Vesselin Tomov

Virus-helminth coinfection reveals a microbiota-independent mechanism of immunomodulation

Parasites make it hard to fight viruses Microbial co-infections challenge the immune system—different pathogens often require different flavors of immune responses for their elimination or containment (see the Perspective by Maizels and Gause). Two teams studied what happens when parasitic worms and viruses infect mice at the same time. Reese et al. found that parasite co-infection woke up a dormant virus. Osborne et al. found that mice already infected with parasitic worms were worse at fighting off viruses. In both cases, worms skewed the immune response so that the immune cells and the molecules they secreted created an environment favorable for the worm at the expense of antiviral immunity. Science, this issue p. 573 and p. 578; see also p. 517 Coinfection with intestinal parasites leads to altered antiviral immunity in mice. [Also see Perspective by Maizels and Gause] The mammalian intestine is colonized by beneficial commensal bacteria and is a site of infection by pathogens, including helminth parasites. Helminths induce potent immunomodulatory effects, but whether these effects are mediated by direct regulation of host immunity or indirectly through eliciting changes in the microbiota is unknown. We tested this in the context of virus-helminth coinfection. Helminth coinfection resulted in impaired antiviral immunity and was associated with changes in the microbiota and STAT6-dependent helminth-induced alternative activation of macrophages. Notably, helminth-induced impairment of antiviral immunity was evident in germ-free mice, but neutralization of Ym1, a chitinase-like molecule that is associated with alternatively activated macrophages, could partially restore antiviral immunity. These data indicate that helminth-induced immunomodulation occurs independently of changes in the microbiota but is dependent on Ym1.

Persistent Enteric Murine Norovirus Infection Is Associated with Functionally Suboptimal Virus-Specific CD8 T Cell Responses

ABSTRACT Norovirus (NV) gastroenteritis is a major contributor to global morbidity and mortality, yet little is known about immune mechanisms leading to NV control. Previous studies using the murine norovirus (MNV) model have established a key role for T cells in MNV clearance. Despite these advances, important questions remain regarding the magnitude, location, and dynamics of the MNV-specific T cell response. To address these questions, we identified MNV-specific major histocompatibility complex (MHC) class I immunodominant epitopes using an overlapping peptide screen. One of these epitopes (amino acids 519 to 527 of open reading frame 2 [ORF2519-527]) was highly conserved among all NV genogroups. Using MHC class I peptide tetramers, we tracked MNV-specific CD8 T cells in lymphoid and mucosal sites during infection with two MNV strains with distinct biological behaviors, the acutely cleared strain CW3 and the persistent strain CR6. Here, we show that enteric MNV infection elicited robust T cell responses primarily in the intestinal mucosa and that MNV-specific CD8 T cells dynamically regulated the expression of surface molecules associated with activation, differentiation, and homing. Furthermore, compared to MNV-CW3 infection, chronic infection with MNV-CR6 resulted in fewer and less-functional CD8 T cells, and this difference was evident as early as day 8 postinfection. Finally, MNV-specific CD8 T cells were capable of reducing the viral load in persistently infected Rag1 −/− mice, suggesting that these cells are a crucial component of NV immunity. Collectively, these data provide fundamental new insights into the adaptive immune response to two closely related NV strains with distinct biological behaviors and bring us closer to understanding the correlates of protective antiviral immunity in the intestine.

Gut microbiota and IBD: causation or correlation?

A general consensus exists that IBD is associated with compositional and metabolic changes in the intestinal microbiota (dysbiosis). However, a direct causal relationship between dysbiosis and IBD has not been definitively established in humans. Findings from animal models have revealed diverse and context-specific roles of the gut microbiota in health and disease, ranging from protective to pro-inflammatory actions. Moreover, evidence from these experimental models suggest that although gut bacteria often drive immune activation, chronic inflammation in turn shapes the gut microbiota and contributes to dysbiosis. The purpose of this Review is to summarize current associations between IBD and dysbiosis, describe the role of the gut microbiota in the context of specific animal models of colitis, and discuss the potential role of microbiota-focused interventions in the treatment of human IBD. Ultimately, more studies will be needed to define host–microbial relationships relevant to human disease and amenable to therapeutic interventions.

Cutting Edge: B Cell–Intrinsic T-bet Expression Is Required To Control Chronic Viral Infection

The role of Ab and B cells in preventing infection is established. In contrast, the role of B cell responses in containing chronic infections remains poorly understood. IgG2a (IgG1 in humans) can prevent acute infections, and T-bet promotes IgG2a isotype switching. However, whether IgG2a and B cell–expressed T-bet influence the host–pathogen balance during persisting infections is unclear. We demonstrate that B cell–specific loss of T-bet prevents control of persisting viral infection. T-bet in B cells controlled IgG2a production, as well as mucosal localization, proliferation, glycosylation, and a broad transcriptional program. T-bet controlled a broad antiviral program in addition to IgG2a because T-bet in B cells was important, even in the presence of virus-specific IgG2a. Our data support a model in which T-bet is a universal controller of antiviral immunity across multiple immune lineages.

An optimized patient-reported ulcerative colitis disease activity measure derived from the Mayo Score and the Simple Clinical Colitis Activity Index.

Background:There is a need for simple, noninvasive patient-driven disease assessment instruments in ulcerative colitis (UC). We sought to further assess and refine the previous described 6-point Mayo score. Methods:A cross-sectional study of 282 UC patients was conducted assessing the correlation of the 2 patient-reported Mayo score components (6-point Mayo score) with the simple clinical colitis activity index (SCCAI) and a single Likert scale of patient-reported disease activity. Spearmans correlation, sensitivity, specificity, and area under the receiver operating curves (AUC) were calculated. A separate validation study in 59 UC patients was also conducted. Results:Participants predominantly had long-standing disease (83%) and were in self-reported remission (63%). The 6-point Mayo score correlated well with the SCCAI (rho = 0.71; P < 0.0001) and patient-reported disease activity (rho = 0.65; P < 0.0001). Using a cutpoint of 1.5, the 6-point Mayo score had 83% sensitivity and 72% specificity for patient-defined remission, and 89% sensitivity and 67% specificity for SCCAI-defined remission (score, <2.5). The 6-point Mayo score and SCCAI had similar accuracy of predicting patient-defined remission (AUC = 0.84 and 0.87, respectively). Addition of the SCCAI general well-being question to the 6-point Mayo improved the predictive ability for patient-defined remission; and a new weighted score had an AUC of 0.89 in the development cohort and 0.93 in the validation cohort. The optimal cutpoint was 1.6. Conclusions:The patient-reported UC severity index that includes stool frequency, bleeding, and general well-being accurately measures clinical disease activity without requiring direct physician contact.

Type I Interferon Receptor Deficiency in Dendritic Cells Facilitates Systemic Murine Norovirus Persistence Despite Enhanced Adaptive Immunity

In order for a virus to persist, there must be a balance between viral replication and immune clearance. It is commonly believed that adaptive immunity drives clearance of viral infections and, thus, dysfunction or viral evasion of adaptive immunity is required for a virus to persist. Type I interferons (IFNs) play pleiotropic roles in the antiviral response, including through innate control of viral replication. Murine norovirus (MNoV) replicates in dendritic cells (DCs) and type I IFN signaling in DCs is important for early control of MNoV replication. We show here that the non-persistent MNoV strain CW3 persists systemically when CD11c positive DCs are unable to respond to type I IFN. Persistence in this setting is associated with increased early viral titers, maintenance of DC numbers, increased expression of DC activation markers and an increase in CD8 T cell and antibody responses. Furthermore, CD8 T cell function is maintained during the persistent phase of infection and adaptive immune cells from persistently infected mice are functional when transferred to Rag1 -/- recipients. Finally, increased early replication and persistence are also observed in mixed bone marrow chimeras where only half of the CD11c positive DCs are unable to respond to type I IFN. These findings demonstrate that increased early viral replication due to a cell-intrinsic innate immune deficiency is sufficient for persistence and a functional adaptive immune response is not sufficient for viral clearance.

Differentiation and Protective Capacity of Virus-Specific CD8+ T Cells Suggest Murine Norovirus Persistence in an Immune-Privileged Enteric Niche

&NA; Noroviruses can establish chronic infections with active viral shedding in healthy humans but whether persistence is associated with adaptive immune dysfunction is unknown. We used genetically engineered strains of mouse norovirus (MNV) to investigate CD8+ T cell differentiation during chronic infection. We found that chronic infection drove MNV‐specific tissue‐resident memory (Trm) CD8+ T cells to a differentiation state resembling inflationary effector responses against latent cytomegalovirus with only limited evidence of exhaustion. These MNV‐specific Trm cells remained highly functional yet appeared ignorant of ongoing viral replication. Pre‐existing MNV‐specific Trm cells provided partial protection against chronic infection but largely ceased to detect virus within 72 hours of challenge, demonstrating rapid sequestration of viral replication away from T cells. Our studies revealed a strategy of immune evasion by MNV via the induction of a CD8+ T cell program normally reserved for latent pathogens and persistence in an immune‐privileged enteric niche. Graphical Abstract Figure. No caption available. HighlightsMNV‐specific Trm cells during chronic infection are largely functionalMNV Trm cells are transcriptionally similar to inflationary T cells in latent herpesMNV‐specific CD8+ T cells are protective, but this protection wanes after ˜3 daysCD8+ T cell ignorance in chronic MNV infection is due to poor antigen presentation &NA; Chronic infections often cause T cell dysfunction, but how noroviruses (NV) evade immunity is unknown. Tomov et al. show that gut‐resident T cells against NV remain functional but ignorant of chronic viral replication, suggesting that NV persists in an immune‐privileged enteric niche.

High-dimensional immune phenotyping and transcriptional analyses reveal robust recovery of viable human immune and epithelial cells from frozen gastrointestinal tissue

Simultaneous analyses of peripheral and mucosal immune compartments can yield insight into the pathogenesis of mucosal-associated diseases. Although methods to preserve peripheral immune cells are well established, studies involving mucosal immune cells have been hampered by lack of simple storage techniques. We provide a cryopreservation protocol allowing for storage of gastrointestinal (GI) tissue with preservation of viability and functionality of both immune and epithelial cells. These methods will facilitate translational studies allowing for batch analysis of mucosal tissue to investigate disease pathogenesis, biomarker discovery and treatment responsiveness.