Type I Interferon Impairs Specific Antibody Responses Early during Establishment of LCMV Infection

Type I interferons induce an epigenetically distinct memory B cell subset in chronic viral infection

Memory B cells (MBCs) are key providers of long-lived immunity against infectious disease, yet in chronic viral infection, they do not produce effective protection. How chronic viral infection disrupts MBC development and whether such changes are reversible remain unknown. Through single-cell (sc)ATAC-seq and scRNA-seq during acute versus chronic lymphocytic choriomeningitis viral infection, we identified a memory subset enriched for interferon (IFN)-stimulated genes (ISGs) during chronic infection that was distinct from the T-bet+ subset normally associated with chronic infection. Blockade of IFNAR-1 early in infection transformed the chromatin landscape of chronic MBCs, decreasing accessibility at ISG-inducing transcription factor binding motifs and inducing phenotypic changes in the dominating MBC subset, with a decrease in the ISG subset and an increase in CD11c+CD80+ cells. However, timing was critical, with MBCs resistant to intervention at 4 weeks post-infection. Together, our research identifies a key mechanism to instruct MBC identity during viral infection.

mRNA COVID-19 vaccine elicits potent adaptive immune response without the persistent inflammation seen in SARS-CoV-2 infection

SARS-CoV-2 infection and vaccination elicit potent immune responses. Our study presents a comprehensive multimodal single-cell dataset of peripheral blood of patients with acute COVID-19 and of healthy volunteers before and after receiving the SARS-CoV-2 mRNA vaccine and booster. We compared host immune responses to the virus and vaccine using transcriptional profiling, coupled with B/T cell receptor repertoire reconstruction. COVID-19 patients displayed an enhanced interferon signature and cytotoxic gene upregulation, absent in vaccine recipients. These findings were validated in an independent dataset. Analysis of B and T cell repertoires revealed that, while the majority of clonal lymphocytes in COVID-19 patients were effector cells, clonal expansion was more evident among circulating memory cells in vaccine recipients. Furthermore, while clonal αβ T cell responses were observed in both COVID-19 patients and vaccine recipients, dramatic expansion of clonal γδT cells was found only in infected individuals. Our dataset enables comparative analyses of immune responses to infection versus vaccination, including clonal B and T cell responses. Integrating our data with publicly available datasets allowed us to validate our findings in larger cohorts. To our knowledge, this is the first dataset to include comprehensive profiling of longitudinal samples from healthy volunteers pre/post SARS-CoV-2 vaccine and booster.

Two Novel Adenovirus Vectors Mediated Differential Antibody Responses via Interferon-α and Natural Killer Cells

Recombinant adenovirus vectors have been widely used in vaccine development. To overcome the preexisting immunity of human adenovirus type 5 (Ad5) in populations, a range of chimpanzee or rare human adenovirus vectors have been generated. However, these novel adenovirus vectors mediate the diverse immune responses in the hosts. In this study, we explored the immune mechanism of differential antibody responses to SARS-CoV-2 S protein in mice immunized by our previously developed two novel simian adenovirus type 23 (Sad23L) and human adenovirus type 49 (Ad49L), and Ad5 vectored COVID-19 vaccines. Sad23L-nCoV-S and Ad5-nCoV-S vaccines induced the low level of interferon-α (IFN-α) and the high level of antigen-specific antibody responses in wild-type and IFN-α/β receptor defective (IFNAR-/-) C57 mice, while Ad49L-nCoV-S vaccine induced the high IFN-α and low antibody responses in C57 mice but the high antibody response in IFNAR-/- mice. In addition, the high antibody response was detected in natural killer (NK) cells-blocked but the low in follicular helper T (TFH) cells -blocked C57 mice immunized with Ad49L-nCoV-S vaccine. These results showed that Ad49L vectored vaccine stimulated IFN-α secretion to activate NK cells, and then reduced the number of TFH cells, generation center (GC) B cells and plasma cells, and subsequently reduced antigen-specific antibody production. The different novel adenovirus vectors could be selected for vaccine development according to the need for either humoral or cellular or both immune protections against a particular disease. IMPORTANCE Novel adenovirus vectors are an important antigen delivery platform for vaccine development. Understanding the immune diversity between different adenoviral vectors is critical to design the proper vaccine against an aim disease. In this study, we described the immune mechanism of Sad23L and Ad49L vectored vaccines for raising the equally high specific T cell response but the different level of specific antibody responses in mice. We found that Ad49L-vectored vaccine initiated the high IFN-α and activated NK cells to inhibit antibody response via downregulating the number of CD4+ TFH cells leading to the decline of GC B cells and plasma cells.

Immunomodulatory Role of Interferons in Viral and Bacterial Infections

Interferons are a group of immunomodulatory substances produced by the human immune system in response to the presence of pathogens, especially during viral and bacterial infections. Their remarkably diverse mechanisms of action help the immune system fight infections by activating hundreds of genes involved in signal transduction pathways. In this review, we focus on discussing the interplay between the IFN system and seven medically important and challenging viruses (herpes simplex virus (HSV), influenza, hepatitis C virus (HCV), lymphocytic choriomeningitis virus (LCMV), human immunodeficiency virus (HIV), Epstein-Barr virus (EBV), and SARS-CoV coronavirus) to highlight the diversity of viral strategies. In addition, the available data also suggest that IFNs play an important role in the course of bacterial infections. Research is currently underway to identify and elucidate the exact role of specific genes and effector pathways in generating the antimicrobial response mediated by IFNs. Despite the numerous studies on the role of interferons in antimicrobial responses, many interdisciplinary studies are still needed to understand and optimize their use in personalized therapeutics.

Functional heterogeneity in the memory B-cell response

Most vaccines induce robust antibody and memory B-cell (MBC) responses that are capable of mediating protective immunity. However, antibody titers wane following vaccination necessitating the administration of booster vaccines to maintain a protective antibody titer. MBCs are stably maintained following vaccination and can rapidly give rise to antibody-secreting cells or undergo further affinity maturation upon antigen re-encounter. Repeated antigen encounter results in the development of MBCs that encode antibodies capable of mediating broadly protective immunity against viruses such as SARS-CoV-2 and influenza. Here, we summarize emerging evidence that MBCs are a heterogeneous population composed of transcriptionally and phenotypically distinct subsets that have discrete roles in mediating protective immunity upon antigen re-encounter and examine the implications of these findings for the development of vaccines capable of eliciting broadly protective immunity.

Plasmodium infection disrupts the T follicular helper cell response to heterologous immunization

Naturally acquired immunity to malaria develops only after many years and repeated exposures, raising the question of whether Plasmodium parasites, the etiological agents of malaria, suppress the ability of dendritic cells (DCs) to activate optimal T cell responses. We demonstrated recently that B cells, rather than DCs, are the principal activators of CD4⁺ T cells in murine malaria. In the present study, we further investigated factors that might prevent DCs from priming Plasmodium-specific T helper cell responses. We found that DCs were significantly less efficient at taking up infected red blood cells (iRBCs) compared to soluble antigen, whereas B cells more readily bound iRBCs. To assess whether DCs retained the capacity to present soluble antigen during malaria, we measured responses to a heterologous protein immunization administered to naïve mice or mice infected with P. chabaudi. Antigen uptake, DC activation, and expansion of immunogen-specific T cells were intact in infected mice, indicating DCs remained functional. However, polarization of the immunogen-specific response was dramatically altered, with a near-complete loss of germinal center T follicular helper cells specific for the immunogen, accompanied by significant reductions in antigen-specific B cells and antibody. Our results indicate that DCs remain competent to activate T cells during Plasmodium infection, but that T cell polarization and humoral responses are severely disrupted. This study provides mechanistic insight into the development of both Plasmodium-specific and heterologous adaptive responses in hosts with malaria.

Type I IFN Receptor Signaling on B Cells Promotes Antibody Responses to Polysaccharide Antigens

We previously reported monophosphoryl lipid A (MPL) and synthetic cord factor trehalose-6,6'-dicorynomycolate (TDCM) significantly increase Ab responses to T cell-independent type 2 Ags (TI-2 Ags) in a manner dependent on B cell-intrinsic TLR4 expression, as well as MyD88 and TRIF proteins. Given the capacity of MPL to drive type I IFN production, we aimed to investigate the extent to which type I IFN receptor (IFNAR) signaling was required for TI-2 responses and adjuvant effects. Using Ifnar1-/- mice and IFNAR1 Ab blockade, we found that IFNAR signaling is required for optimal early B cell activation, expansion, and Ab responses to nonadjuvanted TI-2 Ags, including the pneumococcal vaccine. Further study demonstrated that B cell-intrinsic type I IFN signaling on B cells was essential for normal TI-2 Ab responses. In particular, TI-2 Ag-specific B-1b cell activation and expansion were significantly impaired in Ifnar1-/- mice; moreover, IFNAR1 Ab blockade similarly reduced activation, expansion, and differentiation of IFNAR1-sufficient B-1b cells in Ifnar1-/- recipient mice, indicating that B-1b cell-expressed IFNAR supports TI-2 Ab responses. Consistent with these findings, type I IFN significantly increased the survival of TI-2 Ag-activated B-1b cells ex vivo and promoted plasmablast differentiation. Nonetheless, MPL/TDCM adjuvant effects, which were largely carried out through innate B cells (B-1b and splenic CD23- B cells), were independent of type I IFN signaling. In summary, our study highlights an important role for B-1b cell-expressed IFNAR in promoting responses to nonadjuvanted TI-2 Ags, but it nonetheless demonstrates that adjuvants which support innate B cell responses may bypass this requirement.

Single-cell transcriptome profiling and the use of AID deficient mice reveal that B cell activation combined with antibody class switch recombination and somatic hypermutation do not benefit the control of experimental trypanosomosis

Salivarian trypanosomes are extracellular protozoan parasites causing infections in a wide range of mammalian hosts, with Trypanosoma evansi having the widest geographic distribution, reaching territories far outside Africa and occasionally even Europe. Besides causing the animal diseases, T. evansi can cause atypical Human Trypanosomosis. The success of this parasite is attributed to its capacity to evade and disable the mammalian defense response. To unravel the latter, we applied here for the first time a scRNA-seq analysis on splenocytes from trypanosome infected mice, at two time points during infection, i.e. just after control of the first parasitemia peak (day 14) and a late chronic time point during infection (day 42). This analysis was combined with flow cytometry and ELISA, revealing that T. evansi induces prompt activation of splenic IgM+CD1d+ Marginal Zone and IgMIntIgD+ Follicular B cells, coinciding with an increase in plasma IgG2c Ab levels. Despite the absence of follicles, a rapid accumulation of Aicda+ GC-like B cells followed first parasitemia peak clearance, accompanied by the occurrence of Xbp1+ expressing CD138+ plasma B cells and Tbx21+ atypical CD11c+ memory B cells. Ablation of immature CD93+ bone marrow and Vpreb3+Ly6d+Ighm+ expressing transitional spleen B cells prevented mature peripheral B cell replenishment. Interestingly, AID-/- mice that lack the capacity to mount anti-parasite IgG responses, exhibited a superior defense level against T. evansi infections. Here, elevated natural IgMs were able to exert in vivo and in vitro trypanocidal activity. Hence, we conclude that in immune competent mice, trypanosomosis associated B cell activation and switched IgG production is rapidly induced by T. evansi, facilitating an escape from the detrimental natural IgM killing activity, and resulting in increased host susceptibility. This unique role of IgM and its anti-trypanosome activity are discussed in the context of the dilemma this causes for the future development of anti-trypanosome vaccines.

B cell depletion impairs vaccination-induced CD8+ T cell responses in a type I interferon-dependent manner

OBJECTIVES

The monoclonal anti-CD20 antibody rituximab is frequently applied in the treatment of lymphoma as well as autoimmune diseases and confers efficient depletion of recirculating B cells. Correspondingly, B cell-depleted patients barely mount de novo antibody responses during infections or vaccinations. Therefore, efficient immune responses of B cell-depleted patients largely depend on protective T cell responses.

METHODS

CD8⁺ T cell expansion was studied in rituximab-treated rheumatoid arthritis (RA) patients and B cell-deficient mice on vaccination/infection with different vaccines/pathogens.

RESULTS

Rituximab-treated RA patients vaccinated with Influvac showed reduced expansion of influenza-specific CD8⁺ T cells when compared with healthy controls. Moreover, B cell-deficient JHT mice infected with mouse-adapted Influenza or modified vaccinia virus Ankara showed less vigorous expansion of virus-specific CD8⁺ T cells than wild type mice. Of note, JHT mice do not have an intrinsic impairment of CD8⁺ T cell expansion, since infection with vaccinia virus induced similar T cell expansion in JHT and wild type mice. Direct type I interferon receptor signalling of B cells was necessary to induce several chemokines in B cells and to support T cell help by enhancing the expression of MHC-I.

CONCLUSIONS

Depending on the stimulus, B cells can modulate CD8⁺ T cell responses. Thus, B cell depletion causes a deficiency of de novo antibody responses and affects the efficacy of cellular response including cytotoxic T cells. The choice of the appropriate vaccine to vaccinate B cell-depleted patients has to be re-evaluated in order to efficiently induce protective CD8⁺ T cell responses.

B cell intrinsic expression of IFNλ receptor suppresses the acute humoral immune response to experimental blood-stage malaria

Antibodies play a critical protective role in the host response to blood-stage malaria infection. The role of cytokines in shaping the antibody response to blood-stage malaria is unclear. Interferon lambda (IFNλ), a type III interferon, is a cytokine produced early during blood-stage malaria infection that has an unknown physiological role during malaria infection. We demonstrate that B cell-intrinsic IFNλ signals suppress the acute antibody response, acute plasmablast response, and impede acute parasite clearance during a primary blood-stage malaria infection. Our findings demonstrate a previously unappreciated role for B cell intrinsic IFNλ-signaling in the initiation of the humoral immune response in the host response to experimental malaria.

Dysregulation of humoral immunity in chronic infection

Chronic viral infections disrupt the ability of the humoral immune response to produce neutralizing antibody or form effective immune memory, preventing viral clearance and making vaccine design difficult. Multiple components of the B-cell response are affected by pathogens that are not cleared from the host. Changes in the microenvironment shift production of B cells to short-lived plasma cells early in the response. Polyclonal B cells are recruited into both the plasma cell and germinal center compartments, inhibiting the formation of a targeted, high-affinity response. Finally, memory B cells shift toward an "atypical" phenotype, which may in turn result in changes to the functional properties of this population. While similar properties of B-cell dysregulation have been described across different types of persistent infections, key questions about the underlying mechanisms remain. This review will discuss the recent advances in this field, as well as highlight the critical questions about the interplay between viral load, microenvironment, the polyclonal response and atypical memory B cells that are yet to be answered. Design of new preventative treatments will rely on identifying the extrinsic and intrinsic modulators that push B cells toward an ineffective response, and thus identify new ways to guide them back onto the best path for clearance of virus and formation of effective immune memory.

Chronic Lymphocytic Choriomeningitis Infection Causes Susceptibility to Mousepox and Impairs Natural Killer Cell Maturation and Function

Chronic viral infections. like those of humans with cytomegalovirus, human immunodeficiency virus (even when under antiretroviral therapy), and hepatitis C virus or those of mice with lymphocytic choriomeningitis virus (LCMV) clone 13 (CL13), result in immune dysfunction that predisposes the host to severe infections with unrelated pathogens. It is known that C57BL/6 (B6) mice are resistant to mousepox, a lethal disease caused by the orthopoxvirus ectromelia virus (ECTV), and that this resistance requires natural killer (NK) cells and other immune cells. We show that most B6 mice chronically infected with CL13 succumb to mousepox but that most of those that recovered from acute infection with the LCMV Armstrong (Arm) strain survive. We also show that B6 mice chronically infected with CL13 and those that recovered from Arm infection have a reduced frequency and a reduced number of NK cells. However, at steady state, NK cells in mice that have recovered from Arm infection mature normally and, in response to ECTV, get activated, become more mature, proliferate, and increase their cytotoxicity in vivo Conversely, in mice chronically infected with CL13, NK cells are immature and residually activated, and following ECTV infection, they do not mature, proliferate, or increase their cytotoxicity. Given the well-established importance of NK cells in resistance to mousepox, these data suggest that the NK cell dysfunction caused by CL13 persistence may contribute to the susceptibility of CL13-infected mice to mousepox. Whether chronic infections similarly affect NK cells in humans should be explored.IMPORTANCE Infection of adult mice with the clone 13 (CL13) strain of lymphocytic choriomeningitis virus (LCMV) is extensively used as a model of chronic infection. In this paper, we show that mice chronically infected with CL13 succumb to challenge with ectromelia virus (ECTV; the agent of mousepox) and that natural killer (NK) cells in CL13-infected mice are reduced in numbers and have an immature and partially activated phenotype but do respond to ECTV. These data may provide additional clues why humans chronically infected with certain pathogens are less resistant to viral diseases.

USP18 is a significant driver of memory CD4 T-cell reduced viability caused by type I IFN signaling during primary HIV-1 infection

The loss of Memory CD4 T-cells (Mem) is a major hallmark of HIV-1 immuno-pathogenesis and occurs early during the first months of primary infection. A lot of effort has been put into understanding the molecular mechanisms behind this loss, yet they still have not been fully identified. In this study, we unveil the unreported role of USP18 in the deleterious effects of sustained type I IFN signaling on Mem, including HIV-1-specific CD4 T-cells. We find that interfering with IFN-I signaling pathway in infected patients, notably by targeting the interferon-stimulated gene USP18, resulted in reduced PTEN expression similar to those observed in uninfected control donors. We show that AKT activation in response to cytokine treatment, T-cell receptor (TcR) triggering, as well as HIV-1 Gag stimulation was significantly improved in infected patients when PTEN or USP18 were inhibited. Finally, our data demonstrate that higher USP18 in Mem from infected patients prevent proper cell survival and long-lasting maintenance in an AKT-dependent manner. Altogether, we establish a direct role for type I IFN/USP18 signaling in the maintenance of total and virus-specific Mem and provide a new mechanism for the reduced survival of these populations during primary HIV-1 infection.

In this study, we expend our knowledge of how type I interferons (IFN-I) leads to memory CD4 T-cell defective survival by unveiling the molecular mechanism behind such impairments, placing USP18 at its center. Our data further deciphers the specific USP18-related mechanism that is responsible for such impairments by implicating AKT inhibition in a PTEN-dependent manner. Our findings also point to a potential use of neutralizing anti-interferon α/β receptor antibodies to rescue the defective memory CD4 T-cell survival during HIV-1 infection, even in HIV-1 specific CD4 T-cell. To conclude, our findings provide the characterization of the molecular pathway leading to disturbances caused by sustained IFN-I signaling which occurs early during primary HIV-1 infection, complementing current knowledge which placed sustained IFN-I signaling as detrimental to the host during this infection.

Hypergammaglobulinemia sustains the development of regulatory responses during chronic Leishmania donovani infection in mice

Visceral leishmaniasis, a chronic, potentially fatal disease, is characterized by high production of low-affinity antibodies. In humans, hypergammaglobulinemia is prediction of disease progression. Nevertheless, the contribution of hypermutated and/or class-switched immunoglobulins to disease pathogenesis has never been studied. Using Aicda^-/- mice and the experimental model of Leishmania donovani infection, we demonstrate that the absence of hypermutated and/or class-switched antibodies was associated with increased resistance to disease, stronger protective Th1 responses, and a lower frequency of regulatory IFNγ⁺ IL-10⁺ CD4 T cells. Interestingly, stronger Th1 responses and the absence of IFNγ⁺ IL-10⁺ CD4 T cells during chronic infection in infected Aicda^-/- mice were not caused by a T-cell intrinsic effect of AID, but by changes in the cytokine environment during chronic disease. Indeed TNF, IL-10 and IFN-ß expressions were only upregulated in the presence of hypermutated, class-switched antibodies and hypergammaglobulinemia at later stages of infection. Taken together, our results suggest that hypergammaglobulinemia sustains inhibitory responses during chronic visceral leishmaniasis.

Complexities of Type I Interferon Biology: Lessons from LCMV

Over the past decades, infection of mice with lymphocytic choriomeningitis virus (LCMV) has provided an invaluable insight into our understanding of immune responses to viruses. In particular, this model has clarified the central roles that type I interferons play in initiating and regulating host responses. The use of different strains of LCMV and routes of infection has allowed us to understand how type I interferons are critical in controlling virus replication and fostering effective antiviral immunity, but also how they promote virus persistence and functional exhaustion of the immune response. Accordingly, these discoveries have formed the foundation for the development of novel treatments for acute and chronic viral infections and even extend into the management of malignant tumors. Here we review the fundamental insights into type I interferon biology gained using LCMV as a model and how the diversity of LCMV strains, dose, and route of administration have been used to dissect the molecular mechanisms underpinning acute versus persistent infection. We also identify gaps in the knowledge regarding LCMV regulation of antiviral immunity. Due to its unique properties, LCMV will continue to remain a vital part of the immunologists' toolbox.

DNA prime/MVTT boost regimen with HIV-1 mosaic Gag enhances the potency of antigen-specific immune responses

HIV-1 diversity and latent reservoir are the major challenges for the development of an effective AIDS vaccine. It is well indicated that Gag-specific CD8⁺ T cells serve as the dominant host immune surveillance for HIV-1 control, but it still remains a challenge for vaccine design to induce broader and stronger cytotoxic T cell immunity against the virus. Genetic variation of the HIV-1 gag gene across different clades is one of the reasons for the reduction of antigenic epitope coverage. Here, we report an immunization strategy with heterologous vaccines expressing a mosaic Gag antigen aimed to increase antigenic breadth against a wider spectrum of HIV-1 strains. Priming using a DNA vaccine via in vivo electroporation, followed by boosting with a live replication-competent modified vaccinia TianTan (MVTT) vectored vaccine, elicited greater and broader protective Gag-specific immune responses in mice. Compared to DNA or MVTT homologous immunization, the heterologous DNA/MVTT vaccination resulted in higher frequencies of broadly reactive, Gag-specific, polyfunctional, long-lived cytotoxic CD8⁺ T cells, as well as increased anti-Gag antibody titer. Importantly, the DNA/MVTT heterologous vaccination induced protection against EcoHIV and mesothelioma AB1-Gag challenges. In summary, the stronger protective Gag-specific immunity induced by the heterologous regimen using two safe vectors shows promise for further development to enhance anti-HIV-1 immunity. Our study has important implications for immunogen design and the development of an effective HIV-1 heterologous vaccination strategy.

Sustained IFN-I Expression during Established Persistent Viral Infection: A "Bad Seed" for Protective Immunity

Type I interferons (IFN-I) are one of the primary immune defenses against viruses. Similar to all other molecular mechanisms that are central to eliciting protective immune responses, IFN-I expression is subject to homeostatic controls that regulate cytokine levels upon clearing the infection. However, in the case of established persistent viral infection, sustained elevation of IFN-I expression bears deleterious effects to the host and is today considered as the major driver of inflammation and immunosuppression. In fact, numerous emerging studies place sustained IFN-I expression as a common nexus in the pathogenesis of multiple chronic diseases including persistent infections with the human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus (SIV), as well as the rodent-borne lymphocytic choriomeningitis virus clone 13 (LCMV clone 13). In this review, we highlight recent studies illustrating the molecular dysregulation and resultant cellular dysfunction in both innate and adaptive immune responses driven by sustained IFN-I expression. Here, we place particular emphasis on the efficacy of IFN-I receptor (IFNR) blockade towards improving immune responses against viral infections given the emerging therapeutic approach of blocking IFNR using neutralizing antibodies (Abs) in chronically infected patients.

Alpha/beta interferon receptor deficiency in mice significantly enhances susceptibility of the animals to pseudorabies virus infection

Pseudorabies virus, one of the neurotropic viruses, can infect numerous mammals. In particular, pseudorabies virus infection of swine occurs worldwide, and is a major threat to swine industry. However, the mechanism underlying the interaction between pseudorabies virus and host innate immune system is not fully understood. Here, we investigated the involvement of interferon α/β (IFN-α/β) receptor (IFNAR) in the pathogenesis of pseudorabies virus in a mouse model. The results showed that IFNAR-deficient (IFNAR^-/-) mice were highly susceptible to the virus infection, as evidenced by markedly reduced survival rate of infected animals and increased viral replication. The expression of IFN-α/β and relevant interferon-stimulated genes in IFNAR^-/- mice was significantly lower than that in wild-type (WT) littermates after the viral infection. Moreover, in response to the virus challenge, IFNAR^-/- mice displayed elevated levels of inflammatory cytokines including interleukin 6 (IL-6) and IL-1β, and IFNAR^-/- cells showed increased phosphorylation of STAT3. Collectively, these data reveal that the IFNAR^-/- mice are more sensitive to pseudorabies virus infection than WT animals, and excessive IL-6/STAT3 response in IFNAR^-/- mice may contribute to the pathogenesis. Our findings suggest that type I IFNs/IFNAR-dependent homeostatic control of the innate immunity is required for host defense against pseudorabies virus infection.

Type-I Interferon Responses: From Friend to Foe in the Battle against Chronic Viral Infection

Type I interferons (IFN-I) have long been heralded as key contributors to effective antiviral responses. More widely understood in the context of acute viral infection, the role of this pleiotropic cytokine has been characterized as triggering antiviral states in cells and potentiating adaptive immune responses. Upon induction in the innate immune response, IFN-I triggers the expression of interferon-stimulated genes (ISGs), which upregulate the effector function of immune cells (e.g., dendritic cells, B cells, and T cells) toward successful resolution of infections. However, emerging lines of evidence reveal that viral persistence in the course of chronic infections could be driven by deleterious immunomodulatory effects upon sustained IFN-I expression. In this setting, elevation of IFN-I and ISGs is directly correlated to viral persistence and elevated viral loads. It is important to note that the correlation among IFN-I expression, ISGs, and viral persistence may be a cause or effect of chronic infection and this is an important distinction to make toward establishing the dichotomous nature of IFN-I responses. The aim of this mini review is to (i) summarize the interaction between IFN-I and downstream effector responses and therefore (ii) delineate the function of this cytokine on positive and negative immunoregulation in chronic infection. This is a significant consideration given the current therapeutic administration of IFN-I in chronic viral infections whose therapeutic significance is projected to continue despite emergence of increasingly efficacious antiviral regimens. Furthermore, elucidation of the interplay between virus and the antiviral response in the context of IFN-I will elucidate avenues toward more effective therapeutic and prophylactic measures against chronic viral infections.