produce new, infectious virus. Despite the presence of a massive and sustained anti-HCMV immune response, productively infected individuals can shed virus for extended periods of time, and once latent infection is established, it is never cleared from the host. It has been proposed that HCMV must therefore encode functions which help to evade immune mediated clearance during productive virus replication and latency. Molecular mimicry is a strategy used by many viruses to subvert and regulate anti-viral immunity and HCMV has hijacked/developed a range of functions that imitate host encoded immunomodulatory proteins. This review will focus on the HCMV encoded homologs of cellular cytokines/chemokines and their receptors, with an emphasis on how these virus encoded homologs may facilitate viral evasion of immune clearance.

Host immune responses to a viral immune modulating protein: immunogenicity of viral interleukin-10 in rhesus cytomegalovirus-infected rhesus macaques

Background

Considerable evidence has accumulated that multiple viruses, bacteria, and protozoa manipulate interleukin-10 (IL-10)-mediated signaling through the IL-10 receptor (IL-10R) in ways that could enable establishment of a persistent microbial infection. This suggests that inhibition of pathogen targeting of IL-10/IL-10R signaling could prevent microbial persistence. Human cytomegalovirus (HCMV) and rhesus cytomegalovirus (RhCMV) express a viral interleukin-10 (cmvIL-10 and rhcmvIL-10, respectively) with comparable immune modulating properties in vitro to that of their host's cellular IL-10 (cIL-10). A prior study noted that rhcmvIL-10 alters innate and adaptive immunity to RhCMV in vivo, consistent with a central role for rhcmvIL-10 during acute virus-host interactions. Since cmvIL-10 and rhcmvIL-10 are extremely divergent from the cIL-10 of their respective hosts, vaccine-mediated neutralization of their function could inhibit establishment of viral persistence without inhibition of cIL-10.

Methods and Findings

As a prelude to evaluating cmvIL-10-based vaccines in humans, the rhesus macaque model of HCMV was used to interrogate peripheral and mucosal immune responses to rhcmvIL-10 in RhCMV-infected animals. ELISA were used to detect rhcmvIL-10-binding antibodies in plasma and saliva, and an IL-12-based bioassay was used to quantify plasma antibodies that neutralized rhcmvIL-10 function. rhcmvIL-10 is highly immunogenic during RhCMV infection, stimulating high avidity rhcmvIL-10-binding antibodies in the plasma of all infected animals. Most infected animals also exhibited plasma antibodies that partially neutralized rhcmvIL-10 function but did not cross-neutralize the function of rhesus cIL-10. Notably, minimally detectable rhcmvIL-10-binding antibodies were detected in saliva.

Conclusion

This study demonstrates that rhcmvIL-10, as a surrogate for cmvIL-10, is a viable vaccine candidate because (1) it is highly immunogenic during natural RhCMV infection, and (2) neutralizing antibodies to rhcmvIL-10 do not cross-react with rhesus cIL-10. Exceedingly low rhcmvIL-10 antibodies in saliva further suggest that the oral mucosa, which is critical in RhCMV natural history, is associated with suboptimal anti-rhcmvIL-10 antibody responses.