IRF-8 regulates expansion of myeloid-derived suppressor cells and Foxp3+ regulatory T cells and modulates Th2 immune responses to gastrointestinal nematode infection

Interferon regulatory factor-8 (IRF-8) is critical for Th1 cell differentiation and negatively regulates myeloid cell development including myeloid-derived suppressor cells (MDSC). MDSC expand during infection with various pathogens including the gastrointestinal (GI) nematode Heligmosomoides polygyrus bakeri (Hpb). We investigated if IRF-8 contributes to Th2 immunity to Hpb infection. Irf8 expression was down-regulated in MDSC from Hpb-infected C57BL/6 (B6) mice. IRF-8 deficient Irf8^-/- and BXH-2 mice had significantly higher adult worm burdens than B6 mice after primary or challenge Hpb infection. During primary infection, MDSC expanded to a significantly greater extent in mesenteric lymph nodes (MLN) and spleens of Irf8^-/- and BXH-2 than B6 mice. CD4⁺GATA3⁺ T cells numbers were comparable in MLN of infected B6 and IRF-8 deficient mice, but MLN cells from infected IRF-8 deficient mice secreted significantly less parasite-specific IL-4 ex vivo. The numbers of alternatively activated macrophages in MLN and serum levels of Hpb-specific IgG1 and IgE were also significantly less in infected Irf8^-/- than B6 mice. The frequencies of antigen-experienced CD4⁺CD11a^hiCD49d^hi cells that were CD44^hiCD62L^- were similar in MLN of infected Irf8^-/- and B6 mice, but the proportions of CD4⁺GATA3⁺ and CD4⁺IL-4⁺ T cells were lower in infected Irf8^-/- mice. CD11b⁺Gr1⁺ cells from naïve or infected Irf8^-/- mice suppressed CD4⁺ T cell proliferation and parasite-specific IL-4 secretion in vitro albeit less efficiently than B6 mice. Surprisingly, there were significantly more CD4⁺ T cells in infected Irf8^-/- mice, with a higher frequency of CD4⁺CD25⁺Foxp3⁺ T (Tregs) cells and significantly higher numbers of Tregs than B6 mice. In vivo depletion of MDSC and/or Tregs in Irf8^-/- mice did not affect adult worm burdens, but Treg depletion resulted in higher egg production and enhanced parasite-specific IL-5, IL-13, and IL-6 secretion ex vivo. Our data thus provide a previously unrecognized role for IRF-8 in Th2 immunity to a GI nematode.

We investigated if IRF-8, which is critical for Th1 immunity and negatively regulates myeloid cell development including MDSC, contributes to Th2 immunity to the gastrointestinal nematode Heligmosomoides polygyrus bakeri (Hpb). Irf8 expression was down-regulated in MDSC from infected C57BL/6 (B6) mice. Hpb-infected IRF-8 deficient mice had significantly higher adult worm burdens than B6 mice. There were significantly more MDSC, fewer alternatively activated macrophages, lower serum levels of Hpb-specific antibodies in infected IRF-8 deficient than B6 mice, and MLN cells from infected IRF-8 deficient mice secreted less parasite-specific IL-4 ex vivo. There were similar frequencies of antigen-experienced CD4⁺CD11a^hiCD49d^hi T cells in MLN that were CD44^hiCD62L^- in infected Irf8^-/- and B6 mice, but lower proportions of CD4⁺GATA3⁺ and CD4⁺IL-4⁺ T cells in Irf8^-/- mice. Infected Irf8^-/- mice had a higher frequency of CD4⁺Foxp3⁺ T (Tregs) cells and significantly higher numbers of Tregs compared to infected B6 mice. MDSC from infected Irf8^-/- mice suppressed CD4⁺ T cell effector functions in vitro albeit less efficiently than B6 mice. Treg and/or MDSC depletion did not affect adult worm burdens in infected Irf8^-/- mice, but Treg depletion partially restored Th2 cytokine responses. These data highlight the importance of IRF-8 in Th2 immunity to Hpb infection.

Pplase of Dermatophagoides farinae promotes ovalbumin-induced airway allergy by modulating the functions of dendritic cells in a mouse model

Our previous studies revealed that many proteins in addition to the known allergens of D. farinae have not been fully characterized. We observed that Pplase did not respond to serum collected from patients sensitized to D. farinae. In a mouse model, Pplase significantly enhanced airway hyperresponsiveness (AHR) and Th2 responses induced by ovalbumin (OVA) compared with mice treated with OVA alone. Moreover, exposure to Pplase significantly increased the expression of IRF4, CD80, CD83, MHCII and TNF-α in DC2.4 cells, which was abolished in the presence of a TLR4 inhibitor. In vitro T cell polarization experiments revealed that Pplase alone could not induce T cell polarization but enhanced T cell polarization together with OVA. In addition, transfer of Pplase-primed bone marrow-derived DCs (BMDCs) to naïve mice enhanced AHR and Th2 immune responses in mice sensitized to OVA. In conclusion, Pplase is not an allergen of D. farinae but can activate DC cells to facilitate OVA-induced allergic responses.

Human Blood CD1c+ Dendritic Cells Encompass CD5high and CD5low Subsets That Differ Significantly in Phenotype, Gene Expression, and Functions

There are three major dendritic cell (DC) subsets in both humans and mice, that is, plasmacytoid DCs and two types of conventional DCs (cDCs), cDC1s and cDC2s. cDC2s are important for polarizing CD4+ naive T cells into different subsets, including Th1, Th2, Th17, Th22, and regulatory T cells. In mice, cDC2s can be further divided into phenotypically and functionally distinct subgroups. However, subsets of human cDC2s have not been reported. In the present study, we showed that human blood CD1c+ cDCs (cDC2s) can be further separated into two subpopulations according to their CD5 expression status. Comparative transcriptome analyses showed that the CD5high DCs expressed higher levels of cDC2-specific genes, including IFN regulatory factor 4, which is essential for the cDC2 development and its migration to lymph nodes. In contrast, CD5low DCs preferentially expressed monocyte-related genes, including the lineage-specific transcription factor MAFB. Furthermore, compared with the CD5low subpopulation, the CD5high subpopulation showed stronger migration toward CCL21 and overrepresentation among migratory DCs in lymph nodes. Additionally, the CD5high DCs induced naive T cell proliferation more potently than did the CD5low DCs. Moreover, CD5high DCs induced higher levels of IL-10-, IL-22-, and IL-4-producing T cell formation, whereas CD5low DCs induced higher levels of IFN-γ-producing T cell formation. Thus, we show that human blood CD1c+ cDC2s encompass two subsets that differ significantly in phenotype, that is, gene expression and functions. We propose that these two subsets of human cDC2s could potentially play contrasting roles in immunity or tolerance.

[Interleukin-2 signaling pathway regulating molecules in systemic lupus erythematosus]

Systemic lupus erythematosus (SLE) is a prototypic systemic autoimmune disease, which characterized by complex immunological abnormalities and multiple tissue and organ damages. The etiology and pathogenesis of SLE have not been entirely recognized. Genetic, environmental and viral infections and other factors might be related to the pathogenetic mechanisms of SLE. Interleukin-2 (IL-2) is a critical cytokine produced by T cells upon activation and is important for the generation of T regulatory cells and activation-induced cell death. In SLE patients, T cells display decreased capacity to produce IL-2. Impaired IL-2 expression resulted in decreased generation of regulatory T lymphocytes, and defect of activation-induced cell death. Former researches indicated that IL-2 deficiency in SLE is important for the pathogenesis and treatment of SLE. Several regulating molecules can affect the transcription of IL-2 gene and had an important role in the pathogenesis of SLE. These molecules include cyclic AMP-responsive element modulator (CREM), protein phosphatase 2A (PP2A), E-74 like factor 1 (Elf-1), B lymphocyte induced maturation protein-1 (Blimp-1) and interferon regulator factor 5 (IRF-5). CREM is a transcriptional inhibitor that can repress the transcription of the IL-2 gene by binding to the promoter of the IL-2 gene. PP2A is a Ser/Thr phosphatase that expressed in eukaryotic cells ubiquitously, it represents a negative regulator of the IL-2 gene promoter activity. Elf-1 belongs to the Ets family of transcription factors and can promote the expression of IL-2. Blimp-1 is a crucial transcription factors for regulating B lymphocyte terminal differentiation, an important function of Blimp-1 in T cells is to repress IL-2 gene transcription directly. Interferon regulatory factors (IRFs) are distinctive transcriptional regulators of type I interferons (IFNs) and IFN inducible genes, IRF-5 is a member of the IRFs family. IRF-5 is found to be increased in SLE and can regulate the production of IL-2 negatively. PP2A can inhibit the synthesis of IL-2 in two ways: on the one hand, activating the IL-2 transcription inhibitory factor CREMα, on the other hand, inhibiting IL-2 stimulating transcription factor Elf-1. While IRF-5 can activate the IL-2 transcription negative regulator Blimp-1 as to inhibit IL-2 expression. These molecules participate in the regulation of IL-2 through different pathways. This paper reviews the current knowledge of IL-2 signaling pathway regulating molecules in SLE.

Biallelic mutations in IRF8 impair human NK cell maturation and function

Human NK cell deficiencies are rare yet result in severe and often fatal disease, particularly as a result of viral susceptibility. NK cells develop from hematopoietic stem cells, and few monogenic errors that specifically interrupt NK cell development have been reported. Here we have described biallelic mutations in IRF8, which encodes an interferon regulatory factor, as a cause of familial NK cell deficiency that results in fatal and severe viral disease. Compound heterozygous or homozygous mutations in IRF8 in 3 unrelated families resulted in a paucity of mature CD56dim NK cells and an increase in the frequency of the immature CD56bright NK cells, and this impairment in terminal maturation was also observed in Irf8-/-, but not Irf8+/-, mice. We then determined that impaired maturation was NK cell intrinsic, and gene expression analysis of human NK cell developmental subsets showed that multiple genes were dysregulated by IRF8 mutation. The phenotype was accompanied by deficient NK cell function and was stable over time. Together, these data indicate that human NK cells require IRF8 for development and functional maturation and that dysregulation of this function results in severe human disease, thereby emphasizing a critical role for NK cells in human antiviral defense.

Total cellular protein presence of the transcription factor IRF8 does not necessarily correlate with its nuclear presence

The transcription factor interferon regulatory factor-8 (IRF8) plays an essential role in myeloid differentiation and lineage commitment, based largely on molecular and genetic studies. The detection of IRF8 in specific cell populations by flow cytometry (FCM) has the potential to provide new insights into normal and pathologic myelopoiesis, but critical validation of this protein-based approach, particularly in human samples, is lacking. In this study, the assessment of total cellular IRF8 presence was compared to its specific nuclear presence as assessed by imaging flow cytometry (IFC) analysis. Peptide neutralization of the IRF8-specific antibody that has been predominantly used to date in the literature served as a negative control for the immunofluorescent labeling. Expression of total IRF8 was analyzed by total cellular fluorescence analogous to the mean fluorescence intensity readout of conventional FCM. Additionally, specific nuclear fluorescence and the similarity score between the nuclear image (DAPI) and the corresponding IRF8 image for each cell were analyzed as parameters for nuclear localization of IRF8. IFC showed that peptide blocking eliminated binding of the IRF8 antibody in the nucleus. It also reduced cytoplasmic binding of the antibody but not to the extent observed in the nucleus. In agreement with the similarity score data, the total cellular IRF8 as well as nuclear IRF8 intensities decreased with peptide blocking. In healthy donor peripheral blood subpopulations and a positive control cell line (THP-1), the assessment of IRF8 by total cellular presence correlated well with its specific nuclear presence and correlated with the known distribution of IRF8 in these cells. In clinical samples of myeloid-derived suppressors cells derived from patients with renal carcinoma, however, total cellular IRF8 did not necessarily correlate with its nuclear presence. Discordance was primarily associated with peptide blocking having a proportionally greater effect on the IRF8 nuclear localization versus total fluorescence assessment. The data thus indicate that IRF8 can have cytoplasmic presence and that during disease its nuclear-cytoplasmic distribution may be altered, which may provide a basis for potential myeloid defects during certain pathologies.

Anti-Citrullinated Protein Antibodies Induce Macrophage Subset Disequilibrium in RA Patients

We used samples from rheumatoid arthritis (RA) patients to examine whether Anti-citrullinated protein antibodies (ACPAs) alter macrophage subset distribution and promote RA development. Macrophage subset distributions and interferon regulatory factor 4 (IRF4) and IRF5 expressions were analyzed. ACPAs were purified by affinity column. After RA and osteoarthritis (OA) patients' macrophages were cocultured with ACPAs, macrophage subsets and IRF4 and IRF5 expressions were measured. Small interfering RNAs (siRNAs) were transfected into ACPA-activated cells to suppress IRF4 or IRF5. Fluorescence-activated cell sorting (FACS), Western blot, and immunohistochemistry were performed. Macrophage subset disequilibrium occurred in RA patient synovial fluids. IRF4 and IRF5 were all expressed in the synovial fluid and synovium. ACPAs (40 IU/ml) could induce macrophages to polarize to M1 subsets, and the percentage of increased M1/M2 ratio of RA patients was higher than that of the OA patients. ACPAs also induce IRF4 and IRF5 protein expressions. IRF5 siRNA transfection impaired ACPA activity significantly. We demonstrated that macrophage subset disequilibrium occurred in RA patients. ACPAs induced IRF5 activity and led to M1 macrophage polarization.

Interferon Regulatory Factor 6 Has a Protective Role in the Host Response to Endotoxic Shock

Interferon Regulatory Factor (IRF) 6, a member of the IRF family, is essential for epidermal and orofacial embryonic development. Irf6 is strongly expressed in keratinocytes, in which it regulates epidermal proliferation, differentiation, and migration. A recent role for Irf6 in Toll-like receptor 2-dependent chemokine gene expression was also reported in an epithelial cell line. However, a function for Irf6 in innate immune cells was not previously reported. In the present study, we investigated the expression and function of Irf6 in bone marrow-derived neutrophils and macrophages. We show here, using a conditional knockout of Irf6 in lysosymeM expressing cells, that Irf6 is required for resistance to LPS-induced endotoxic shock. In addition, Irf6-deficient bone marrow-derived neutrophils exhibited increased chemotactic index and velocity compared with wild-type cells in vitro. TLR4-specific KC and IL6 secretions were upregulated in Irf6-deficient bone marrow-derived macrophages in vitro. These cells also exhibited an increased level of phosphorylated IkBa. Collectively, our findings suggest a role for Irf6 in the resistance to endotoxic shock due to NFk-B-mediated alteration of cytokine production.

Primary B Lymphocytes Infected with Kaposi's Sarcoma-Associated Herpesvirus Can Be Expanded In Vitro and Are Recognized by LANA-Specific CD4+ T Cells

Kaposi's sarcoma-associated herpesvirus (KSHV) has tropism for B lymphocytes, in which it establishes latency, and can also cause lymphoproliferative disorders of these cells manifesting as primary effusion lymphoma (PEL) and multicentric Castleman disease (MCD). T cell immunity is vital for the control of KSHV infection and disease; however, few models of B lymphocyte infection exist to study immune recognition of such cells. Here, we developed a model of B lymphocyte infection with KSHV in which infected tonsillar B lymphocytes were expanded by providing mitogenic stimuli and then challenged with KSHV-specific CD4(+)T cells. The infected cells expressed viral proteins found in PELs, namely, LANA and viral IRF3 (vIRF3), albeit at lower levels, with similar patterns of gene expression for the major latency, viral interleukin 6 (vIL-6), and vIRF3 transcripts. Despite low-level expression of open reading frame 50 (ORF50), transcripts for the immune evasion genes K3 and K5 were detected, with some downregulation of cell surface-expressed CD86 and ICAM. The vast majority of infected lymphocytes expressed IgM heavy chains with Igλ light chains, recapitulating the features seen in infected cells in MCD. We assessed the ability of the infected lymphocytes to be targeted by a panel of major histocompatibility complex (MHC) class II-matched CD4(+)T cells and found that LANA-specific T cells restricted to different epitopes recognized these infected cells. Given that at least some KSHV latent antigens are thought to be poor targets for CD8(+)T cells, we suggest that CD4(+)T cells are potentially important effectors for thein vivocontrol of KSHV-infected B lymphocytes.

IMPORTANCE

KSHV establishes a latent reservoir within B lymphocytes, but few models exist to study KSHV-infected B cells other than the transformed PEL cell lines, which have likely accrued mutations during the transformation process. We developed a model of KSHV-infected primary B lymphocytes that recapitulates features seen in PEL and MCD by gene expression and cell phenotype analysis, allowing the study of T cell recognition of these cells. Challenge of KSHV-infected B cells with CD4(+)T cells specific for LANA, a protein expressed in all KSHV-infected cells and malignanciesin vivo, showed that these effectors could efficiently recognize such targets. Given that the virus expresses immune evasion genes or uses proteins with intrinsic properties, such as LANA, that minimize epitope recognition by CD8(+)T cells, CD4(+)T cell immunity to KSHV may be important for maintaining the virus-host balance.

CCR7 and IRF4-dependent dendritic cells regulate lymphatic collecting vessel permeability

Lymphatic collecting vessels direct lymph into and from lymph nodes (LNs) and can become hyperpermeable as the result of a previous infection. Enhanced permeability has been implicated in compromised immunity due to reduced flow of lymph and immune cells to LNs, which are the primary site of antigen presentation to T cells. Presently, very little is known about the molecular signals that affect lymphatic collecting vessel permeability. Here, we have shown that lymphatic collecting vessel permeability is controlled by CCR7 and that the chronic hyperpermeability of collecting vessels observed in Ccr7-/- mice is followed by vessel fibrosis. Reexpression of CCR7 in DCs, however, was sufficient to reverse the development of such fibrosis. IFN regulatory factor 4-positive (IRF4+) DCs constitutively interacted with collecting lymphatics, and selective ablation of this DC subset in Cd11c-Cre Irf4fl/fl mice also rendered lymphatic collecting vessels hyperpermeable and fibrotic. Together, our data reveal that CCR7 plays multifaceted roles in regulating collecting vessel permeability and fibrosis, with one of the key players being IRF4-dependent DCs.

Multifunctional role of the transcription factor Blimp-1 in coordinating plasma cell differentiation

The transcription factor Blimp-1 is necessary for the generation of plasma cells. Here we studied its functions in plasmablast differentiation by identifying regulated Blimp-1 target genes. Blimp-1 promoted the migration and adhesion of plasmablasts. It directly repressed genes encoding several transcription factors and Aicda (which encodes the cytidine deaminase AID) and thus silenced B cell-specific gene expression, antigen presentation and class-switch recombination in plasmablasts. It directly activated genes, which led to increased expression of the plasma cell regulator IRF4 and proteins involved in immunoglobulin secretion. Blimp-1 induced the transcription of immunoglobulin genes by controlling the 3' enhancers of the loci encoding the immunoglobulin heavy chain (Igh) and κ-light chain (Igk) and, furthermore, regulated the post-transcriptional expression switch from the membrane-bound form of the immunoglobulin heavy chain to its secreted form by activating Ell2 (which encodes the transcription-elongation factor ELL2). Notably, Blimp-1 recruited chromatin-remodeling and histone-modifying complexes to regulate its target genes. Hence, many essential functions of plasma cells are under the control of Blimp-1.

Cigarette smoke inhibits ROCK2 activation in T cells and modulates IL-22 production

Gene-environment interactions are known to play a key role in the development of rheumatoid arthritis (RA). Exposure to cigarette smoke (CS) is one of the strongest environmental risk factors associated with RA and has been shown to mediate a range of complex immunomodulatory effects from decreased T and B cell activation to depressed phagocytic function. The effects of CS on the function of TH17 cells, one of the key TH effector subsets implicated in RA pathogenesis, are not fully understood. IRF4 is one of the crucial transcription factors involved in TH-17 differentiation and is absolutely required for the production of IL-17 and IL-21 but, interestingly, inhibits the synthesis of IL-22. The production of IL-17 and IL-21 by IRF4 can be augmented by its phosphorylation by the serine-threonine kinase ROCK2. Given that CS has been reported to increase ROCK activity in endothelial cells, here we investigated the effects of CS on the ROCK2-IRF4 axis in T cells. Surprisingly, we found that CS leads to decreased ROCK2 activation and IRF4 phosphorylation in T cells. This effect was associated with increased IL-22 production. Using a GEF pull-down assay we furthermore identify ARHGEF1 as a key upstream regulator of ROCK2 whose activity in T cells is inhibited by CS. Thus CS can inhibit the ROCK2-IRF4 axis and modulate T cell production of IL-22.

Regulatory T Cell Induction and Retention in the Lungs Drives Suppression of Detrimental Type 2 Th Cells During Pulmonary Cryptococcal Infection

Lethal disease caused by the fungus Cryptococcus neoformans is a consequence of the combined failure to control pulmonary fungal replication and immunopathology caused by induced type 2 Th2 cell responses in animal models. In order to gain insights into immune regulatory networks, we examined the role of regulatory T (Treg) cells in suppression of Th2 cells using a mouse model of experimental cryptococcosis. Upon pulmonary infection with Cryptococcus, Treg cells accumulated in the lung parenchyma independently of priming in the draining lymph node. Using peptide-MHC class II molecules to identify Cryptococcus-specific Treg cells combined with genetic fate-mapping, we noted that a majority of the Treg cells found in the lungs were induced during the infection. Additionally, we found that Treg cells used the transcription factor, IFN regulatory factor 4, to dampen harmful Th2 cell responses, as well as mediate chemokine retention of Treg cells in the lungs. Taken together, induction and IFN regulatory factor 4-dependent localization of Treg cells in the lungs allow Treg cells to suppress the deleterious effects of Th2 cells during cryptococcal infection.

Antiviral innate immunity through the lens of systems biology

Cellular innate immunity poses the first hurdle against invading viruses in their attempt to establish infection. This antiviral response is manifested with the detection of viral components by the host cell, followed by transduction of antiviral signals, transcription and translation of antiviral effectors and leads to the establishment of an antiviral state. These events occur in a rather branched and interconnected sequence than a linear path. Traditionally, these processes were studied in the context of a single virus and a host component. However, with the advent of rapid and affordable OMICS technologies it has become feasible to address such questions on a global scale. In the discipline of Systems Biology', extensive omics datasets are assimilated using computational tools and mathematical models to acquire deeper understanding of complex biological processes. In this review we have catalogued and discussed the application of Systems Biology approaches in dissecting the antiviral innate immune responses.

Functions of the two zebrafish MAVS variants are opposite in the induction of IFN1 by targeting IRF7

IFNs create the first line of host cells to defense viral infection, however, unrestricted expression of IFN can be hazardous to the host. IRF7 is the master regulator of type I IFN expression. To our knowledge, non research about the inhibition of IFN expression by targeting IRF7 has been reported in fish. In this study, we reported that the splicing variant of wildtype MAVS (MAVS_tv1), MAVS_tv2, negatively regulated IRF7-mediated IFN production. Firstly, in vivo, the transcriptional levels of MAVS_tv2 in trunk kidney and spleen from the zebrafish infected with SVCV were monitored. Then, in vitro, the protein expression pattern of MAVS_tv2 in zebrafish cell lines was detected using anti-MAVS_tv2 antibody. Furthermore, overexpression of MAVS_tv2 decreased the activation of IFN1 promoter that induced by IRF7 in a dose-dependent manner, whereas it had little effect on IRF3, a close relative of IRF7. In addition, such inhibition was also observed in IRF7-mediated epcIFN promoter and ISRE activities, but not in the activation of the promoters of type II IFNs and NF-ĸB, due to IRF7 not regulating their expression. Lastly, overexpression of MAVS_tv2 decreased the transcriptional levels of several IFN-stimulated genes activated by IRF7. These findings suggest that MAVS_tv2 is a negative regulator of IFN1 by targeting IRF7.

Genome-wide transcriptional profiling reveals that HIV-1 Vpr differentially regulates interferon-stimulated genes in human monocyte-derived dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells (APCs) that directly link the innate and adaptive immune responses. HIV-1 infection of DCs leads to a diverse array of changes in gene expression and play a major role in dissemination of the virus into T-cells. Although HIV-1 Vpr is a pleiotropic protein involved in HIV-1 replication and pathogenesis, its exact role in APCs such as DCs remains elusive. In this study, utilizing a microarray-based systemic biology approach, we found that HIV-1 Vpr differentially regulates (fold change >2.0) more than 200 genes, primarily those involved in the immune response and innate immune response including type I interferon signaling pathway. The differential expression profiles of select genes involved in innate immune responses (interferon-stimulated genes [ISGs]), including MX1, MX2, ISG15, ISG20, IFIT1, IFIT2, IFIT3, IFI27, IFI44L, and TNFSF10, were validated by real-time quantitative PCR; the results were consistent with the microarray data. Taken together, our findings are the first to demonstrate that HIV-1 Vpr induces ISGs and activates the type I IFN signaling pathway in human DCs, and provide insights into the role of Vpr in HIV-1 pathogenesis.

IRF-5-Mediated Inflammation Limits CD8+ T Cell Expansion by Inducing HIF-1α and Impairing Dendritic Cell Functions during Leishmania Infection

Inflammation is known to be necessary for promoting, sustaining, and tuning CD8⁺ T cell responses. Following experimental Leishmania donovani infection, the inflammatory response is mainly induced by the transcription factor IRF-5. IRF-5 is responsible for the activation of several genes encoding key pro-inflammatory cytokines, such as IL-6 and TNF. Here, we investigate the role of IRF-5-mediated inflammation in regulating antigen-specific CD8⁺ T cell responses during L. donovani infection. Our data demonstrate that the inflammatory response induced by IRF-5 limits CD8⁺ T cell expansion and induces HIF-1α in dendritic cells. Ablation of HIF-1α in CD11c⁺ cells resulted into a higher frequency of short-lived effector cells (SLEC), enhanced CD8⁺ T cell expansion, and increased IL-12 expression by splenic DCs. Moreover, mice with a targeted depletion of HIF-1α in CD11c⁺ cells had a significantly lower splenic parasite burden, suggesting that induction of HIF-1α may represent an immune evasive mechanism adopted by Leishmania parasites to establish persistent infections.

Inflammation is essential for inducing, sustaining, and regulating CD8⁺ T cell responses. The transcription factor IRF-5 is mainly responsible for initiating the inflammatory response following experimental Leishmani donovani infection. IRF-5 activates several genes encoding key pro-inflammatory cytokines, such as IL-6 and TNF. In this study, we investigate the role of IRF-5-mediated inflammation in regulating antigen-specific CD8⁺ T cell responses during L. donovani infection. Our data demonstrate that the inflammatory response induced by IRF-5 limits the expansion CD8⁺ T cell. This negative effect is mediated by the induction of HIF-1α in dendritic cells. Indeed, we observed a significant increase in CD8⁺ T cell expansion in mice lacking HIF-1α expression in dendritic cells. Moreover, these mice had a significantly lower parasite burden in the spleen, suggesting that induction of HIF-1α may represent an immune evasive mechanism adopted by Leishmania parasites to establish persistent infections.

Characterization and expression analyses of five interferon regulatory factor transcripts (Irf4a, Irf4b, Irf7, Irf8, Irf10) in Atlantic cod (Gadus morhua)

The interferon regulatory factor (IRF) family of genes encodes a group of transcription factors that have important roles not only in regulating the expression of Type I interferons (IFNs) and other genes in the IFN pathway, but also in growth, development and the regulation of oncogenesis. In this study, several IRF family members (Irf4a, Irf4b, Irf7, Irf8, Irf10) in Atlantic cod (Gadus morhua) were characterized at the cDNA and putative amino acid levels, allowing for phylogenetic analysis of these proteins in teleost fish, as well as the development of gene-specific primers used in RT-PCR and quantitative PCR (QPCR) analyses. Two Atlantic cod Irf10 splice variants were identified and their presence confirmed by sequencing of the Irf10 genomic region. RT-PCR showed that Irf7, Irf8 and both Irf10 transcripts were expressed in all 15 cod tissues tested, while Irf4a and Irf4b were absent in some tissues. QPCR analysis of spleen expression expanded upon this, and upon previous work. All IRF transcripts in the study were responsive to stimulation by the viral mimic poly(I:C), and all except Irf4a were responsive to exposure to formalin-killed Aeromonas salmonicida (ASAL). These IRF genes, thus, are likely important in the cod immune response to both viral and bacterial infections. Increased temperature (10 °C to 16 °C) was also observed to modulate the antibacterial responses of all IRF transcripts, and the antiviral responses of Irf4b and Irf10-v2. This research supports earlier studies which reported that elevated temperature modulates the expression of many immune genes in Atlantic cod.

Molecular characterization and expression analysis of eleven interferon regulatory factors in half-smooth tongue sole, Cynoglossus semilaevis

Interferon regulatory factors (IRFs) act as transcription mediators in virus-, bacteria-, and interferon (IFN)-induced signaling pathways and play diverse functions in antimicrobial defense, immune modulation, hematopoietic differentiation, and cell apoptosis. In this study, we described for the first time eleven IRFs (IRF1, IRF1L, IRF2X1, IRF3, IRF4a, IRF4b, IRF5, IRF6, IRF7, IRF8, and IRF9) from half-smooth tongue sole (Cynoglossus semilaevis) and examined their tissue distributions and expression patterns under different conditions. The deduced protein sequences of these IRFs (except IRF1) share high identities (71.8-86.6%) with other corresponding IRFs in other teleosts, whereas the sequence identity of IRF1 with the corresponding IRF1 in other teleosts is only 58.1%. A conserved N-terminal DNA binding domain (DBD), which is characterized by a winged type helix-loop-helix motif with four to six tryptophan repeats, is present in all IRFs. Another conserved IRF associated domain (IAD), which mediates the interactions in the C-terminal part of the protein, is present in all IRFs except IRF1 and IRF2X1, which instead contain the IAD2 domain. Several special domains also were found, including a serine-rich domain (SRD) in IRF3, IRF4a, IRF4b, and IRF7; a proline-rich domain (PRD) in IRF9; nuclear localization signals (NLSs) in IRF5, IRF8, and IRF9; and a virus activated domain (VAD) in IRF5. Quantitative real time RT-PCR (qRT-PCR) analysis showed that expression of all IRFs occurred in multiple tissues. IRF1, IRF2X1, IRF4a, IRF5, IRF7, and IRF8 exhibited relatively high levels of expression in immune organs, whereas the other five IRFs displayed high levels of expression in non-immune organs. Infection with extracellular and intracellular bacterial pathogens and virus upregulated the expression of IRFs in a manner that depended on tissue type, pathogen, and infection stage. Specifically, IRF1 and IRF2X1 were highly induced by bacterial and viral pathogens; IRF1L and IRF6 responded mainly to extracellular and intracellular bacterial pathogens; IRF3, IRF5, IRF7, IRF8, and IRF9 were markedly induced by intracellular bacterial pathogen and virus; IRF4a and IRF4b were mainly induced by virus and intracellular bacterial pathogen respectively. These results indicate that the IRFs of C. semilaevis can be categorized into several groups which exhibit different expression patterns in response to the infection of different microbial pathogens. These results provide new insights into the roles of teleost IRFs in antimicrobial immunity.

Hepatitis C virus and antiviral innate immunity: Who wins at tug-of-war?

Hepatitis C virus (HCV) is a major human pathogen of chronic hepatitis and related liver diseases. Innate immunity is the first line of defense against invading foreign pathogens, and its activation is dependent on the recognition of these pathogens by several key sensors. The interferon (IFN) system plays an essential role in the restriction of HCV infection via the induction of hundreds of IFN-stimulated genes (ISGs) that inhibit viral replication and spread. However, numerous factors that trigger immune dysregulation, including viral factors and host genetic factors, can help HCV to escape host immune response, facilitating viral persistence. In this review, we aim to summarize recent advances in understanding the innate immune response to HCV infection and the mechanisms of ISGs to suppress viral survival, as well as the immune evasion strategies for chronic HCV infection.

Comparative analysis of selected innate immune-related genes following infection of immortal DF-1 cells with highly pathogenic (H5N1) and low pathogenic (H9N2) avian influenza viruses

H5N1 and H9N2 viruses are important causes of avian influenza in China. H5N1 is typically associated with severe to fatal disease in poultry, while H9N2 is usually associated with mild disease. Differences in viral virulence prompted us to investigate whether innate immune responses would be differentially regulated following infection by H5N1 and H9N2 viruses. To address this hypothesis, expression of a panel of innate immune-related genes including IFN-α, IFN-β, Mx1, OASL, ISG12, IFIT5, IRF7, USP18, SST, and KHSRP in immortal DF-1 cells following H5N1 and H9N2 infection was analyzed and compared by real-time quantitative RT-PCR. Cells infected by either virus overall exhibited a similar expression profile for four ISGs (Mx1, OASL, ISG12, and IFIT5), IFN-α, IFN-β, and SST gene. However, two immune-regulatory genes (IRF7 and KHSRP) were not responsive to highly pathogenic H5N1 infection but were strongly up-regulated in DF-1 cells infected with low pathogenic H9N2 infection. The subtype-dependent host response observed in this study offers new insights into the potential roles of IRF7 and KHSRP in control and modulation of the replication and virulence of different subtypes or strains of avian influenza A virus.

IFN-gamma AU-rich element removal promotes chronic IFN-gamma expression and autoimmunity in mice

We generated a mouse model with a 162 nt AU-rich element (ARE) region deletion in the 3' untranslated region (3'UTR) of the interferon-gamma (IFN-γ) gene that results in chronic circulating serum IFN-γ levels. Mice homozygous for the ARE deletion (ARE-Del) (-/-) present both serologic and cellular abnormalities typical of patients with systemic lupus erythematosus (SLE). ARE-Del(-/-) mice display increased numbers of pDCs in bone marrow and spleen. Addition of IFN-γ to Flt3-ligand (Flt3L) treated in vitro bone marrow cultures results in a 2-fold increase in pDCs with concurrent increases in IRF8 expression. Marginal zone B (MZB) cells and marginal zone macrophages (MZMs) are absent in ARE-Del(-/-) mice. ARE-Del(+/-) mice retain both MZB cells and MZMs and develop no or mild autoimmunity. However, low dose clodronate treatment in ARE-Del(+/-) mice specifically eliminates MZMs and promotes anti-DNA antibody development and glomerulonephritis. Our findings demonstrate the consequences of a chronic IFN-γ milieu on B220(+) cell types and in particular the impact of MZB cell loss on MZM function in autoimmunity. Furthermore, similarities between disease states in ARE-Del(-/-) mice and SLE patients suggest that IFN-γ may not only be a product of SLE but may be critical for disease onset and progression.

Phenotypes and distribution of mucosal memory B-cell populations in the SIV/SHIV rhesus macaque model

As vaccine-elicited antibodies have now been associated with HIV protective efficacy, a thorough understanding of mucosal and systemic B-cell development and maturation is needed. We phenotyped mucosal memory B-cells, investigated isotype expression and homing patterns, and defined plasmablasts and plasma cells at three mucosal sites (duodenum, jejunum and rectum) in rhesus macaques, the commonly used animal model for pre-clinical vaccine studies. Unlike humans, macaque mucosal memory B-cells lacked CD27 expression; only two sub-populations were present: naïve (CD21(+)CD27(-)) and tissue-like (CD21(-)CD27(-)) memory. Similar to humans, IgA was the dominant isotype expressed. The homing markers CXCR4, CCR6, CCR9 and α4β7 were differentially expressed between naïve and tissue-like memory B-cells. Mucosal plasmablasts were identified as CD19(+)CD20(+/-)HLA-DR(+)Ki-67(+)IRF4(+)CD138(+/-) and mucosal plasma cells as CD19(+)CD20(-)HLA-DR(-)Ki-67(-)IRF4(+)CD138(+). Both populations were CD39(+/-)CD27(-). Plasma cell phenotype was confirmed by spontaneous IgA secretion by ELISpot of positively-selected cells and J-chain expression by real-time PCR. Duodenal, jejunal and rectal samples were similar in B-cell memory phenotype, isotype expression, homing receptors and plasmablast/plasma cell distribution among the three tissues. Thus rectal biopsies adequately monitor B-cell dynamics in the gut mucosa, and provide a critical view of mucosal B-cell events associated with development of vaccine-elicited protective immune responses and SIV/SHIV pathogenesis and disease control.

RNA-sequence analysis of primary alveolar macrophages after in vitro infection with porcine reproductive and respiratory syndrome virus strains of differing virulence

Porcine reproductive and respiratory syndrome virus (PRRSV) mainly infects porcine alveolar macrophages (PAMs), resulting in porcine reproductive and respiratory syndrome (PRRS) in pigs. Most of the transcriptomic studies on PAMs infected with PRRSV conducted thus far have made use of microarray technology. Here, we investigated the transcriptome of PAMs in vitro at 12 h post-infection with two European PRRSV strains characterized by low (Lelystad, LV) and high (Lena) virulence through RNA-Seq. The expression levels of genes, isoforms, alternative transcription start sites (TSS) and differential promoter usage revealed a complex pattern of transcriptional and post-transcriptional gene regulation upon infection with the two strains. Gene ontology analysis confirmed that infection of PAMs with both the Lena and LV strains affected signaling pathways directly linked to the innate immune response, including interferon regulatory factors (IRF), RIG1-like receptors, TLRs and PKR pathways. The results confirmed that interferon signaling is crucial for transcriptional regulation during PAM infection. IFN-β1 and IFN-αω, but not IFN-α, were up-regulated following infection with either the LV or Lena strain. The down-regulation of canonical pathways, such as the interplay between the innate and adaptive immune responses, cell death and TLR3/TLR7 signaling, was observed for both strains, but Lena triggered a stronger down-regulation than LV. This analysis contributes to a better understanding of the interactions between PRRSV and PAMs and outlines the differences in the responses of PAMs to strains with different levels of virulence, which may lead to the development of new PRRSV control strategies.

Value of melanocytic-associated immunohistochemical markers in the diagnosis of malignant melanoma: a review and update

Since the identification of S100 protein as an immunohistochemical marker that could be useful in the diagnosis of melanoma in the early 1980s, a large number of other melanocytic-associated markers that could potentially be used to assist in the differential diagnosis of these tumors have also been investigated. A great variation exists, however, among these markers, not only in their expression in some subtypes of melanoma, particularly desmoplastic melanoma, but also in their specificity because some of them can also be expressed in nonmelanocytic neoplasms, including various types of soft tissue tumors and carcinomas. This article reviews the information that is currently available on the practical value of some of the markers that have more often been recommended for assisting in the diagnosis of melanomas, including those that have only recently become available.