LAG-3 Confers a Competitive Disadvantage upon Antiviral CD8 + T Cell Responses

Ongoing clinical trials are evaluating the benefits of systemic blockade of lymphocyte activation gene-3 (LAG-3) signals to improve immunity to tumors. Those studies are founded on the well-established inhibitory role of LAG-3 in regulating CD8+ T cells during chronic virus infection and anti-tumor responses. However, the T cell response in LAG-3 deficient mice is similar in size and function to that in wild type animals, suggesting LAG-3 has nuanced immune-regulatory functions. We performed a series of adoptive transfer experiments in mice to better understand the T cell-intrinsic functions of LAG-3 in the regulation of CD8+ T cell responses. Our results indicate that LAG-3 expression by CD8+ T cells inhibits their competitive fitness and results in a slightly reduced rate of cell division in comparison to LAG-3 deficient cells. This cell-intrinsic effect of LAG-3 was consistent across both acute and chronic virus infections. These data show that LAG-3 directly modulates the size of the T cell response and support the use of LAG-3 blockade regimens to enhance CD8+ T cell responses

B Cell Depletion Curtails CD4+ T Cell Memory and Reduces Protection against Disseminating Virus Infection

Dynamic interactions between CD4+ T cells and B cells are needed for humoral immunity and CD4+ T cell memory. It is not known whether B cells are needed early on to induce the formation of memory precursor cells or are needed later to sustain memory cells. Herein, primary and memory CD4+ T cells responses were followed in wildtype mice that were depleted of mature B cells by anti-CD20 before or different times after acute lymphocytic choriomeningitis virus (LCMV) infection. The antibody treatment led to a 1000-fold reduction in B cell number that lasted 6 weeks. Primary virus-specific CD4+ Th1 cells were generated in B cell-depleted mice, however, there was a decrease in the CD4+Ly6CloTbet+ memory precursor population and a corresponding 4-fold reduction in CD4+ memory cell number. Memory T cells showed impaired cytokine production when they formed without B cells. B cell-depletion had no effect on established memory populations. During disseminating virus infection, B cell depletion led to sustained weight loss, functional exhaustion of CD4+ and CD8+ T cells, and prevented mice from resolving the infection. Thus, B cells contribute to the establishment and survival of memory CD4+ T cells following acute infection and play an essential role in immune protection against disseminating virus infection

IFN- Exerts Opposing Effects on T Cell Responses Depending on the Chronicity of the Virus Infection

IFN-lambda (IFN-λ) induces an antiviral state in many cell types and may contribute to the overall inflammatory environment following infection. Either of these effects may influence adaptive immune responses, but the role of type-3 interferons in the development of primary and memory T cell responses to infection has not been evaluated. Herein, we examined T cell responses to acute or persistent lymphocytic choriomeningitis virus (LCMV) infection in IFN-λR1-deficient mice. Following acute infection, we find that IFN-λR1-deficient mice produced normal levels of interferon, robust NK cell responses, but greater than normal CD4+ and CD8+ T cell responses compared to WT Balb/c mice. There were more T cells that were IL-7Rhi and, correspondingly, the IFN-λR-deficient mice showed a 2–3-fold increase in memory T cell number. The inhibitory effect of IFN-λR expression was independent of direct cytokine signaling into T cells. In contrast to acute infection, the IFN-λR-deficient mice generated markedly diminished T cell responses and had greater weight loss compared to WT mice when confronted with a highly disseminating variant of LCMV. These data indicate that IFN-λR limits T cell responses and memory following transient infection but augments T cell responses during persisting infection. Thus, the immune regulatory functions for IFN-λR are complex and vary with the overall inflammatory environment

Interferon-γ acts directly on CD8+ T cells to increase their abundance during virus infection

Interferon-γ (IFNγ) is important in regulating the adaptive immune response, and most current evidence suggests that it exerts a negative (proapoptotic) effect on CD8+ T cell responses. We have developed a novel technique of dual adoptive transfer, which allowed us to precisely compare, in normal mice, the in vivo antiviral responses of two T cell populations that differ only in their expression of the IFNγ receptor. We use this technique to show that, contrary to expectations, IFNγ strongly stimulates the development of CD8+ T cell responses during an acute viral infection. The stimulatory effect is abrogated in T cells lacking the IFNγ receptor, indicating that the cytokine acts directly upon CD8+ T cells to increase their abundance during acute viral infection

The Depletion of NK Cells Prevents T Cell Exhaustion to Efficiently Control Disseminating Virus Infection

NK cells have well-established functions in immune defense against virus infections and cancer through their cytolytic activity and production of cytokines. In this study, we examined the frequency of NK cells and their influence on T cell responses in mice given variants of lymphocytic choriomeningitis virus that cause acute or persisting infection. We found increased frequencies of circulating NK cells during disseminating infection compared with uninfected or acutely infected mice. Consistent with recent reports, we observed that the depletion of NK cells in mice with disseminated infection increased peak numbers of virus-specific cytokine producing CD8(+) T cells and resulted in the rapid resolution of disseminated infection. Additionally, we show that NK cell depletion sustained T cell responses across time and protected against T cell exhaustion. The positive effects of NK cell depletion on T cell responses only occurred when NK cells were depleted within the first 2 d of infection. We find that the improved CD8(+) T cell response correlated with an enhanced ability of APCs from NK cell-depleted mice to stimulate T cell proliferation, independently of the effects of NK cells on CD4(+) T cells. These results indicate that NK cells play an integral role in limiting the CD8 T cell response and contribute to T cell exhaustion by diminishing APC function during persisting virus infection

Editorial: The role of adipose tissue and resident immune cells in infections

Adipose tissues are distributed throughout the body and are in direct contact with sites of infection entry, such as mucosal tissues, gut, and skin. There is increasing appreciation that adipose tissue can influence local and systemic immune responses to infection. The adipose tissue can modulate immune responses through changes in the expression of pro- and anti-inflammatory cytokines, adipokines, and hormones that regulate general metabolism. Immune cells within adipose show differentiation states that are distinct from those in circulation or in lymphoid tissues, suggesting that the adipose environment regulates immune cell activity. The mechanisms leading to immune cell recruitment and maintenance within adipose remain enigmatic. Changes in diet that lead to obesity can alter the frequencies of regulatory or effector cells within adipose, potentially affecting local and systemic immune protection. Obesity is associated with higher susceptibility to infections possibly due to alterations in immune cells residing in adipose tissue. The interplay between immune cells and adipose is complex and bi-directional: immune cells residing within adipose tissue can perturb adipose tissue homeostasis and whole-body metabolism and, conversely, metabolic cues can modulate immune responses. Several reports demonstrate that microorganisms can target and even persist in adipose tissues. However, relatively few studies have addressed the immunological consequences of adipose tissue infection

Epigenetic Dysfunction in Turner Syndrome Immune Cells

Turner syndrome (TS) is a chromosomal condition associated with partial or complete absence of the X chromosome that involves characteristic findings in multiple organ systems. In addition to well-known clinical characteristics such as short stature and gonadal failure, TS is also associated with T cell immune alterations and chronic otitis media, suggestive of a possible immune deficiency. Recently, ubiquitously transcribed tetratricopeptide repeat on the X chromosome (UTX), a histone H3 lysine 27 (H3K27) demethylase, has been identified as a downregulated gene in TS immune cells. Importantly, UTX is an X-linked gene that escapes X-chromosome inactivation and thus is haploinsufficient in TS. Mice with T cell-specific UTX deficiency have impaired clearance of chronic viral infection due to decreased frequencies of T follicular helper (Tfh) cells, which are critical for B cell antibody generation. In parallel, TS patients have decreased Tfh frequencies in peripheral blood. Together, these findings suggest that haploinsufficiency of the X-linked UTX gene in TS T cells underlies an immune deficit, which may manifest as increased predisposition to chronic otitis media

NK Cells and Their Ability to Modulate T Cells during Virus Infections

Natural killer (NK) cells are important in protection against virus infections, and many viruses have evolved mechanisms to thwart NK cell activity. NK cells respond to inflammatory signals at an early stage of virus infection, resulting in proliferation, cytokine production, and cytolytic activity that can reduce virus loads. Moreover, the rapid kinetics of the NK cell response enables NK cells to influence other populations of innate immune cells, affect the inflammatory milieu, and guide adaptive immune responses to infection. Early NK cell interactions with other leukocytes can have long-lasting effects on the number and quality of memory T cells, as well as impact the exhaustion of T cells during chronic infections. The ability of NK cells to modulate T cell responses can be mediated through direct T-NK interactions, cytokine production, or indirectly through dendritic cells and other cell types. Herein, we summarize our current understanding of how NK cells interact with T cells, dendritic cells, B cells, and other cell types involved in adaptive immune responses to virus infection. We outline several mechanisms by which NK cells enhance or suppress adaptive immune response and long-lived immunological memory

Coxsackievirus B3 Inhibits Antigen Presentation In Vivo, Exerting a Profound and Selective Effect on the MHC Class I Pathway

Many viruses encode proteins whose major function is to evade or disable the host T cell response. Nevertheless, most viruses are readily detected by host T cells, and induce relatively strong T cell responses. Herein, we employ transgenic CD4+ and CD8+ T cells as sensors to evaluate in vitro and in vivo antigen presentation by coxsackievirus B3 (CVB3), and we show that this virus almost completely inhibits antigen presentation via the MHC class I pathway, thereby evading CD8+ T cell immunity. In contrast, the presentation of CVB3-encoded MHC class II epitopes is relatively unencumbered, and CVB3 induces in vivo CD4+ T cell responses that are, by several criteria, phenotypically normal. The cells display an effector phenotype and mature into multi-functional CVB3-specific memory CD4+ T cells that expand dramatically following challenge infection and rapidly differentiate into secondary effector cells capable of secreting multiple cytokines. Our findings have implications for the efficiency of antigen cross-presentation during coxsackievirus infection