Helminth-induced IL-4 expands bystander memory CD8+ T cells for early control of viral infection

The Effect of Unconventional Cytokine Combinations on NK-Cell Responses to Viral Infection

Cytokines are soluble and membrane-bound factors that dictate immune responses. Dogmatically, cytokines are divided into families that promote type 1 cell-mediated immune responses (e.g., IL-12) or type 2 humoral responses (e.g., IL-4), each capable of antagonizing the opposing family of cytokines. The discovery of additional families of cytokines (e.g., IL-17) has added complexity to this model, but it was the realization that immune responses frequently comprise mixtures of different types of cytokines that dismantled this black-and-white paradigm. In some cases, one type of response may dominate these mixed milieus in disease pathogenesis and thereby present a clear therapeutic target. Alternatively, synergistic or blended cytokine responses may obfuscate the origins of disease and perplex clinical decision making. Most immune cells express receptors for many types of cytokines and can mediate a myriad of functions important for tolerance, immunity, tissue damage, and repair. In this review, we will describe the unconventional effects of a variety of cytokines on the activity of a prototypical type 1 effector, the natural killer (NK) cell, and discuss how this may impact the contributions of these cells to health and disease.

Enteric helminth coinfection enhances host susceptibility to neurotropic flaviviruses via a tuft cell-IL-4 receptor signaling axis

Although enteric helminth infections modulate immunity to mucosal pathogens, their effects on systemic microbes remain less established. Here, we observe increased mortality in mice coinfected with the enteric helminth Heligmosomoides polygyrus bakeri (Hpb) and West Nile virus (WNV). This enhanced susceptibility is associated with altered gut morphology and transit, translocation of commensal bacteria, impaired WNV-specific T cell responses, and increased virus infection in the gastrointestinal tract and central nervous system. These outcomes were due to type 2 immune skewing, because coinfection in Stat6-/- mice rescues mortality, treatment of helminth-free WNV-infected mice with interleukin (IL)-4 mirrors coinfection, and IL-4 receptor signaling in intestinal epithelial cells mediates the susceptibility phenotypes. Moreover, tuft cell-deficient mice show improved outcomes with coinfection, whereas treatment of helminth-free mice with tuft cell-derived cytokine IL-25 or ligand succinate worsens WNV disease. Thus, helminth activation of tuft cell-IL-4-receptor circuits in the gut exacerbates infection and disease of a neurotropic flavivirus.

The role of CD8 T cells in controlling HIV beyond the antigen-specific face

OBJECTIVES

Understanding the determinants of HIV immune control is important for seeking viable HIV prevention, treatment and curative strategies. The antigen-specific roles of CD8 T cells in controlling primary HIV infection have been well documented, but their abilities to control the latent HIV reservoir is less well studied.

METHODS

The scientific literature on this issue was searched on PubMed.

RESULTS

Recent reports have demonstrated that CD8 T cells are also involved in the control of viral replication in HIV-infected individuals receiving antiretroviral therapy (ART). However, based on accumulating evidence, the antiviral role of CD8 T cells in ART patients may not be achieved via an antigen-specific manner as HIV-specific CD8 T cells can sense, but not effectively eliminate, cells harbouring intact provirus without first being activated. Our recent study indicated that virtual memory CD8 T cells, a semi-differentiated component of CD8 T cells, may be involved in the mechanism restraining the HIV DNA reservoir in ART patients.

CONCLUSIONS

In this review, we summarize recent findings on the role of CD8 T cells in controlling HIV, highlighting differences between conventional antigen-specific and innate-like CD8 T cells. A better understanding of the roles of CD8 T cells during HIV infection should benefit the informed design of immune-based treatment strategies.

Transkingdom Interactions Important for the Pathogenesis of Human Viruses

The bacterial, fungal, and helminthic species that comprise the microbiome of the mammalian host have profound effects on health and disease. Pathogenic viruses must contend with the microbiome during infection and likely have evolved to exploit or evade the microbiome. Both direct interactions between the virions and the microbiota and immunomodulation and tissue remodeling caused by the microbiome alter viral pathogenesis in either host- or virus-beneficial ways. Recent insights from in vitro and murine models of viral pathogenesis have highlighted synergistic and antagonistic, direct and indirect interactions between the microbiome and pathogenic viruses. This review will focus on the transkingdom interactions between human gastrointestinal and respiratory viruses and the constituent microbiome of those tissues.

Impact of Helminth Infections on Female Reproductive Health and Associated Diseases

A growing body of knowledge exists on the influence of helminth infections on allergies and unrelated infections in the lung and gastrointestinal (GI) mucosa. However, the bystander effects of helminth infections on the female genital mucosa and reproductive health is understudied but important considering the high prevalence of helminth exposure and sexually transmitted infections in low- and middle-income countries (LMICs). In this review, we explore current knowledge about the direct and systemic effects of helminth infections on unrelated diseases. We summarize host disease-controlling immunity of important sexually transmitted infections and introduce the limited knowledge of how helminths infections directly cause pathology to female reproductive tract (FRT), alter susceptibility to sexually transmitted infections and reproduction. We also review work by others on type 2 immunity in the FRT and hypothesize how these insights may guide future work to help understand how helminths alter FRT health.

Hiding in Plain Sight: Virtually Unrecognizable Memory Phenotype CD8+ T cells

Virtual memory T (T_VM) cells are a recently described population of conventional CD8⁺ T cells that, in spite of their antigen inexperience, express markers of T cell activation. T_VM cells exhibit rapid responsiveness to both antigen-specific and innate stimuli in youth but acquire intrinsic antigen-specific response defects in the elderly. In this article, we review how the identification of T_VM cells necessitates a re-evaluation of accepted paradigms for conventional memory T (T_MEM) cells, the potential for heterogeneity within the T_VM population, and the defining characteristics of T_VM cells. Further, we highlight recent literature documenting the development of T_VM cells as a distinct CD8⁺ T cell lineage as well their biological significance in the context of disease.

Pathophysiology and potential future therapeutic targets using preclinical models of COVID-19

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) gains entry into the lung epithelial cells by binding to the surface protein angiotensin-converting enzyme 2. Severe SARS-CoV-2 infection, also known as coronavirus disease 2019 (COVID-19), can lead to death due to acute respiratory distress syndrome mediated by inflammatory immune cells and cytokines. In this review, we discuss the molecular and biochemical bases of the interaction between SARS-CoV-2 and human cells, and in doing so we highlight knowledge gaps currently precluding development of new effective therapies. In particular, discovery of novel treatment targets in COVID-19 will start from understanding pathologic changes based on a large number of autopsy lung tissue samples. Pathogenetic roles of potential molecular targets identified in human lung tissues must be validated in established animal models. Overall, this stepwise approach will enable appropriate selection of candidate therapeutic modalities targeting SARS-CoV2 and the host inflammatory response.

A compendium answering 150 questions on COVID-19 and SARS-CoV-2

In December 2019, China reported the first cases of the coronavirus disease 2019 (COVID-19). This disease, caused by the severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2), has developed into a pandemic. To date, it has resulted in ~9 million confirmed cases and caused almost 500 000 related deaths worldwide. Unequivocally, the COVID-19 pandemic is the gravest health and socioeconomic crisis of our time. In this context, numerous questions have emerged in demand of basic scientific information and evidence-based medical advice on SARS-CoV-2 and COVID-19. Although the majority of the patients show a very mild, self-limiting viral respiratory disease, many clinical manifestations in severe patients are unique to COVID-19, such as severe lymphopenia and eosinopenia, extensive pneumonia, a "cytokine storm" leading to acute respiratory distress syndrome, endothelitis, thromboembolic complications, and multiorgan failure. The epidemiologic features of COVID-19 are distinctive and have changed throughout the pandemic. Vaccine and drug development studies and clinical trials are rapidly growing at an unprecedented speed. However, basic and clinical research on COVID-19-related topics should be based on more coordinated high-quality studies. This paper answers pressing questions, formulated by young clinicians and scientists, on SARS-CoV-2, COVID-19, and allergy, focusing on the following topics: virology, immunology, diagnosis, management of patients with allergic disease and asthma, treatment, clinical trials, drug discovery, vaccine development, and epidemiology. A total of 150 questions were answered by experts in the field providing a comprehensive and practical overview of COVID-19 and allergic disease.

New Insights into the Immune System Using Dirty Mice

The mouse (Mus musculus) is the dominant organism used to investigate the mechanisms behind complex immunological responses because of their genetic similarity to humans and our ability to manipulate those genetics to understand downstream function. Indeed, our knowledge of immune system development, response to infection, and ways to therapeutically manipulate the immune response to combat disease were, in large part, delineated in the mouse. Despite the power of mouse-based immunology research, the translational efficacy of many new therapies from mouse to human is far from ideal. Recent data have highlighted how the naive, neonate-like immune system of specific pathogen-free mice differs dramatically in composition and function to mice living under barrier-free conditions (i.e., "dirty" mice). In this review, we discuss major findings to date and challenges faced when using dirty mice and specific areas of immunology research that may benefit from using animals with robust and varied microbial exposure.

Will helminth co-infection modulate COVID-19 severity in endemic regions?

Helminth co-infections can skew systemic immunity towards type 2 responses. Here, Bradbury and colleagues consider how this may impact the severity of COVID-19 in helminth-endemic regions.

Building a T cell compartment: how immune cell development shapes function

We are just beginning to understand the diversity of the peripheral T cell compartment, which arises from the specialization of different T cell subsets and the plasticity of individual naive T cells to adopt different fates. Although the progeny of a single T cell can differentiate into many phenotypes following infection, individual T cells are biased towards particular phenotypes. These biases are typically ascribed to random factors that occur during and after antigenic stimulation. However, the T cell compartment does not remain static with age, and shifting immune challenges during ontogeny give rise to T cells with distinct functional properties. Here, we argue that the developmental history of naive T cells creates a 'hidden layer' of diversity that persists into adulthood. Insight into this diversity can provide a new perspective on immunity and immunotherapy across the lifespan.

Virtual memory CD8+ T cells restrain the viral reservoir in HIV-1-infected patients with antiretroviral therapy through derepressing KIR-mediated inhibition

The viral reservoir is the major hurdle in developing and establishing an HIV cure. Understanding factors affecting the size and decay of this reservoir is crucial for the development of therapeutic strategies. Recent work highlighted that CD8+ T cells are involved in the control of viral replication in ART-treated HIV-1-infected individuals, but how CD8+ T cells sense and restrict the HIV reservoir are not fully understood. Here, we demonstrate that a population of unconventional CD45RA+, PanKIR+, and/or NKG2A+ virtual memory CD8+ T cells (T_VM cells), which confer rapid and robust protective immunity against pathogens, plays an important role in restraining the HIV DNA reservoir in HIV-1-infected patients with effective ART. In patients undergoing ART, T_VM cells negatively correlate with HIV DNA and positively correlate with circulating IFN-α2 and IL-15. Moreover, T_VM cells constitutively express high levels of cytotoxic granule components, including granzyme B, perforin and granulysin, and demonstrate the capability to control HIV replication through both cytolytic and noncytolytic mechanisms. Furthermore, by using an ex vivo system, we showed that HIV reactivation is effectively suppressed by T_VM cells through KIR-mediated recognition. This study suggests that T_VM cells are a promising target to predict posttreatment virological control and to design immune-based interventions to reduce the reservoir size in ART-treated HIV-1-infected individuals.

IL-4/IL-13 polarization of macrophages enhances Ebola virus glycoprotein-dependent infection

BACKGROUND

Ebolavirus (EBOV) outbreaks, while sporadic, cause tremendous morbidity and mortality. No therapeutics or vaccines are currently licensed; however, a vaccine has shown promise in clinical trials. A critical step towards development of effective therapeutics is a better understanding of factors that govern host susceptibility to this pathogen. As macrophages are an important cell population targeted during virus replication, we explore the effect of cytokine polarization on macrophage infection.

METHODS/MAIN FINDINGS

We utilized a BSL2 EBOV model virus, infectious, recombinant vesicular stomatitis virus encoding EBOV glycoprotein (GP) (rVSV/EBOV GP) in place of its native glycoprotein. Macrophages polarized towards a M2-like anti-inflammatory state by combined IL-4 and IL-13 treatment were more susceptible to rVSV/EBOV GP, but not to wild-type VSV (rVSV/G), suggesting that EBOV GP-dependent entry events were enhanced by these cytokines. Examination of RNA expression of known surface receptors that bind and internalize filoviruses demonstrated that IL-4/IL-13 stimulated expression of the C-type lectin receptor DC-SIGN in human macrophages and addition of the competitive inhibitor mannan abrogated IL-4/IL-13 enhanced infection. Two murine DC-SIGN-like family members, SIGNR3 and SIGNR5, were upregulated by IL-4/IL-13 in murine macrophages, but only SIGNR3 enhanced virus infection in a mannan-inhibited manner, suggesting that murine SIGNR3 plays a similar role to human DC-SIGN. In vivo IL-4/IL-13 administration significantly increased virus-mediated mortality in a mouse model and transfer of ex vivo IL-4/IL-13-treated murine peritoneal macrophages into the peritoneal cavity of mice enhanced pathogenesis.

SIGNIFICANCE

These studies highlight the ability of macrophage polarization to influence EBOV GP-dependent virus replication in vivo and ex vivo, with M2a polarization upregulating cell surface receptor expression and thereby enhancing virus replication. Our findings provide an increased understanding of the host factors in macrophages governing susceptibility to filoviruses and identify novel murine receptors mediating EBOV entry.

EOMES interacts with RUNX3 and BRG1 to promote innate memory cell formation through epigenetic reprogramming

Memory CD8⁺ T cells have the ability to provide lifelong immunity against pathogens. Although memory features generally arise after challenge with a foreign antigen, naïve CD8 single positive (SP) thymocytes may acquire phenotypic and functional characteristics of memory cells in response to cytokines such as interleukin-4. This process is associated with the induction of the T-box transcription factor Eomesodermin (EOMES). However, the underlying molecular mechanisms remain ill-defined. Using epigenomic profiling, we show that these innate memory CD8SP cells acquire only a portion of the active enhancer repertoire of conventional memory cells. This reprograming is secondary to EOMES recruitment, mostly to RUNX3-bound enhancers. Furthermore, EOMES is found within chromatin-associated complexes containing BRG1 and promotes the recruitment of this chromatin remodelling factor. Also, the in vivo acquisition of EOMES-dependent program is BRG1-dependent. In conclusion, our results support a strong epigenetic basis for the EOMES-driven establishment of CD8⁺ T cell innate memory program.

Similar but different: virtual memory CD8 T cells as a memory-like cell population

Immunological memory is a phenomenon where the immune system can respond more rapidly to pathogens and immunological challenges that it has previously encountered. It is defined by several key hallmarks. After an initial encounter, immune cells (1) expand and (2) differentiate to form memory cell populations. Memory cells are (3) long-lived and (4) facilitate more rapid immune responses to subsequent infection because of (i) an increase in cell number, (ii) a decrease in the signaling threshold required for entry into cell cycle or effector function and (iii) localization of cells to tissue sites for surveillance. Classically, immunological memory has been antigen specific but it is becoming apparent that mechanisms of immunological memory can be co-opted by innate or antigen-inexperienced immune cells to generate heterogeneity in immune responses. One such cell is the virtual memory CD8 T (T_VM ) cell, which is a semi-differentiated but antigen-naïve CD8 T-cell population. This review will summarize current knowledge of how T_VM cells are generated, their memory-like hallmarks, how they are maintained during steady state, infection and aging, and propose a model to integrate key signaling pathways during their generation.

Aquatic Exercise at Thermoneutral Water Temperature Enhances Antitumor Immune Responses

Despite the broad rehabilitative potential of aquatic exercises, the relationship between aquatic exercise and the immune system has not been fully elucidated to date. In particular, there are few specific and delicate immunological approaches to the effect of water temperature on immunity. Thus, we examined the effect of water temperature on immunity during aquatic exercise. The animal tumor model was adopted to examine the impact of aquatic exercise at thermoneutral temperature (TT; 29°C) on immunity compared with aquatic exercise at body temperature (BT; 36°C). Tumor-bearing mice were made to swim in TT water or in BT water for 3 wk and immune cells and their functional activity were analyzed using FACS. Tumor growth was significantly suppressed in mice that exercised in TT than in BT water. The tumor control correlated with the increased number of NK (2-fold), γδT cells (2.5-fold), NKT (2.5-fold), and cytotoxic CD8⁺ T cells (1.6-fold), which play a critical role in anti-tumor immune responses. Furthermore, the functional activity was dramatically improved in the TT group, showing enhanced production of IFNγ in CD8⁺ T cells compared with the BT group. This study demonstrates that aquatic exercise in TT water may improve protective immune responses more effectively than in BT water. Although the effects of water temperature on immune function need further verification in humans, this study suggests that water temperature in human hydrotherapy may be important for improving immune function.