Engagement of T-cell antigen receptor and CD4/CD8 co-receptors induces prolonged STAT activation through autocrine/paracrine stimulation in human primary T cells

Release from persistent T cell receptor engagement and blockade of aryl hydrocarbon receptor activity enhance IL-6-dependent mouse follicular helper T-like cell differentiation in vitro

Follicular helper T (Tfh) cells are crucial for humoral immunity. Dysregulation of Tfh cell differentiation can cause infectious, allergic, and autoimmune diseases. To elucidate the molecular mechanisms underlying Tfh cell differentiation, we attempted to establish an in vitro mouse model of Tfh cell differentiation in the absence of other cell types. Various cytokines and cell surface molecules are suggested to contribute to the differentiation. We found that stimulating naïve CD4+ T cells with immobilized antibodies to CD3, ICOS, and LFA-1 in the presence of soluble anti-CD28 antibody, IL-6, and antibodies that block IL-2 signaling for 3 days induced the expression of Bcl6 and Rorc(γt), master regulator genes of Tfh and Th17 cells, respectively. TGF-β significantly enhanced cell proliferation and Bcl6 and Rorc(γt) expression. An additional 2 days of culture without immobilized antibodies selectively downregulated Rorc(γt) expression. These cells produced IL-21 and promoted B cells to produce IgG antibodies. Adding the aryl hydrocarbon receptor (AhR) antagonist CH-223191 to the T cell culture further downregulated Rorc(γt) expression without significantly affecting Bcl6 expression, and upregulated expression of a key Tfh marker, CXCR5. Although their CXCR5 expression levels were still not high, the CH-223191-treated cells showed chemotactic activity towards the CXCR5 ligand CXCL13. On the other hand, AhR agonists upregulated Rorc(γt) expression and downregulated CXCR5 expression. These findings suggest that AhR activity and the duration of T cell receptor stimulation contribute to regulating the balance between Tfh and Th17 cell differentiation. Although this in vitro system needs to be further improved, it may be useful for elucidating the mechanisms of Tfh cell differentiation as well as for screening physiological or pharmacological factors that affect Tfh cell differentiation including CXCR5 expression.

Beep Test Does Not Induce Phosphorylation of Ras/MAPK- or JAK/STAT-Related Proteins in Peripheral Blood T Lymphocytes

The Th1 cell subset is involved in the immunological response induced by physical exercise. The aim of this work is to evaluate the post-effort activation of Ras/MAPK and JAK/STAT signaling pathways in T cells of young, physically active men. Seventy-six physically active, healthy men between 15 and 21 years old performed a standard physical exercise protocol (Beep test). Phosphorylation levels of Ras/MAPK-(p38 MAPK, ERK1/2) and JAK/STAT-related (STAT1, STAT3, STAT5, and STAT6) proteins were evaluated by flow cytometry in Th and Tc cells post-effort and during the lactate recovery period. The performed physical effort was not a strong enough physiological stimulant to provoke the phosphorylation of ERK1/2, p38 MAPK, STAT1, STAT3, STAT5, and STAT6 in T cells, at least for the duration of our study (the end of the lactate recovery period). We conclude that more observation time-points, including shorter and longer times after the exercise, are required to determine if the Ras/MAPK signaling pathway is involved in modulating the post-effort immunological response.

Intracellular K+ and water content in human blood lymphocytes during transition from quiescence to proliferation

Many evidence shows that K⁺ ions are required for cell proliferation, however, changes in intracellular K⁺ concentration during transition of cells from quiescence to cycling are insufficiently studied. Here, we show using flame emission assay that a long-term increase in cell K⁺ content per g cell protein is a mandatory factor for transition of quiescent human peripheral blood lymphocytes (PBL) to proliferation induced by phytohemagglutinin, phorbol ester with ionomycin, and anti-CD3 antibodies with interleukin-2 (IL-2). The long-term increase in K⁺ content is associated with IL-2-dependent stage of PBL activation and accompanies the growth of small lymphocytes and their transformation into blasts. Inhibition of PBL proliferation with drugs specific for different steps of G0/G1/S transit prevented both blast-transformation and an increase in K⁺ content per cell protein. Determination of the water content in cells by measuring the density of cells in the Percoll gradient showed that, unlike the K⁺ content, the concentration of K⁺ in cell water remains unchanged, since water and K⁺ change in parallel. Correlation of proliferation with high cell K⁺ and water content has been confirmed by the data obtained in comparative study of PBL and permanently cycling Jurkat cells. Our data suggest that K⁺ is important for successful proliferation as the main intracellular ion that participates in regulation of cell water content during cell transition from quiescence to proliferation. We concluded that high K⁺ content in cells and the associated high water content is a characteristic feature of proliferating cells.

Reporters of TCR signaling identify arthritogenic T cells in murine and human autoimmune arthritis

How arthritis-causing T cells trigger rheumatoid arthritis (RA) is not understood since it is difficult to differentiate T cells activated by inflammation in arthritic joints from those activated through their T cell antigen receptor (TCR) by self-antigens. We developed a model to identify and study antigen-specific T cell responses in arthritis. Nur77—a specific marker of TCR signaling—was used to identify antigen-activated T cells in the SKG arthritis model and in patients with RA. Nur77 could distinguish highly arthritogenic and autoreactive T cells in SKG mice. The enhanced autoreactivity was associated with increased interleukin-6 (IL-6) receptor signaling, likely contributing to their arthritogenicity. These data highlight a functional correlate between Nur77 expression, arthritogenic T cell populations, and heightened IL-6 sensitivity in SKG mice with translatable implications for human RA.

How pathogenic cluster of differentiation 4 (CD4) T cells in rheumatoid arthritis (RA) develop remains poorly understood. We used Nur77—a marker of T cell antigen receptor (TCR) signaling—to identify antigen-activated CD4 T cells in the SKG mouse model of autoimmune arthritis and in patients with RA. Using a fluorescent reporter of Nur77 expression in SKG mice, we found that higher levels of Nur77-eGFP in SKG CD4 T cells marked their autoreactivity, arthritogenic potential, and ability to more readily differentiate into interleukin-17 (IL-17)–producing cells. The T cells with increased autoreactivity, nonetheless had diminished ex vivo inducible TCR signaling, perhaps reflective of adaptive inhibitory mechanisms induced by chronic autoantigen exposure in vivo. The enhanced autoreactivity was associated with up-regulation of IL-6 cytokine signaling machinery, which might be attributable, in part, to a reduced amount of expression of suppressor of cytokine signaling 3 (SOCS3)—a key negative regulator of IL-6 signaling. As a result, the more autoreactive GFP^hi CD4 T cells from SKGNur mice were hyperresponsive to IL-6 receptor signaling. Consistent with findings from SKGNur mice, SOCS3 expression was similarly down-regulated in RA synovium. This suggests that despite impaired TCR signaling, autoreactive T cells exposed to chronic antigen stimulation exhibit heightened sensitivity to IL-6, which contributes to the arthritogenicity in SKG mice, and perhaps in patients with RA.

T-cell receptor-mediated characteristic signaling pathway of peripheral blood T cells in dermatomyositis and polymyositis

The characteristics of T cell expression in peripheral blood have been previously described in dermatomyositis (DM) and polymyositis (PM); however, their intracellular signaling profiles remain unknown. The purpose of this study was to investigate the T-cell receptor (TCR)-mediated intracellular signaling in peripheral blood T cells in DM and PM. Peripheral blood T cells from 86 patients with DM (n = 57) and PM (n = 29) were used for experimental investigations. T-cell subtypes and TCR-induced phosphorylated zeta-chain-associated protein kinase 70 (pZAP70) were analyzed by flow cytometry. Signal transducer and activator of transcription (STAT) and some inhibitory factors in T cells with TCR stimulation were also investigated by quantitative real-time polymerase chain reaction. T cell counts were significantly lower in DM than in PM. In addition, STAT, forkhead box transcription factor (FoxP3), and pZAP70 expression in CD4⁺ T cells was suppressed in DM, whereas STAT and pZAP70 expression in CD8⁺ T cells was induced in PM. Especially in DM, a positive correlation between CD4⁺ T cell counts and STAT expression was detected. In addition, low CD4⁺ T cell counts as well as reduced STAT expression were prominent in patients with interstitial lung disease. STAT and pZAP70 expression significantly improved after clinical remission in both DM and PM, although expression of FoxP3 remained suppressed. Besides, upregulation of suppressor of cytokine signaling-3 (SOCS3) and downregulation of interleukin 6 signal transducer (IL6ST) in CD4⁺ T cells were observed in both DM and PM; however, no significant improvements were detected after clinical remission. The results of the present study suggested that TCR-mediated signaling may be a key pathway to determine the different characteristics of peripheral blood T cells between DM and PM. In addition, upregulation of SOCS3 and downregulation of IL6ST and FoxP3 in CD4⁺ T cells may cause an imbalance in intracellular signaling, especially in DM, suggesting that further studies are required to identify how the impaired signaling contributes to the development of the disease.

Interferon-γ derived from cytotoxic lymphocytes directly enhances their motility and cytotoxicity

Interferon gamma (IFNγ) is a key moderator of cell-mediated immunity with diverse, mainly pro-inflammatory actions on immunocytes and target tissue. Recent studies have shown it may enhance anti-tumor and antiviral effects of CD8 T cells. Here we investigate the mechanisms by which IFNγ mediates CD8 T-cell cytotoxic function. We show that in vivo, antigen-specific CD8 T cells that produce INFγ are necessary to effect rejection of skin grafts expressing OVA as a transgene in keratinocytes. The ability of CD8 T cells to produce IFNγ enhanced their ability to migrate to the site of antigen-presenting skin cells. By in vivo imaging, we show that CTL motility, particularly speed, during graft rejection was enhanced by locally available IFNγ. We then used a reductionist two-cell model of CTL effectors and keratinocyte targets to investigate the effects of locally available (paracrine) and CTL-producing (autocrine) IFNγ on the motility behavior and killing ability of the CTL. Using live-cell imaging by prolonged time-lapse microscopy of primary effector CD8 T cells and antigen-expressing primary keratinocyte targets, we show that CD8 T-cell cytotoxic function and motility is enhanced by locally available IFNγ. Conversely, deprivation of either autocrine or paracrine IFNγ, or blockade of IFNγ signaling to CTL markedly reduced their cytotoxic function, their kinematics, and effector cell survival. We conclude that in vitro and in vivo, autocrine production of IFNγ by CTL enhances their motility and promotes killing of primary target keratinocytes. The absolute need for local IFNγ to enable cytotoxic CD8 T-cell function is of significance for immunotherapy for chronic viral infection and for cancer.

Time-Dependent Regulation of IL-2R α-Chain (CD25) Expression by TCR Signal Strength and IL-2-Induced STAT5 Signaling in Activated Human Blood T Lymphocytes

The expression of the IL-2R α-chain (IL-2Rα) is regulated at the transcriptional level via TCR- and IL-2R-signaling. The question is how to precede in time the activation signals to induce the IL-2Rα expression in native primary T cells. By comparing the effects of selective drugs on the dynamics of CD25 expression during the mitogen stimulation of human peripheral blood lymphocytes, we identified distinct Src- and JAK-dependent stages of IL-2Rα upregulation. PP2, a selective inhibitor of TCR-associated Src kinase, prevents CD25 expression at initial stages of T cell activation, prior to the cell growth. This early IL-2Rα upregulation underlies the T cell competence and the IL-2 responsiveness. We found that the activated with “weak” mitogen, the population of blood lymphocytes has some pool of competent CD25+ cells bearing a high affinity IL-2R. A distinct pattern of IL-2R signaling in resting and competent T lymphocytes has been shown. Based on the inhibitory effect of WHI-P131, a selective drug of JAK3 kinase activity, we concluded that in quiescent primary T lymphocytes, the constitutive STAT3 and the IL-2-induced prolonged STAT5 activity (assayed by tyrosine phosphorylation) is mostly JAK3-independent. In competent T cells, in the presence of IL-2 JAK3/STAT5 pathway is switched to maintain the higher and sustained IL-2Rα expression as well as cell growth and proliferation. We believe that understanding the temporal coordination of antigen- and cytokine-evoked signals in primary T cells may be useful for improving immunotherapeutic strategies.

Biomaterial Strategies for Immunomodulation

Strategies to enhance, suppress, or qualitatively shape the immune response are of importance for diverse biomedical applications, such as the development of new vaccines, treatments for autoimmune diseases and allergies, strategies for regenerative medicine, and immunotherapies for cancer. However, the intricate cellular and molecular signals regulating the immune system are major hurdles to predictably manipulating the immune response and developing safe and effective therapies. To meet this challenge, biomaterials are being developed that control how, where, and when immune cells are stimulated in vivo, and that can finely control their differentiation in vitro. We review recent advances in the field of biomaterials for immunomodulation, focusing particularly on designing biomaterials to provide controlled immunostimulation, targeting drugs and vaccines to lymphoid organs, and serving as scaffolds to organize immune cells and emulate lymphoid tissues. These ongoing efforts highlight the many ways in which biomaterials can be brought to bear to engineer the immune system.

Lymphocyte-specific protein tyrosine kinase (Lck) interacts with CR6-interacting factor 1 (CRIF1) in mitochondria to repress oxidative phosphorylation

BACKGROUND

Many cancer cells exhibit reduced mitochondrial respiration as part of metabolic reprogramming to support tumor growth. Mitochondrial localization of several protein tyrosine kinases is linked to this characteristic metabolic shift in solid tumors, but remains largely unknown in blood cancer. Lymphocyte-specific protein tyrosine kinase (Lck) is a key T-cell kinase and widely implicated in blood malignancies. The purpose of our study is to determine whether and how Lck contributes to metabolic shift in T-cell leukemia through mitochondrial localization.

METHODS

We compared the human leukemic T-cell line Jurkat with its Lck-deficient derivative Jcam cell line. Differences in mitochondrial respiration were measured by the levels of mitochondrial membrane potential, oxygen consumption, and mitochondrial superoxide. Detailed mitochondrial structure was visualized by transmission electron microscopy. Lck localization was evaluated by subcellular fractionation and confocal microscopy. Proteomic analysis was performed to identify proteins co-precipitated with Lck in leukemic T-cells. Protein interaction was validated by biochemical co-precipitation and confocal microscopy, followed by in situ proximity ligation assay microscopy to confirm close-range (<16 nm) interaction.

RESULTS

Jurkat cells have abnormal mitochondrial structure and reduced levels of mitochondrial respiration, which is associated with the presence of mitochondrial Lck and lower levels of mitochondrion-encoded electron transport chain proteins. Proteomics identified CR6-interacting factor 1 (CRIF1) as the novel Lck-interacting protein. Lck association with CRIF1 in Jurkat mitochondria was confirmed biochemically and by microscopy, but did not lead to CRIF1 tyrosine phosphorylation. Consistent with the role of CRIF1 in functional mitoribosome, shRNA-mediated silencing of CRIF1 in Jcam resulted in mitochondrial dysfunction similar to that observed in Jurkat. Reduced interaction between CRIF1 and Tid1, another key component of intramitochondrial translational machinery, in Jurkat further supports the role of mitochondrial Lck as a negative regulator of CRIF1 through competitive binding.

CONCLUSIONS

This is the first report demonstrating the role of mitochondrial Lck in metabolic reprogramming of leukemic cells. Mechanistically, it is distinct from other reported mitochondrial protein tyrosine kinases. In a kinase-independent manner, mitochondrial Lck interferes with mitochondrial translational machinery through competitive binding to CRIF1. These findings may reveal novel approaches in cancer therapy by targeting cancer cell metabolism.

Nuclear lymphocyte-specific protein tyrosine kinase and its interaction with CR6-interacting factor 1 promote the survival of human leukemic T cells

Overexpression and hyperactivation of lymphocyte-specific protein tyrosine kinase (Lck) have been associated with leukemia development. We previously showed that, other than its known function as a cytoplasmic signal transducer, Lck also acts as a nuclear transcription factor in mouse leukemic cells. In the present study, we demonstrated the presence of nuclear Lck in human leukemic T cells and in primary cells. We further established a positive correlation between Lck nuclear localization and its kinase activity. Proteomic analysis identified CR6-interacting factor 1 (CRIF1) as one of the Lck-interacting proteins. CRIF1 and Lck association in the nucleus was confirmed both by immunofluorescence microscopy and co-immunoprecipitation in human leukemic T cells. Close-range interaction between Lck and CRIF1 was validated by in situ proximity ligation assay (PLA). Consistent with the role of nuclear CRIF1 as a tumor suppressor, CRIF1 silencing promotes leukemic T cell survival in the absence of growth factors. This protective effect can be recapitulated by endogenous Lck or reconstituted Lck in leukemic T cells. All together, our results support a novel function of nuclear Lck in promoting human leukemic T cell survival through interaction with a tumor suppressor. It has important implications in defining a paradigm shift of non-canonical protein tyrosine kinase signaling.

Exchange protein directly activated by cAMP modulates regulatory T-cell-mediated immunosuppression

The cAMP signalling pathway plays an essential role in immune functions. In the present study we examined the role of the cAMP/EPAC1 (exchange protein directly activated by cAMP) axis in regulatory T-cell (Treg)-mediated immunosuppression using genetic and pharmacological approaches. Genetic deletion of EPAC1 in Tregs and effector T-cells (Teffs) synergistically attenuated Treg-mediated suppression of Teffs. Mechanistically, EPAC1 inhibition enhanced activation of the transcription factor STAT3 (signal transducer and activator of transcription 3) and up-regulated SMAD7 expression while down-regulating expression of SMAD4. Consequently, CD4+ T-cells were desensitized to transforming growth factor (TGF) β1, a cytokine employed by Tregs to exert a broad inhibitory function within the immune system. Furthermore, deletion of EPAC1 led to production of significant levels of ovalbumin IgG antibodies in a low-dose, oral-tolerance mouse model. These in vivo observations are consistent with the finding that EPAC1 plays an important role in Treg-mediated suppression. More importantly, pharmacological inhibition of EPAC1 using an EPAC-specific inhibitor recapitulates the EPAC1 deletion phenotype both in vivo and in vitro. The results of the present study show that EPAC1 boosts Treg-mediated suppression, and identifies EPAC1 as a target with broad therapeutic potential because Tregs are involved in numerous pathologies, including autoimmunity, infections and a wide range of cancers.