Gammaherpesvirus latency differentially impacts the generation of primary versus secondary memory CD8+ T cells during subsequent infection

Age-associated B cells are long-lasting effectors that impede latent γHV68 reactivation

Age-associated B cells (ABCs; CD19⁺CD11c⁺T-bet⁺) are a unique population that are increased in an array of viral infections, though their role during latent infection is largely unexplored. Here, we use murine gammaherpesvirus 68 (γHV68) to demonstrate that ABCs remain elevated long-term during latent infection and express IFNγ and TNF. Using a recombinant γHV68 that is cleared following acute infection, we show that ABCs persist in the absence of latent virus, though their expression of IFNγ and TNF is decreased. With a fluorescent reporter gene-expressing γHV68 we demonstrate that ABCs are infected with γHV68 at similar rates to other previously activated B cells. We find that mice without ABCs display defects in anti-viral IgG2a/c antibodies and are more susceptible to reactivation of γHV68 following virus challenges that typically do not break latency. Together, these results indicate that ABCs are a persistent effector subset during latent viral infection that impedes γHV68 reactivation.

Age-associated B cells are long-lasting effectors that impede latent γHV68 reactivation

Age-associated B cells (ABCs; CD19⁺CD11c⁺T-bet⁺) are a unique population that are increased in an array of viral infections, though their role during latent infection is largely unexplored. Here, we use murine gammaherpesvirus 68 (γHV68) to demonstrate that ABCs remain elevated long-term during latent infection and express IFNγ and TNF. Using a recombinant γHV68 that is cleared following acute infection, we show that ABCs persist in the absence of latent virus, though their expression of IFNγ and TNF is decreased. With a fluorescent reporter gene-expressing γHV68 we demonstrate that ABCs are infected with γHV68 at similar rates to other previously activated B cells. We find that mice without ABCs display defects in anti-viral IgG2a/c antibodies and are more susceptible to reactivation of γHV68 following virus challenges that typically do not break latency. Together, these results indicate that ABCs are a persistent effector subset during latent viral infection that impedes γHV68 reactivation.

Latent gammaherpesvirus exacerbates arthritis through modification of age-associated B cells

Epstein-Barr virus (EBV) infection is associated with rheumatoid arthritis (RA) in adults, though the nature of the relationship remains unknown. Herein, we have examined the contribution of viral infection to the severity of arthritis in mice. We have provided the first evidence that latent gammaherpesvirus infection enhances clinical arthritis, modeling EBV's role in RA. Mice latently infected with a murine analog of EBV, gammaherpesvirus 68 (γHV68), develop more severe collagen-induced arthritis and a Th1-skewed immune profile reminiscent of human disease. We demonstrate that disease enhancement requires viral latency and is not due to active virus stimulation of the immune response. Age-associated B cells (ABCs) are associated with several human autoimmune diseases, including arthritis, though their contribution to disease is not well understood. Using ABC knockout mice, we have provided the first evidence that ABCs are mechanistically required for viral enhancement of disease, thereby establishing that ABCs are impacted by latent gammaherpesvirus infection and provoke arthritis.

Master manipulators: how herpesviruses alter immune responses to RSV

In this commentary on “A gammaherpesvirus licenses CD8 T cells to protect the host from pneumovirus-induced immunopathologies”, the authors highlight the growing literature suggesting that herpesvirus infections shape subsequent immune responses to other pathogens, especially by broadening CD8+T-cell responses. These observations have implications for vaccine development against other important pathogens, such as Respiratory Syncytial Virus.

Molecular Basis of the Differentiation and Function of Virus Specific Follicular Helper CD4+ T Cells

During viral infection, virus-specific follicular helper T cells provide important help to cognate B cells for their survival, consecutive proliferation and mutation and eventual differentiation into memory B cells and antibody-secreting plasma cells. Similar to Tfh cells generated in other conditions, the differentiation of virus-specific Tfh cells can also be characterized as a process involved multiple factors and stages, however, which also exhibits distinct features. Here, we mainly focus on the current understanding of Tfh fate commitment, functional maturation, lineage maintenance and memory transition and formation in the context of viral infection.

Lifelong CMV infection improves immune defense in old mice by broadening the mobilized TCR repertoire against third-party infection

Lifelong interactions between host and the ubiquitous and persistent cytomegalovirus (CMV) have been proposed to contribute to the age-related decline in immunity. Prior work from us and others found some support for that idea, yet evidence that this led to increased vulnerability to other infections was not obtained. Moreover, evidence has accumulated that CMV infection can be beneficial to immune defense in young/adult mice and humans, dominantly via enhanced innate immunity. Here, we describe an unexpected impact of murine CMV (MCMV) upon the T cell response of old mice to Listeria monocytogenes expressing the model antigen, OVA (Lm-OVA). Single-cell sequencing of the OVA-specific CD8 T cell receptor β (TCRβ) repertoire of old mice demonstrated that old MCMV-infected mice recruited many diverse clonotypes that afforded broad and often more efficient recognition of antigenic peptide variants. This stood in contrast to old control mice, which exhibited strong narrowing and homogenization of the elicited repertoire. High-throughput sequencing of the total naïve CD8 TCRβ repertoire showed that many of these diverse OVA-specific clonotypes were present in the naïve CD8 repertoire of mice in all groups (adult, old control, and old MCMV⁺) yet were only recruited into the Lm-OVA response in MCMV⁺ old mice. These results have profound implications for our understanding of T cell immunity over a life span and suggest that our coevolution with CMV may include surprising, potentially positive impacts on adaptive heterologous immunity in late life.

Known unknowns: how might the persistent herpesvirome shape immunity and aging?

The microbial community that colonizes all living organisms is gaining appreciation for its contributions to both physiologic and pathogenic processes. The virome, a subset of the overall microbiome, large and diverse, including viruses that persistently inhabit host cells, endogenous viral elements genomically or epigenomically integrated into cells, and viruses that infect the other (bacterial, protozoan, fungal, and archaeal) microbiome phylla. These viruses live in the organism for its life, and therefore are to be considered part of the aging process experienced by the organism. This review considers the impact of the persistent latent virome on immune aging. Specific attention will be devoted to the role of herpesviruses, and within them, the cytomegalovirus, as the key modulators of immune aging.

The association between clinical outcome and CD8+ lymphocytic infiltration in advanced stages of colorectal cancer differs by latent virus infection in tumour tissue

AIMS

In the near future, an immunoscore based on the quantification of lymphocytic populations can be expected as a fundamental supplement of colorectal cancer (CRC) classification. This study explored whether latent viral infection has an influence on prognostically relevant host immunity in CRC.

METHODS AND RESULTS

CD8⁺ lymphocytic infiltration in three tumour compartments of 121 CRC was compared with clinical data and occurrence of latent infection with herpes simplex virus (HSV1, HSV2), cytomegalovirus (CMV), human papillomavirus (HPV16 and HPV18) in the tumour tissue, which was determined by polymerase chain reaction (PCR). Intraepithelial CD8⁺ lymphocytic infiltration (IE_CD8+ ) showed a trend towards correlation with clinical stage (P = 0.073), significant differences between CRC with and without metastases (P = 0.001) and a significant correlation with overall survival (OS, P = 0.001). Each of these three clinical parameters showed a significant link to IE_CD8+ in the virus DNA-negative (P-values: 0.001-0.036), but no significant differences in the virus DNA-positive subgroup, which is consistent with a moderating effect of virus DNA on these associations. A significant correlation of CD8⁺ infiltration in the invasive margin (IM_CD8+ ) with OS (P = 0.016) was also moderated by virus DNA.

CONCLUSION

Our data suggest a possible influence of latent viral infection on the association between clinical outcome and CD8⁺ lymphocytic infiltration in CRC tissue. After confirmation of these results by large cohort studies, a potential interaction between microbial pathogens and host immunity in CRC and its impact on prognostic immunoscores and/or new therapeutic strategies should be investigated further.

Unsupervised learning techniques reveal heterogeneity in memory CD8+ T cell differentiation following acute, chronic and latent viral infections

CD8⁺ T lymphocytes are critical for the control of gammaherpesvirus latency. To determine how memory CD8⁺ T cells generated during latency differ from those primed during acute or chronic viral infection, we adoptively transferred naive P14 CD8⁺ T cells into uninfected recipients, and examined surface proteins, cytokines and transcription factors following infection with the Armstrong (acute) or Clone 13 (chronic) strains of lymphocytic choriomeningitis virus (LCMV), or murine gammaherpesvirus 68 (MHV68) expressing the LCMV epitope D^bGP33-41. By performing k-means clustering and generating self organizing maps (SOM), we observed increased short-lived effector-like, CD27^lo CD62L^lo and Bcl-6^lo CD8⁺ T cells following latent infection. In addition, we found that memory CD8⁺ T cells from latent primed mice underwent less expansion following adoptive transfer and antigen rechallenge. Data from cluster models were combined and visualized by principal component analysis (PCA) demonstrating memory CD8⁺ T cells from latent infection occupy an intermediate differentiation space.

Making Mouse Models That Reflect Human Immune Responses

Humans are infected with a variety of acute and chronic pathogens over the course of their lives, and pathogen-driven selection has shaped the immune system of humans. The same is likely true for mice. However, laboratory mice we use for most biomedical studies are bred in ultra-hygienic environments, and are kept free of specific pathogens. We review recent studies that indicate that pathogen infections are important for the basal level of activation and the function of the immune system. Consideration of these environmental exposures of both humans and mice can potentially improve mouse models of human disease.

Role of Feline Immunodeficiency Virus in Lymphomagenesis--Going Alone or Colluding?

Feline immunodeficiency virus (FIV) is a naturally occurring lentivirus of domestic and nondomestic feline species. Infection in domestic cats leads to immune dysfunction via mechanisms similar to those caused by human immunodeficiency virus (HIV) and, as such, is a valuable natural animal model for acquired immunodeficiency syndrome (AIDS) in humans. An association between FIV and an increased incidence of neoplasia has long been recognized, with frequencies of up to 20% in FIV-positive cats recorded in some studies. This is similar to the rate of neoplasia seen in HIV-positive individuals, and in both species neoplasia typically requires several years to arise. The most frequently reported type of neoplasia associated with FIV infection is lymphoma. Here we review the possible mechanisms involved in FIV lymphomagenesis, including the possible involvement of coinfections, notably those with gamma-herpesviruses.

Coinfections: Another Variable in the Herpesvirus Latency-Reactivation Dynamic

Chronic viruses, such as herpesviruses, shape host physiology. These viruses modulate the inflammatory state of the immune system and have evolved to harness inflammation as a mechanism to regulate viral latency and reactivation. In this review, I examine some of the recent work demonstrating the important role of inflammation in the regulation of the herpesvirus life cycle and discuss recent work that implicates coinfection in the regulation of herpesvirus latency.

Sequential Infection with Common Pathogens Promotes Human-like Immune Gene Expression and Altered Vaccine Response

Immune responses differ between laboratory mice and humans. Chronic infection with viruses and parasites are common in humans, but are absent in laboratory mice, and thus represent potential contributors to inter-species differences in immunity. To test this, we sequentially infected laboratory mice with herpesviruses, influenza, and an intestinal helminth and compared their blood immune signatures to mock-infected mice before and after vaccination against yellow fever virus (YFV-17D). Sequential infection altered pre- and post-vaccination gene expression, cytokines, and antibodies in blood. Sequential pathogen exposure induced gene signatures that recapitulated those seen in blood from pet store-raised versus laboratory mice, and adult versus cord blood in humans. Therefore, basal and vaccine-induced murine immune responses are altered by infection with agents common outside of barrier facilities. This raises the possibility that we can improve mouse models of vaccination and immunity by selective microbial exposure of laboratory animals to mimic that of humans.