Targeted disruption of the interferon-gamma receptor 2 gene results in severe immune defects in mice

Endothelial Erg Regulates Expression of Pulmonary Lymphatic Junctional and Inflammation Genes in Mouse Lungs Impacting Lymphatic Transport

The ETS transcription factor ERG is a master regulator of endothelial gene specificity and highly enriched in the capillary, vein, and arterial endothelial cells. ERG expression is critical for endothelial barrier function, permeability, and vascular inflammation. A dysfunctional vascular endothelial ERG has been shown to impair lung capillary homeostasis, contributing to pulmonary fibrosis as previously observed in IPF lungs. Our preliminary observations indicate that lymphatic endothelial cells (LEC) in the human IPF lung also lack ERG. To understand the role of ERG in pulmonary LECs, we developed LEC-specific inducible Erg-CKO and Erg-GFP-CKO conditional knockout (CKO) mice under Prox1 promoter. Whole lung microarray analysis, flow cytometry, and qPCR confirmed an inflammatory and pro-lymphvasculogenic predisposition in Erg-CKO lung. FITC-Dextran tracing analysis showed an increased pulmonary interstitial lymphatic fluid transport from the lung to the axial lymph node. Single-cell transcriptomics confirmed that genes associated with cell junction integrity were downregulated in Erg-CKO pre-collector and collector LECs. Integrating Single-cell transcriptomics and CellChatDB helped identify LEC specific communication pathways contributing to pulmonary inflammation, trans-endothelial migration, inflammation, and Endo-MT in Erg-CKO lung. Our findings suggest that downregulation of lymphatic Erg crucially affects LEC function, LEC permeability, pulmonary LEC communication pathways and lymphatic transcriptomics.

The immune-adjunctive potential of recombinant LAB vector expressing murine IFNλ3 (MuIFNλ3) against Type A Influenza Virus (IAV) infection

BACKGROUND

The conventional means of controlling the recurring pandemics of Type A Influenza Virus (IAV) infections remain challenging primarily because of its high mutability and increasing drug resistance. As an alternative to control IAV infections, the prophylactic use of cytokines to drive immune activation of multiple antiviral host factors has been progressively recognized. Among them, Type III Interferons (IFNs) exhibit a pivotal role in inducing potent antiviral host responses by upregulating the expression of several antiviral genes, including the Interferon-Stimulated Genes (ISGs) that specifically target the virus replication machinery. To harness the immuno-adjunctive potential, we examined whether pre-treatment of IFNλ3, a Type III IFN, can activate antiviral host responses against IAV infections.

METHODS

In the present study, we bioengineered a food-grade lactic acid-producing bacteria (LAB), Lactococcus lactis (L. lactis), to express and secrete functional murine IFNλ3 (MuIFNλ3) protein in the extracellular milieu. To test the immune-protective potential of MuIFNλ3 secreted by recombinant L. lactis (rL. lactis), we used murine B16F10 cells as an in vitro model while mice (BALB/c) were used for in vivo studies.

RESULTS

Our study demonstrated that priming with MuIFNλ3 secreted by rL. lactis could upregulate the expression of several antiviral genes, including Interferon Regulatory Factors (IRFs) and ISGs, without exacerbated pulmonary or intestinal inflammatory responses. Moreover, we also showed that pre-treatment of B16F10 cells with MuIFNλ3 can confer marked immune protection against mice-adapted influenza virus, A/PR/8/1934 (H1N1) infection.

CONCLUSION

Since the primary target for IAV infections is the upper respiratory and gastrointestinal tract, immune activation without affecting the tissue homeostasis suggests the immune-adjunctive potential of IFNλ3 against IAV infections.

A single dominant locus restricts retrovirus replication in YBR/Ei mice

Differential responses to viral infections are influenced by the genetic makeup of the host. Studies of resistance to retroviruses in human populations are complicated due to the inability to conduct proof-of-principle studies. Inbred mouse lines, which have a range of susceptible phenotypes to retroviruses, are an ideal tool to identify and characterize mechanisms of resistance and define their genetic underpinnings. YBR/Ei mice become infected with Mouse Mammary Tumor Virus, a mucosally transmitted murine retrovirus, but eliminate the virus from their pedigrees. Virus elimination correlates with a lack of virus-specific neonatal oral tolerance, which is a major mechanism for blocking the anti-virus response in susceptible mice. Virus control is unrelated to virus-neutralizing antibodies, cytotoxic CD8+ T cells, NK cells, and NK T cells, which are the best characterized mechanisms of resistance to retroviruses. We identified a single, dominant locus that controls the resistance mechanism, which we provisionally named attenuation of virus titers (Avt) and mapped to the distal region of chromosome 18. IMPORTANCE Elucidation of the mechanism that mediates resistance to retroviruses is of fundamental importance to human health, as it will ultimately lead to knowledge of the genetic differences among individuals in susceptibility to microbial infections.

Interferon-induced GTPases orchestrate host cell-autonomous defence against bacterial pathogens

Interferon (IFN)-induced guanosine triphosphate hydrolysing enzymes (GTPases) have been identified as cornerstones of IFN-mediated cell-autonomous defence. Upon IFN stimulation, these GTPases are highly expressed in various host cells, where they orchestrate anti-microbial activities against a diverse range of pathogens such as bacteria, protozoan and viruses. IFN-induced GTPases have been shown to interact with various host pathways and proteins mediating pathogen control via inflammasome activation, destabilising pathogen compartments and membranes, orchestrating destruction via autophagy and the production of reactive oxygen species as well as inhibiting pathogen mobility. In this mini-review, we provide an update on how the IFN-induced GTPases target pathogens and mediate host defence, emphasising findings on protection against bacterial pathogens.

Myeloid cell responsiveness to interferon-gamma is sufficient for initial resistance to Listeria monocytogenes

The type II interferon (IFNγ) promotes resistance to intracellular pathogens. Most immune and somatic cells also express the IFNγ receptor (IFNGR) and respond to IFNγ. While myeloid cell have been implicated as important targets of IFNγ, it remains unknown if IFNγ signaling to myeloid cell types suffices for resistance to infection. Here, we addressed this question by generating mice in which IFNGR1 is selectively expressed by myeloid cells. These “MSGR1” (myeloid selective IFNGR1) mice express an epitope-tagged Ifngr1 transgene (fGR1) from the myeloid-specific c-fms promoter in a background lacking endogenous Ifngr1. IFNGR staining was selectively observed on myeloid cells in the MSGR1 mice and correlated with responsiveness of these cells to IFNγ. During systemic infection by the bacterium Listeria monocytogenes, activation marker staining was comparable on monocytes from MSGR1 and control B6 mice. Bacterial burdens and survival were also equivalent in MSGR1 and wildtype B6 animals at a timepoint when B6.Ifngr1^−/− mice began to succumb. These data confirm that activation of inflammatory monocytes and neutrophils is a key mechanism by which IFNγ promotes innate anti-bacterial immunity and suggest that IFNγ targeting of myeloid cells is largely sufficient to mediate protection against systemic L. monocytogenes.

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Expression of IFNGR1 is restricted to monocytes and neutrophils in “MSGR1” (myeloid selective IFNGR1) mice.

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Myeloid cells from MSGR1 mice are responsive to IFNγ and show elevated activation compared to cells from B6.Ifngr1^−/− mice.

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MSGR1 myeloid cells respond to Listeria monocytogenes infection and promote early resistance.

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IFNγ stimulation of myeloid cells can thus protect against infection independent of effects on other hematopoietic and non-hematopoietic cell populations.

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Particularly in female mice, IFNγ stimulation of non-myeloid cells may also contribute to improved survival.

Direct Antiviral Mechanisms of Interferon-Gamma

Interferon-gamma (IFNG) is a pleiotropic cytokine that modulates both innate and adaptive immune networks; it is the most potent activator of macrophages and a signature cytokine of activated T lymphocytes. Though IFNG is now appreciated to have a multitude of roles in immune modulation and broad-spectrum pathogen defense, it was originally discovered, and named, as a secretory factor that interferes with viral replication. In contrast to the prototypical type I interferons produced by any cells upon viral infection, only specific subsets of immune cells can produce IFNG upon infection or stimulation with antigen or mitogen. Still, virtually all cells can respond to both types of interferons. This makes IFNG a versatile anti-microbial cytokine and also gives it a unique position in the antiviral defense system. The goal of this review is to highlight the direct antiviral mechanisms of IFNG, thereby clarifying its antiviral function in the effective control of viral infections.

T cells presenting viral antigens or autoantigens induce cytotoxic T cell anergy

In the course of modeling the naturally occurring tumor immunity seen in patients with paraneoplastic cerebellar degeneration (PCD), we discovered an unexpectedly high threshold for breaking CD8+ cytotoxic T cell (CTL) tolerance to the PCD autoantigen, CDR2. While CDR2 expression was previously found to be strictly restricted to immune-privileged cells (cerebellum, testes, and tumors), unexpectedly we have found that T cells also express CDR2. This expression underlies inhibition of CTL activation; CTLs that respond to epithelial cells expressing CDR2 fail to respond to T cells expressing CDR2. This was a general phenomenon, as T cells presenting influenza (flu) antigen also fail to activate otherwise potent flu-specific CTLs either in vitro or in vivo. Moreover, transfer of flu peptide-pulsed T cells into flu-infected mice inhibits endogenous flu-specific CTLs. Our finding that T cells serve as a site of immune privilege, inhibiting effector CTL function, uncovers an autorepressive loop with general biologic and clinical relevance.

TNF signalling drives expansion of bone marrow CD4+ T cells responsible for HSC exhaustion in experimental visceral leishmaniasis

Visceral leishmaniasis is associated with significant changes in hematological function but the mechanisms underlying these changes are largely unknown. In contrast to naïve mice, where most long-term hematopoietic stem cells (LT-HSCs; LSK CD150⁺ CD34^- CD48^- cells) in bone marrow (BM) are quiescent, we found that during Leishmania donovani infection most LT-HSCs had entered cell cycle. Loss of quiescence correlated with a reduced self-renewal capacity and functional exhaustion, as measured by serial transfer. Quiescent LT-HSCs were maintained in infected RAG2 KO mice, but lost following adoptive transfer of IFNγ-sufficient but not IFNγ-deficient CD4⁺ T cells. Using mixed BM chimeras, we established that IFNγ and TNF signalling pathways converge at the level of CD4⁺ T cells. Critically, intrinsic TNF signalling is required for the expansion and/or differentiation of pathogenic IFNγ⁺CD4⁺ T cells that promote the irreversible loss of BM function. These findings provide new insights into the pathogenic potential of CD4⁺ T cells that target hematopoietic function in leishmaniasis and perhaps other infectious diseases where TNF expression and BM dysfunction also occur simultaneously.

Visceral leishmaniasis (VL) is a chronic often fatal disease caused by the protozoan parasites Leishmania donovani and L. infantum. Progressive disease in humans and in animal models is associated with parasite replication at systemic sites, including the bone marrow (BM) and results in significant changes in hematological profile. The mechanisms underlying hematologic dysregulation during infection are largely unknown. Using a panel of stem cell markers, we characterized murine haematopoietic stem and progenitor cells in the BM over the course of L. donovani-infection in C57BL/6 (B6) mice. Most long-term hematopoietic stem cells (LT-HSCs) in naïve mice are found in a quiescent state, representing cells with the highest degree of reconstitution potential. In contrast, during L. donovani infection, most LT-HSCs had entered cell-cycle and this correlated with a reduced potential to engraft into syngeneic recipients. HSC exhaustion and other alterations in the hematopoietic compartment did not occur in infected immunodeficient mice, but adoptive transfer of IFNγ-sufficient CD4⁺ T cells restored this phenotype. Using mixed BM chimeras, we established that IFNγ signalling and TNF signalling pathways converge at the level of BM CD4⁺ T cells, with intrinsic TNF signalling being critical for the expansion / differentiation of CD4⁺ T cells that are responsible for HSC exhaustion. Contrary to commonly held views, in the setting of experimental visceral leishmaniasis neither IFNγ nor TNF signalling in HSCs was required for their functional exhaustion. Hence, pro-inflammatory cytokines commonly associated with host protection in leishmaniasis and many other infectious diseases can also drive the development of pathogenic CD4⁺ T cells that cause long term irreversible alterations in HSC function.

B cells responses and cytokine production are regulated by their immune microenvironment

The adaptive immune system consists of two types of lymphocytes: T and B cells. These two lymphocytes originate from a common precursor, yet are fundamentally different with B cells mediating humoral immunity while T cells mediate cell mediated immunity. In cytokine production, naïve T cells produce multiple cytokines upon activation while naïve activated B cells do not. B cells are capable of producing cytokines, but their cytokine production depends on their differentiation state and activation conditions. Hence, unlike T cells that can produce a large amount of cytokines upon activation, B cells require specific differentiation and activation conditions to produce cytokines. Many cytokines act on B cells as well. Here, we discuss several cytokines and their effects on B cells including: Interleukins, IL-7, IL-4, IL-6, IL-10, and Interferons, IFN-α, IFN-β, IFN-γ. These cytokines play important roles in the development, survival, differentiation and/or proliferation of B cells. Certain chemokines also play important roles in B cell function, namely antibody production. As an example, we discuss CCL28, a chemokine that directs the migration of plasma cells to mucosal sites. We conclude with a brief overview of B cells as cytokine producers and their likely functional consequences on the immune response.

Critical role of the endogenous interferon ligand-receptors in type I and type II interferons response

Separate ligand-receptor paradigms are commonly used for each type of interferon (IFN). However, accumulating evidence suggests that type I and type II IFNs may not be restricted to independent pathways. Using different cell types deficient in IFNAR1, IFNAR2, IFNGR1, IFNGR2 and IFN-γ, we evaluated the contribution of each element of the IFN system to the activity of type I and type II IFNs. We show that deficiency in IFNAR1 or IFNAR2 is associated with impairment of type II IFN activity. This impairment, presumably resulting from the disruption of the ligand-receptor complex, is obtained in all cell types tested. However, deficiency of IFNGR1, IFNGR2 or IFN-γ was associated with an impairment of type I IFN activity in spleen cells only, correlating with the constitutive expression of type II IFN (IFN-γ) observed on those cells. Therefore, in vitro the constitutive expression of both the receptors and the ligands of type I or type II IFN is critical for the enhancement of the IFN activity. Any IFN deficiency can totally or partially impair IFN activity, suggesting the importance of type I and type II IFN interactions. Taken together, our results suggest that type I and type II IFNs may regulate biological activities through distinct as well as common IFN receptor complexes.

Long-term functional duration of immune responses to HCV NS3/4A induced by DNA vaccination

We have investigated the ability of hepatitis C virus non-structural (NS) 3/4A-DNA-based vaccines to activate long-term cell-mediated immune responses in mice. Wild-type and synthetic codon optimized (co) NS3/4A DNA vaccines have previously been shown to be immunogenic in mice, rabbits and humans, although we have very poor knowledge about the longevity of the immune responses primed. We therefore analyzed the functionality of primed NS3/4A-specific immune responses in BALB/c (H-2^d) and/or C57BL/6J (H-2^b) mice 1, 2, 3, 4, 6, 12 and 16 months after the last immunization. Mice were immunized one, two, three or four times using gene gun delivery to the skin or by intramuscular administration. Immunological responses after immunization were monitored by protection against in vivo challenge of NS3/4A-expressing syngeneic tumor cells. In addition, functionality of the NS3/4A-specific T cells was analyzed by a standard cytotoxicity assay. First, we identified a new unique murine H-2^d-restricted NS3/4A cytotoxic T lymphocyte (CTL) epitope, which enabled us to study the epitope-specific immune responses. Our results show that the coNS3/4A vaccine was highly immunogenic by determination of interferon-γ/tumor necrosis factor-α production and lytic cytotoxic T cells, which could efficiently inhibit in vivo tumor growth. Importantly, we showed that one to four monthly immunizations protected mice from tumor development when challenged up to 16 months after the last immunization. When determining the functionality of NS3/4A-specific T cells in vitro, we showed detectable lytic activity up to 12 months after the last immunization. Thus, NS3/4A-based DNA vaccines activate potent cellular immune responses that are present and function in both BALB/c and C57BL/6J mice up to 12–16 months after the last immunization. The induction of long-term immunity after NS3/4A DNA immunization has not been shown previously and supports the use of NS3/4A in hepatitis C virus vaccine compositions.

STAT1β is not dominant negative and is capable of contributing to gamma interferon-dependent innate immunity

The transcription factor STAT1 is essential for interferon (IFN)-mediated immunity in humans and mice. STAT1 function is tightly regulated, and both loss- and gain-of-function mutations result in severe immune diseases. The two alternatively spliced isoforms, STAT1α and STAT1β, differ with regard to a C-terminal transactivation domain, which is absent in STAT1β. STAT1β is considered to be transcriptionally inactive and to be a competitive inhibitor of STAT1α. To investigate the functions of the STAT1 isoforms in vivo, we generated mice deficient for either STAT1α or STAT1β. As expected, the functions of STAT1α and STAT1β in IFN-α/β- and IFN-λ-dependent antiviral activity are largely redundant. In contrast to the current dogma, however, we found that STAT1β is transcriptionally active in response to IFN-γ. In the absence of STAT1α, STAT1β shows more prolonged IFN-γ-induced phosphorylation and promoter binding. Both isoforms mediate protective, IFN-γ-dependent immunity against the bacterium Listeria monocytogenes, although with remarkably different efficiencies. Our data shed new light on the potential contributions of the individual STAT1 isoforms to STAT1-dependent immune responses. Knowledge of STAT1β's function will help fine-tune diagnostic approaches and help design more specific strategies to interfere with STAT1 activity.

Lymphoid tissue phospholipase A2 group IID resolves contact hypersensitivity by driving antiinflammatory lipid mediators

PLA2G2D ameliorates skin inflammation through mobilizing pro-resolving lipid mediators.

Resolution of inflammation is an active process that is mediated in part by antiinflammatory lipid mediators. Although phospholipase A₂ (PLA₂) enzymes have been implicated in the promotion of inflammation through mobilizing lipid mediators, the molecular entity of PLA₂ subtypes acting upstream of antiinflammatory lipid mediators remains unknown. Herein, we show that secreted PLA₂ group IID (PLA2G2D) is preferentially expressed in CD11c⁺ dendritic cells (DCs) and macrophages and displays a pro-resolving function. In hapten-induced contact dermatitis, resolution, not propagation, of inflammation was compromised in skin and LNs of PLA2G2D-deficient mice (Pla2g2d^−/−), in which the immune balance was shifted toward a proinflammatory state over an antiinflammatory state. Bone marrow-derived DCs from Pla2g2d^−/− mice were hyperactivated and elicited skin inflammation after intravenous transfer into mice. Lipidomics analysis revealed that PLA2G2D in the LNs contributed to mobilization of a pool of polyunsaturated fatty acids that could serve as precursors for antiinflammatory/pro-resolving lipid mediators such as resolvin D1 and 15-deoxy-Δ^12,14-prostaglandin J₂, which reduced Th1 cytokine production and surface MHC class II expression in LN cells or DCs. Altogether, our results highlight PLA2G2D as a “resolving sPLA₂” that ameliorates inflammation through mobilizing pro-resolving lipid mediators and points to a potential use of this enzyme for treatment of inflammatory disorders.

Prevention of type 1 diabetes through infection with an intestinal nematode parasite requires IL-10 in the absence of a Th2-type response

Helminth infection can prevent type 1 diabetes (T1D); however, the regulatory mechanisms inhibiting disease remain largely undefined. In these studies, nonobese diabetic (NOD) IL-4(-/-) mice were infected with the strictly enteric nematode parasite, Heligmosomoides polygyrus. Short-term infection, 5-7 weeks of age, inhibited T1D onset, as late as 40 weeks of age. CD4(+) T-cell STAT6 phosphorylation was inhibited, while suppressed signal transducer and activator of transcription 1 phosphorylation was sustained, as were increases in FOXP3(-), CD4(+) T-cell interleukin (IL)-10 production. Blockade of IL-10 signaling in NOD-IL-4(-/-), but not in NOD, mice during this short interval abrogated protective effects resulting in pancreatic β-cell destruction and ultimately T1D. Transfer of CD4(+) T cells from H. polygyrus (Hp)-inoculated NOD IL-4(-/-) mice to NOD mice blocked the onset of T1D. These studies indicate that Hp infection induces non-T-regulatory cells to produce IL-10 independently of STAT6 signaling and that in this Th2-deficient environment IL-10 is essential for T1D inhibition.

Suppression of collagen-induced arthritis in growth arrest and DNA damage-inducible protein 45β-deficient mice

OBJECTIVE

Growth arrest and DNA damage-inducible protein 45β (GADD45β) is involved in stress responses, cell cycle regulation, and oncogenesis. Previous studies demonstrated that GADD45β deficiency exacerbates K/BxN serum-induced arthritis and experimental allergic encephalomyelitis (EAE) in mice, indicating that GADD45β plays a suppressive role in innate and adaptive immune responses. To further understand how GADD45β regulates autoimmunity, we evaluated collagen-induced arthritis in GADD45β-/- mice.

METHODS

Wild-type (WT) and GADD45β-/- DBA/1 mice were immunized with bovine type II collagen (CII). Serum anticollagen antibody levels were quantified by enzyme-linked immunosorbent assay. Expression of cytokines and matrix metalloproteinases in the joint and spleen was determined by quantitative polymerase chain reaction. The in vitro T cell cytokine response to CII was measured by multiplex analysis. CD4+CD25+ Treg cells and Th17 cells were quantified using flow cytometry.

RESULTS

GADD45β-/- mice showed significantly lower arthritis severity and joint destruction compared with WT mice. MMP-3 and MMP-13 expression was also markedly reduced in GADD45β-/- mice. However, serum anti-CII antibody levels were similar in both groups. FoxP3 and interleukin-10 (IL-10) expression was increased 2-3-fold in splenocytes from arthritic GADD45β-/- mice compared with those from WT mice. Flow cytometric analysis showed greater numbers of CD4+CD25+ Treg cells in the spleen of GADD45β-/- mice than in the spleen of WT mice. In vitro studies showed that interferon-γ and IL-17 production by T cells was significantly decreased in GADD45β-/- mice.

CONCLUSION

Unlike passive K/BxN arthritis and EAE, GADD45β deficiency in CIA was associated with lower arthritis severity, elevated IL-10 expression, decreased IL-17 production, and increased numbers of Treg cells. The data suggest that GADD45β plays a complex role in regulating adaptive immunity and, depending on the model, either enhances or suppresses inflammation.

IFNγR signaling mediates alloreactive T-cell trafficking and GVHD

The clinical goal of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is to minimize GVHD while maintaining GvL. Here, we show that interferon γ receptor-deficient (IFNγR(-/-)) allogeneic Tconv, which possess normal alloreactivity and cytotoxicity, induce significantly less GVHD than wild-type (WT) Tconv. This effect is mediated by altered trafficking of IFNγR(-/-) Tconv to GVHD target organs, especially the gastrointestinal (GI) tract. We show that the chemokine receptor CXCR3 is induced via IFNγR-mediated signaling and partially contributes to the trafficking of WT Tconv to GVHD target organs. Indeed, CXCR3(-/-) Tconv recapitulate the reduced GVHD potential of IFNγR(-/-) Tconv in a minor-mismatched GVHD model. Most importantly, IFNγR(-/-) (and CXCR3(-/-)) Tconv mediate a robust and beneficial GvL effect. In addition, we show that IFNγR(-/-) regulatory T cells (Tregs) are fully suppressive in vitro although defective in suppressor function in vivo and that WT Tregs suppress GVHD in vivo only when allogeneic Tconv produce interferon γ (IFNγ), suggesting that the IFNγR signaling pathway is the major mechanism for both Tregs and Tconv to migrate to GVHD target organs. Finally, pharmacologic inhibition of IFNγR signaling with inhibitors of JAK1/JAK2, which are mediators of IFNγR signaling, results in the decreased expression of CXCR3 and reduced GVHD and improved survival after allo-HSCT and this effect is mediated by altered trafficking of Tconv to GVHD target organs.

Update of immune events in the murine contact hypersensitivity model: toward the understanding of allergic contact dermatitis

Allergic contact dermatitis (ACD) is one of the most common skin diseases, consisting of sensitization and elicitation phases. With the advancement of technology and the discovery of new types of immune cells, our knowledge of the immunological mechanisms of contact hypersensitivity (CHS) as a murine model of ACD has expanded significantly in the past decade. For example, by introducing regulatory T cells, CD4(+) T-helper 17 cells, and Langerin-positive dermal dendritic cells, the initiation and termination mechanism of CHS has been revealed. In addition, the role of mast cells in CHS, long a matter of debate, has become apparent by developing conditional mast cell-deficient mice. Moreover, the role of the innate immunity system, such as that of Toll-like receptor signaling, has made a breakthrough in this field. In this review, we will integrate the recent advancement of immunological mechanisms of both the sensitization and elicitation phases of CHS into the classic view, and we will discuss updated mechanisms on its development and future directions.

Conditional Stat1 ablation reveals the importance of interferon signaling for immunity to Listeria monocytogenes infection

Signal transducer and activator of transcription 1 (Stat1) is a key player in responses to interferons (IFN). Mutations of Stat1 cause severe immune deficiencies in humans and mice. Here we investigate the importance of Stat1 signaling for the innate and secondary immune response to the intracellular bacterial pathogen Listeria monocytogenes (Lm). Cell type-restricted ablation of the Stat1 gene in naïve animals revealed unique roles in three cell types: macrophage Stat1 signaling protected against lethal Lm infection, whereas Stat1 ablation in dendritic cells (DC) did not affect survival. T lymphocyte Stat1 reduced survival. Type I IFN (IFN-I) signaling in T lymphocytes reportedly weakens innate resistance to Lm. Surprisingly, the effect of Stat1 signaling was much more pronounced, indicating a contribution of Stat1 to pathways other than the IFN-I pathway. In stark contrast, Stat1 activity in both DC and T cells contributed positively to secondary immune responses against Lm in immunized animals, while macrophage Stat1 was dispensable. Our findings provide the first genetic evidence that Stat1 signaling in different cell types produces antagonistic effects on innate protection against Lm that are obscured in mice with complete Stat1 deficiency. They further demonstrate a drastic change in the cell type-dependent Stat1 requirement for memory responses to Lm infection.

Signal transducer and activator of transcription 1 (Stat1) is an indispensable component of the cellular response to interferons (IFN) during immune reactions to pathogens. Stat1 deficiency leads to severe immune defects in humans and mice. The sensitivity of animals with complete Stat1 ablation to microbial pathogens prevented determining its contribution to various effector systems of the immune response. By way of tissue-restricted Stat1 ablation we now decipher the impact of Stat1 signaling in different cell populations on the innate and adaptive immune response to the intracellular pathogen Listeria monocytogenes. Our data highlight the importance of and requirement for IFNγ-activated macrophages for clearance of the pathogen during early phases of infection, and show a yet unanticipated detrimental role for T cell Stat1. During secondary responses the picture changes and Stat1 in T cells is crucial for proper clearance of L. monocytogenes. Likewise, Stat1 signaling in dendritic cells plays a fundamental role for adaptive immunity to L. monocytogenes. Exploring the local response to L. monocytogenes infection we reveal a role of Stat1 in shaping the cellular composition of inflammatory infiltrates. Furthermore, Stat1 deficiency in dendritic cells increases the proliferation of regulatory T cells, an effect likely to dampen the antibacterial response.

Memory CD4+ T cells: fate determination, positive feedback and plasticity

Naïve CD4(+) T cells undergo massive cell proliferation upon encountering their cognate ligand. This proliferation depends upon appropriate cues from the antigen-presenting cells that have processed the antigen and present the peptide to the T cells, and requires the establishment of a cytokine environment that can support such proliferation. Expansion of antigen-specific CD4(+) T cells needs to be coupled with differentiation into one of several effector/regulatory phenotypes if the priming event is to result in cells that can initially act to control the particular pathogen that elicited the response, and later to serve as memory cells to insure an appropriate response upon reintroduction of the pathogen. Here, we discuss the initiation of T helper lineage commitment, the positive feedback regulation by the cytokine environment to enhance and stabilize the differentiation into distinct T helper subsets, and the biological significance of CD4(+) T cell plasticity and long-term CD4(+) T cell memory.

Interferon-lambda: a new addition to an old family

The discovery and initial description of the interferon-lambda (IFN-lambda) family in early 2003 opened an exciting new chapter in the field of IFN research. There are 3 IFN-lambda genes that encode 3 distinct but highly related proteins denoted IFN-lambda1, -lambda2, and -lambda3. These proteins are also known as interleukin-29 (IL-29), IL-28A, and IL-28B, respectively. Collectively, these 3 cytokines comprise the type III subset of IFNs. They are distinct from both type I and type II IFNs for a number of reasons, including the fact that they signal through a heterodimeric receptor complex that is different from the receptors used by type I or type II IFNs. Although type I IFNs (IFN-alpha/beta) and type III IFNs (IFN-lambda) signal via distinct receptor complexes, they activate the same intracellular signaling pathway and many of the same biological activities, including antiviral activity, in a wide variety of target cells. Consistent with their antiviral activity, expression of the IFN-lambda genes and their corresponding proteins is inducible by infection with many types of viruses. Therefore, expression of the type III IFNs (IFN-lambdas) and their primary biological activity are very similar to the type I IFNs. However, unlike IFN-alpha receptors which are broadly expressed on most cell types, including leukocytes, IFN-lambda receptors are largely restricted to cells of epithelial origin. The potential clinical importance of IFN-lambda as a novel antiviral therapeutic agent is already apparent. In addition, preclinical studies by several groups indicate that IFN-lambda may also be useful as a potential therapeutic agent for other clinical indications, including certain types of cancer.

Amphiregulin is not essential for induction of contact hypersensitivity

BACKGROUND

Amphiregulin (AR) is expressed in Th2 cells, rather than Th1 cells, and plays an important role in Th2 cell/cytokine-mediated host defense against nematodes. We also found earlier that AR mRNA expression was strongly upregulated in inflamed tissue during Th2 cell/cytokine-mediated fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS), suggesting a contribution of AR to the induction of those responses.

METHODS

To elucidate the role of AR in the induction of FITC- or dinitrofluorobenzene (DNFB)-induced CHS, AR-deficient mice were sensitized and/or challenged with FITC or DNFB epicutaneously. The levels of FITC-mediated skin dendritic cell (DC) migration and FITC-specific lymph node cell proliferation and cytokine production were assessed by flow cytometry, [3H]-thymidine incorporation and ELISA, respectively, after FITC sensitization. The degree of ear swelling, the activities of myeloperoxidase (MPO) and eosinophil peroxidase (EPO) in inflammatory sites and the levels of FITC-specific immunoglobulin (Ig) in sera were determined by histological analysis, colorimetric assay and ELISA, respectively, after FITC challenge.

RESULTS

DC migration and FITC-specific lymph node cell proliferation and cytokine production were normal in the AR-deficient mice. Ear swelling, tissue MPO and EPO activities and FITC-specific serum Ig levels were also similar in AR-deficient and -sufficient mice.

CONCLUSIONS

Amphiregulin is not essential for the induction of FITC- or DNFB-induced CHS responses in mice.

Antagonistic crosstalk between type I and II interferons and increased host susceptibility to bacterial infections

Type I and II interferons (IFNs αβ and γ) have opposing effects on immune resistance to certain pathogenic bacteria. While IFNγ generally plays a protective role, IFNαβ exacerbates Listeria monocytogenes and Mycobacterium tuberculosis infections. Our findings provided evidence that this increased susceptibility reflects a novel antagonistic cross talk between IFNαβ and IFNγ. Macrophages infected with L. monocytogenes strains that induce IFNαβ production responded poorly to IFNγ, as measured by reduced phosphorylation of STAT1 and reduced IFNγ-dependent gene expression. The impaired responsiveness to IFNγ correlated with reduced expression of its receptor, IFNGR, by both infected and bystander macrophages. Down regulation of IFNGR was dependent on responsiveness to IFNγ and mimicked by recombinant IFNβ. Mice lacking responsiveness to IFNαβ (IFNAR1 (-/-)) retained high IFNGR expression, developed higher expression of MHC-II on macrophages and DCs, and were more resistant to systemic L. monocytogenes infection--but only in the presence of IFNγ. Thus, the ability of IFNαβ to down regulate IFNGR provides an explanation for its ability to reduce responsiveness to IFNγ and to increase host susceptibility to bacterial infection. It remains to be determined whether and how such antagonistic interferon crosstalk benefits the host.

Gender specificity of altered human immune cytokine profiles in aging

Cytokine generation by T cells and monocytes was determined for 50 subjects aged 65 yr or older and concurrently studied young subjects individually matched to each old subject for sex, race, and national origin. Highly significant differences between cytokine levels of old and young subjects all were gender specific. For T cells stimulated with anti-CD3 plus anti-CD28 antibodies, mean ratios of IFN-gamma generation for healthy old to young subjects were 0.22 for men (P<0.001; n=15) and 3.35 for women (P<0.001; n=13), and those of IL-17 were 0.30 for men (P<0.001) and no difference for women. CD8 T cells were the source of high IFN-gamma in healthy old women. For old men with an inflammatory or immune disease (n=10), mean old to young ratios of T-cell-generated IFN-gamma and IL-17 increased with disease severity up to 5.78 and 2.97 (both P<0.01), respectively, without changes for old women with similar diseases (n=12). For differentiated LPS-stimulated monocytes, old to young ratios of TNF-alpha and IL-6 generation were high only in women with immune or inflammatory disease (2.38, P<0.05 and 1.62, P<0.01, respectively), whereas ratios of IFN-gamma-evoked IP-10 chemokine were low in all groups. Alterations in immune cytokine profiles with aging show significant gender specificity.

Protosappanin A induces immunosuppression of rats heart transplantation targeting T cells in grafts via NF-kappaB pathway

Protosappanin A as one major and effective ingredient from Caesalpinia sappan L. exhibited antirejection activity obviously in heart-transplanted rat. The present study was designed to screen out the potential target genes of protosappanin A with microarray technology and reveal some molecular mechanism of immunosuppressive effect. Rats performed with ectopic peritoneal heart transplantation were randomized into three groups receiving different treatments for 7 days: protosappanin A group (25 mg kg(-1)), cyclosporine A group (10 mg kg(-1)), and control group. The differentially expressed genes responding to protosappanin A were analyzed with microarrays. Among common differentially expressed genes, the ones of interest were selected for further evaluation by real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), Western blot, immunochemistry, immunofluorescence, and ELISA. Among the 146 common differentially expressed genes, NF-kappaB and related genes like IkappaBa, IFN-r, and IP10 were selected for verification. The results of qRT-PCR, Western blot, immunochemistry, and ELISA showed that protosappanin A significantly reduced the expression of NF-kappaB, IFN-r, and IP10 (p < 0.05) and increased IkappaBa expression (p < 0.05) in graft. Moreover, the immunochemistry staining of NF-kappaB and IkappaBa was mainly observed in infiltrating mononuclear cells. Strikingly, immunofluorescent staining localized NF-kappaB to the TCR-positive T cells in graft. Furthermore, protosappanin A exhibited inhibitory effect on T cell proliferation in recipients after 7-day treatment. In conclusion, protosappanin A might act on T cells through inhibiting NF-kappaB activation and downstream gene expressions of IFN-r and IP10, meanwhile reducing T cell proliferation responding to alloantigen, so as to induce immunosuppressive effect. The results encourage a potential therapeutic evaluation of protosappanin A for clinical organ transplantation or other T cell-mediated immune disorders. Additionally, our study also verified the feasibility of microarray utilization in Chinese herb research to explore molecular mechanism and promote development of scientific theories.

The C-terminus of interferon gamma receptor beta chain (IFNgammaR2) has antiapoptotic activity as a Bax inhibitor

Bax is a pro-apoptotic protein that mediates intrinsic cell-death signaling. Using a yeast-based functional screening approach, we identified interferon gamma receptor beta chain (IFNgammaR2) as a new Bax suppressor. IFNgammaR2 is a component of the IFNgamma receptor complex along with the IFNgammaR alpha chain (IFNgammaR1). Upon IFNgamma binding, a conformational change in the receptor complex occurs that activates the Jak2/STAT1 signaling cascade. We found that the C-terminal region (amino acids 296-337) of IFNgammaR2 (IFNgammaR2(296-337)) contains a novel Bax inhibitory domain. This portion does not contain the Jak2-binding domain; therefore, the antiapoptotic function of IFNgammaR2 is independent of JAK/STAT signaling. IFNgammaR2(296-337) rescued human cells from apoptosis induced by overexpression of Bax but not Bak. Overexpression of IFNgammaR2 (wild type and IFNgammaR2(296-337)) rescued cells from etoposide and staurosporine, which are known to induce Bax-mediated cell death. Interestingly, IFNgammaR2 inhibited apoptosis induced by the BH3-only protein Bim-EL, suggesting that IFNgammaR2 inhibits Bax activation through a BH3-only protein. Bax and IFNgammaR2 were co-immunoprecipitated from cell lysates prepared from HEK293 and DAMI cells. Furthermore, direct binding of purified recombinant proteins of Bax and IFNgammaR2 was also confirmed. Addition of recombinant Bcl-2 protein to cell lysates significantly reduced the interaction of IFNgammaR2 and Bax, suggesting that Bcl-2 and IFNgammaR2 bind a similar domain of Bax. We found that the C-terminal fragment (cytoplasmic domain) of IFNgammaR2 is expressed in human cancer cell lines of megakaryocytic cancer (DAMI), breast cancer (MDA-MD-468), and prostate cancer (PC3 cells). The presence of the C-terminal fragment of IFNgammaR2 may confer on cancer cells resistance to apoptotic stresses. Our discovery of the anti-Bax activity of the cytoplasmic domain of IFNgammaR2 may shed new light on the mechanism of how cell death is controlled by IFNgamma and Bax.

Endotoxin augmented antigen-induced Th1 cell trafficking amplifies airway neutrophilic inflammation

CD4(+) Th1 cells play a critical role in orchestrating host defense against pathogens and in the pathogenesis of many immune-mediated diseases. The control of Th1 cell trafficking into sites of infection and inflammation is an important determinant of Th1 cell function. We have previously shown that trafficking of adoptively transferred Ag-specific Th1 cells into the lung following airway Ag challenge depends on CXCR3 expression on Th1 cells and STAT1-inducible CXCR3 ligands in the lung. In this study, we show that LPS alters the mechanisms of Th1 cell recruitment. After a single intranasal dose of LPS, trafficking of adoptively transferred Ag-specific Th1 cell into the lung in response to airway Ag challenges was no longer dependent on CXCR3 and its ligands and instead was mediated through additional Galphai-coupled chemoattractant receptor pathways, including CCR5. In addition, LPS markedly increased the magnitude of Ag-specific Th1 cell homing into the airways following airway Ag challenges. The increased trafficking of Ag-activated Th1 cells, in turn, dramatically amplified LPS-induced airway neutrophilic infiltration by maintaining high levels of the neutrophil active chemokines, KC and MIP-2, through an IFN-gamma dependent mechanism. Therefore, LPS increases Ag-specific Th1 cell trafficking into the airways and Ag-specific Th1 cells amplify the airway neutrophilic inflammatory response initiated by LPS. This reciprocal interaction between LPS and Ag-activated Th1 cells represents a collaborative connection between the innate and adaptive arms of the immune system.

IL-17 and IFN-gamma mediate the elicitation of contact hypersensitivity responses by different mechanisms and both are required for optimal responses

Hapten-induced contact hypersensitivity (CHS) in the skin is a delayed type cellular immune response that can be mediated by CD8(+) T cells that produce IFN-gamma or IL-17. However, mechanisms for these cytokines in the elicitation of CHS remain to be fully elucidated. In this study, we show that adoptive transfer of CHS with hapten-primed wild-type (WT) CD8(+) T cells is reduced in IFN-gammaR(-/-) or IL-17R(-/-) mice compared with WT controls. The infiltration of granulocytes and macrophages in the hapten challenged skin of IL-17R(-/-) recipients is significantly reduced whereas it is less affected in IFN-gammaR(-/-) recipients although CD8(+) T cell infiltration is inhibited in both recipients. In contrast, the activity of reactive oxidative species is significantly inhibited in IFN-gammaR(-/-) but is less affected in IL-17R(-/-) recipients. Further analysis reveals that the expression of chemokines and cytokines is differentially regulated in the hapten-challenged skin of IFN-gammaR(-/-) or IL-17R(-/-) recipients compared with WT controls. Interestingly, injection of rIL-17 in the skin induces inflammation with a high level of leukocyte infiltration whereas injection of IFN-gamma induces inflammation with a high level of reactive oxidative species. Moreover, neutralization of IL-17 in IFN-gammaR(-/-) or IFN-gamma in IL-17R(-/-) mice further suppresses the adoptive transfer of CHS by hapten-primed WT CD8(+) T cells. The study demonstrates that IFN-gamma and IL-17 mediate the elicitation of CHS by different mechanisms and that both cytokines are required for optimal responses. This outcome improves understanding of pathogenesis and provides new insights into therapeutic strategies for CHS.

The roles of IL-17A in inflammatory immune responses and host defense against pathogens

T-helper 17 (Th17) cells are a newly discovered CD4(+) helper T-cell subset that produces interleukin-17A (IL-17A) and IL-17F. IL-17A plays important roles in allergic responses such as delayed-type hypersensitivity, contact hypersensitivity, and allergic airway inflammation. IL-17A promotes inflammation by inducing various proinflammatory cytokines and chemokines, recruiting neutrophils, enhancing antibody production, and activating T cells. IL-17A expression is also augmented in autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. Using mouse models of these diseases, we found that IL-17A plays a central role in their development. IL-6 is required for the development of Th17 cells and tumor necrosis factor functions downstream of IL-17A during the effector phase. IL-1 is important both for developing Th17 cells and eliciting inflammation. Th17 cells, like Th1 and Th2 cells, are involved in host defense against infections, but the contribution of these Th subsets to defense mechanisms differs among pathogens. The roles of IL-17F remain largely unknown. In this review, we introduce how IL-17A/IL-17F are involved in inflammatory immune responses and host defense mechanisms and discuss their relationship with other cytokines in the development of inflammatory and infectious diseases.

Th17 and allergy

The identification of novel helper T (Th) cell subsets, i.e., IL-17-producing Th cells (Th17 cells) and regulatory T cells (Treg cells), provided new insight into our understanding of the molecular mechanisms involved in the development of infectious and autoimmune diseases as well as immune responses, and thus led to revision of the classic Th1/Th2 paradigm. Several current lines of evidence from gene-deficient mice indicate that IL-17 and Th17 cells, but not IFN-gamma and Th1 cells, are responsible for the development of autoimmune diseases such as murine arthritis and encephalomyelitis, which have classically been considered to be Th1-mediated disorders. Th17 cells may also contribute to the pathogenesis of classically recognized Th2-mediated allergic disorders. In this review, we summarize the current knowledge regarding IL-17 and Th17 cells and discuss their potential roles in the pathogenesis of allergic disorders.

Nonredundant functions of alphabeta and gammadelta T cells in acrolein-induced pulmonary pathology

Acrolein exposure represents a significant human health hazard. Repeated acrolein exposure causes the accumulation of monocytes/macrophages and lymphocytes, mucous cell metaplasia, and epithelial injury. Currently, the mechanisms that control these events are unclear, and the relative contribution of T-cell subsets to pulmonary pathologies following repeated exposures to irritants is unknown. To examine whether lymphocyte subpopulations regulate inflammation and epithelial cell pathology, we utilized a mouse model of pulmonary pathology induced by repeated acrolein exposures. The role of lymphocyte subsets was examined by utilizing transgenic mice genetically deficient in either alphabeta T cells or gammadelta T cells, and changes in cellular, molecular, and pathologic outcomes associated with repeated inhalation exposure to 2.0 and 0.5 ppm acrolein were measured. To examine the potential functions of lymphocyte subsets, we purified these cells from the lungs of mice repeatedly exposed to 2.0 ppm acrolein, isolated and amplified messenger RNA, and performed microarray analysis. Our data demonstrate that alphabeta T cells are required for macrophage accumulation, whereas gammadelta T cells are critical regulators of epithelial cell homeostasis, as identified by epithelial cell injury and apoptosis, following repeated acrolein exposure. This is supported by microarray analyses that indicated the T-cell subsets are unique in their gene expression profiles following acrolein exposures. Microarray analyses identified several genes that may contribute to phenotypes mediated by T-cell subpopulations including those involved in cytokine receptor signaling, chemotaxis, growth factor production, lymphocyte activation, and apoptosis. These data provide strong evidence that T-cell subpopulations in the lung are major determinants of pulmonary pathology and highlight the advantages of dissecting their effector functions in response to toxicant exposures.

Plasmacytoid dendritic cells and the regulation of immunoglobulin heavy chain class switching

By substituting the heavy chain constant region of IgM and IgD with that of IgG, IgA or IgE, immunoglobulin class switching endows antibodies with novel effector functions that enhance the ability of the immune system to effectively clear invading pathogens. Plasmacytoid dendritic cells critically link innate immunity with adaptive immunity by producing massive amounts of type 1 IFN in response to viruses. We have recently found that type 1 IFN triggers class switching by inducing myeloid dendritic cells to upregulate the expression of BAFF and APRIL, two powerful B cell-activating molecules. In this paper, we propose that IFN-producing plasmacytoid dendritic cells modulate class switching by activating B cells through both T cell-dependent and T cell-independent pathways. A better understanding of these pathways may facilitate the development of novel antiviral vaccine strategies and aid in identifying new therapies for antibody-mediated autoimmune disorders, such as lupus.

Facilitation of Th1-mediated immune response by prostaglandin E receptor EP1

Prostaglandin E₂ (PGE₂) exerts its actions via four subtypes of the PGE receptor, EP1–4. We show that mice deficient in EP1 exhibited significantly attenuated Th1 response in contact hypersensitivity induced by dinitrofluorobenzene (DNFB). This phenotype was recapitulated in wild-type mice by administration of an EP1-selective antagonist during the sensitization phase, and by adoptive transfer of T cells from sensitized EP1^−/− mice. Conversely, an EP1-selective agonist facilitated Th1 differentiation of naive T cells in vitro. Finally, CD11c⁺ cells containing the inducible form of PGE synthase increased in number in the draining lymph nodes after DNFB application. These results suggest that PGE₂ produced by dendritic cells in the lymph nodes acts on EP1 in naive T cells to promote Th1 differentiation.

NK dendritic cells are innate immune responders to Listeria monocytogenes infection

NK dendritic cells (NKDC) are recently described immunologic cells that possess both lytic and Ag-presenting function and produce prolific quantities of IFN-gamma. The role of NKDC in innate immunity to bacterial infection is unknown. Because IFN-gamma is important in the immune response to Listeria monocytogenes (LM), we hypothesized that NKDC play a critical role during LM infection in mice. We found that LM increased the frequency and activation state of NKDC in vivo. Using in vivo intracellular cytokine analysis, we demonstrated that NKDC are a major source of early IFN-gamma during infection with LM. Adoptive transfer of wild-type NKDC into IFN-gamma-deficient recipients that were subsequently infected with LM decreased bacterial burden in the liver and spleen and prolonged survival. In contrast, NK cells were depleted early during LM infection, produced less IFN-gamma, and conferred less protection upon adoptive transfer into IFN-gamma-deficient mice. In vitro, LM induction of IFN-gamma secretion by NKDC depended on TLR9, in addition to IL-18 and IL-12. Our study establishes NKDC as innate immune responders to bacterial infection by virtue of their ability to secrete IFN-gamma.

Expression of the p60 autolysin enhances NK cell activation and is required for listeria monocytogenes expansion in IFN-gamma-responsive mice

Both peptidoglycan and muropeptides potently modulate inflammatory and innate immune responses. The secreted Listeria monocytogenes p60 autolysin digests peptidoglycan and promotes bacterial infection in vivo. Here, we report that p60 contributes to bacterial subversion of NK cell activation and innate IFN-gamma production. L. monocytogenes deficient for p60 (Deltap60) competed well for expansion in mice doubly deficient for IFNAR1 and IFN-gammaR1 or singly deficient for IFN-gammaR1, but not in wild-type, IFNAR1(-/-), or TLR2(-/-) mice. The restored competitiveness of p60-deficient bacteria suggested a specific role for p60 in bacterial subversion of IFN-gamma-mediated immune responses, since in vivo expansion of three other mutant L. monocytogenes strains (DeltaActA, DeltaNamA, and DeltaPlcB) was not complemented in IFN-gammaR1(-/-) mice. Bacterial expression of p60 was not required to induce socs1, socs3, and il10 expression in infected mouse bone marrow macrophages but did correlate with enhanced production of IL-6, IL-12p70, and most strikingly IFN-gamma. The primary source of p60-dependent innate IFN-gamma was NK cells, whereas bacterial p60 expression did not significantly alter innate IFN-gamma production by T cells. The mechanism for p60-dependent NK cell stimulation was also indirect, given that treatment with purified p60 protein failed to directly activate NK cells for IFN-gamma production. These data suggest that p60 may act on infected cells to indirectly enhance NK cell activation and increase innate IFN-gamma production, which presumably promotes early bacterial expansion through its immunoregulatory effects on bystander cells. Thus, the simultaneous induction of IFN-gamma production and factors that inhibit IFN-gamma signaling may be a common strategy for misdirection of early antibacterial immunity.

Skin inflammation in RelB−/− mice leads to defective immunity and impaired clearance of vaccinia virus

BACKGROUND

Atopic dermatitis (AD) is an inflammatory skin disorder occurring in genetically predisposed individuals with a systemic T(H)2 bias. Atopic dermatitis patients exposed to the smallpox vaccine, vaccinia virus (VV), occasionally develop eczema vaccinatum (EV), an overwhelming and potentially lethal systemic infection with VV.

OBJECTIVE

To establish a murine model of EV and examine the effects of skin inflammation on VV immunity.

METHODS

The skin of RelB(-/-) mice, like that of chronic AD lesions in humans, exhibits thickening, eosinophilic infiltration, hyperkeratosis, and acanthosis. RelB(-/-) and wild-type (WT) control mice were infected with VV via skin scarification. Viral spread, cytokine levels, IgG2a responses and VV-specific T cells were measured.

RESULTS

Cutaneously VV-infected RelB(-/-), but not WT mice, exhibited weight loss, markedly impaired systemic clearance of the virus and increased contiguous propagation from the inoculation site. This was associated with a dramatically impaired generation of IFN-gamma-producing CD8(+) vaccinia-specific T cells along with decreased secretion of IFN-gamma by VV-stimulated splenocytes. The T(H)2 cytokines-IL-4, IL-5, IL-13, and IL-10-on the other hand, were overproduced. When infected intraperitoneally, RelB(-/-) mice generated robust T cell responses with good IFN-gamma production.

CONCLUSION

Allergic inflammation in RelB(-/-) mice is associated with dysregulated immunity to VV encountered via the skin. We speculate that susceptibility of AD patients to overwhelming vaccinia virus infection is similarly related to ineffective T cell responses.

CLINICAL IMPLICATIONS

The susceptibility of patients with AD to EV following cutaneous contact with VV is related to ineffective antiviral immune responses.

CD8+ IL-17-producing T cells are important in effector functions for the elicitation of contact hypersensitivity responses

Allergen-induced contact hypersensitivity (CHS) is a T cell-mediated delayed-type immune response which has been considered to be primarily mediated by CD8+ T cytotoxic type I (Tc1) cells. IFN-gamma, the prototype Tc1 (Th1) cytokine, has been implicated as the primary inflammatory cytokine for CHS. In this study, we demonstrate that neutralization of IL-17 rather than IFN-gamma suppresses the elicitation of CHS. The suppression does not result from inhibition of the proliferation of allergen-activated T cells. Allergen sensitization induces the development of distinct CD8+ T cell subpopulations that produce IFN-gamma or IL-17. Although CD8+ IL-17-producing cells are stimulated by IL-23, they are inhibited by IL-12, a prototypical stimulator of IFN-gamma-producing Tc1 cells. This indicates that CD8+ IL-17-producing cells are distinct from Tc1 cells and are important in effector functions at the elicitation of CHS. These studies provide insights into a novel mechanism for CHS.

Th1 and type 1 cytotoxic T cells dominate responses in T-bet overexpression transgenic mice that develop contact dermatitis

Contact dermatitis in humans and contact hypersensitivity (CHS) in animal models are delayed-type hypersensitivity reactions mediated by hapten-specific T cells. Recently, it has become clear that both CD4(+) Th1 and CD8(+) type 1 cytotoxic T (Tc1) cells can act as effectors in CHS reactions. T-bet has been demonstrated to play an important role in Th1 and Tc1 cell differentiation, but little is known about its contribution to CHS. In the present study, we used C57BL/6 mice transgenic (Tg) for T-bet to address this issue. These Tg mice, which overexpressed T-bet in their T lymphocytes, developed dermatitis characterized by swollen, flaky, and scaly skin in regions without body hair. Skin histology showed epidermal hyperkeratosis, neutrophil, and lymphocyte infiltration similar to that seen in contact dermatitis. T-bet overexpression in Tg mice led to elevated Th1 Ig (IgG2a) and decreased Th2 Ig (IgG1) production. Intracellular cytokine analyses demonstrated that IFN-gamma was increased in both Th1 and Tc1 cells. Furthermore, Tg mice had hypersensitive responses to 2,4-dinitrofluorobenzene, which is used for CHS induction. These results suggest that the level of expression of T-bet might play an important role in the development of contact dermatitis and that these Tg mice should be a useful model for contact dermatitis.

Induced Expression of Murine γ2a by CD40 Ligation Independently of IFN-γ

IgG2a, with gamma2a H chains, is important for protection against viruses and other intracellular pathogens. Although a large portion of IgG2a expression is dependent upon IFN-gamma, some germline transcription and switch recombination to the murine gamma2a H chain gene expression are independent of IFN-gamma. We found that agonistic anti-CD40 Abs injected into IFN-gamma-deficient mice induce a > 200-fold increase in the amount of serum Ig2a, while other Ig isotypes are increased by 16-fold or less. In vitro, ligation of CD40 on B cells, without the addition of other B cell activators or cytokines, results in germline transcription and switch recombination that are largely restricted to the gamma2a gene. These results suggest that some immune responses to infectious agents can result in large amounts of IgG2a expression through ligation of CD40, without the expression of IFN-gamma by Th1 or other cells.

Characterization of the mouse IFN-lambda ligand-receptor system: IFN-lambdas exhibit antitumor activity against B16 melanoma

Recently discovered type III IFNs (IFN-lambda) exert their antiviral and immunomodulatory activities through a unique receptor complex composed of IFN-lambdaR1 and interleukin-10 receptor 2. To further study type III IFNs, we cloned and characterized mouse IFN-lambda ligand-receptor system. We showed that, similar to their human orthologues, mIFN-lambda2 and mIFN-lambda3 signal through the IFN-lambda receptor complex, activate IFN stimulated gene factor 3, and are capable of inducing antiviral protection and MHC class I antigen expression in several cell types including B16 melanoma cells. We then used the murine B16 melanoma model to investigate the potential antitumor activities of IFN-lambdas. We developed B16 cells constitutively expressing murine IFN-lambda2 (B16.IFN-lambda2 cells) and evaluated their tumorigenicity in syngeneic C57BL/6 mice. Although constitutive expression of mIFN-lambda2 in melanoma cells did not affect their proliferation in vitro, the growth of B16.IFN-lambda2 cells, when injected s.c. into mice, was either retarded or completely prevented. We found that rejection of the modified tumor cells correlated with their level of IFN-lambda2 expression. We then developed IFN-lambda-resistant B16.IFN-lambda2 cells (B16.IFN-lambda2Res cells) and showed that their tumorigenicity was also highly impaired or completely abolished similar to B16.IFN-lambda2 cells, suggesting that IFN-lambdas engage host mechanisms to inhibit melanoma growth. These in vivo experiments show the antitumor activities of IFN-lambdas and suggest their strong therapeutic potential.

Gene expression in splenic CD4 and CD8 cells from BALB/c mice immunized with Porphyromonas gingivalis

BACKGROUND

T cells are fundamental in the pathogenesis of periodontal disease. Suppression of cell-mediated responses is associated with disease progression together with the concomitant increase in plaque pathogens including Porphyromonas gingivalis. The aim of the present study was to examine gene expression in T cells in response to P. gingivalis in mice.

METHODS

BALB/c mice were given weekly intraperitoneal injections of P. gingivalis outer-membrane antigens with Freund's incomplete adjuvant for 3 weeks, whereas control mice received phosphate buffered saline (PBS) and adjuvant only. Splenic CD4 and CD8 subpopulations were isolated by magnetic cell separation and their responses investigated using microarray analysis.

RESULTS

Most genes coded for enzymes concerned with metabolic pathways. Only five and 28 genes, respectively, were upregulated in CD4 and CD8 cells extracted from P. gingivalis-immunized mice, including immunoglobulin (Ig) heavy-chain genes for IgG1 and IgG2a in CD4 cells. In contrast, 1,141 and 1,175 genes, respectively, were downregulated. A total of 60 and 65 genes, respectively, coded for immune response proteins or those relevant to periodontal disease pathogenesis. The overlap of genes in the two subsets was 21%. One of the major effects, apart from T-cell function suppression, was the shift away from Th1 responses, although there was also a downregulation of two genes and upregulation of one Th2-response gene. Genes downregulated included those encoding cytokines, proteins involved in Ig binding, antigen presentation, innate immunity, extracellular matrix, and cell adhesion molecules that could result in dysregulation in the progressive periodontal lesion.

CONCLUSIONS

Early findings in humans demonstrated that periodontopathic bacteria induce immunosuppressive effects on T cells. The present study has shown that P. gingivalis had a predominant downregulatory effect on gene expression in CD4 and CD8 T cells in mice.

Epitope-specific regulation of immunoglobulin class switching in mice immunized with malarial merozoite surface proteins

Antibodies that bind to Fc receptors and activate complement are implicated in the efficient control of pathogens, but the processes that regulate their induction are still not well understood. To investigate antigen-dependent factors that regulate class switching, we have developed an in vivo model of class switching to immunoglobulin G2b (IgG2b) using the malaria antigen Plasmodium falciparum merozoite surface protein 2 (MSP2). C57BL/6 mice were immunized with recombinant proteins representing discrete domains of MSP2, and a T-cell epitope (C8) was identified within the conserved C terminus of the protein that preferentially induces IgG2b antibodies. The ability of C8 to induce IgG2b is ablated in both homozygous gamma interferon-negative and interleukin 10-negative mice. The IgG2b-inducing properties of C8 override the IgG1-inducing properties of both the fusion protein partner, glutathione S-transferase, and the adjuvant. Furthermore, when attached to other proteins that normally induce IgG1 responses, C8 induces a switch to IgG2b secretion. This is the first description of a defined T-cell epitope that drives specific IgG2b subclass switching, and our data offer proof of the concept that chimeric vaccines incorporating specific T-cell "switch epitopes" might be used to enhance qualitative aspects of the antibody response.

Inherited defects in the interferon-gamma receptor or interleukin-12 signalling pathways are not sufficient to cause allergic disease in children

T-helper (Th)2 cells, which produce the cytokines interleukins (IL)-4, IL-5 and IL-13, dominate T cell responses in allergic diseases. The Th1-type cytokines IL-12 and interferon-gamma (IFNgamma) are important in down-regulating Th2 responses to allergens. Patients with defects in the IL-12 receptor (IL-12R) or IFNgamma receptor (IFNgammaR) have abnormal responses to IL-12 or IFNgamma and a failure to produce normal levels of IFNgamma. Current paradigms of T-helper subset balance would predict a high prevalence of atopic illness in this group. We have studied a cohort of patients (n =29) with defects in these pathways to assess the prevalence of allergic disease. A questionnaire based on those developed for the International Study of Asthma and Allergy in Childhood (ISAAC) was used in conjunction with analysis of total and specific IgE to common aeroallergens. The prevalence of asthma, eczema and rhino-conjunctivitis (13.7%, 17.5% and 6.8% respectively) in this group was no higher than in comparable populations where prevalences of 13.9%, 7.9% and 13.5% are reported for asthma, eczema and rhinoconjunctivitis respectively. Patients with IFNgammaR defects had higher rates of clinical atopic illness than control populations and patients with IL-12R defects, with 28.5% prevalences for asthma and eczema, respectively. None of the patients suffered from severe clinical atopic disease. Defects in interferon-gamma receptor/interleukin-12 receptor responses are not sufficient to cause clinical allergic disease. Patients with defects in the interferon-gamma receptor pathway have a higher prevalence of high IgE and clinical atopic illness compared to control populations, supporting the concept that interferon-gamma receptor signalling plays a role in down-regulating type-2 cytokine responses.

Gadd45 beta and Gadd45 gamma are critical for regulating autoimmunity

The number of effector T cells is controlled by proliferation and programmed cell death. Loss of these controls on self-destructive effector T cells may precipitate autoimmunity. Here, we show that two members of the growth arrest and DNA damage-inducible (Gadd45) family, β and γ, are critical in the development of pathogenic effector T cells. CD4⁺ T cells lacking Gadd45β can rapidly expand and invade the central nervous system in response to myelin immunization, provoking an exacerbated and prolonged autoimmune encephalomyelitis in mice. Importantly, mice with compound deficiency in Gadd45β and Gadd45γ spontaneously developed signs of autoimmune lymphoproliferative syndrome and systemic lupus erythematosus. Our findings therefore identify the Gadd45β/Gadd45γ-mediated control of effector autoimmune lymphocytes as an attractive novel target for autoimmune disease therapy.

In vivo generation of pathogen-specific Th1 cells in the absence of the IFN-gamma receptor

The precise mechanisms that govern the commitment of CD4 T cells to become Th1 or Th2 cells in vivo are incompletely understood. Recent experiments demonstrate colocalization of the IFN-gammaR chains with the TCR during activation of naive CD4 T cells, suggesting that association of these molecules may be involved in determining lineage commitment. To test the role of IFN-gamma and its receptor in the generation of Th1 Ag-specific CD4 T cells, we analyzed mice after infection with Listeria monocytogenes or lymphocytic choriomeningitis virus. In the absence of IFN-gamma, Ag-specific CD4 T cells were generated in response to both these infections. In addition, IFN-gamma-producing (Th1) Ag-specific CD4 T cells were generated in mice lacking the ligand-binding chain of the IFN-gammaR (IFN-gammaR1-/-) or the signaling chain (IFN-gammaR2-/-). There was no increase in the number of IL-4-producing Ag-specific CD4 T cells, nor was there a decrease in the expression of T-bet in the absence of functional IFN-gamma signaling, indicating that the cells were committed Th1 cells. Thus, both chains of the IFN-gammaR are dispensable for the generation of Th1 Ag-specific CD4 T cells after infection in vivo.

Dynamic regulation of IFN-gamma signaling in antigen-specific CD8+ T cells responding to infection

IFN-gamma plays a critical role in the CD8(+) T cell response to infection, but when and if this cytokine directly signals CD8(+) T cells during an immune response is unknown. We show that naive Ag-specific CD8(+) T cells receive IFN-gamma signals within 12 h after in vivo infection with Listeria monocytogenes and then become unresponsive to IFN-gamma throughout the ensuing Ag-driven expansion phase. Ag-specific CD8(+) T cells regain partial IFN-gamma responsiveness throughout the contraction phase, whereas the memory pool exhibits uniform, but reduced, responsiveness that is also modulated during the secondary response. The responsiveness of Ag-specific CD8(+) T cells to IFN-gamma correlated with modulation in the expression of IFN-gammaR2, but not with IFN-gammaR1 or suppressor of cytokine signaling-1. This dynamic regulation suggests that early IFN-gamma signals participate in regulation of the primary CD8(+) T cell response program, but that evading or minimizing IFN-gamma signals during expansion and the memory phase may contribute to appropriate regulation of the CD8(+) T cell response.

Regulation of IFN-gamma production by B effector 1 cells: essential roles for T-bet and the IFN-gamma receptor

This manuscript systematically identifies the molecular mechanisms that regulate the ability of B cells to produce the critical type 1 cytokine, IFN-gamma. B cells produce IFN-gamma in response to IL-12 and IL-18 and when primed by Th1 cells. We show that development of IFN-gamma-producing B cells by either Th1 cells or IL-12/IL-18 is absolutely dependent on expression of the IFN-gammaR and the T-box transcription factor, T-bet. Interestingly, although T-bet up-regulation in developing B effector 1 (Be1) cells is controlled by IFN-gammaR-mediated signals, STAT1-deficient B cells up-regulate T-bet and produce IFN-gamma, indicating that additional transcriptional activators must be coupled to the IFN-gammaR in B cells. Finally, we show that although IL-12/IL-18 or IFN-gamma-producing Th1 cells are required to initiate transcription of the IFN-gamma gene in B cells, sustained expression of IFN-gamma and T-bet by B cells is dependent on an IFN-gamma/IFN-gammaR/T-bet autocrine feedback loop. These findings have significant implications, because they suggest that IFN-gamma-producing B cells not only amplify Th1 responses, but also imprint a type 1 phenotype on B cells themselves. In the case of immune responses to bacterial or viral pathogens, this B cell-driven autocrine feedback loop is likely to be beneficial; however, in the case of B cell responses to autoantigens, it may result in amplification of the autoimmune loop and increased pathology.

B cell antigen receptor signaling enhances IFN-gamma-induced Stat1 target gene expression through calcium mobilization and activation of multiple serine kinase pathways

The signal transducers and activators of transcription 1 (Stat1) are essential for the majority of interferon-gamma (IFN-gamma)-regulated gene expression. Phosphorylation of serine 727 in the transcription activation domain of Stat1 is induced in response to IFN-gamma for maximal transcription activity. In this report, we show that crosslinking of B cell antigen receptor (BCR) or T cell antigen receptor (TCR) can enhance S727 phosphorylation in Stat1 and result in increased expression of Stat1 target genes. We further demonstrate that this enhancement by BCR cross-linking involves the widely used secondary messenger Ca2+ and simultaneous activation of multiple serine kinase pathways. When cells are exposed to both IFN-gamma and a Ca2+ fluxing reagent, the level of S727 phosphorylation is enhanced, resulting in increased transcription activation of Stat1 target genes. We directly demonstrate that the biochemical function of phospho-Ser-727 is to enhance the recruitment of transcription coactivator CBP/p300 to the promoters of Stat1 target genes. Furthermore, we show that both the p38 mitogen-activated protein kinase (MAPK) and the Ca(2+)/calmodulin-dependent kinase (CaMKII) are activated in response to BCR signaling to converge on Stat1 S727 for maximal gene expression. These studies demonstrate that a wide variety of noncytokine signaling pathways can modulate cytokine signaling through modulation of Stat1 serine phosphorylation.