Chelsea L. Edwards

Type I IFN signaling in CD8– DCs impairs Th1-dependent malaria immunity

Many pathogens, including viruses, bacteria, and protozoan parasites, suppress cellular immune responses through activation of type I IFN signaling. Recent evidence suggests that immune suppression and susceptibility to the malaria parasite, Plasmodium, is mediated by type I IFN; however, it is unclear how type I IFN suppresses immunity to blood-stage Plasmodium parasites. During experimental severe malaria, CD4+ Th cell responses are suppressed, and conventional DC (cDC) function is curtailed through unknown mechanisms. Here, we tested the hypothesis that type I IFN signaling directly impairs cDC function during Plasmodium infection in mice. Using cDC-specific IFNAR1-deficient mice, and mixed BM chimeras, we found that type I IFN signaling directly affects cDC function, limiting the ability of cDCs to prime IFN-γ-producing Th1 cells. Although type I IFN signaling modulated all subsets of splenic cDCs, CD8- cDCs were especially susceptible, exhibiting reduced phagocytic and Th1-promoting properties in response to type I IFNs. Additionally, rapid and systemic IFN-α production in response to Plasmodium infection required type I IFN signaling in cDCs themselves, revealing their contribution to a feed-forward cytokine-signaling loop. Together, these data suggest abrogation of type I IFN signaling in CD8- splenic cDCs as an approach for enhancing Th1 responses against Plasmodium and other type I IFN-inducing pathogens.

Blimp-1-Dependent IL-10 Production by Tr1 Cells Regulates TNF-Mediated Tissue Pathology

Tumor necrosis factor (TNF) is critical for controlling many intracellular infections, but can also contribute to inflammation. It can promote the destruction of important cell populations and trigger dramatic tissue remodeling following establishment of chronic disease. Therefore, a better understanding of TNF regulation is needed to allow pathogen control without causing or exacerbating disease. IL-10 is an important regulatory cytokine with broad activities, including the suppression of inflammation. IL-10 is produced by different immune cells; however, its regulation and function appears to be cell-specific and context-dependent. Recently, IL-10 produced by Th1 (Tr1) cells was shown to protect host tissues from inflammation induced following infection. Here, we identify a novel pathway of TNF regulation by IL-10 from Tr1 cells during parasitic infection. We report elevated Blimp-1 mRNA levels in CD4+ T cells from visceral leishmaniasis (VL) patients, and demonstrate IL-12 was essential for Blimp-1 expression and Tr1 cell development in experimental VL. Critically, we show Blimp-1-dependent IL-10 production by Tr1 cells prevents tissue damage caused by IFNγ-dependent TNF production. Therefore, we identify Blimp-1-dependent IL-10 produced by Tr1 cells as a key regulator of TNF-mediated pathology and identify Tr1 cells as potential therapeutic tools to control inflammation.

Type I Interferons Regulate Immune Responses in Humans with Blood-Stage Plasmodium falciparum Infection

Summary The development of immunoregulatory networks is important to prevent disease. However, these same networks allow pathogens to persist and reduce vaccine efficacy. Here, we identify type I interferons (IFNs) as important regulators in developing anti-parasitic immunity in healthy volunteers infected for the first time with Plasmodium falciparum. Type I IFNs suppressed innate immune cell function and parasitic-specific CD4+ T cell IFNγ production, and they promoted the development of parasitic-specific IL-10-producing Th1 (Tr1) cells. Type I IFN-dependent, parasite-specific IL-10 production was also observed in P. falciparum malaria patients in the field following chemoprophylaxis. Parasite-induced IL-10 suppressed inflammatory cytokine production, and IL-10 levels after drug treatment were positively associated with parasite burdens before anti-parasitic drug administration. These findings have important implications for understanding the development of host immune responses following blood-stage P. falciparum infection, and they identify type I IFNs and related signaling pathways as potential targets for therapies or vaccine efficacy improvement.

Spatiotemporal requirements for IRF7 in mediating type I IFN-dependent susceptibility to blood-stage Plasmodium infection

Type I IFN signaling suppresses splenic T helper 1 (Th1) responses during blood‐stage Plasmodium berghei ANKA (PbA) infection in mice, and is crucial for mediating tissue accumulation of parasites and fatal cerebral symptoms via mechanisms that remain to be fully characterized. Interferon regulatory factor 7 (IRF7) is considered to be a master regulator of type I IFN responses. Here, we assessed IRF7 for its roles during lethal PbA infection and nonlethal Plasmodium chabaudi chabaudi AS (PcAS) infection as two distinct models of blood‐stage malaria. We found that IRF7 was not essential for tissue accumulation of parasites, cerebral symptoms, or brain pathology. Using timed administration of anti‐IFNAR1 mAb, we show that late IFNAR1 signaling promotes fatal disease via IRF7‐independent mechanisms. Despite this, IRF7 significantly impaired early splenic Th1 responses and limited control of parasitemia during PbA infection. Finally, IRF7 also suppressed antiparasitic immunity and Th1 responses during nonlethal PcAS infection. Together, our data support a model in which IRF7 suppresses antiparasitic immunity in the spleen, while IFNAR1‐mediated, but IRF7‐independent, signaling contributes to pathology in the brain during experimental blood‐stage malaria.

Combined Immune Therapy for the Treatment of Visceral Leishmaniasis.

Chronic disease caused by infections, cancer or autoimmunity can result in profound immune suppression. Immunoregulatory networks are established to prevent tissue damage caused by inflammation. Although these immune checkpoints preserve tissue function, they allow pathogens and tumors to persist, and even expand. Immune checkpoint blockade has recently been successfully employed to treat cancer. This strategy modulates immunoregulatory mechanisms to allow host immune cells to kill or control tumors. However, the utility of this approach for controlling established infections has not been extensively investigated. Here, we examined the potential of modulating glucocorticoid-induced TNF receptor-related protein (GITR) on T cells to improve anti-parasitic immunity in blood and spleen tissue from visceral leishmaniasis (VL) patients infected with Leishmania donovani. We found little effect on parasite growth or parasite-specific IFNγ production. However, this treatment reversed the improved anti-parasitic immunity achieved by IL-10 signaling blockade. Further investigations using an experimental VL model caused by infection of C57BL/6 mice with L. donovani revealed that this negative effect was prominent in the liver, dependent on parasite burden and associated with an accumulation of Th1 cells expressing high levels of KLRG-1. Nevertheless, combined anti-IL-10 and anti-GITR mAb treatment could improve anti-parasitic immunity when used with sub-optimal doses of anti-parasitic drug. However, additional studies with VL patient samples indicated that targeting GITR had no overall benefit over IL-10 signaling blockade alone at improving anti-parasitic immune responses, even with drug treatment cover. These findings identify several important factors that influence the effectiveness of immune modulation, including parasite burden, target tissue and the use of anti-parasitic drug. Critically, these results also highlight potential negative effects of combining different immune modulation strategies.

IL-17A–Producing γδ T Cells Suppress Early Control of Parasite Growth by Monocytes in the Liver

Intracellular infections, such as those caused by the protozoan parasite Leishmania donovani, a causative agent of visceral leishmaniasis (VL), require a potent host proinflammatory response for control. IL-17 has emerged as an important proinflammatory cytokine required for limiting growth of both extracellular and intracellular pathogens. However, there are conflicting reports on the exact roles for IL-17 during parasitic infections and limited knowledge about cellular sources and the immune pathways it modulates. We examined the role of IL-17 in an experimental model of VL caused by infection of C57BL/6 mice with L. donovani and identified an early suppressive role for IL-17 in the liver that limited control of parasite growth. IL-17–producing γδ T cells recruited to the liver in the first week of infection were the critical source of IL-17 in this model, and CCR2+ inflammatory monocytes were an important target for the suppressive effects of IL-17. Improved parasite control was independent of NO generation, but associated with maintenance of superoxide dismutase mRNA expression in the absence of IL-17 in the liver. Thus, we have identified a novel inhibitory function for IL-17 in parasitic infection, and our results demonstrate important interactions among γδ T cells, monocytes, and infected macrophages in the liver that can determine the outcome of parasitic infection.

Correction: Blimp-1-Dependent IL-10 Production by Tr1 Cells Regulates TNF-Mediated Tissue Pathology.

The following information is missing from the Funding section: This study was supported by funding from the National Institute of Allergy and Infectious Diseases, National Institutes of Health Tropical Medicine Research Centre Program, Grant ID No: 2P50AI7434.

Coinfection with Blood-Stage Plasmodium Promotes Systemic Type I Interferon Production during Pneumovirus Infection but Impairs Inflammation and Viral Control in the Lung

ABSTRACT Acute lower respiratory tract infections (ALRTI) are the leading cause of global childhood mortality, with human respiratory syncytial virus (hRSV) being a major cause of viral ALRTI in young children worldwide. In sub-Saharan Africa, many young children experience severe illnesses due to hRSV or Plasmodium infection. Although the incidence of malaria in this region has decreased in recent years, there remains a significant opportunity for coinfection. Recent data show that febrile young children infected with Plasmodium are often concurrently infected with respiratory viral pathogens but are less likely to suffer from pneumonia than are non-Plasmodium-infected children. Here, we hypothesized that blood-stage Plasmodium infection modulates pulmonary inflammatory responses to a viral pathogen but does not aid its control in the lung. To test this, we established a novel coinfection model in which mice were simultaneously infected with pneumovirus of mice (PVM) (to model hRSV) and blood-stage Plasmodium chabaudi chabaudi AS (PcAS) parasites. We found that PcAS infection was unaffected by coinfection with PVM. In contrast, PVM-associated weight loss, pulmonary cytokine responses, and immune cell recruitment to the airways were substantially reduced by coinfection with PcAS. Importantly, PcAS coinfection facilitated greater viral dissemination throughout the lung. Although Plasmodium coinfection induced low levels of systemic interleukin-10 (IL-10), this regulatory cytokine played no role in the modulation of lung inflammation or viral dissemination. Instead, we found that Plasmodium coinfection drove an early systemic beta interferon (IFN-β) response. Therefore, we propose that blood-stage Plasmodium coinfection may exacerbate viral dissemination and impair inflammation in the lung by dysregulating type I IFN-dependent responses to respiratory viruses.

IFN Regulatory Factor 3 Balances Th1 and T Follicular Helper Immunity during Nonlethal Blood-Stage Plasmodium Infection

Differentiation of CD4+ Th cells is critical for immunity to malaria. Several innate immune signaling pathways have been implicated in the detection of blood-stage Plasmodium parasites, yet their influence over Th cell immunity remains unclear. In this study, we used Plasmodium-reactive TCR transgenic CD4+ T cells, termed PbTII cells, during nonlethal P. chabaudi chabaudi AS and P. yoelii 17XNL infection in mice, to examine Th cell development in vivo. We found no role for caspase1/11, stimulator of IFN genes, or mitochondrial antiviral-signaling protein, and only modest roles for MyD88 and TRIF-dependent signaling in controlling PbTII cell expansion. In contrast, IFN regulatory factor 3 (IRF3) was important for supporting PbTII expansion, promoting Th1 over T follicular helper (Tfh) differentiation, and controlling parasites during the first week of infection. IRF3 was not required for early priming by conventional dendritic cells, but was essential for promoting CXCL9 and MHC class II expression by inflammatory monocytes that supported PbTII responses in the spleen. Thereafter, IRF3-deficiency boosted Tfh responses, germinal center B cell and memory B cell development, parasite-specific Ab production, and resolution of infection. We also noted a B cell–intrinsic role for IRF3 in regulating humoral immune responses. Thus, we revealed roles for IRF3 in balancing Th1- and Tfh-dependent immunity during nonlethal infection with blood-stage Plasmodium parasites.

Rapid loss of group 1 innate lymphoid cells during blood stage Plasmodium infection

Innate lymphoid cells (ILCs) share many characteristics with CD4+ T cells, and group 1 ILCs share a requirement for T‐bet and the ability to produce IFNγ with T helper 1 (Th1) cells. Given this similarity, and the importance of Th1 cells for protection against intracellular protozoan parasites, we aimed to characterise the role of group 1 ILCs during Plasmodium infection.