Acute Lymphocytic Choriomeningitis Virus Research Articles

Mitochondrial antiviral signaling molecule-mediated mitochondrial calcium regulates CD8 T cell function during acute virus infection (VIR6P.1163)

Abstract MAVS is a crucial adaptor molecule through which RIG-I-like receptors (RLR)s signal to mediate downstream innate antiviral and inflammatory responses. However a role for MAVS in directly programming adaptive immunity has not been defined. Here we identified a cell-intrinsic role for MAVS in programming CD8 T cells following virus infection. We utilized a mouse model of acute Lymphocytic choriomeningitis virus (LCMV) infection to define the actions of adoptively transferred WT or MAVS deficient CD8 T cells. Lack of MAVS lead to defects in CD8 T cell expansion as well as function as measured by cytokine and cytotoxic T cell effector molecule production but these parameters were not deficient in double knockout mice lacking the RLRs MDA5 and RIG-I. We identified defects in total cytoplasmic calcium, mitochondrial calcium as well as mitochondrial membrane potential in MAVS-/- CD8 T cells in vivo. We found that the inflammatory conditions of LCMV -induced cell proliferation place a metabolic load on CD8 T cells and their mitochondria such that the absence of MAVS lead to defects in mitochondrial calcium independently of the RLRs. Importantly, the MAVS defect associated with defective nuclear factor of activated T cells c1 (NFATc1) activation and consequently decreased IL-2 production. Our study assigns a cell-intrinsic role for MAVS in regulating adaptive immunity following viral infection by means of regulating mitochondrial calcium and thereby affecting T cell fitness.

IL-21 signaling modulates the differentiation, distribution, and abundance of CD8 T cell subsets (LYM7P.616)

Abstract The activation of naïve CD8 T cells typically results in the formation of effector (TE) cells as well as memory cells that are retained over time. Memory CD8 T cells can be further subdivided into central memory (TCM), effector memory (TEM) and tissue-resident memory (TRM) subsets, which cooperate to confer immunological protection. Using adoptive transfer studies and mixed bone marrow chimeras in which CD8 T cells either do or do not express the IL-21 receptor (IL-21R), we discovered that under homeostatic or lymphopenic conditions IL-21 acts directly on CD8 T cells to favor the accumulation of TE/TEM populations. The inability to perceive IL-21 signals resulted in reduced accumulation of CD8 T cells in various tissues including the small intestine intraepithelial lymphocyte compartment. The reduced fraction of IL-21R-/- CD8 TRM cells in the small intestine also displayed markedly lower levels of the cytolytic effector molecule granzyme B. Notably, IL-21 signaling was associated with the expression of the chemokine receptor CX3CR1 and the integrin α4β7 on circulating CD8 T cells in the mixed bone marrow chimeras. Acute lymphocytic choriomeningitis virus infection overcame the necessity for IL-21 to establish CD8 TE/TEM and TRM subsets. Overall, this study demonstrates that IL-21 modulates the differentiation, accumulation, and function of effector-phenotype CD8 T cells in a context-dependent manner.

Differential role of B7 co-stimulation on B cells and dendritic cells for Th1 and Tfh differentiation (LYM8P.631)

Abstract Upon activation CD4 T cells differentiate into different subsets that have distinct functions in the immune response. Antigen presentation in the presence of co-stimulation and cytokines is required for optimal CD4 T cell activation and differentiation. Cytokines play a well-described crucial role driving CD4 T cell differentiation, but the role of different antigen presenting cells and co-stimulation remains relatively unexplored. To address this question we developed mice that lack B7-1 expression on B cells or on dendritic cells (DCs), on a B7-2 deficient background. CD4 differentiation was studied in the context of acute lymphocytic choriomeningitis virus (LCMV) infection. We find that mice lacking B7-1 on DCs have a profound defect on virus-specific CD4 T cell expansion that affects Th1 and Tfh numbers, but with the most drastic reduction in Th1 differentiation. In contrast, mice lacking B7-1 on B cells have similar numbers of LCMV-specific CD4 T cells as control mice. However, even though CXCR5 expressing LCMV-specific CD4 T cells numbers appear unaffected by B7-1 deficiency on B cells, there was a reduction in cells expressing high levels of CXCR5, PD-1 and Bcl-6 and a profound defect in LCMV-specific long lived plasma cells and antibodies. We conclude that CD4 T cell differentiation requires cell-type specific co-stimulation, and co-stimulation by B cells is essential to obtain functional Tfh and long-term humoral responses after acute viral infection.

T cell lipid peroxidation induces ferroptosis and prevents immunity to infection.

The selenoenzyme glutathione peroxidase 4 (Gpx4) is a major scavenger of phospholipid hydroperoxides. Although Gpx4 represents a key component of the reactive oxygen species-scavenging network, its relevance in the immune system is yet to be defined. Here, we investigated the importance of Gpx4 for physiological T cell responses by using T cell-specific Gpx4-deficient mice. Our results revealed that, despite normal thymic T cell development, CD8(+) T cells from T(ΔGpx4/ΔGpx4) mice had an intrinsic defect in maintaining homeostatic balance in the periphery. Moreover, both antigen-specific CD8(+) and CD4(+) T cells lacking Gpx4 failed to expand and to protect from acute lymphocytic choriomeningitis virus and Leishmania major parasite infections, which were rescued with diet supplementation of high dosage of vitamin E. Notably, depletion of the Gpx4 gene in the memory phase of viral infection did not affect T cell recall responses upon secondary infection. Ex vivo, Gpx4-deficient T cells rapidly accumulated membrane lipid peroxides and concomitantly underwent cell death driven by ferroptosis but not necroptosis. These studies unveil an essential role of Gpx4 for T cell immunity.

Bone Marrow Memory CD8+ T Cells Play a Supporting Role in Hematopoiesis

The bone marrow (BM) has an important function as primary lymphoid organ through the process of hematopoiesis. This process is sustained by hematopoietic stem cells (HSCs) and their life-long production of new blood cells, which is made possible by their unique ability to self-renew. Next to this, BM also functions as a secondary lymphoid organ, as it can mediate primary T cell responses against invading pathogens. We and others have shown that activated T cells can influence the hematopoietic process through the production of pro-inflammatory cytokines. This indicates that adaptive immune responses and hematopoiesis are intertwined in the BM, though most of the cellular and molecular interactions that occur during this crosstalk are yet unknown.Based on previous observations that T cell deficient mice have altered hematopoiesis and that depletion of T cells from allogeneic BM grafts compromises HSC engraftment, we questioned to what extent BM T cells can directly affect the function of HSCs. To test this, we sorted and co-cultured murine BM T cells with HSCs (Lin-Sca-1+c-Kit+CD48-CD150+). We found that particularly BM CD8+ central memory (CD44+CD62L+) T cells (Tcm) enhance the capacity of HSCs to self-renew. Furthermore, we found that TCR-transgenic mice, which do not have memory T cells, have lower numbers of HSCs, which could subsequently be increased by transferring BM CD8+ Tcm. Remarkably, an increase in HSC numbers was also observed when HSCs were cultured with only supernatant derived from BM CD8+ Tcm. Moreover, HSCs cultured with supernatant from BM CD8+ Tcm and later transplanted in myeloablated hosts displayed a strongly enhanced ability to restore hematopoiesis. Importantly, the strong impact of BM T cells on HSCs was not only apparent in the steady state situation, but also following a viral infection with either acute or chronic lymphocytic choriomeningitis virus (LCMV). We could establish that both acute and chronic LCMV-specific CD8+ T cells or supernatant from these cells could increase the HSC self-renewal capacity.In conclusion, our findings demonstrate that BM memory CD8+ T cells can positively influence the function of HSC through soluble mediators. We postulate that this process is particularly relevant after immune activation, in order to protect and/or restore the HSC pool and the subsequent hematopoietic recovery. We are currently using a proteomics approach to identify these soluble mediator produced by CD8+ T cells. DisclosuresNo relevant conflicts of interest to declare.

Autophagy is essential for effector CD8(+) T cell survival and memory formation.

The importance of autophagy in memory CD8 T cell differentiation in vivo is not well defined. We show here that autophagy is dynamically regulated in virus-specific CD8 T cells during acute lymphocytic choriomeningitis virus infection. Autophagy decreased in activated proliferating T cells, and was then upregulated at the peak of the effector T cell response. Consistent with this model, deletion of the key autophagy genes Atg7 or Atg5 in virus-specific CD8 T cells had minimal effect on generating effector cells but greatly enhanced their death during the contraction phase resulting in compromised memory formation. These findings provide insight into when autophagy is needed during effector and memory T cell differentiation in vivo and also warrant a re-examination of our current concepts about the relationship between T cell activation and autophagy.

Natural killer cells suppress humoral immunity and development of neutralizing antibodies (VIR1P.962)

Abstract Pathogen-specific neutralizing antibodies (nAbs) are a key component of protective immunity after infection or vaccination. However, broadly-specific nAbs that can prevent infections with highly mutable viruses like HIV are rarely seen in infected patients and are poorly elicited by current vaccines. Therefore, new vaccine strategies are needed to enhance the induction of nAbs, potentially by augmenting the germinal center (GC) reactions that facilitate somatic hypermutation, affinity maturation and development of high-affinity nAbs. Here, we demonstrate that natural killer (NK) cells impair humoral immunity by contributing to a weak GC response and subdued generation of virus-specific nAbs after acute lymphocytic choriomeningitis virus (LCMV) infection of mice. The magnitude and duration of the LCMV-induced GC response was substantially reduced by NK cells, which constricted the number of both follicular helper T cells (Tfh) and GC B cells present in lymphoid tissues. NK cell-mediated suppression of GC responses was also observed in different stains of mice and after infection with a variety of dissimilar pathogens, suggesting that NK cell suppression of humoral immunity is a universal feature of infection. Notably, NK cell inhibition of the GC response during LCMV infection resulted in a markedly delayed and relatively weak nAb response. Thus, targeting of immunosuppressive NK cells could represent a revolutionary method to enhance the efficacy of future vaccine regimens.

Polyclonal CD4 TCR Affinities are not altered in chronic viral infection (VIR7P.1058)

Abstract The range of polyclonal CD4 T cell receptor (TCR) affinities that participate during the response to viral infection is currently unknown. Utilizing a highly sensitive two-dimensional micropipette adhesion frequency assay (2D), we determined the TCR affinity and frequency of CD4 T cells that expand and survive throughout multiple phases of the chronic and acute lymphocytic choriomeningitis virus (LCMV) T cell response. We discovered consistently more (4-5 fold) CD4 T cells specific for the IAb GP66-77 LCMV epitope than detected with pMHC II tetramer. The 2D identified lower affinity cells participate in the anti-viral response and are apparent at all time points of acute and chronic infection. Average TCR affinities measured at peak and later stages of the chronic response remained constant and equivalent to corresponding acute response measurements. However, programmed death 1 (PD-1) expressing CD4+ T cells late in chronic infection are functionally unresponsive despite static affinities. In contrast, memory cells in the acute response have a higher functional avidity compared to peak effectors (produce IFNγ in response to lower amount of peptide antigen) yet T cell memory is not restricted to select TCR affinities. Our findings suggest long term antigen exposure and functional enhancement/impairment exert no selective pressure in the survival or deletion of specific CD4 TCR affinities and TCR affinity alone does not always predict biological response.

Mechanisms underlying specificity of natural killer cell regulation of adaptive immunity (IRC8P.485)

Abstract Viral persistence is determined in part by the regulatory activities of murine natural killer (NK) cells, including the lysis of activated CD4 T cells. We now find that NK cells also impair virus-specific memory T cell responses [and repress humoral immunity (separate abstract)] after acute Pichinde or lymphocytic choriomeningitis virus infections. Hence, limiting NK cell inhibition of adaptive immunity during vaccination could enhance long-lived protective immunity. To enable selective targeting of this NK cell activity in a vaccine, the molecular mechanisms of such suppression must be ascertained. Thus, we have explored changes in the expression of NK cell receptors (NKR) and their ligands (NKRL) on both NK cells and target T cells after infection. This analysis revealed that: 1) suppression of adaptive immunity corresponded with reduced inhibitory NKR expression on NK cells; 2) archetypical activating NKR such as NKG2D were dispensable in our system; and 3) susceptibility of activated CD4 T cells to NK cell lysis correlated with reduced expression of inhibitory NKRL (e.g. CD48) and corresponding higher levels of activating NKRL (e.g. Ly108), than were present on NK cell-resistant CD8 T cells. Further, the selectivity of NK cell killing of different T cells could be deregulated by altering NKR/NKRL expression. Our findings may facilitate development of innovative strategies to harness or inhibit NK cell lysis of T cells in the context of vaccination or immune therapy.

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

IFN-λ induces an antiviral state in many cell types and may contribute to the overall inflammatory environment after infection. Either of these effects may influence adaptive immune responses, but the role of type 3 IFNs in the development of primary and memory T cell responses to infection has not been evaluated. In this study, we examined T cell responses to acute or persistent lymphocytic choriomeningitis virus infection in IFN-λR1-deficient mice. Following acute infection, we find that IFN-λR1-deficient mice produced normal levels of IFN, robust NK cell responses, but greater than normal CD4+ and CD8+ T cell responses compared with wild type BALB/c mice. There were more T cells that were IL-7R(hi) and, correspondingly, the IFN-λR-deficient mice showed a 2- to 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 with acute infection, the IFN-λR-deficient mice generated markedly diminished T cell responses and had greater weight loss compared with wild type mice when confronted with a highly disseminating variant of lymphocytic choriomeningitis virus. These data indicate that IFN-λR limits T cell responses and memory after 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.

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. In this study, primary and memory CD4(+) T cells responses were followed in wild-type mice that were depleted of mature B cells by anti-CD20 before or different times after acute lymphocytic choriomeningitis virus infection. The Ab treatment led to a 1000-fold reduction in B cell number that lasted 6 wk. Primary virus-specific CD4(+) Th1 cells were generated in B cell-depleted mice; however, there was a decrease in the CD4(+)Ly6C(lo)Tbet(+) 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 and 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 post-acute infection and play an essential role in immune protection against disseminating virus infection.

Differential T Cell Responses to Residual Viral Antigen Prolong CD4+ T Cell Contraction following the Resolution of Infection

The contraction phase of the T cell response is a poorly understood period after the resolution of infection when virus-specific effector cells decline in number and memory cells emerge with increased frequencies. CD8(+) T cells plummet in number and quickly reach stable levels of memory following acute lymphocytic choriomeningitis virus infection in mice. In contrast, virus-specific CD4(+) T cells gradually decrease in number and reach homeostatic levels only after many weeks. In this study, we provide evidence that MHCII-restricted viral Ag persists during the contraction phase following this prototypical acute virus infection. We evaluated whether the residual Ag affected the cell division and number of virus-specific naive and memory CD4(+) T cells and CD8(+) T cells. We found that naive CD4(+) T cells underwent cell division and accumulated in response to residual viral Ag for >2 mo after the eradication of infectious virus. Surprisingly, memory CD4(+) T cells did not undergo cell division in response to the lingering Ag, despite their heightened capacity to recognize Ag and make cytokine. In contrast to CD4(+) T cells, CD8(+) T cells did not undergo cell division in response to the residual Ag. Thus, CD8(+) T cells ceased division within days after the infection was resolved, indicating that CD8(+) T cell responses are tightly linked to endogenous processing of de novo synthesized virus protein. Our data suggest that residual viral Ag delays the contraction of CD4(+) T cell responses by recruiting new populations of CD4(+) T cells.

Differentiation of Antigen-Specific T Cells with Limited Functional Capacity during Mycobacterium tuberculosis Infection

Despite the generation of Mycobacterium tuberculosis-specific T cell immune responses during the course of infection, only 5 to 10% of exposed individuals develop active disease, while others develop a latent infection. This phenomenon suggests defective M. tuberculosis-specific immunity, which necessitates more careful characterization of M. tuberculosis-specific T cell responses. Here, we longitudinally analyzed the phenotypes and functions of M. tuberculosis-specific T cells. In contrast to the functional exhaustion of T cells observed after chronic infection, M. tuberculosis-specific CD8(+) T cells differentiated into either effector (CD127(lo) CD62L(lo)) or effector memory (CD127(hi) CD62L(lo)) cells, but not central memory cells (CD127(hi) CD62L(hi)), with low programmed death 1 (PD-1) expression, even in the presence of high levels of bacteria. Additionally, M. tuberculosis-specific CD8(+) and CD4(+) T cells produced substantial levels of tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ), but not interleukin 2 (IL-2), upon in vitro restimulation. Among M. tuberculosis-specific CD8(+) T cells, CD127(hi) effector memory cells displayed slower ongoing turnover but greater survival potential. In addition, these cells produced more IFN-γ and TNF-α and displayed lytic activity upon antigen stimulation. However, the effector function of M. tuberculosis-specific CD8(+) CD127(hi) effector memory T cells was inferior to that of canonical CD8(+) CD127(hi) memory T cells generated after acute lymphocytic choriomeningitis virus infection. Collectively, our data demonstrate that M. tuberculosis-specific T cells can differentiate into memory T cells during the course of M. tuberculosis infection independent of the bacterial burden but with limited functionality. These results provide a framework for further understanding the mechanisms of M. tuberculosis infection that can be used to develop more effective vaccines.

Global DNA methylation remodeling accompanies CD8 T cell effector function.

The differentiation of CD8 T cells in response to acute infection results in the acquisition of hallmark phenotypic effector functions; however, the epigenetic mechanisms that program this differentiation process on a genome-wide scale are largely unknown. In this article, we report the DNA methylomes of Ag-specific naive and day-8 effector CD8 T cells following acute lymphocytic choriomeningitis virus infection. During effector CD8 T cell differentiation, DNA methylation was remodeled such that changes in DNA methylation at gene promoter regions correlated negatively with gene expression. Importantly, differentially methylated regions were enriched at cis-elements, including enhancers active in naive T cells. Differentially methylated regions were associated with cell type-specific transcription factor binding sites, and these transcription factors clustered into modules that define networks targeted by epigenetic regulation and control of effector CD8 T cell function. Changes in the DNA methylation profile following CD8 T cell activation revealed numerous cellular processes, cis-elements, and transcription factor networks targeted by DNA methylation. Together, the results demonstrated that DNA methylation remodeling accompanies the acquisition of the CD8 T cell effector phenotype and repression of the naive cell state. Therefore, these data provide the framework for an epigenetic mechanism that is required for effector CD8 T cell differentiation and adaptive immune responses.

Cell intrinsic role for MAVS in regulating CD8 T cell fitness during acute virus infection (P6113)

Abstract Mitochondrial antiviral Signaling molecule (MAVS) has been described in it’s role as an adaptor molecule that links viral RNA sensing by RIG-I-like receptors (RLR)s to type I IFN and inflammatory cytokine production. However it’s role in adaptive immune responses to viruses is not well defined. Using an adoptive cell transfer system we examined the requirement for MAVS directly in CD8 T cells during adaptive responses following acute Lymphocytic choriomeningitis virus (LCMV) infection. Here, we found that MAVS plays an RLR-independent role in determining CD8 effector T cell fitness. MAVS-deficient cells were deficient in virus-induced expansion and cytokine production. This deficiency correlated with altered cell size and granularity, differential mitochondrial membrane potential and reduced levels of steady-state intracellular calcium. We found cytokine production deficiencies were acute at earlier stages of CD8 cell expansion, suggesting that the requirement for MAVS is most critical when cellular need for mitochondrial metabolism is maximal. These results suggest that MAVS is required for metabolic support of CD8 effector cell expansion during acute virus infection. Our study therefore assigns a novel metabolic role to MAVS in adaptive CD8 T cell energetics. Defining the function of MAVS in enhancing T cell metabolism therefore has implications for vaccine strategies that aim to increase the quality and quality of the CD8 T cell response to virus infection.

O032 Timing and magnitude of Type I interferon responses by distinct viral sensors impact CD8 T cell exhaustion and chronic infection

Viral infection triggers a Type I Interferon (IFN-I) response in most cells by stimulating sensors that detect viral nucleic acids. Toll-like receptor (TLR) 7/9-equipped plasmacytoid dendritic cells (pDCs) are specialized IFN-I-producing cells that are capable of secreting large amounts of IFN-I. IFN-I is also produced by infected cells through RIG-I like receptors (RLR) such as Melanoma Differentiation-Associated Gene 5 (MDA5). While it has been established that IFN-I is critical for the generation of CD8 T cell responses, the impact of disparate sources and signaling pathways of IFN-I during this process remains poorly understood. To more precisely define the role of IFN-I on the generation of antiviral CD8 T cell responses, we chose to study acute and chronic lymphocytic choriomeningitis virus (LCMV) infections in the mouse. WT, BDCA2-DTR, MDA5−/− as well as various TLR-deficient mice were infected with acute or chronic strains of LCMV. Serum IFN-α, antiviral CD8 T cell responses and viral burden were determined at various time points post-infection. We found that while pDC depletion had an early impact on the IFN-I response, it did not affect CD8 T cell responses. However, MDA5 was the key source of IFN-I required for anti-LCMV CD8 T cell responses. During acute infection, the CD8 T cell response relied on CD4 T cell help in the absence of MDA5, while CD8 T cell exhaustion and persistent infection ensue in the absence of both MDA5 and CD4 T cells. Moreover, we found that chronic LCMV infection rapidly attenuated the IFN-I response while early administration of exogenous IFN-I rescued the CD8 T cell response promoting viral clearance. We conclude that induction of effective antiviral CD8 T cells depends on the timing and magnitude of the IFN-I response. IFN-I production by pDCs is too little and too transient to facilitate CD8 T cell responses to LCMV. The magnitude and duration of MDA5-induced IFN-I is adequate to elicit effective CD8 T cell responses and control infection during acute, but not chronic infection, which replicates more rapidly and impairs both MDA5 and CD4 T cell function.Thus, timely administration of exogenous IFN-I may rescue CD8 T cell functions during human chronic viral infections.

Foxp4 Is Dispensable for T Cell Development, but Required for Robust Recall Responses

Transcription factors regulate T cell fates at every stage of development and differentiation. Members of the Foxp family of forkhead transcription factors are essential for normal T lineage development; Foxp3 is required for T regulatory cell generation and function, and Foxp1 is necessary for generation and maintenance of naïve T cells. Foxp4, an additional member of the Foxp family, is highly homologous to Foxp1 and has been shown to dimerize with other Foxp proteins. We report the initial characterization of Foxp4 in T lymphocytes. Foxp4 is expressed in both thymocytes and peripheral CD4+ and CD8+ T cells. We used a CD4Cre mediated approach to evaluate the cell autonomous role for Foxp4 in murine T lymphocytes. T cell development, peripheral cellularity and cell surface phenotype are normal in the absence of Foxp4. Furthermore, Foxp3+ T regulatory cells develop normally in Foxp4 deficient animals and naïve Foxp4 deficient CD4 T cells can differentiate to inducible T regulatory cells in vitro. In wild-type T cells, expression of Foxp4 increases following activation, but deletion of Foxp4 does not affect T cell proliferative responses or in vitro effector T cell differentiation. In vivo, despite effective control of Toxoplasma gondii and acute lymphocytic choriomeningitis virus infections, effector cytokine production during antigen specific recall responses are reduced in the absence of Foxp4. We conclude that Foxp4 is dispensable for T cell development, but necessary for normal T cell cytokine recall responses to antigen following pathogenic infection.

Role of Interferon Regulatory Factor 7 in T Cell Responses during Acute Lymphocytic Choriomeningitis Virus Infection

Type I interferons (IFNs), predominantly IFN-α and -β, play critical roles in both innate and adaptive immune responses against viral infections. Interferon regulatory factor 7 (IRF7), a key innate immune molecule in the type I IFN signaling pathway, is essential for the type I IFN response to many viruses, including lymphocytic choriomeningitis virus (LCMV). Here, we show that although IRF7 knockout (KO) mice failed to control the replication of LCMV in the early stages of infection, they were capable of clearing LCMV infection. Despite the lack of type I IFN production, IRF7 KO mice generated normal CD4(+) T cell responses, and the expansion of naïve CD8(+) T cells into primary CD8(+) T cells specific for LCMV GP(33-41) was relatively normal. In contrast, the expansion of the LCMV NP(396)-specific CD8(+) T cells was severely impaired in IRF7 KO mice. We demonstrated that this defective CD8(+) T cell response is due neither to an impaired antigen-presenting system nor to any intrinsic role of IRF7 in CD8(+) T cells. The lack of a type I IFN response in IRF7 KO mice did not affect the formation of memory CD8(+) T cells. Thus, the present study provides new insight into the impact of the innate immune system on viral pathogenesis and demonstrates the critical contribution of innate immunity in controlling virus replication in the early stages of infection, which may shape the quality of CD8(+) T cell responses.

Timing and magnitude of type I interferon responses by distinct sensors impact CD8 T cell exhaustion and chronic viral infection.

Type I interferon (IFN-I) promotes antiviral CD8(+)T cell responses, but the contribution of different IFN-I sources and signaling pathways are ill defined. While plasmacytoid dendritic cells (pDCs) produce IFN-I upon TLR stimulation, IFN-I is induced in most cells by helicases like MDA5. Using acute and chronic lymphocytic choriomeningitis virus (LCMV) infection models, we determined that pDCs transiently produce IFN-I that minimally impacts CD8(+)T cell responses and viral persistence. Rather, MDA5 is the key sensor that induces IFN-I required for CD8(+)T cell responses. In the absence of MDA5, CD8(+)T cell responses to acute infection rely on CD4(+)T cell help, and loss of both CD4(+)T cells and MDA5 results in CD8(+)T cell exhaustion and persistent infection. Chronic LCMV infection rapidly attenuates IFN-I responses, but early administration of exogenous IFN-I rescues CD8(+)T cells, promoting viral clearance. Thus, effective antiviral CD8(+)T cell responses depend on the timing and magnitude of IFN-I production.

CD8 T cell memory precursors are found in bone marrow upon activation after acute LCMV infection (105.14)

Abstract The amount and quality of CD8 T cell memory generated in response to an acute infection with an intracellular pathogen is influenced by the signals present in the tissues in which CD8 T cells are activated. Here, we investigated if location dictates the phenotype and functional properties of CD8 T cells responding to acute lymphocytic choriomeningitis virus (LCMV) infection in different lymphoid tissues. First, we show that CD8 T cells isolated 3 days post infection (p.i.) from bone marrow (BM) displayed a memory precursor phenotype, CD62LloCD25loLy6Chi different to the phenotype observed in LCMV-specific CD8 T cells from spleen or peripheral lymph nodes (PLN). Second, we show that T-bet, a T-box transcription factor found predominantly in terminally differentiated effector CD8 T cells, is almost absent in LCMV-specific CD8 T cells from BM in contrast to the high T-bet expression found on LCMV-specific CD8 T cells from PLN and spleen. Differences in T-bet are also detected after acute infection with vesicular stomatitis virus and L. monocytogenes. Finally, we find that CD8 T cells from BM recall better upon secondary challenge when compared to CD8 T cells from spleen or PLN. These findings strongly suggest that CD8 T cell memory precursors can arise in BM early after acute infection with an intracellular pathogen and further investigation is needed to define the environmental signals influencing CD8 T cell memory differentiation.