Cutting edge: Type I IFN reverses human Th2 commitment and stability by suppressing GATA3

T helper 2 cells regulate inflammatory responses to helminth infections while also mediating pathological processes of asthma and allergy. IL-4 promotes Th2 development by inducing the expression of the GATA3 transcription factor, and the Th2 phenotype is stabilized by a GATA3-dependent autoregulatory loop. In this study, we found that type I IFN (IFN-alpha/beta) blocked human Th2 development and inhibited cytokine secretion from committed Th2 cells. This negative regulatory pathway was operative in human but not mouse CD4(+) T cells and was selective to type I IFN, as neither IFN-gamma nor IL-12 mediated such inhibition. IFN-alpha/beta blocked Th2 cytokine secretion through the inhibition of GATA3 during Th2 development and in fully committed Th2 cells. Ectopic expression of GATA3 via retrovirus did not overcome IFN-alpha/beta-mediated inhibition of Th2 commitment. Thus, we demonstrate a novel role for IFN-alpha/beta in blocking Th2 cells, suggesting its potential as a promising therapy for atopy and asthma.

Acquistion of Effector and Memory Responses is Reciprocally Regulated by IL-12 and IFN-α/β in Human CD8+ T Cells (96.8)

The innate cytokines IL-12 and IFN-α/β act in concert to facilitate clearance of intracellular pathogens. However their precise role in promoting human T cell responses is still unclear. In this study, we demonstrate that these cytokines regulate distinct aspects of effector and memory human CD8+ T cell differentiation. We found that IL-12 programs the development of TEM cells which secrete high levels of IFN-γand TNF-α and attain strong cytolytic activity. Programming of TEM cells by IL-12 correlated to the induction of the IL-12 receptor β 2 (IL-2Rβ2) and was associated with cells which had undergone rapid division. Alternatively, IFN- α/β enhanced a population of TCM cells which expressed high levels of the lymph node homing receptor CCR7. This population did not display immediate effector activity however, upon secondary activation, were capable of rapid proliferation and acquisition of both memory and effector phenotypes. TCM development was regulated by IFN-αand proceeded by slowing the progression of cell division in a subpopulation of cells that selectively expressed elevated IFN- α/βreceptor-2 (IFNAR2). We further examined the effects of the strength of TCR signal on TEM and TCM development. In the presence of both IL-12 and IFN- α/β, these cytokine signals were amplified as the strength of the TCR signal was increased, promoting the simultaneous development of both TCM and TEM. Together, our results support a novel model in which IL-12 and IFN- α/βact in a non-redundant manner to regulate the co-linear generation of both effector and memory cells.

This study is supported by a grant from the National Institutes of Health/National Institute of Allergy and Infectious Disease (AI56222) and by a predoctoral fellowship from the National Instititue of Health/Nation Institute of Allergy and Infectious Disease (AI68622).

Negative Regulation of Human Th2 cells by Type I Interferon (140.15)

Type I interferon (IFN-α/β) is a potent anti-viral cytokine that regulates multiple aspects of innate and adaptive responses to viral infections. As some respiratory viral infections have been linked to the etiology and exacerbation of asthma, we wished to determine the effects of IFN-α/β on driving the development of human Th2 cells. In these studies, we found that IFNα/β inhibited the ability of IL-4 to promote Th2 differentiation and significantly de-stablized cytokine expression from fully polarized Th2 cells. Further, this effect was specific to IFNα/β as neither IL-12 nor IFNγ inhibited IL-4-regulated Th2 development or stability. IFNα/β inhibited Th2 development by blocking the induction of GATA-3, and this effect was found to bypass the induction of GATA3 via IL-4-mediated STAT6 activation. Finally, IFNα/β also potently inhibited Th2 cytokine secretion from fully committed CRTH2+ cells isolated directly from peripheral blood. Thus, we have found a novel function of IFNα/β in the inhibition of Th2 responses that may be useful as a therapeutic approach for the treatment of asthma.

Cutting edge: a T-bet-independent role for IFN-alpha/beta in regulating IL-2 secretion in human CD4+ central memory T cells

IL-2 is a hallmark cytokine secreted by central memory CD4(+) T cells (T(CM)). Although naive cells rapidly secrete IL-2 in response to Ag stimulation, IL-12 inhibits IL-2 secretion in daughter cells as they differentiate into Th1 cells. In this study, we uncover a unique role for IFN-alpha in regulating IL-2 secretion by human T(CM) cells. IFN-alpha synergized with IL-12 to enhance a subset of cells that secreted high and sustained levels of IL-2. These IL-2-secreting cells displayed phenotypic and functional characteristics of T(CM) and were capable of generating IFN-gamma-secreting effectors upon secondary activation. T-bet has been implicated in negatively regulating IL-2 secretion in murine T cells; however, T-bet expression did not inhibit IFN-alpha-dependent IL-2 secretion in human T(CM) cells. Thus, our results highlight a unique role for IFN-alpha in regulating the development of IL-2-secreting human T(CM) cells.

The protein tyrosine phosphatase PTPN4/PTP-MEG1, an enzyme capable of dephosphorylating the TCR ITAMs and regulating NF-kappaB, is dispensable for T cell development and/or T cell effector functions

T cell receptor signaling processes are controlled by the integrated actions of families of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPases). Several distinct cytosolic protein tyrosine phosphatases have been described that are able to negatively regulate TCR signaling pathways, including SHP-1, SHP-2, PTPH1, and PEP. Using PTPase substrate-trapping mutants and wild type enzymes, we determined that PTPN4/PTP-MEG1, a PTPH1-family member, could complex and dephosphorylate the ITAMs of the TCR zeta subunit. In addition, the substrate-trapping derivative augmented basal and TCR-induced activation of NF-kappaB in T cells. To characterize the contribution of this PTPase in T cells, we developed PTPN4-deficient mice. T cell development and TCR signaling events were comparable between wild type and PTPN4-deficient animals. The magnitude and duration of TCR-regulated ITAM phosphorylation, as well as overall protein phosphorylation, was unaltered in the absence of PTPN4. Finally, Th1- and Th2-derived cytokines and in vivo immune responses to Listeria monocytogenes were equivalent between wild type and PTPN4-deficient mice. These findings suggest that additional PTPases are involved in controlling ITAM phosphorylations.

Blockade of virus infection by human CD4+ T cells via a cytokine relay network

CD4(+) T cells directly participate in bacterial clearance through secretion of proinflammatory cytokines. Although viral clearance relies heavily on CD8(+) T cell functions, we sought to determine whether human CD4(+) T cells could also directly influence viral clearance through cytokine secretion. We found that IFN-gamma and TNF-alpha, secreted by IL-12-polarized Th1 cells, displayed potent antiviral effects against a variety of viruses. IFN-gamma and TNF-alpha acted directly to inhibit hepatitis C virus replication in an in vitro replicon system, and neutralization of both cytokines was required to block the antiviral activity that was secreted by Th1 cells. IFN-gamma and TNF-alpha also exerted antiviral effects against vesicular stomatitis virus infection, but in this case, functional type I IFN receptor activity was required. Thus, in cases of vesicular stomatitis virus infection, the combination of IFN-gamma and TNF-alpha secreted by human Th1 cells acted indirectly through the IFN-alpha/beta receptor. These results highlight the importance of CD4(+) T cells in directly regulating antiviral responses through proinflammatory cytokines acting in both a direct and indirect manner.

IFN-alpha is not sufficient to drive Th1 development due to lack of stable T-bet expression

During inflammatory immune responses, the innate cytokine IL-12 promotes CD4+ Th-1 development through the activation of the second messenger STAT4 and the subsequent expression of T-bet. In addition, type I IFN (IFN-alphabeta), secreted primarily during viral and intracellular bacterial infections, can promote STAT4 activation in human CD4+ T cells. However, the role of IFN-alphabeta in regulating Th1 development is controversial, and previous studies have suggested a species-specific pathway leading to Th1 development in human but not mouse CD4+ T cells. In this study, we found that although both IFN-alpha and IL-12 can promote STAT4 activation, IFN-alpha failed to promote Th1 commitment in human CD4+ T cells. The difference between these innate signaling pathways lies with the ability of IL-12 to promote sustained STAT4 tyrosine phosphorylation, which correlated with stable T-bet expression in committed Th1 cells. IFN-alpha did not promote Th1 development in human CD4+ T cells because of attenuated STAT4 phosphorylation, which was insufficient to induce stable expression of T-bet. Further, the defect in IFN-alpha-driven Th1 development was corrected by ectopic expression of T-bet within primary naive human CD4+ T cells. These results indicate that IL-12 remains unique in its ability to drive Th1 development in human CD4+ T cells and that IFN-alpha lacks this activity due to its inability to promote sustained T-bet expression.

Distinct Effects of IL-12 and IFN-a/b on CD8 T cell Effector Functions (95.18)

During viral infections, CD8 T cells act to promote immunity by eliminating virally infected cells. To accomplish this they employ immediate effector functions and promote the generation of memory populations with the capacity to respond to secondary challenge. The innate cytokines IL-12 and type I interferon (IFNa/b) have been shown to participate in both the effector and memory CD8 T cell response. However, the independent and direct pathways they activate have not been well characterized. We have recently examined the direct and independent roles of these cytokines on naïve human CD45RA+ CD27+CD8+ T cells developing in vitro. In these studies, we observed that IL-12 but not IFNa/b promote the generation of CD8 T cells capable of secreting IFN-g upon secondary challenge. Further, this correlates to enhanced CXCR3 expression, a chemokine receptor which homes cells to the site of primary infection. In contrast IFNa/b enhanced the expression of CCR7 which plays an important role in the trafficking of cells to the secondary lymphoid organs. Both IL-12 and IFNa/b augmented the expression of the cytolytic factors perforin and granzyme, however, polarization with both IL-12 and IFNa/b promoted enhanced cytolytic killing than polarization by either cytokine alone. Taken together, these results demonstrate that IL-12 and IFNa/b participate in both overlapping as well as unique pathways in human CD8 T cell development which may function to promote diverse immune responses dependent on the pathogen or cytokine milieu encountered during infection.

Measurement of nuclear translocation in primary cells using correlation analysis of images obtained on the ImageStream imaging flow cytometer (87.13)

Signal transduction pathways regulate T cell activation and differentiation and have a critical influence on the outcome of adaptive immune responses. It has recently been shown that nuclear translocation events within non-adherent tumor cells can be quantified by correlating transnscription factor and nuclear images collected on the ImageStream multispectral imaging flow cytometer. Here we extend the quantitative technique to the study of nuclear localization within primary human or murine T cells in the following systems:

translocation of T-bet in CD4 cells derived from murine spleen and lymph node cellstranslocation of NFAT in tetramer positive CD8 cells from human peripheral blood,translocation of NFκB in CD4+CD8+ thymocytes involved in conjugates with APC presenting cognate peptide, andlocalization of phosphorylated STAT4 in human CD4 cells following cytokine stimulation.

These data demonstrate image-based nuclear localzation within primary cells with large nuclear to cytoplasmic area ratios using ImageStream technology.

Type I interferon and IL-12 induce phenotypic variegation of human CD4+ T cells (43.7)

Antigen presenting cells secrete distinct patterns of innate cytokines upon activation via Toll-like receptors (TLRs). These innate cytokines shape adaptive immune responses to pathogens. For example, interleukin 12 (IL-12) is produced in response to bacterial recognition via TLRs 2, 4, 5, and 6. IL-12 induces CD4+ T helper 1 (Th1) cell development through the activation of signal transducer and activator of transcription 4 (STAT4), leading to the secretion of interferon gamma (IFN-γ). Conversely, during viral infection, signaling through TLRs 3, 7, and 9 results in the secretion of both IL-12 and type I interferon (IFN-α/β). The effects of combined IL-12 and IFN-α/β stimulation on T helper development are not well-studied. We have demonstrated that activation of naïve CD4+ T cells in the presence of IFN-α/β alone fails to induce Th1 development. However, a combination of IL-12 and IFN-α/β induces phenotypic variegation to generate two populations of T helper cells. An effector population secretes both IFN-γ and IFN-α/β, and these cells are efficient in eliminating viral infections in vitro. A second subset displays memory properties and may be involved in long-term viral immunity. Furthermore, these two subsets can be distinguished by expression of chemokine receptors. These data have important implications for the understanding of viral infections as well as for the development of novel vaccines and therapies.

Distinct characteristics of murine STAT4 activation in response to IL-12 and IFN-alpha

The role of type I IFN in Th1 development, STAT4 activation, and IFN-gamma production in murine T cells has remained unresolved despite extensive examination. Initial studies indicated that IFN-alpha induced Th1 development and IFN-gamma production in human, but not murine, T cells, suggesting species-specific differences in signaling. Later studies suggested that IFN-alpha also induced Th1 development in mice, similar to IL-12. More recent studies have questioned whether IFN-alpha actually induces Th1 development even in the human system. In the present study, we compared the capacity of IL-12 and IFN-alpha to induce Th1 differentiation, STAT4 phosphorylation, and IFN-gamma production in murine T cells. First, we show that IFN-alpha, in contrast to IL-12, cannot induce Th1 development. However, in differentiated Th1 cells, IFN-alpha can induce transient, but not sustained, STAT4 phosphorylation and, in synergy with IL-18, can induce transient, but not sustained, IFN-gamma production in Th1 cells, in contrast to the sustained actions of IL-12. Furthermore, loss of STAT1 increases IFN-alpha-induced STAT4 phosphorylation, but does not generate levels of STAT4 activation or IFN-gamma production achieved by IL-12 or convert transient STAT4 activation into a sustained response. Our findings agree with recent observations in human T cells that IFN-alpha-induced STAT4 activation is transient and unable to induce Th1 development, and indicate that IFN-alpha may act similarly in human and murine T cells.

Pre-assembly of STAT4 with the human IFN-alpha/beta receptor-2 subunit is mediated by the STAT4 N-domain

CD4(+) T cells regulate adaptive responses to pathogens by secreting unique subsets of cytokines that mediate inflammatory processes. The innate cytokines IL-12 and IFN-alpha/beta regulate type I responses and promote acute IFN-gamma secretion through the activation of the STAT4 transcription factor. Although IL-12-induced STAT4 activation is a conserved pathway across species, IFN-alpha/beta-dependent STAT4 phosphorylation does not occur as efficiently in mice as it does in human T cells. In order to understand this species-specific pathway for IFN-alpha/beta-dependent STAT4 activation, we have examined the molecular basis of STAT4 recruitment by the human IFNAR. In this report, we demonstrate that the N-domain of STAT4 interacts with the cytoplasmic domain of the human, but not the murine IFNAR2 subunit. This interaction mapped to a membrane-proximal segment of the hIFNAR2 spanning amino acids 299-333. Deletion of this region within the hIFNAR2 completely abolishes IFN-alpha/beta-dependent STAT4 tyrosine phosphorylation when expressed in human IFNAR2-deficient fibroblasts. Thus, the human IFNAR2 cytoplasmic domain serves to link STAT4 to the IFNAR as a pre-assembled complex that facilitates cytokine-driven STAT4 activation.

IL-12, but not IFN-alpha, promotes STAT4 activation and Th1 development in murine CD4+ T cells expressing a chimeric murine/human Stat2 gene

Humans and mice have evolved distinct pathways for Th1 cell development. Although IL-12 promotes CD4(+) Th1 development in both murine and human T cells, IFN-alphabeta drives Th1 development only in human cells. This IFN-alphabeta-dependent pathway is not conserved in the mouse species due in part to a specific mutation within murine Stat2. Restoration of this pathway in murine T cells would provide the opportunity to more closely model specific human disease states that rely on CD4(+) T cell responses to IFN-alphabeta. To this end, the C terminus of murine Stat2, harboring the mutation, was replaced with the corresponding human Stat2 sequence by a knockin targeting strategy within murine embryonic stem cells. Chimeric m/h Stat2 knockin mice were healthy, bred normally, and exhibited a normal lymphoid compartment. Furthermore, the murine/human STAT2 protein was expressed in murine CD4(+) T cells and was activated by murine IFN-alpha signaling. However, the murine/human STAT2 protein was insufficient to restore full IFN-alpha-driven Th1 development as defined by IFN-gamma expression. Furthermore, IL-12, but not IFN-alpha, promoted acute IFN-gamma secretion in collaboration with IL-18 stimulation in both CD4(+) and CD8(+) T cells. The inability of T cells to commit to Th1 development correlated with the lack of STAT4 phosphorylation in response to IFN-alpha. This finding suggests that, although the C terminus of human STAT2 is required for STAT4 recruitment and activation by the human type I IFNAR (IFN-alphabetaR), it is not sufficient to restore this process through the murine IFNAR complex.

Frontline: absence of functional STAT4 activation despite detectable tyrosine phosphorylation induced by murine IFN-alpha

We previously reported that IL-12, but not IFN-alphaA/D, induces T helper type (Th) 1 development and STAT4 phosphorylation in murine CD4+ T cells. However, a recent study reported that IFN-alphaA/D and recombinant murine IFN-alphaA can induce STAT4 phosphorylation, although more weakly than IL-12, largely in CD8+ rather than CD4+ T cells. That report did not examine Th1 development or directly demonstrate induction of IFN-gamma by IFN-alpha. To address these differences, we compared IFN-alphaA/D, murine IFN-alphaA, and IL-12 for STAT4 phosphorylation, formation of active nuclear DNA binding complexes, induction of Th1 development, and production of IFN-gamma in murine CD4+ T cells. IFN-alphaA induced detectable STAT4 phosphorylation, although at significantly lower levels than induced by IL-12. Furthermore, in contrast to IL-12, IFN-alphaA failed to induce Th1 development or the formation of DNA binding complexes or to synergize with IL-18 for induction of IFN-gamma production. STAT1-deficient CD4+ T cells showed increased IFN-alphaA-induced STAT4 phosphorylation but still exhibited significantly lower amounts of cytokine-induced IFN-gamma compared to IL-12. In summary, these results suggest that in contrast to IL-12, IFN-alphaA does not play a functionally significant role in meditating the STAT4-dependent induction of Th1 development or IFN-gamma production in CD4+ T cells.

DDT toxicity and critical body residue in the amphipod Leptocheirus plumulosus in exposures to spiked sediment

The lethal and sublethal toxicity of dichlorodiphenyltrichloroethane (DDT) to the estuarine amphipod Leptocheirus plumulosus was determined using sediment spiked with (14)C-labeled compound. Juvenile amphipods were exposed to concentrations up to 9.9 nmol/g dry weight (3.5 microg/g). Acute effects on survival were determined in a 10-day experiment. Chronic effects on survival, growth, and reproduction were assessed in a 28-day experiment. The DDT in the sediments transformed to dichlorodiphenyldichloroethane (DDD), dichlorodiphenyldichloroethylene (DDE), and polar metabolites during the 14-day sediment storage prior to exposing the amphipods. The mixture of DDT and its breakdown products (tDDT) was comprised mostly of DDT at the beginning of the exposures. DDD was the prevalent compound at termination of the 28-day exposure. Complete mortality occurred at sediment concentrations of tDDT as low as 7 nmol/g (2.3 microg/g) in both acute and chronic experiments. Most of the mortality appeared to have occurred within the first 4 days of exposure. No sublethal reductions in growth or reproduction were observed in the 28-day experiment. In the 10-day experiment, where amphipods did not receive supplemental food, growth was significantly increased in DDT treatments where survival was not affected. The concentration of tDDT in amphipod tissues was determined at exposure termination. In the 10-day experiment, a mean body residue of 14 nmol/g wet weight was associated with significant mortality (30%). Lower critical body residues were observed in the 28-day experiment, where the median lethal tissue residue (LR(50)) was 7.6 (6.8--8.4, 95% confidence interval) nmol/g wet weight. Based on previous studies, the lethal critical body residue for L. plumulosus is similar to those determined for freshwater amphipods and substantially lower than those determined for cladocerans and polychaetes.

Toxicity of sediment-associated nitroaromatic and cyclonitramine compounds to benthic invertebrates

The toxicity of nitroaromatic (2,4-diaminonitrotoluene [2,4-DANT] and 1,3,5-trinitrobenzene [TNB]) and 14C-labeled cyclonitramine compounds (hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX] and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine [HMX]) to the marine polychaete Neanthes arenaceodentata and the estuarine amphipod Leptocheirus plumulosus following 10- or 28-d exposures to spiked sediments was investigated. Organismal-level effects on survival, growth, and reproduction and cellular-level effects on apoptosis (programmed cell death) were evaluated. Because cyclonitramines have low affinity for sediment, overlying water was not exchanged in the RDX and HMX exposures. Nitroaromatics sorbed strongly to sediment, resulting in near complete resistance to solvent extraction. Cyclonitramines sorbed weakly to sediment, as more 14C-activity was found in the overlying water than in the sediment at exposure termination. No significant decrease in survival or growth was observed with cyclonitramines at initial sediment concentrations as high as 1,000 microg/g. Survival was significantly affected by nitroaromatics at nominal sediment concentrations as low as 200 microg/g, with L. plumulosus being more sensitive than N. arenaceodentata. Growth was significantly decreased at sublethal concentrations of 2,4-DANT for N. arenaceodentata. Reproduction, measured only with L. plumulosus, was significantly decreased only in the highest RDX treatment and also in the lower TNB treatment. However, no decrease was observed in higher concentrations of TNB. Body burden at exposure termination was below detection limit (1 microg/kg) for all compounds. Significant inhibition of apoptosis was not accompanied by significant decreases in growth or reproduction. Because of its critical function in many biological processes. alterations in this endpoint may result in adverse effects on the organism and could be used as an early indicator of toxicity.

An instructive component in T helper cell type 2 (Th2) development mediated by GATA-3

Although interleukin (IL)-12 and IL-4 polarize naive CD4(+) T cells toward T helper cell type 1 (Th1) or Th2 phenotypes, it is not known whether cytokines instruct the developmental fate in uncommitted progenitors or select for outgrowth of cells that have stochastically committed to a particular fate. To distinguish these instructive and selective models, we used surface affinity matrix technology to isolate committed progenitors based on cytokine secretion phenotype and developed retroviral-based tagging approaches to directly monitor individual progenitor fate decisions at the clonal and population levels. We observe IL-4-dependent redirection of phenotype in cells that have already committed to a non-IL-4-producing fate, inconsistent with predictions of the selective model. Further, retroviral tagging of naive progenitors with the Th2-specific transcription factor GATA-3 provided direct evidence for instructive differentiation, and no evidence for the selective outgrowth of cells committed to either the Th1 or Th2 fate. These data would seem to exclude selection as an exclusive mechanism in Th1/Th2 differentiation, and support an instructive model of cytokine-driven transcriptional programming of cell fate decisions.

Role of the Stat4 N domain in receptor proximal tyrosine phosphorylation

Stat4 is activated by the cytokines interleukin 12 and alpha interferon (IFN-alpha) and plays a significant role in directing development of naïve CD4(+) T cells to the Th1 phenotype. Signal transducers and activators of transcription (STAT) proteins undergo phosphorylation on a conserved tyrosine residue, resulting in homo- and heterodimerization, nuclear translocation, and DNA binding. Stat4 can bind to single IFN-gamma-activated sites (GASs) as a dimer or bind two tandem GASs as a pair of STAT dimers, or tetramer, stabilized through N-terminal domain (N domain) interactions between dimers. We uncovered an unexpected effect of the Stat4 N domain in controlling the proximal activation of Stat4 by tyrosine phosphorylation at activated receptor complexes. Mutation of the N domain at tryptophan residue W37, predicted to interrupt N domain dimer formation, unexpectedly prevented IFN-alpha-induced tyrosine phosphorylation of the Stat4 monomer, blocking dimer formation and nuclear translocation. Furthermore, N domains appear to exert private STAT functions, since interchanging the N domains between Stat1 and Stat4 prevented receptor-mediated tyrosine phosphorylation in one case and interrupted STAT-specific gene activation in another. Finally, replacement of the N domain of Stat1 with that of Stat4 abrogated the normal Stat2 dependence of Stat1 phosphorylation, again suggesting the domains are not equivalent. Thus, in addition to its role in STAT tetramerization, the conserved STAT N domain appears to participate in very proximal steps of receptor-mediated ligand-induced tyrosine phosphorylation.