Translational control of interleukin 2 messenger RNA as a molecular mechanism of T cell anergy

Protein turnover regulation is critical for influenza A virus infection

The abundance of a protein is defined by its continuous synthesis and degradation, a process known as protein turnover. Here, we systematically profiled the turnover of proteins in influenza A virus (IAV)-infected cells using a pulse-chase stable isotope labeling by amino acids in cell culture (SILAC)-based approach combined with downstream statistical modeling. We identified 1,798 virus-affected proteins with turnover changes (tVAPs) out of 7,739 detected proteins (data available at pulsechase.innatelab.org). In particular, the affected proteins were involved in RNA transcription, splicing and nuclear transport, protein translation and stability, and energy metabolism. Many tVAPs appeared to be known IAV-interacting proteins that regulate virus propagation, such as KPNA6, PPP6C, and POLR2A. Notably, our analysis identified additional IAV host and restriction factors, such as the splicing factor GPKOW, that exhibit significant turnover rate changes while their total abundance is minimally affected. Overall, we show that protein turnover is a critical factor both for virus replication and antiviral defense.

Time-resolved assessment of single-cell protein secretion by sequencing

Secreted proteins play critical roles in cellular communication. Methods enabling concurrent measurement of cellular protein secretion, phenotypes and transcriptomes are still unavailable. Here we describe time-resolved assessment of protein secretion from single cells by sequencing (TRAPS-seq). Released proteins are trapped onto the cell surface and probed by oligonucleotide-barcoded antibodies before being simultaneously sequenced with transcriptomes in single cells. We demonstrate that TRAPS-seq helps unravel the phenotypic and transcriptional determinants of the secretion of pleiotropic TH1 cytokines (IFNγ, IL-2 and TNF) in activated T cells. In addition, we show that TRAPS-seq can be used to track the secretion of multiple cytokines over time, uncovering unique molecular signatures that govern the dynamics of single-cell cytokine secretions. Our results revealed that early central memory T cells with CD45RA expression (TCMRA) are important in both the production and maintenance of polyfunctional cytokines. TRAPS-seq presents a unique tool for seamless integration of secretomics measurements with multi-omics profiling in single cells.

Toxicological and pharmacological assessment of AGEN1884, a novel human IgG1 anti-CTLA-4 antibody

CTLA-4 and CD28 exemplify a co-inhibitory and co-stimulatory signaling axis that dynamically sculpts the interaction of antigen-specific T cells with antigen-presenting cells. Anti-CTLA-4 antibodies enhance tumor-specific immunity through a variety of mechanisms including: blockade of CD80 or CD86 binding to CTLA-4, repressing regulatory T cell function and selective elimination of intratumoral regulatory T cells via an Fcγ receptor-dependent mechanism. AGEN1884 is a novel IgG1 antibody targeting CTLA-4. It potently enhanced antigen-specific T cell responsiveness that could be potentiated in combination with other immunomodulatory antibodies. AGEN1884 was well-tolerated in non-human primates and enhanced vaccine-mediated antigen-specific immunity. AGEN1884 combined effectively with PD-1 blockade to elicit a T cell proliferative response in the periphery. Interestingly, an IgG2 variant of AGEN1884 revealed distinct functional differences that may have implications for optimal dosing regimens in patients. Taken together, the pharmacological properties of AGEN1884 support its clinical investigation as a single therapeutic and combination agent.

Posttranscriptional control of T cell effector function by aerobic glycolysis

A "switch" from oxidative phosphorylation (OXPHOS) to aerobic glycolysis is a hallmark of T cell activation and is thought to be required to meet the metabolic demands of proliferation. However, why proliferating cells adopt this less efficient metabolism, especially in an oxygen-replete environment, remains incompletely understood. We show here that aerobic glycolysis is specifically required for effector function in T cells but that this pathway is not necessary for proliferation or survival. When activated T cells are provided with costimulation and growth factors but are blocked from engaging glycolysis, their ability to produce IFN-γ is markedly compromised. This defect is translational and is regulated by the binding of the glycolysis enzyme GAPDH to AU-rich elements within the 3' UTR of IFN-γ mRNA. GAPDH, by engaging/disengaging glycolysis and through fluctuations in its expression, controls effector cytokine production. Thus, aerobic glycolysis is a metabolically regulated signaling mechanism needed to control cellular function.

Posttranscriptional control of T cell effector function by aerobic glycolysis

A "switch" from oxidative phosphorylation (OXPHOS) to aerobic glycolysis is a hallmark of T cell activation and is thought to be required to meet the metabolic demands of proliferation. However, why proliferating cells adopt this less efficient metabolism, especially in an oxygen-replete environment, remains incompletely understood. We show here that aerobic glycolysis is specifically required for effector function in T cells but that this pathway is not necessary for proliferation or survival. When activated T cells are provided with costimulation and growth factors but are blocked from engaging glycolysis, their ability to produce IFN-γ is markedly compromised. This defect is translational and is regulated by the binding of the glycolysis enzyme GAPDH to AU-rich elements within the 3' UTR of IFN-γ mRNA. GAPDH, by engaging/disengaging glycolysis and through fluctuations in its expression, controls effector cytokine production. Thus, aerobic glycolysis is a metabolically regulated signaling mechanism needed to control cellular function.

Posttranscriptional silencing of effector cytokine mRNA underlies the anergic phenotype of self-reactive T cells

Self-reactive T cell clones that escape negative selection are either deleted or rendered functionally unresponsive (anergic), thus preventing them from propagating host tissue damage. By using an in vivo model, we investigated molecular mechanisms for T cell tolerance, finding that despite a characteristic inability to generate effector cytokine proteins, self-reactive T cells express large amounts of cytokine mRNAs. This disconnect between cytokine message and protein was not observed in T cells mounting productive responses to foreign antigens but, instead, was seen only in those responding to self, where the block in protein translation was shown to involve conserved AU-rich elements within cytokine 3'UTRs. These studies reveal that translation of abundant cytokine mRNAs is limited in self-reactive T cells and, thus, identify posttranscriptional silencing of antigen-driven gene expression as a key mechanism underlying the anergic phenotype of self-reactive T cells.

Function of the nucleotide exchange activity of vav1 in T cell development and activation

The guanine nucleotide exchange factor (GEF) Vav1 is essential for transducing T cell antigen receptor (TCR) signals and therefore plays a critical role in the development and activation of T cells. It has been presumed that the GEF activity of Vav1 is important for its function; however, there has been no direct demonstration of this. Here, we generated mice expressing enzymatically inactive, but normally folded, Vav1 protein. Analysis of these mice showed that the GEF activity of Vav1 was necessary for the selection of thymocytes and for the optimal activation of T cells, including signal transduction to Rac1, Akt, and integrins. In contrast, the GEF activity of Vav1 was not required for TCR-induced calcium flux, activation of extracellular signal-regulated kinase and protein kinase D1, and cell polarization. Thus, in T cells, the GEF activity of Vav1 is essential for some, but not all, of its functions.

TRANSLATIONAL CONTROL IN T LYMPHOCYTES

Translational control is an important but relatively unappreciated mechanism that regulates levels of protein products. In addition to a global translational control that regulates the cell's response to external stimuli such as growth factors, cytokines, stress, and viral infections, selective translational control has recently been demonstrated to affect many genes related to growth and apoptotic processes. Translational infidelity has recently been suggested as a new mechanism of T cell dysregulation in SLE. This review discusses current data on translational control of T cell biology and the central aspect of translational control in the signalling pathway leading to T cell proliferation, apoptotic response, and cytokine production. The utility for global analysis by genomics to study translational control of T cell gene expression is also discussed.

Digital NFATc2 activation per cell transforms graded T cell receptor activation into an all-or-none IL-2 expression

The expression of interleukin-2 (IL-2) is a key event in T helper (Th) lymphocyte activation, controlling both, the expansion and differentiation of effector Th cells as well as the activation of regulatory T cells. We demonstrate that the strength of TCR stimulation is translated into the frequency of memory Th cells expressing IL-2 but not into the amount of IL-2 per cell. This molecular switch decision for IL-2 expression per cell is located downstream of the cytosolic Ca²⁺ level. Here we show that in a single activated Th cell, NFATc2 activation is digital but NF-κB activation is graded after graded T cell receptor (TCR) signaling. Subsequently, NFATc2 translocates into the nucleus in an all-or-none fashion per cell, transforming the strength of TCR-stimulation into the number of nuclei positive for NFATc2 and IL-2 transcription. Thus, the described NFATc2 switch regulates the number of Th cells actively participating in an immune response.

Immune reconstitution after autologous hematopoietic transplantation with Lin-, CD34+, Thy-1lo selected or intact stem cell products

In sequential studies, we compared immune reconstitution following high-dose chemotherapy (HDT) and stem cell transplantation (SCT) using intact mobilized peripheral blood stem cell (PSC) in intermediate grade non-Hodgkin's lymphoma (NHL) patients and CD34(+), lineage-negative (Lin(-)), Thy-1(lo) (CD34(+)Lin(-)Thy-1(lo)) stem cells in low-grade NHL patients. Cytokine expression and cellular phenotype and function were used as the basis of comparison. Despite differences in cellular composition of the stem cell grafts, immune reconstitution in both groups was similar. Significantly higher levels of type 1- and 2-associated cytokine messenger ribonucleic acid (mRNA) were observed both prior to and following transplant in the peripheral blood (PB) of both cohorts as compared to normal individuals. Similar levels of interleukin (IL)-4, IL-10, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) messenger ribonucleic acid (mRNA) were seen in PB mononuclear cells following transplant with either product. In contrast, patients receiving isolated CD34(+)Lin(-)Thy-1(lo) cells expressed significantly higher IL-2 levels at all times examined post-transplant. Despite the high levels of cytokine gene expression and rapid restoration to pretransplant levels of CD3 cell number by day 30, T cell function and CD4:CD8 and CD4(+)CD45RA:CD4(+)CD45RO(+) ratios were significantly depressed in both cohorts compared to normal donors, and significantly lower in patients transplanted with CD34(+)Lin(-)Thy-1(lo) compared to patients receiving an intact PSC product. These data suggest that the peripheral tolerance in patients receiving HDT and an autologous SCT occurs independent of graft composition, although immune function and CD4 recovery are better facilitated by transplantation of an intact product.

Isolation of polysome-bound mRNA from solid tissues amenable for RT-PCR and profiling experiments

Using cell lines and primary cells, it has been shown that translation control plays a key role regulating gene expression during physiological and pathological conditions. The relevance of this type of regulation in vivo (tissues, organs) remains to be elucidated, due to the lack of an efficient method for polysome-bound fractionation of solid tissue RNA samples. A simple and efficient method is described, in which tissue samples were pulverized in liquid nitrogen and lysed with NP40-lysis buffer in the presence of the RNAse inhibitors RNAsin and vanadyl-ribonucleoside complex. After cell lysis, the cytoplasmic extract was loaded into sucrose gradients, fractionated, and RNA prepared from each fraction. The obtained RNA was reverse transcribed with a low efficiency, a problem that was overcome by purifying polyA+ RNA. Aiming to use small quantities of solid tissue samples (10-20 mg/sample), polyA+ RNA purification was discarded, and the different components were individually screened for a negative effect on reverse transcription. The polysaccharide heparin, which is present as a nonspecific RNAse inhibitor, inhibits reverse transcriptase activity, and must be removed from RNA samples for an efficient reaction. Heparin was successfully removed by precipitation of the RNA with lithium chloride, as demonstrated by the reversal of the inhibition on RT-PCR reactions. In summary, we present a reliable method allowing us to prepare high-quality polysome-bound mRNA from small quantities of liquid-nitrogen-frozen solid tissue samples from both human and mouse origin, amenable for Northern blotting, RT-PCR reactions, and expression profiling analyses.

Engagement of CD28 outside of the immunological synapse results in up-regulation of IL-2 mRNA stability but not IL-2 transcription

During T cell activation by APC, CD28 is colocalized with TCR in the central supramolecular activation cluster (cSMAC) region of the immunological synapse. CD28 signaling through PI3K results in the recruitment of protein kinase C (PKC)theta to the cSMAC, activation of NF-kappaB, and induction of IL-2 transcription. These results suggest that localized engagement of CD28 within the cSMAC may be required for CD28 activation and/or signal integration with TCR signals. To test this model we have examined the mechanism of CD28-mediated induction of IL-2 secretion when CD28 is engaged outside of the immunological synapse. CD4 T cells were stimulated with Ag presented by B7-negative APC and CD28 costimulation was provided in trans by anti-CD28-coated beads or by class II-negative, B7-positive cells. We show that induction of IL-2 secretion under these conditions did not require expression of PKCtheta and did not induce NF-kappaB activation or IL-2 transcription. In contrast, CD28 costimulation in trans did induce IL-2 mRNA stability, accounting for the up-regulation of IL-2 secretion. These data indicate that the ability of CD28 to up-regulate IL-2 transcription requires colocalization of TCR and CD28 at the plasma membrane, possibly within the cSMAC of the immunological synapse. In contrast, the ability of CD28 to promote IL-2 mRNA stability can be transduced from a distal site from the TCR, suggesting that signal integration occurs downstream from the plasma membrane. These data support the potential role of trans costimulation in tumor and allograft rejection, but limit the potential functional impact that trans costimulation may have on T cell activation.

Interaction of anti-proliferative protein Tob with poly(A)-binding protein and inducible poly(A)-binding protein: implication of Tob in translational control

Tob is a member of an emerging family of anti-proliferative proteins that suppress cell growth when over-expressed. tob mRNA is highly expressed in anergic T cells and over-expression of Tob suppresses transcription of interleukin-2 (IL-2) through its interaction with Smads. Here, we identified two types of cDNA clones coding for poly(A)-binding protein (PABP) and inducible PABP (iPABP) by screening an expression cDNA library with the GST-Tob probe. Co-immunoprecipitation and GST-pull down experiments showed that Tob associated with the carboxyl-terminal region of iPABP. We then found that iPABP, like PABP, was involved in regulation of translation: iPABP enhanced translation of IL-2 mRNA in vitro. The enhanced translation of IL-2 mRNA required the 3'UTR and poly(A) sequences. Tob abrogated the enhancement of translation through its interaction with carboxyl-terminal region of iPABP in vitro. Consistently, over-expression of Tob in NIH3T3 cells, in which exogenous iPABP was stably expressed, resulted in suppression of IL-2 production from the simultaneously transfected IL-2 expression plasmid. Finally, Tob, whose expression was induced by anergic stimulation, was co-immunoprecipitated with iPABP in human T cells. These findings suggest that Tob is involved in the translational suppression of IL-2 mRNA in anergic T cells through its interaction with iPABP.

IL-2 secretion by CD4+ T cells in vivo is rapid, transient, and influenced by TCR-specific competition

The secretion of IL-2 is a critical and early landmark in the activation program of CD4(+) T cells in vitro, but the lack of sensitive assays has limited its application for studying T cell activation in vivo. Using a mouse cytokine capture assay we were able to detect the rapid secretion of IL-2 after an in vivo stimulus by 1-2 h in naive T cells and as early as 30 min in memory T cells. Maximal secretion was achieved within 1-2 h for memory cells or 6-8 h for naive T cells. Surprisingly IL-2 production terminated quickly in vivo and secretion was undetectable by 20-24 h in either cell type. We further demonstrated that this short duration of secretion can be influenced by cellular competition between Ag-specific CD4(+) T cells. The consequences of competition were mimicked by reducing the strength of the antigenic stimulus. These data argue that early competition between T cells influences both the eventual frequency of IL-2 producers in the population and also the duration of their secretion, potentially by altering the strength or duration of the stimulus available to each T cell.

Preferential activation of an IL-2 regulatory sequence transgene in TCR gamma delta and NKT cells: subset-specific differences in IL-2 regulation

A transgene with 8.4-kb of regulatory sequence from the murine IL-2 gene drives consistent expression of a green fluorescent protein (GFP) reporter gene in all cell types that normally express IL-2. However, quantitative analysis of this expression shows that different T cell subsets within the same mouse show divergent abilities to express the transgene as compared with endogenous IL-2 genes. TCR gamma delta cells, as well as alpha beta TCR-NKT cells, exhibit higher in vivo transgene expression levels than TCR alpha beta cells. This deviates from patterns of normal IL-2 expression and from expression of an IL-2-GFP knock-in. Peripheral TCR gamma delta cells accumulate GFP RNA faster than endogenous IL-2 RNA upon stimulation, whereas TCR alpha beta cells express more IL-2 than GFP RNA. In TCR gamma delta cells, IL-2-producing cells are a subset of the GFP-expressing cells, whereas in TCR alpha beta cells, endogenous IL-2 is more likely to be expressed without GFP. These results are seen in multiple independent transgenic lines and thus reflect functional properties of the transgene sequences, rather than copy number or integration site effects. The high ratio of GFP: endogenous IL-2 gene expression in transgenic TCR gamma delta cells may be explained by subset-specific IL-2 gene regulatory elements mapping outside of the 8.4-kb transgene regulatory sequence, as well as accelerated kinetics of endogenous IL-2 RNA degradation in TCR gamma delta cells. The high levels and percentages of transgene expression in thymic and splenic TCR gamma delta and NKT cells, as well as skin TCR gamma delta-dendritic epidermal T cells, indicate that the IL-2-GFP-transgenic mice may provide valuable tracers for detecting developmental and activation events in these lineages.

Zwitterionic polysaccharides stimulate T cells with no preferential V beta usage and promote anergy, resulting in protection against experimental abscess formation

Zwitterionic polysaccharides (Zps) from pathogenic bacteria, such as Bacteroides fragilis, are virulence factors responsible for abscess formation associated with intra-abdominal sepsis. The underlying cellular mechanism for abscess formation requires T cell activation. Conversely, abscess formation can be prevented by prophylactic s.c. injection of purified Zps alone, a process also dependent on T cells. Hence, the modulatory role of T cells in abscess formation was investigated. We show that Zps interact directly with T cells with fast association/dissociation kinetics. Vbeta repertoire analysis using RT-PCR demonstrates that Zps have broad Vbeta usage. Zps-specific hybridomas responded to a variety of other Zps, but not to a nonzwitterionic polysaccharide, indicating cross-reactivity between different Zps. Furthermore, Zps-reactive T cell hybridomas could effectively transfer protection against abscess formation. Analysis of the proliferative capacity of T cells recovered from Zps-treated animals revealed that these T cells are anergic to subsequent stimulation by the different Zps or to alloantigens in an MLR. This anergic response was relieved by addition of IL-2. Taken together, the data show that this class of polysaccharides interacts directly with T cells in a nonbiased manner to elicit an IL-2-dependent anergic response that confers protection against abscess formation.

Regulated control by granulocyte-macrophage colony-stimulating factor AU-rich element during mouse embryogenesis

In vitro studies have indicated that the granulocyte-macrophage colony-stimulating factor (GM-CSF) gene expression is regulated at the posttranscriptional level by the AU-rich element (ARE) sequence present in its 3' untranslated region (UTR). This study investigated the importance of the ARE in the control of GM-CSF gene expression in vivo. For this purpose, transgenic mice bearing GM-CSF gene constructs containing or lacking the ARE (GM-CSF AU(+) or GM-CSF AU(-), respectively) were generated. Both transgenes were under the transcriptional control of the immediate early promoter of the cytomegalovirus (CMV) to ensure their early, widespread, and constitutive expression. The regulation imposed by the ARE was revealed by comparing transgene expression at day 14 of embryonic development (E14); only the ARE-deleted but not the ARE-containing construct was expressed. Although GM-CSF AU(+) embryos were phenotypically normal, overexpression of GM-CSF in E14 GM-CSF AU(-) embryos led to severe hematopoietic alterations such as abnormal proliferation of granulocytes and macrophages accompanied by an increased number of peroxidase-expressing cells, their putative progenitor cells. These abnormalities compromise development because no viable GM-CSF AU(-) transgenic pups could be obtained. Surprisingly, by E18, significant accumulation of transgene messenger RNA was also observed in GM-CSF AU(+) embryos leading to similar phenotypic abnormalities. Altogether, these observations reveal that GM-CSF ARE is a developmentally controlled regulatory element and highlight the consequences of GM-CSF overexpression on myeloid cell proliferation and differentiation.

Extensive repertoire of membrane-bound and soluble dendritic cell-specific ICAM-3-grabbing nonintegrin 1 (DC-SIGN1) and DC-SIGN2 isoforms. Inter-individual variation in expression of DC-SIGN transcripts

Expression in dendritic cells (DCs) of DC-SIGN, a type II membrane protein with a C-type lectin ectodomain, is thought to play an important role in establishing the initial contact between DCs and resting T cells. DC-SIGN is also a unique type of human immunodeficiency virus-1 (HIV-1) attachment factor and promotes efficient infection in trans of cells that express CD4 and chemokine receptors. We have identified another gene, designated here as DC-SIGN2, that exhibits high sequence homology with DC-SIGN. Here we demonstrate that alternative splicing of DC-SIGN1 (original version) and DC-SIGN2 pre-mRNA generates a large repertoire of DC-SIGN-like transcripts that are predicted to encode membrane-associated and soluble isoforms. The range of DC-SIGN1 mRNA expression was significantly broader than previously reported and included THP-1 monocytic cells, placenta, and peripheral blood mononuclear cells (PBMCs), and there was cell maturation/activation-induced differences in mRNA expression levels. Immunostaining of term placenta with a DC-SIGN1-specific antiserum showed that DC-SIGN1 is expressed on endothelial cells and CC chemokine receptor 5 (CCR5)-positive macrophage-like cells in the villi. DC-SIGN2 mRNA expression was high in the placenta and not detectable in PBMCs. In DCs, the expression of DC-SIGN2 transcripts was significantly lower than that of DC-SIGN1. Notably, there was significant inter-individual heterogeneity in the repertoire of DC-SIGN1 and DC-SIGN2 transcripts expressed. The genes for DC-SIGN1, DC-SIGN2, and CD23, another Type II lectin, colocalize to an approximately 85 kilobase pair region on chromosome 19p13.3, forming a cluster of related genes that undergo highly complex alternative splicing events. The molecular diversity of DC-SIGN-1 and -2 is reminiscent of that observed for certain other adhesive cell surface proteins involved in cell-cell connectivity. The generation of this large collection of polymorphic cell surface and soluble variants that exhibit inter-individual variation in expression levels has important implications for the pathogenesis of HIV-1 infection, as well as for the molecular code required to establish complex interactions between antigen-presenting cells and T cells, i.e. the immunological synapse.

Impaired translational response and increased protein kinase PKR expression in T cells from lupus patients

Activation of peripheral blood T cells results in a rapid and substantial rise in translation rates and proliferation, but proliferation in response to mitogen stimulation is impaired in systemic lupus erythematosus (SLE). We have investigated translation rates and initiation factor activities in T cells from SLE patients in response to activating signals. Activation by PMA plus ionomycin strongly increased protein synthesis in control T cells but not in T cells from SLE patients. The rate of protein synthesis is known to be strongly dependent on the activity of two eukaryotic translation initiation factors, eIF4E and eIF2alpha. We show that following stimulation, eIF4E expression and phosphorylation increased equivalently in control and SLE T cells. Expression of eIF4E interacting proteins - eIF4G, an inducer, and 4E-BP1 and 4E-BP2, two specific repressors of eIF4E function - and the phosphorylation level of 4E-BP1, were all identical in control and SLE T cells. In contrast, the protein kinase PKR, which is responsible for the phosphorylation and consequent inhibition of eIF2alpha activity, was specifically overexpressed in activated SLE T cells, correlating with an increase in eIF2alpha phosphorylation. Therefore, high expression of PKR and subsequent eIF2alpha phosphorylation is likely responsible, at least in part, for impaired translational and proliferative responses to mitogens in T cells from SLE patients.

Mechanisms of immune dysfunction in stem cell transplantation

High dose therapy (HDT) and stem cell transplantation (SCT) results in alterations in the immunologic network, thymic re-education and the induction of peripheral tolerance. The changes to the immunoregulatory cascade and tolerance induction associated with autotransplants have been investigated in a series of studies focused on leukocyte reconstitution and function following HDT and autologous SCT. In these studies, we observed a significant decrease in the CD4:CD8 T cell ratio post-transplantation compared to normal peripheral blood (PB) donors due to a decrease in CD4+ cells. In addition, T cell function (phytohemagglutinin (PHA) mitogenesis) was consistently depressed compared to samples obtained from normal PB donors. The loss of T cell function was associated with an increased frequency of circulating monocytes, their expression of Fas ligand (FasL) and a high frequency of apoptotic CD4+ T cells. Indeed, 28-51% of circulating CD4+ T cells were observed to be apoptotic during the first 100 days following HDT and SCT. These studies suggest that 'primed' or activated Fas+ CD4+ lymphocytes interact with FasL+ monocytes, resulting in apoptosis, leading to the preferential deletion of CD4+ T cells, a decrease in the CD4:CD8 T cell ratio and depressed T cell function. Further, as discussed herein, the T cells are activated with a predominantly type 2 phenotype, which may also contribute to the maintenance of the immunosuppressive condition. Therefore, there is the potential to regulate immune recovery by stem cell product manipulation or post-transplantation cytokine administration.

Tumor necrosis factor-alpha mRNA remains unstable and hypoadenylated upon stimulation of macrophages by lipopolysaccharides

TNF-alpha gene expression is regulated at transcriptional and post-transcriptional levels in mouse macrophages. The post-transcriptional regulation is mediated by the AU-rich element (ARE) located in the TNF-alpha mRNA 3' untranslated region (UTR), which controls its translation and stability. In resting macrophages, the ARE represses TNF-alpha mRNA translation. Activation of macrophages with various agents [for example lipopolysaccharide (LPS), viruses] results in translational derepression, leading to the production of high levels of TNF-alpha. TNF-alpha ARE has also been shown to confer mRNA instability as its deletion from the mouse genome leads to an increase in the TNF-alpha mRNA half-life [Kontoyiannis, D., Pasparakis, M., Pizzaro, T., Cominelli, F. & Kollias, G. (1999) Immunity 10, 387-398]. In this study, we measured the half-life as well as the poly(A) tail length of TNF-alpha mRNA in the course of macrophage activation by LPS. We report that TNF-alpha mRNA is short lived even in conditions of maximal TNF-alpha synthesis. Moreover, TNF-alpha mRNA is hypoadenylated in a constitutive manner. These results reveal that TNF-alpha mRNA rapid turnover does not constitute a regulatory step of TNF-alpha biosynthesis in macrophages and that TNF-alpha mRNA translational activation upon LPS stimulation is not accompanied by a change of poly(A) tail length.

Immune dysfunction despite high levels of immunoregulatory cytokine gene expression in autologous peripheral blood stem cell transplanted non-Hodgkin's lymphoma patients

OBJECTIVE

In the present studies, we examined the role of immunoregulatory cytokine gene expression in immune reconstitution following high-dose chemotherapy and peripheral stem cell transplantation.

MATERIALS AND METHODS

We analyzed the steady-state mRNA cytokine levels and the immune phenotype and function in the peripheral blood mononuclear cells from intermediate-grade non-Hodgkin's lymphoma patients prior to and following high-dose chemotherapy and peripheral stem cell transplantation.

RESULTS

Significantly higher mRNA levels of both type 1 and type 2 cytokines and monokines were observed in patients undergoing high-dose chemotherapy and peripheral stem cell transplantation as compared with normal healthy individuals. Pretransplant mRNA levels of interleukin-2, -4, -8, -10, interferon-gamma and tumor necrosis factor-alpha were significantly higher than in normal individuals. In addition, on days 30 and 100 following transplantation interleukin-10 levels were significantly increased compared with pretreatment levels. In contrast, the levels of interleukin-2 mRNA and interferon-gamma were decreased significantly on day 365 compared with pretransplant levels.

CONCLUSIONS

The high levels of cytokine mRNA transcripts, both prior to and following peripheral stem cell transplantation, were not due to an increased cellular frequency; rather, they appear to be due to abnormal cellular activation. However, T-cell function is significantly depressed compared with normal donors, which is associated with significantly higher levels of cellular-dependent T cell inhibitory activity and, we suggest herein, high levels of interleukin-10, a type 2 cytokine.

The Destabilization of IL-2 mRNA by a Premature Stop Codon and Its Differential Stabilization by Trans-Acting Inhibitors of Protein Synthesis Do Not Support a Role for Active Translation in mRNA Stability

To investigate the role that translation plays in the stabilization of the IL-2 mRNA, we inhibited protein synthesis in both cis and trans. To block translation in trans, we utilized the inhibitors puromycin (PUR) and cycloheximide (CHX), which differentially effect polysome structure. We found that CHX enhances the stability of IL-2 mRNA in cells stimulated with anti-TCR Ab alone, but it inhibits CD28-induced message stabilization in costimulated cells. In contrast, PUR had a minimal effect on IL-2 mRNA stability in either the presence or absence of costimulation. The differential effects of these two inhibitors suggest that: 1) CHX is unlikely to stabilize the IL-2 mRNA by inhibiting the expression of a labile RNase; 2) CD28-mediated IL-2 mRNA stabilization does not require translation; and 3) IL-2 mRNA decay is not coupled to translation. To block translation in cis, we generated sequence-tagged IL-2 genomic reporters that contain a premature termination codon (PTC). In both the presence and absence of costimulation, these PTC-containing mRNAs exhibit drastically diminished stability. Interestingly, the addition of CHX but not PUR completely restored CD28-mediated stabilization, suggesting that CHX can block the enhanced decay induced by a PTC. Finally, CHX was able to superinduce IL-2 mRNA levels in anti-TCR Ab-stimulated cells but not in CD28-costimulated cells, suggesting that CHX may also act by other mechanisms.

Inhibition of apoptosis by ionomycin and zinc in peripheral blood mononuclear cells (PBMC) of leprosy patients

PBMC from tuberculoid (BT/TT) and lepromatous leprosy (BL/LL) leprosy patients showed spontaneous apoptosis when cultured in the absence of mitogen for 24 h, which was inhibited by anti-tumour necrosis factor-alpha (TNF-alpha) antibodies. Apoptosis was also inhibited by ionomycin and zinc, which also increased IL-2 and decreased TNF-alpha production. The increase in IL-2 production suggests a mechanism whereby dietary supplements with zinc might alter the cell-mediated immunity response in leprosy patients.

Calcium-induced ERK activation in human T lymphocytes

We have previously shown that stimulation of B lymphocytes with calcium ionophores lead to the phosphorylation and enzymatic activation of ERK2. We have now determined that stimulation of human primary and Jurkat T lymphocytes with ionomycin also results in the activation of ERK1 and 2 as determined by; shifts in the mobility of this enzyme on SDS PAGE gels, the binding of an antibody that recognizes only the activated form of this enzyme, and increased ability to phosphorylate myelin basic protein (MBP). Another calcium ionophore, A23187, also induced activation of ERK1 and 2 in human primary and Jurkat T lymphocytes demonstrating that this is a general effect of calcium ionophores and is not limited to ionomycin. The activation of ERK1 and 2 by calcium ionophores was rapid, transient, and occurred in a dose-dependent manner. Activation of ERK1 and 2 by increases in intracellular calcium were blocked by the MEK inhibitor PD98059. These data point to a new role for calcium fluxes in T lymphocytes.

Repression of interleukin-2 mRNA translation in primary human breast carcinoma tumor-infiltrating lymphocytes

Human breast carcinoma tumor-infiltrating lymphocytes (TIL) express activation antigens in situ indicative of ongoing immune response-CD28, CD45RO, CD69, CD71, and DR. However, interleukin 2 (IL-2) receptor was poorly expressed: CD25 was detected in only 1/24 samples and CD122 in only 2/24 samples. Furthermore, isolated breast cancer TIL were defective in proliferative response but recover when treated with recombinant IL-2. Nineteen of 24 tumor samples expressed B7-1, B7-2, and CD28 protein, showing that absence of costimulator proteins or counter ligand was not the basis for TIL proliferative deficit. Expression of IL-2 activity was not detected; however, mRNA encoding IL-2 was produced and translatable in vitro. These findings show that human breast cancer tumor-induced repression of IL-2 RNA translation is the basis of failure of TIL to express the IL-2 receptor and subsequent T cell hyporesponsiveness.

Molecular regulation of interleukin-2 expression by CD28 co-stimulation and anergy

The consequences of T-cell receptor engagement (signal 1) are profoundly affected by the presence or absence of co-stimulation (signal 2). T-cell receptor (TCR) stimulation in the absence of CD28-mediated co-stimulation not only results in little interleukin (IL)-2 production, but induces a long lasting hyporesponsive state known as T-cell clonal anergy. The addition of CD28 ligation to signal 1, on the other hand, results in the production of copious amounts of IL-2. Our laboratory has utilized CD4+ Th 1 clones in an effort to understand the molecular events resulting in enhanced IL-2 production by co-stimulation and the inhibition of IL-2 production in anergy. Our current studies have focused on defining the post-transcriptional effects of CD28-enhanced IL-2 production. The data suggest that a major component of CD28's ability to regulate IL-2 production occurs at the level of message stability and involves the 3'-untranslated region of the message. In terms of anergy, our recent studies support the notion that it is not the result of TCR engagement in the absence of co-stimulation, but rather signal 1 in the absence of IL-2 receptor signaling and proliferation. Furthermore, T-cell anergy appears to be an active negative state in which IL-2 production is inhibited both at the level of signal transduction and by cis-dominant repression at the level of the IL-2 promoter.

Translational control: a general mechanism for gene regulation during T cell activation

Distributional changes of individual mRNAs between free ribonucleoprotein particles (mRNP) and ribosome-bound transcripts are used to assess translational control. Simultaneous analysis of many mRNA species is required to estimate the overall contribution of translation to the regulation of gene expression. To this purpose, total cytoplasmic RNA was fractionated in sucrose step gradients and poly(A)+ RNA was prepared from mRNP and ribosome-bound fractions. Since direct, simultaneous analysis of a profusion of mRNAs is not feasible, distribution of their in vitro translation products was examined after separation in 2-dimensional gels, followed by computer-based analysis of autoradiographs. When this analysis was applied to antigenically stimulated T cells, 36% of in vitro translation products showed a greater than 10-fold increase in intensity, suggesting transcriptional activation of the corresponding mRNAs. In comparison, 7.9% of individual mRNAs (54 of 685 species) were translationally activated. They were redistributed from free mRNP to ribosome-associated fractions; 4.7% (32 species) were translationally repressed, as indicated by the opposite pattern. The differential recruitment of 12.6% of mRNA species demonstrates specificity and the general significance of translational control during T cell activation, which implies that translation may play a similar role in regulating gene expression in a variety of physiological processes.

Abnormal intracellular IL-2 and interferon-gamma (IFN-gamma) production as HIV-1-assocated markers of immune dysfunction

We used three-colour cytometry to analyse intracellular cytokine production in activated whole blood cultures derived from patients with HIV-1 infection. We assessed mitogen-induced IL-2, IL-4 and IFN-gamma production from T cells as possible markers of immune dysfunction. The percentages of T cells staining for IL-2 were significantly reduced in stimulated cultures from HIV+ individuals relative to normal controls (P<0.0001); this reduction was observed in both the CD4+ and the CD8+ subsets. IL-2 production was significantly reduced in CD4+ T cells from HIV+ individuals clinically classified as symptomatics compared with HIV+ asymptomatics (P<0.001); in addition, production of IL-2 inversely correlated with viral load (r2=0.832). On the other hand, HIV+ individuals showed significantly more T cells staining positive for IFN-gamma (P<0.0001); subset analysis identified these T cells as CD8+. Increased IFN-gamma production in the CD8+ T cell subset of HIV+ individuals correlated neither with clinical status nor with plasma viral load. IL-4 staining in activated T cells was low (<5%) and no differences were observed between HIV+ and control groups. Three-colour FACS analysis of whole blood provides a sensitive, rapid and relatively easy means to detect cytokine profiles within T cell subpopulations. Only small volumes of blood are required (0.5 ml), since there is no need for cell isolation, making it more practical than ELISA or reverse transcriptase-polymerase chain reaction (RT-PCR) for the analysis of immune function in HIV+ individuals. This technique could therefore play a role in mapping the dynamics and extent of immune recovery in AIDS patients undergoing triple combination therapy.