Enhancer role of STAT5 in CD2 activation of IFN-gamma gene expression

Comprehensive analysis of early T cell responses to acute Zika Virus infection during the first epidemic in Bahia, Brazil

BACKGROUND

In most cases, Zika virus (ZIKV) causes a self-limited acute illness in adults, characterized by mild clinical symptoms that resolve within a few days. Immune responses, both innate and adaptive, play a central role in controlling and eliminating virus-infected cells during the early stages of infection.

AIM

To test the hypothesis that circulating T cells exhibit phenotypic and functional activation characteristics during the viremic phase of ZIKV infection.

METHODS

A comprehensive analysis using mass cytometry was performed on peripheral blood mononuclear cells obtained from patients with acute ZIKV infection (as confirmed by RT-PCR) and compared with that from healthy donors (HD). The frequency of IFN-γ-producing T cells in response to peptide pools covering immunogenic regions of structural and nonstructural ZIKV proteins was quantified using an ELISpot assay.

RESULTS

Circulating CD4+ and CD8+ T lymphocytes from ZIKV-infected patients expressed higher levels of IFN-γ and pSTAT-5, as well as cell surface markers associated with proliferation (Ki-67), activation ((HLA-DR, CD38) or exhaustion (PD1 and CTLA-4), compared to those from HD. Activation of CD4+ and CD8+ memory T cell subsets, including Transitional Memory T Cells (TTM), Effector Memory T cells (TEM), and Effector Memory T cells Re-expressing CD45RA (TEMRA), was prominent among CD4+ T cell subset of ZIKV-infected patients and was associated with increased levels of IFN-γ, pSTAT-5, Ki-67, CTLA-4, and PD1, as compared to HD. Additionally, approximately 30% of ZIKV-infected patients exhibited a T cell response primarily directed against the ZIKV NS5 protein.

CONCLUSION

Circulating T lymphocytes spontaneously produce IFN-γ and express elevated levels of pSTAT-5 during the early phase of ZIKV infection whereas recognition of ZIKV antigen results in the generation of virus-specific IFN-γ-producing T cells.

NK Cell Responses in Zika Virus Infection Are Biased towards Cytokine-Mediated Effector Functions

Zika virus (ZIKV) is a mosquito-borne flavivirus that has emerged as a global concern because of its impact on human health. ZIKV infection during pregnancy can cause microcephaly and other severe brain defects in the developing fetus and there have been reports of the occurrence of Guillain-Barré syndrome in areas affected by ZIKV. NK cells are activated during acute viral infections and their activity contributes to a first line of defense because of their ability to rapidly recognize and kill virus-infected cells. To provide insight into NK cell function during ZIKV infection, we have profiled, using mass cytometry, the NK cell receptor-ligand repertoire in a cohort of acute ZIKV-infected female patients. Freshly isolated NK cells from these patients contained distinct, activated, and terminally differentiated, subsets expressing higher levels of CD57, NKG2C, and KIR3DL1 as compared with those from healthy donors. Moreover, KIR3DL1⁺ NK cells from these patients produced high levels of IFN-γ and TNF-α, in the absence of direct cytotoxicity, in response to in vitro stimulation with autologous, ZIKV-infected, monocyte-derived dendritic cells. In ZIKV-infected patients, overproduction of IFN-γ correlated with STAT-5 activation (r = 0.6643; p = 0.0085) and was mediated following the recognition of MHC class 1-related chain A and chain B molecules expressed by ZIKV-infected monocyte-derived dendritic cells, in synergy with IL-12 production by the latter cells. Together, these findings suggest that NK cells contribute to the generation of an efficacious adaptive anti-ZIKV immune response that could potentially affect the outcome of the disease and/or the development of persistent symptoms.

Twins with different personalities: STAT5B-but not STAT5A-has a key role in BCR/ABL-induced leukemia

Deregulation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway is found in cancer with STAT5A/B controlling leukemic cell survival and disease progression. As mutations in STAT5B, but not STAT5A, have been frequently described in hematopoietic tumors, we used BCR/ABL as model systems to investigate the contribution of STAT5A or STAT5B for leukemogenesis. The absence of STAT5A decreased cell survival and colony formation. Even more drastic effects were observed in the absence of STAT5B. STAT5B-deficient cells formed BCR/ABL+ colonies or stable cell lines at low frequency. The rarely evolving Stat5b-/- cell lines expressed enhanced levels of BCR/ABL oncoprotein compared to wild-type cells. In line, Stat5b-/- leukemic cells induced leukemia with a significantly prolonged disease onset, whereas Stat5a-/- cells rapidly caused a fatal disease superimposable to wild-type cells. RNA-sequencing (RNA-seq) profiling revealed a marked enhancement of interferon (IFN)-α and IFN-γ signatures in Stat5b-/- cells. Inhibition of IFN responses rescued BCR/ABL+ colony formation of Stat5b-/--deficient cells. A downregulated IFN response was also observed in patients suffering from leukemia carrying STAT5B mutations. Our data define STAT5B as major STAT5 isoform driving BCR/ABL+ leukemia. STAT5B enables transformation by suppressing IFN-α/γ, thereby facilitating leukemogenesis. Our findings might help explain the high frequency of STAT5B mutations in hematopoietic tumors.

Regulation of IFN-γ Expression

Interferon gamma, referred to here as IFN-γ, is a major component in immunological cell signaling and is a critical regulatory protein for overall immune system function. First discovered in 1965 (Wheelock Science 149: (3681)310-311, 1965), IFN-γ is the only Type II interferon identified. Its expression is both positively and negatively controlled by different factors. In this chapter, we will review the transcriptional and post-transcriptional control of IFN-γ expression. In the transcriptional control part, the regular activators and suppressors are summarized, we will also focus on the epigenetic control, such as chromosome access, DNA methylation, and histone acetylation. The more we learn about the control of this regulatory protein will allow us to apply this knowledge in the future to effectively manipulate IFN-γ expression for the treatment of infections, cancer, inflammation, and autoimmune diseases.

Memory-Like NK Cells: Remembering a Previous Activation by Cytokines and NK Cell Receptors

Natural Killer (NK) cells are cytotoxic innate lymphoid cells serving at the front line against infection and cancer. In inflammatory microenvironments, multiple soluble and contact-dependent signals modulate NK cell responsiveness. Besides their innate cytotoxic and immunostimulatory activity, it has been uncovered in recent years that NK cells constitute a heterogeneous and versatile cell subset. Persistent memory-like NK populations that mount a robust recall response were reported during viral infection, contact hypersensitivity reactions, and after stimulation by pro-inflammatory cytokines or activating receptor pathways. In this review, we highlight recent findings on the generation, functionality, and clinical applicability of memory-like NK cells and describe common features in comparison to other recent concepts of memory NK cells. Understanding of these features will facilitate the conception and design of novel NK cell-based immunotherapies.

A Synthetic Disaccharide Derivative of Diphyllin, TAARD, Activates Human Natural Killer Cells to Secrete Interferon-Gamma via Toll-Like Receptor-Mediated NF-κB and STAT3 Signaling Pathways

Natural products and their derivatives have long been used as pharmacological agents in the fight against cancer. Human natural killer (NK) cells are critical in our immune system in that they are capable of destroying tumor cells directly. However, there are few reports that elucidate the role of natural products in activating NK cells. In this study, we discovered that a synthetic disaccharide derivative of diphyllin, 4-O-{[2′′,3′′,4′′-tri-O-acetyl-α-D-arabinopyranosyl-(1′′→4′)]-2′,3′-di-O-acetyl-α-L-rhamnopyranosyl}diphyllin (TAARD), can alone stimulate interferon (IFN)-γ secretion in primary human NK cells and the NKL cell line. Additionally, it had an additive effect with IL-12 or IL-15 on IFN-γ production, but little adverse effects on NK cells. Mechanistically, TAARD induced the phosphorylation of NF-κB and STAT3, resulting in their binding on the IFNG promoter, which was dependent on TLR1 and TLR3 signaling, respectively. STAT3 and NF-κB knockdown with lentivirus shRNA as well as the NF-κB-specific inhibitor, N-tosyl-l-phenylalaninechloromethyl ketone, significantly suppressed TAARD-induced IFN-γ generation in primary NK cells. Blockade of TLR1 and TLR3 with neutralizing antibodies considerably decreased TAARD-induced activation of NF-κB and STAT3, respectively, as well as IFN-γ generation in NK cells. Collectively, our data suggest that TAARD can induce NK cell IFN-γ production through TLR1-NF-κB and TLR3-STAT3 signaling pathways, rendering its potential use as an agent for cancer prevention or treatment.

Dysregulation of the IFN-γ-STAT1 signaling pathway in a cell line model of large granular lymphocyte leukemia

T cell large granular lymphocyte leukemia (T-LGLL) is a rare incurable disease that is characterized by defective apoptosis of cytotoxic CD8+ T cells. Chronic activation of the Janus Kinase-Signal Transducer and Activator of Transcription (JAK-STAT) pathway is a hallmark of T-LGLL. One manifestation is the constitutive phosphorylation of tyrosine 701 of STAT1 (p-STAT1). T-LGLL patients also exhibit elevated serum levels of the STAT1 activator, interferon-γ (IFN-γ), thus contributing to an inflammatory environment. In normal cells, IFN-γ production is tightly controlled through induction of IFN-γ negative regulators. However, in T-LGLL, IFN-γ signaling lacks this negative feedback mechanism as evidenced by excessive IFN-γ production and decreased levels of suppressors of cytokine signaling 1 (SOCS1), a negative regulator of IFN-γ. Here we characterize the IFN-γ-STAT1 pathway in TL-1 cells, a cell line model of T-LGLL. TL-1 cells exhibited lower IFN-γ receptor protein and mRNA expression compared to an IFN-γ responsive cell line. Furthermore, IFN-γ treatment did not induce JAK2 or STAT1 activation or transcription of IFN-γ-inducible gene targets. However, IFN-β induced p-STAT1 and subsequent STAT1 gene transcription, demonstrating a specific IFN-γ signaling defect in TL-1 cells. We utilized siRNA targeting of STAT1, STAT3, and STAT5b to probe their role in IL-2-mediated IFN-γ regulation. These studies identified STAT5b as a positive regulator of IFN-γ production. We also characterized the relationship between STAT1, STAT3, and STAT5b proteins. Surprisingly, p-STAT1 was positively correlated with STAT3 levels while STAT5b suppressed the activation of both STAT1 and STAT3. Taken together, these results suggest that the dysregulation of the IFN-γ-STAT1 signaling pathway in TL-1 cells likely results from low levels of the IFN-γ receptor. The resulting inability to induce negative feedback regulators explains the observed elevated IL-2 driven IFN-γ production. Future work will elucidate the best way to target this pathway, with the ultimate goal to find a better therapeutic for T-LGLL.

The competitive nature of signal transducer and activator of transcription complex formation drives phenotype switching of T cells

Signal transducers and activators of transcription (STATs) are key molecular determinants of T-cell fate and effector function. Several inflammatory diseases are characterized by an altered balance of T-cell phenotypes and cytokine secretion. STATs, therefore, represent viable therapeutic targets in numerous pathologies. However, the underlying mechanisms by which the same STAT proteins regulate both the development of different T-cell phenotypes and their plasticity during changes in extracellular conditions remain unclear. In this study, we investigated the STAT-mediated regulation of T-cell phenotype formation and plasticity using mathematical modelling and experimental data for intracellular STAT signalling proteins. The close fit of our model predictions to the experimental data allows us to propose a potential mechanism for T-cell switching. According to this mechanism, T-cell phenotype switching is the result of the relative redistribution of STAT dimer complexes caused by the extracellular cytokine-dependent STAT competition effects. The developed model predicts that the balance between the intracellular STAT species defines the amount of the produced cytokines and thereby T-cell phenotypes. The model predictions are consistent with the experimentally observed interferon-γ to interleukin-10 switching that regulates human T helper type 1/type 1 regulatory T-cell responses. The proposed model is applicable to a number of STAT signalling circuits.

IL-12 and IL-18 induce interferon-γ production and de novo CD2 expression in porcine γδ T cells

γδ T cells are highly abundant in the blood and spleen of pigs but little is known about their functional differentiation. In this study the potential of the type-1 polarizing cytokines IL-12 and IL-18 in combination with IL-2 and Concanavalin A (ConA) to stimulate porcine γδ T cells was investigated. Stimulation of purified γδ T cells with ConA and IL-2 induced a strong proliferation of CD2(-) γδ T cells, whereas additional stimulation with IL-12 and IL-18 caused a stronger proliferation of CD2(+) γδ T cells. IFN-γ could only be detected in supernatants of γδ T-cell cultures supplemented with IL-12 and IL-18. Experiments with sorted CD2/SWC5-defined γδ T-cell subsets revealed that CD2(+)SWC5(-) γδ T cells are the main producers of IFN-γ following stimulation with IL-2/IL-12/IL-18. Additional stimulation with ConA led to an upregulation of CD2 within the CD2(-) γδ T cell subsets, indicating a previously unnoticed plasticity of CD2-defined γδ T cell subsets.

IL-2 phosphorylates STAT5 to drive IFN-γ production and activation of human dendritic cells

Human dendritic cells (hDCs) produce IL-2 and express IL-2R α-chain (CD25), but the role of IL-2 in DC functions is not well defined. A recent study suggested that the main function of CD25 on hDCs was to transpresent IL-2 to activate T lymphocytes. Our results demonstrate the expression of the three chains of the IL-2R on hDCs and that IL-2 induces STAT5 phosphorylation. Interestingly, use of inhibitors of p-STAT5 revealed that IL-2 increases LPS-induced IFN-γ through STAT5 phosphorylation. Finally, we report that IL-2 increases the ability of hDCs to activate helpless CD8(+) T cells, most likely because of IL-2-triggered IFN-γ synthesis, as we previously described. For the first time, to our knowledge, we disclose that IL-2 induces monocyte-derived hDC's functional maturation and activation through IL-2R binding. Interestingly, our study suggests a direct effect of anti-CD25 mAbs on hDCs that may contribute to their clinical efficacy.

Leukemic priming of resting NK cells is killer Ig-like receptor independent but requires CD15-mediated CD2 ligation and natural cytotoxicity receptors

Resting human NK cells require a two-stage activation process that we have previously described as "priming" and "triggering." NK-sensitive tumor cells provide both priming and triggering signals. NK-resistant tumors evade lysis, mostly by failure to prime; however, we recently reported a tumor cell line (CTV-1) that primes resting NK cells but fails to trigger lysis. In this article, we report two additional leukemia cell lines that prime NK cells but are resistant to lysis. Tumor-mediated NK priming is via CD2 binding to a ligand within CD15 on the tumor cell. NK-resistant RAJI cells became susceptible to NK lysis following transfection and expression of CD15. Blockade of CD15 on K562 cells or on CD15(+) RAJI cells significantly inhibited lysis, as did blockade of CD2 on resting NK cells. NK priming via CD2 induced CD16 shedding, releasing CD3ζ to the CD2, leading to its phosphorylation and the subsequent phosphorylation of linker for activation of T cells and STAT-5 and synthesis of IFN-γ. Blockade of C-type lectin receptors significantly suppressed the tumor-mediated priming of NK cells, whereas blockade of Ig-superfamily-like receptors had no effect at the NK-priming stage. Tumor priming of resting NK cells was irrespective of HLA expression, and blockade of HLA-killer Ig-like receptor interactions did not influence the incidence or degree of priming. However, CD15-CD2 interactions were critical for NK priming and were required, even in the absence of HLA-mediated NK inhibition. Tumor-mediated priming led to a sustained primed state, and the activated NK cells retained the ability to lyse NK-resistant tumors, even after cryopreservation.

Kaposi's sarcoma-associated herpesvirus viral interferon regulatory factor 3 inhibits gamma interferon and major histocompatibility complex class II expression

Kaposi's sarcoma-associated herpesvirus (KSHV) carries four genes with homology to human interferon regulatory factors (IRFs). One of these IRFs, the viral interferon regulatory factor 3 (vIRF-3), is expressed in latently infected primary effusion lymphoma (PEL) cells and required for their continuous proliferation. Moreover, vIRF-3 is known to be involved in modulation of the type I interferon (IFN) response. We now show that vIRF-3 also interferes with the type II interferon system and antigen presentation to the adaptive immune system. Starting with an analysis of the transcriptome, we show that vIRF-3 inhibits expression of major histocompatibility complex class II (MHC II) molecules: small interfering RNA (siRNA)-mediated knockdown of vIRF-3 in KSHV-infected PEL cell lines resulted in increased MHC II levels; overexpression of vIRF-3 in KSHV-negative B cells leads to downmodulation of MHC II. This regulation could be traced back to inhibition of class II transactivator (CIITA) transcription by vIRF-3. Reporter assays revealed that the gamma interferon (IFN-γ)-sensitive CIITA promoters PIV and PIII were inhibited by vIRF-3. Consistently, IFN-γ levels increased upon vIRF-3 knockdown in PEL cells. IFN-γ regulation by vIRF-3 was confirmed in reporter assays as well as by upregulation of typical IFN-γ target genes upon knockdown of vIRF-3 in PEL cells. In summary, we conclude that vIRF-3 contributes to the viral immunoevasion by downregulation of IFN-γ and CIITA and thus MHC II expression.

Modulation of IL-2 expression after uptake of hepatitis C virus non-enveloped capsid-like particles: the role of p38 kinase

Hepatitis C virus (HCV) has been shown to actively replicate in cells of the immune system, altering both their function and cytokine expression. Naked nucleocapsids have been reported in the serum of infected patients. We investigated interference of recombinant non-enveloped capsid-like particles with signaling pathways in T cells. HCV non-enveloped particles (HCVne) internalization was verified in Jurkat and Hut 78 T cells, as well as primary human peripheral blood and intrahepatic mononuclear cells. HCVne uptake leads to activation of the MAPKs-p38 signaling pathway. Using specific phosphoantibodies, signaling pathways inhibitors, and chemical agents, it was demonstrated that p38 activation in T cells correlated with IL-2 transcriptional activation and was accompanied by a parallel increase of IL-2 cytokine secretion. c-fos and egr-1, two transcription factors, essential for IL-2 promoter activity, were also found to be elevated. We propose that HCVne uptake by T lymphocytes results in increased MAPKs-p38 activity and IL-2 expression, thus altering the host immune response.

Janus-kinase-3-dependent signals induce chromatin remodeling at the Ifng locus during T helper 1 cell differentiation

Differentiation of naive CD4+ T cells into T helper type 1 (Th1) effector cells requires both T cell receptor (TCR) signaling and cytokines such as interleukin-12 and interferon gamma (IFN-gamma). Here, we report that a third cytokine signal, mediated by the Janus family tyrosine kinase 3 (Jak3) and signal transducer and activator of transcription 5 (STAT5) pathway, is also required for Th1 cell differentiation. In the absence of Jak3-dependent signals, naive CD4+ T cells proliferate robustly but produce little IFN-gamma after Th1 cell polarization in vitro. This defect is not due to reduced activation of STAT1 or STAT4 or to impaired upregulation of the transcription factor T-bet. Instead, we find that T-bet binding to the Ifng promoter is greatly diminished in the absence of Jak3-dependent signals, correlating with a decrease in Ifng promoter accessibility and histone acetylation. These data indicate that Jak3 regulates epigenetic modification and chromatin remodeling of the Ifng locus during Th1 cell differentiation.

Regulation of interferon-gamma during innate and adaptive immune responses

Interferon-gamma (IFN-gamma) is crucial for immunity against intracellular pathogens and for tumor control. However, aberrant IFN-gamma expression has been associated with a number of autoinflammatory and autoimmune diseases. This cytokine is produced predominantly by natural killer (NK) and natural killer T (NKT) cells as part of the innate immune response, and by Th1 CD4 and CD8 cytotoxic T lymphocyte (CTL) effector T cells once antigen-specific immunity develops. Herein, we briefly review the functions of IFN-gamma, the cells that produce it, the cell extrinsic signals that induce its production and influence the differentiation of naïve T cells into IFN-gamma-producing effector T cells, and the signaling pathways and transcription factors that facilitate, induce, or repress production of this cytokine. We then review and discuss recent insights regarding the molecular regulation of IFN-gamma, focusing on work that has led to the identification and characterization of distal regulatory elements and epigenetic modifications with the IFN-gamma locus (Ifng) that govern its expression. The epigenetic modifications and three-dimensional structure of the Ifng locus in naive CD4 T cells, and the modifications they undergo as these cells differentiate into effector T cells, suggest a model whereby the chromatin architecture of Ifng is poised to facilitate either rapid opening or silencing during Th1 or Th2 differentiation, respectively.

Expression of Jak2V617F causes a polycythemia vera-like disease with associated myelofibrosis in a murine bone marrow transplant model

An acquired somatic mutation, Jak2V617F, was recently discovered in most patients with polycythemia vera (PV), chronic idiopathic myelofibrosis (CIMF), and essential thrombocythemia (ET). To investigate the role of this mutation in vivo, we transplanted bone marrow (BM) transduced with a retrovirus expressing either Jak2 wild-type (wt) or Jak2V617F into lethally irradiated syngeneic recipient mice. Expression of Jak2V617F, but not Jak2wt, resulted in clinicopathologic features that closely resembled PV in humans. These included striking elevation in hemoglobin level/hematocrit, leukocytosis, megakaryocyte hyperplasia, extramedullary hematopoiesis resulting in splenomegaly, and reticulin fibrosis in the bone marrow. Histopathologic and flow cytometric analyses showed an increase in maturing myeloid lineage progenitors, although megakaryocytes showed decreased polyploidization and staining for acetylcholinesterase. In vitro analysis of primary cells showed constitutive activation of Stat5 and cytokine-independent growth of erythroid colony-forming unit (CFU-E) and erythropoietin hypersensitivity, and Southern blot analysis for retroviral integration indicated that the disease was oligoclonal. Furthermore, we observed strain-specific differences in phenotype, with Balb/c mice demonstrating markedly elevated leukocyte counts, splenomegaly, and reticulin fibrosis compared with C57Bl/6 mice. We conclude that Jak2V617F expression in bone marrow progenitors results in a PV-like syndrome with myelofibrosis and that there are strain-specific modifiers that may in part explain phenotypic pleiotropy of Jak2V617F-associated myeloproliferative disease in humans.

IL-2 absorption affects IFN-γ and IL-5, but not IL-4 producing memory T cells in double color cytokine ELISPOT assays

Cytokine assays are gaining increasing importance for human immune monitoring because they reliably detect antigen-specific T cells in primary PBMC, even at low clonal sizes. Double color ELISPOT assays permit the simultaneous visualization of cells producing two different cytokines. Permitting the simultaneous assessment of type 1 and 2 immunity and due to the limited numbers of PBMC available from human study subjects, double color assays should be particularly attractive for clinical trials. Since the performance of double color assays has not yet been validated, we set out to compare them to single color measurements. Testing the recall antigen-induced cytokine response of PBMC, we found that double color assays regularly provided lower numbers of IFN-gamma and IL-5 spots than single color measurements when IL-2 detection was part of the double color assay. We showed that the inhibitory effect resulted from IL-2 absorption and could be overcome by either antibody free preactivation cultures or by inclusion of anti-CD28 antibody. In contrast, the simultaneous detection of IL-2 did not affect the numbers of IL-4 spots. Therefore, unlike IL-2/IL-4 and IFN-gamma/IL-5 assays, IL-2/IFN-gamma, and IL-2/IL-5 assays require compensation for the IL-2 capture to provide accurate numbers for the frequencies of cytokine producing memory T cells.