Type I interferon protects antiviral CD8+ T cells from NK cell cytotoxicity

The viral context instructs the redundancy of costimulatory pathways in driving CD8(+) T cell expansion

Signals delivered by costimulatory molecules are implicated in driving T cell expansion. The requirements for these signals, however, vary from dispensable to essential in different infections. We examined the underlying mechanisms of this differential T cell costimulation dependence and found that the viral context determined the dependence on CD28/B7-mediated costimulation for expansion of naive and memory CD8⁺ T cells, indicating that the requirement for costimulatory signals is not imprinted. Notably, related to the high-level costimulatory molecule expression induced by lymphocytic choriomeningitis virus (LCMV), CD28/B7-mediated costimulation was dispensable for accumulation of LCMV-specific CD8⁺ T cells because of redundancy with the costimulatory pathways induced by TNF receptor family members (i.e., CD27, OX40, and 4-1BB). Type I IFN signaling in viral-specific CD8⁺ T cells is slightly redundant with costimulatory signals. These results highlight that pathogen-specific conditions differentially and uniquely dictate the utilization of costimulatory pathways allowing shaping of effector and memory antigen-specific CD8⁺ T cell responses.

DOI:http://dx.doi.org/10.7554/eLife.07486.001

When the immune system detects a virus in the body it mounts a response to eliminate it. Immune cells called CD8⁺ T cells detect fragments of virus proteins that are presented on the surface of other immune cells. The CD8⁺ T cells then rapidly divide to form populations that roam the body to kill cells that are infected with the virus. Afterwards, some of the CD8⁺ T cells become ‘memory T cells’, which allow the immune system to respond more rapidly if the virus returns. This means that a subsequent infection of the same virus is usually stopped before it can become severe enough for an individual to feel unwell.

Vaccines take advantage of the activities of CD8⁺ T cells to enable a person to become ‘immune’ to a virus without having to experience the disease. Vaccines contain dead or weakened viruses that can't spread in the body, but are able to activate the CD8⁺ T cells. However, a vaccine may not be as effective in activating the T cells as the live virus, perhaps because it fails to trigger the production of other molecules in the host that promote T cell activation. There are many of these ‘co-stimulatory molecules’ in the body, but it is not clear exactly how they work.

Now, Welten et al. show that the role of co-stimulatory molecules in the activation of CD8⁺ T cells depends on the type of virus and how it affects cells. Mice that were genetically engineered to lack two co-stimulatory molecules called CD80 and CD86 failed to accumulate active CD8⁺ T cells in response to infection with a herpes-like virus. However, if these mice were infected with a different virus called LCMV—which causes swelling of the brain and spinal cord—they produced many active CD8⁺ T cells to fight the infection.

Welten et al. found that other co-stimulatory molecules are able to compensate for the loss of CD80 and CD86 to boost the activation of T cells in response to LCMV, but not the herpes-like virus. Further experiments showed that LCMV triggers a lot more inflammation in infected cells than the other virus. This leads to the production of many different types of co-stimulatory molecules, which ensures that if one fails to boost the activation of CD8⁺ T cells, another molecule can do so instead. Better understanding of how these co-stimulatory molecules work could help scientists to develop more effective vaccines in future.

DOI:http://dx.doi.org/10.7554/eLife.07486.002

Boosting vaccine efficacy the natural (killer) way

Coordination of the innate and adaptive immune systems is paramount to the development of protective humoral and cellular immunity following vaccination. Natural killer (NK) cells are front-line soldiers of the innate immune system, and recent studies have revealed functions for NK cells in long-lived immune memory and the regulation of adaptive immune responses. These findings suggest that NK cells may play important roles in the development of efficacious vaccines, as well as, in some contexts, failed immunizations. Here, we review the current understanding of the immunomodulatory and memory differentiation capabilities of NK cells. We examine the context dependency of the mechanisms and the nature of NK cell-mediated modulation of the immune response, and discuss how these insights may impact immunization strategies and the development of next-generation vaccines.

Prognostic and Predictive Value of DAMPs and DAMP-Associated Processes in Cancer

It is now clear that human neoplasms form, progress, and respond to therapy in the context of an intimate crosstalk with the host immune system. In particular, accumulating evidence demonstrates that the efficacy of most, if not all, chemo- and radiotherapeutic agents commonly employed in the clinic critically depends on the (re)activation of tumor-targeting immune responses. One of the mechanisms whereby conventional chemotherapeutics, targeted anticancer agents, and radiotherapy can provoke a therapeutically relevant, adaptive immune response against malignant cells is commonly known as “immunogenic cell death.” Importantly, dying cancer cells are perceived as immunogenic only when they emit a set of immunostimulatory signals upon the activation of intracellular stress response pathways. The emission of these signals, which are generally referred to as “damage-associated molecular patterns” (DAMPs), may therefore predict whether patients will respond to chemotherapy or not, at least in some settings. Here, we review clinical data indicating that DAMPs and DAMP-associated stress responses might have prognostic or predictive value for cancer patients.

The oral toll-like receptor-7 agonist GS-9620 in patients with chronic hepatitis B virus infection

BACKGROUND & AIMS

GS-9620 is an oral agonist of toll-like receptor 7, a pattern-recognition receptor whose activation results in innate and adaptive immune stimulation. We evaluated the safety, pharmacokinetics, and pharmacodynamics of GS-9620 in patients with chronic hepatitis B.

METHODS

In two double-blind, phase 1b trials of identical design, 49 treatment-naïve and 51 virologically suppressed patients were randomized 5:1 to receive GS-9620 (at doses of 0.3mg, 1mg, 2mg, 4mg) or placebo as a single dose or as two doses seven days apart. Pharmacodynamic assessment included evaluation of peripheral mRNA expression of interferon-stimulated gene 15 (ISG15), serum interferon gamma-induced protein 10 and serum interferon (IFN)-alpha.

RESULTS

Overall, 74% of patients were male and 75% were HBeAg negative at baseline. No subject discontinued treatment due to adverse events. Fifty-eight percent experienced ⩾1 adverse event, all of which were mild to moderate in severity. The most common adverse event was headache. No clinically significant changes in HBsAg or HBV DNA levels were observed. Overall, a transient dose-dependent induction of peripheral ISG15 gene expression was observed peaking within 48 hours of dosing followed by return to baseline levels within seven days. Higher GS-9620 dose, HBeAg positive status, and low HBsAg level at baseline were independently associated with greater probability of ISG15 response. Most patients (88%) did not show detectable levels of serum IFN-alpha at any time point.

CONCLUSIONS

Oral GS-9620 was safe, well tolerated, and associated with induction of peripheral ISG15 production in the absence of significant systemic IFN-alpha levels or related symptoms.

Tricking the balance: NK cells in anti-cancer immunity

Natural Killer (NK) cells are classically considered innate immune effector cells involved in the first line of defense against infected and malignant cells. More recently, NK cells have emerged to acquire properties of adaptive immunity in response to certain viral infections such as expansion of specific NK cell subsets and long-lasting virus-specific responses to secondary challenges. NK cells distinguish healthy cells from abnormal cells by measuring the net input of activating and inhibitory signals perceived from target cells through NK cell surface receptors. Acquisition of activating ligands in combination with reduced expression of MHC class I molecules on virus-infected and cancer cells activates NK cell cytotoxicity and release of immunostimulatory cytokines like IFN-γ. In the cancer microenvironment however, NK cells become functionally impaired by inhibitory factors produced by immunosuppressive immune cells and cancer cells. Here we review recent progress on the role of NK cells in cancer immunity. We describe regulatory factors of the tumor microenvironment on NK cell function which determine cancer cell destruction or escape from immune recognition. Finally, recent strategies that focus on exploiting NK cell anti-cancer responses for immunotherapeutic approaches are outlined.

Decades after recovery from hepatitis B and HBsAg clearance the CD8+ T cell response against HBV core is nearly undetectable

BACKGROUND & AIMS

CD8(+) T cells are an essential component of a successful immune response against hepatitis B virus (HBV). Patients who spontaneously clear HBsAg after acute HBV infection have a strong CD8(+) T cell immune response, predominantly directed against the HBV core protein (HBcAg). However, the fate and phenotype of HBcAg-specific CD8(+) T cells after immune control are unclear.

METHODS

The CD8(+) T cell immune response against HBV core was determined in 65 patients with chronic HBV infection, 16 patients after recovery from acute HBV infection, and four patients with acute HBV infection utilizing overlapping peptides and HLA class I/peptide-multimers.

RESULTS

Patients who had cleared HBsAg >30 years ago had significantly weaker CD8(+) T cell responses after antigen-specific expansion compared to patients who had cleared the virus <10 years ago and patients with HBeAg negative chronic infection and low viral load (<2000 IU/ml; p<0.01). Also directly ex vivo, patients who had cleared the HBsAg >30 years ago had less HBV-specific CD8(+) T cells compared to patients with HBeAg negative chronic infection (p=0.0025). In patients with acute HBV infection, the frequency of HBc-specific CD8(+) T cells continued to decline after clearance of HBV-DNA and HBsAg even at a time when ALT levels had already normalized (p=0.0313).

CONCLUSIONS

The frequency of HBcAg-specific CD8(+) T cells continuously declines after HBsAg clearance. In line with clinical observations, this suggests that humoral and not CD8(+) T cell immune responses mainly contribute to prevention of HBV reactivation decades after HBsAg clearance.

Natural killer cells in hepatitis B virus infection

Natural killer cells are a unique type of lymphocytes with cytotoxic capacity, and play important roles against tumors and infections. Recently, natural killer cells have been increasingly valued in their effects in hepatitis B virus infection. Since hepatitis B virus is not cytopathic, the subsequent antiviral immune responses of the host are responsible for sustaining the liver injury, which may result in cirrhosis and even hepatocellular carcinoma. Many studies have confirmed that natural killer cells participate in anti-hepatitis B virus responses both in the early phase after infection and in the chronic phase via cytolysis, degranulation, and cytokine secretion. However, natural killer cells play dichotomic roles: they exert antiviral and immunoregulatory functions whilst contribute to the pathogenesis of liver injury. Here, we review the roles of natural killer cells in hepatitis B virus infection, introducing novel therapeutic strategies for controlling hepatitis B virus infection via the modulation of natural killer cells.

Type I Interferon Elevates Co-Regulatory Receptor Expression on CMV- and EBV-Specific CD8 T Cells in Chronic Hepatitis C

Hepatitis C virus (HCV) readily sets up persistence in a large fraction of infected hosts. Mounting epidemiological and immunological evidence suggest that HCV's persistence could influence immune responses toward unrelated pathogens and vaccines. Nonetheless, the fundamental contribution of the inflammatory milieu during persistent HCV infection in impacting immune cells specific for common pathogens such as CMV and EBV has not been fully studied. As the co-regulatory receptors PD-1, Tim-3, and 2B4 have all been shown to be vital in regulating CD8(+) T cell function, we assessed their expression on CMV/EBV-specific CD8(+) T cells from patients with chronic hepatitis C (CHC) and healthy controls ex vivo and upon stimulation with virus-specific peptides in vitro. Total and CMV/EBV-specific CD8(+) T cells expressing PD-1, Tim-3, and 2B4 were highly enriched in patients with CHC compared to healthy individuals ex vivo. In vitro peptide stimulation further potentiated the differential co-regulatory receptor expression of PD-1, Tim-3, and 2B4, which then culminated in an enhanced functionality of CMV/EBV-specific CD8(+) T cells in CHC patients. Comprehensively analyzing plasma cytokines between the two cohorts, we observed that not only was IFNα-2a dominant among 21 other inflammatory mediators elevated in CHC patients but it also correlated with PD-1 and Tim-3 expressions ex vivo. Importantly, IFNα-2a further caused upregulation of these markers upon in vitro peptide stimulation. Finally, we could prospectively study patients receiving novel IFN-free antiviral therapy. Here, we observed that treatment-induced clearance of HCV resulted in a partial reversion of the phenotype of CMV/EBV-specific CD8(+) T cells in patients with CHC. These data reveal an alteration of the plasma concentrations of IFNα-2a together with other inflammatory mediators during CHC, which appeared to pervasively influence co-regulatory receptor expression on CMV/EBV-specific CD8(+) T cells.

Type I interferons in anticancer immunity

Type I interferons (IFNs) are known for their key role in antiviral immune responses. In this Review, we discuss accumulating evidence indicating that type I IFNs produced by malignant cells or tumour-infiltrating dendritic cells also control the autocrine or paracrine circuits that underlie cancer immunosurveillance. Many conventional chemotherapeutics, targeted anticancer agents, immunological adjuvants and oncolytic viruses are only fully efficient in the presence of intact type I IFN signalling. Moreover, the intratumoural expression levels of type I IFNs or of IFN-stimulated genes correlate with favourable disease outcome in several cohorts of patients with cancer. Finally, new anticancer immunotherapies are being developed that are based on recombinant type I IFNs, type I IFN-encoding vectors and type I IFN-expressing cells.

NK cells inhibit humoral immunity by reducing the abundance of CD4+ T follicular helper cells during a chronic virus infection

There is a need to understand better how to improve B cell responses and immunity to persisting virus infections, which often cause debilitating illness or death. People with chronic virus infection show evidence of improved virus control when there is a strong neutralizing antibody response, and conversely, B cell dysfunction is associated with higher viral loads. We showed previously that NK cells inhibit CD4(+) and CD8(+) T cell responses to disseminating LCMV infection and that depletion of NK cells attenuates chronic infection. Here, we examined the effect of NK cell depletion on B cell responses to LCMV infection in mice. Whereas mice infected acutely generated a peak level of antibody soon after the infection was resolved, mice infected chronically showed a continued increase in antibody levels that exceeded those after acute infection. We found that early NK cell depletion rapidly increased virus-specific antibody levels to chronic infection, and this effect depended on CD4(+) T cells and was associated with elevated numbers of CXCR5(+)CD4(+) TFH cells. However, the NK cell-depleted mice controlled the infection and by 1 mo pi, had lower TFH cell numbers and antibody levels compared with mice with sustained infection. Finally, we show that NK cell depletion improved antiviral CD8(+) T cell responses only when B cells and virus-specific antibody were present. Our data indicate that NK cells diminish immunity to chronic infection, in part, by suppressing TFH cell and antibody responses.

Cytomegalovirus infection drives adaptive epigenetic diversification of NK cells with altered signaling and effector function

The mechanisms underlying human natural killer (NK) cell phenotypic and functional heterogeneity are unknown. Here, we describe the emergence of diverse subsets of human NK cells selectively lacking expression of signaling proteins after human cytomegalovirus (HCMV) infection. The absence of B and myeloid cell-related signaling protein expression in these NK cell subsets correlated with promoter DNA hypermethylation. Genome-wide DNA methylation patterns were strikingly similar between HCMV-associated adaptive NK cells and cytotoxic effector T cells but differed from those of canonical NK cells. Functional interrogation demonstrated altered cytokine responsiveness in adaptive NK cells that was linked to reduced expression of the transcription factor PLZF. Furthermore, subsets of adaptive NK cells demonstrated significantly reduced functional responses to activated autologous T cells. The present results uncover a spectrum of epigenetically unique adaptive NK cell subsets that diversify in response to viral infection and have distinct functional capabilities compared to canonical NK cell subsets.

Human Plasmacytoid Dendritic Cells Elicited Different Responses after Infection with Pathogenic and Nonpathogenic Junin Virus Strains

The arenavirus Junin virus (JUNV) is the etiologic agent of Argentine hemorrhagic fever. We characterized the JUNV infection of human peripheral blood-derived plasmacytoid dendritic cells (hpDC), demonstrating that hpDC are susceptible to infection with the C#1 strain (attenuated) and even more susceptible to infection with the P (virulent) JUNV strain. However, hpDC elicited different responses in terms of viability, activation, maturation, and cytokine expression after infection with both JUNV strains.

Type I interferons in infectious disease

Type I interferons (IFNs) have diverse effects on innate and adaptive immune cells during infection with viruses, bacteria, parasites and fungi, directly and/or indirectly through the induction of other mediators. Type I IFNs are important for host defence against viruses. However, recently, they have been shown to cause immunopathology in some acute viral infections, such as influenza virus infection. Conversely, they can lead to immunosuppression during chronic viral infections, such as lymphocytic choriomeningitis virus infection. During bacterial infections, low levels of type I IFNs may be required at an early stage, to initiate cell-mediated immune responses. High concentrations of type I IFNs may block B cell responses or lead to the production of immunosuppressive molecules, and such concentrations also reduce the responsiveness of macrophages to activation by IFNγ, as has been shown for infections with Listeria monocytogenes and Mycobacterium tuberculosis. Recent studies in experimental models of tuberculosis have demonstrated that prostaglandin E2 and interleukin-1 inhibit type I IFN expression and its downstream effects, demonstrating that a cross-regulatory network of cytokines operates during infectious diseases to provide protection with minimum damage to the host.

A novel immunoregulatory role for NK-cell cytotoxicity in protection from HLH-like immunopathology in mice

NK cytotoxic activity limits HLH-like immunopathology in cytotoxic-deficient mice. NK cytotoxic activity reduces T-cell activation and tissue infiltration of macrophages.

Disease-promoting effects of type I interferons in viral, bacterial, and coinfections

While type I interferons (IFNs) are universally acknowledged for their antiviral and immunostimulatory functions, there is increasing appreciation of the detrimental effects of inappropriate, excessive, or mistimed type I IFN responses in viral and bacterial infections. The underlying mechanisms by which type I IFNs promote susceptibility or severity include direct tissue damage by apoptosis induction or suppression of proliferation in tissue cells, immunopathology due to excessive inflammation, and cell death induced by TRAIL- and Fas-expressing immune cells, as well as immunosuppression through IL-10, IL-27, PD-L1, IL-1Ra, and other regulatory molecules that antagonize the induction or action of IL-1, IL-12, IL-17, IFN-γ, KC, and other effectors of the immune response. Bacterial superinfections following influenza infection are a prominent example of a situation where type I IFNs can misdirect the immune response. This review discusses current understanding of the parameters of signal strength, duration, timing, location, and cellular recipients that determine whether type I IFNs have beneficial or detrimental effects in infection.

Deficiency of the B cell-activating factor receptor results in limited CD169+ macrophage function during viral infection

The B cell-activating factor (BAFF) is critical for B cell development and humoral immunity in mice and humans. While the role of BAFF in B cells has been widely described, its role in innate immunity remains unknown. Using BAFF receptor (BAFFR)-deficient mice, we characterized BAFFR-related innate and adaptive immune functions following infection with vesicular stomatitis virus (VSV) and lymphocytic choriomeningitis virus (LCMV). We identified a critical role for BAFFR signaling in the generation and maintenance of the CD169(+) macrophage compartment. Consequently, Baffr(-) (/) (-) mice exhibited limited induction of innate type I interferon production after viral infection. Lack of BAFFR signaling reduced virus amplification and presentation following viral infection, resulting in highly reduced antiviral adaptive immune responses. As a consequence, BAFFR-deficient mice showed exacerbated and fatal disease after viral infection. Mechanistically, transient lack of B cells in Baffr(-) (/) (-) animals resulted in limited lymphotoxin expression, which is critical for maintenance of CD169(+) cells. In conclusion, BAFFR signaling affects both innate and adaptive immune activation during viral infections.

IMPORTANCE

Viruses cause acute and chronic infections in humans resulting in millions of deaths every year. Innate immunity is critical for the outcome of a viral infection. Innate type I interferon production can limit viral replication, while adaptive immune priming by innate immune cells induces pathogen-specific immunity with long-term protection. Here, we show that BAFFR deficiency not only perturbed B cells, but also resulted in limited CD169(+) macrophages. These macrophages are critical in amplifying viral particles to trigger type I interferon production and initiate adaptive immune priming. Consequently, BAFFR deficiency resulted in reduced enforced viral replication, limited type I interferon production, and reduced adaptive immunity compared to BAFFR-competent controls. As a result, BAFFR-deficient mice were predisposed to fatal viral infections. Thus, BAFFR expression is critical for innate immune activation and antiviral immunity.

Antigen expression determines adenoviral vaccine potency independent of IFN and STING signaling

Recombinant adenoviral vectors (rAds) are lead vaccine candidates for protection against a variety of pathogens, including Ebola, HIV, tuberculosis, and malaria, due to their ability to potently induce T cell immunity in humans. However, the ability to induce protective cellular immunity varies among rAds. Here, we assessed the mechanisms that control the potency of CD8 T cell responses in murine models following vaccination with human-, chimpanzee-, and simian-derived rAds encoding SIV-Gag antigen (Ag). After rAd vaccination, we quantified Ag expression and performed expression profiling of innate immune response genes in the draining lymph node. Human-derived rAd5 and chimpanzee-derived chAd3 were the most potent rAds and induced high and persistent Ag expression with low innate gene activation, while less potent rAds induced less Ag expression and robustly induced innate immunity genes that were primarily associated with IFN signaling. Abrogation of type I IFN or stimulator of IFN genes (STING) signaling increased Ag expression and accelerated CD8 T cell response kinetics but did not alter memory responses or protection. These findings reveal that the magnitude of rAd-induced memory CD8 T cell immune responses correlates with Ag expression but is independent of IFN and STING and provide criteria for optimizing protective CD8 T cell immunity with rAd vaccines.

T cell exhaustion during persistent viral infections

Although robust and highly effective anti-viral T cells contribute to the clearance of many acute infections, viral persistence is associated with the development of functionally inferior, exhausted, T cell responses. Exhaustion develops in a step-wise and progressive manner, ranges in severity, and can culminate in the deletion of the anti-viral T cells. This disarming of the response is consequential as it compromises viral control and potentially serves to dampen immune-mediated damage. Exhausted T cells are unable to elaborate typical anti-viral effector functions. They are characterized by the sustained upregulation of inhibitory receptors and display a gene expression profile that distinguishes them from prototypic effector and memory T cell populations. In this review we discuss the properties of exhausted T cells; the virological and immunological conditions that favor their development; the cellular and molecular signals that sustain the exhausted state; and strategies for preventing and reversing exhaustion to favor viral control.

Lessons from NK Cell Deficiencies in the Mouse

Since their discovery in the late 1970s, in vivo studies on mouse natural killer (NK) cell almost entirely relied on the use of depleting antibodies and were associated with significant limitations. More recently, large-scale gene-expression analyses allowed the identification of NKp46 as one of the best markers of NK cells across mammalian species. Since then, NKp46 has been shown to be expressed on other subsets of innate lymphoid cells (ILCs) such as the closely related ILC1 and the mucosa-associated NCR(+) ILC3. Based on this marker, several mouse models specifically targeting NKp46-expressing cell have recently been produced. Here, we review recent advances in the generation of models of deficiency in NKp46-expressing cells and their use to address the role of NK cells in immunity, notably on the regulation of adaptive immune responses.

Diversification and Functional Specialization of Human NK Cell Subsets

Natural killer (NK) cells are lymphocytes that participate in different facets of immunity. They can act as innate sentinels through recognition and eradication of infected or transformed target cells, so-called immunosurveillance. In addition, they can contain immune responses through the killing of other activated immune cells, so-called immunoregulation. Furthermore, they instruct and regulate immune responses by producing pro-inflammatory cytokines such as IFN-γ, either upon direct target cell recognition or by relaying cytokine cues from various cell types. Recent studies in mouse and man have uncovered infection-associated expansions of NK cell subsets with specific receptor repertoires and diverse patterns of intracellular signaling molecule expression. Moreover, distinct attributes of NK cells in tissues, including tissue-resident subsets, are being further elucidated. Findings support an emerging theme of ever-increasing diversification and functional specialization among different NK cell subsets, with a functional dichotomy between subsets involved in immunoregulation or immunosurveillance. The epigenetic landscapes and transcriptional profiles of different NK cell subsets are providing insights into the molecular regulation of effector functions. Here, we review phenotypic, functional, and developmental characteristics of a spectrum of human NK cell subsets. We also discuss the molecular underpinnings of different NK cell subsets and their potential contributions to immunity as well as disease susceptibility.

NK cells and interferons

The role of Natural Killer cells in host defense against infections as well as in tumour surveillance has been widely appreciated for a number of years. Upon recognition of "altered" cells, NK cells release the content of cytolytic granules, leading to the death of target cells. Moreover, NK cells are powerful producers of chemokines and cytokines, particularly Interferon-γ (IFN-γ), of which they are the earliest source upon a variety of infections. Despite being armed to fight against pathogens, NK cells become fully functional upon an initial phase of activation that requires the action of several cytokines, including type I IFNs. Type I IFNs are now recognized as key players in antiviral defense and immune regulation, and evidences from both mouse models of disease and in vitro studies support the existence of an alliance between type I IFNs and NK cells to ensure effective protection against viral infections. This review will focus on the role of type I IFNs in regulating NK cell functions to elicit antiviral response and on NK cell-produced IFN-γ beneficial and pathological effects.

A stay of execution: type I interferons pardon T cells from death by natural killers

In this issue of Immunity, Crouse et al., (2014) and Xu et al., (2014), show that by modulating the expression of natural killer (NK) cell receptor ligands, type I interferons protect responding T cells against culling by NK cells.

Regulating the diverse outcomes of interferon's interference

Regulatory T cells are crucial for preventing autoimmunity, but how their function is restrained to allow optimal effector T cells responses in appropriate contexts is unclear. In a recent paper in the Journal of Experimental Medicine, Campbell and colleagues demonstrate that virus-induced type I interferon acts directly on Treg cells to allow for functional antiviral T cell responses.