Cell surface molecules and early events involved in human T lymphocyte activation

Adoptive immunotherapy with cells from tumor-draining lymph nodes activated and expanded in vitro

Tumor-draining lymph nodes (tumor-DLNs) provide a rich source of tumor-reactive lymphocytes which can be used in adoptive immunotherapy (AIT) and that circumvent the need to resect autologous tumor, without the challenges and shortcomings associated with using autologous tumor or anti-CD3 monoclonal antibody. Bryostatin/Ionomycin (Bryo/Io) provide a useful method of activating tumor-DLNs such that they can readily be expanded to sufficient numbers to be used in AIT, and growing the tumor-DLN lymphocytes in the gamma chain cytokines IL-7 plus IL-15 is superior to IL-2 in terms of T cell numbers and phenotype. AIT with these cells induces tumor regression and provides protection against metastases and future tumor challenge. Here, we provide a stepwise protocol to sensitize tumor-DLN cells in donor mice, activate tumor-DLN T cells ex vivo using Bryo/Io, expansion of these cells in gamma chain cytokines and adoptive transfer of the expanded cells back into tumor-bearing hosts. Methods relevant to these experiments, such as injecting tumor cells intravenously and monitoring for pulmonary metastases, tumor volume measurement and resection, and use of luciferase-expressing tumor cells to monitor for metastases following resection, are described in detail. The methods outlined herein can be easily adapted to suit similar experiments across multiple tumor cell lines and syngeneic mouse models.

Identifying Key Pathways and Components in Chemokine-Triggered T Lymphocyte Arrest Dynamics Using a Multi-Parametric Global Sensitivity Analysis

Introduction

The arrest of rolling T lymphocytes at specific locations is crucial to proper immune response function. We previously developed a model of chemokine-driven integrin activation, termed integrative signaling adhesive dynamics (ISAD). In addition, we have shown that loss of diacylglycerol kinase (DGK) leads to a gain of function regarding adhesion under shear flow. We undertook this study to understand the sensitivity of adhesion to perturbations in other signaling molecules.

Methods

We adapted multi-parametric sensitivity analysis (MPSA) for use in our ISAD model to identify important parameters, including initial protein concentrations and kinetic rate constants, for T lymphocyte arrest. We also compared MPSA results to those obtained from a single parametric sensitivity analysis.

Results

In addition to the previously shown importance of DGK in lymphocyte arrest, PIP₂ cleavage and Rap1 activation are crucial in determining T cell arrest dynamics, which agree with previous experimental findings. The l-selectin density on the T lymphocyte surface also plays a large role in determining the distance rolled before arrest. Both the MPSA and single-parametric method returned similar results regarding the most sensitive kinetic rate constants.

Conclusion

We show here that the regulation of the amount of second messengers are, in general, more critical for determining T lymphocyte arrest over the initial signaling proteins, highlighting the importance of amplification of signaling in cell adhesion responses. Overall, this work provides a mechanistic insight of the contribution of key pathways and components, thus may help to identify potential therapeutic targets for drug development against immune disorders.

Combining Adhesive Nanostructured Surfaces and Costimulatory Signals to Increase T Cell Activation

Adoptive cell therapies are showing very promising results in the fight against cancer. However, these therapies are expensive and technically challenging in part due to the need of a large number of specific T cells, which must be activated and expanded in vitro. Here we describe a method to activate primary human T cells using a combination of nanostructured surfaces functionalized with the stimulating anti-CD3 antibody and the peptidic sequence arginine-glycine-aspartic acid, as well as costimulatory agents (anti-CD28 antibody and a cocktail of phorbol 12-myristate 13-acetate, ionomycin, and protein transport inhibitors). Thus, we propose a method that combines nanotechnology with cell biology procedures to efficiently produce T cells in the laboratory, challenging the current state-of-the-art expansion methodologies.

TT-seq captures enhancer landscapes immediately after T-cell stimulation

To monitor transcriptional regulation in human cells, rapid changes in enhancer and promoter activity must be captured with high sensitivity and temporal resolution. Here, we show that the recently established protocol TT-seq ("transient transcriptome sequencing") can monitor rapid changes in transcription from enhancers and promoters during the immediate response of T cells to ionomycin and phorbol 12-myristate 13-acetate (PMA). TT-seq maps eRNAs and mRNAs every 5 min after T-cell stimulation with high sensitivity and identifies many new primary response genes. TT-seq reveals that the synthesis of 1,601 eRNAs and 650 mRNAs changes significantly within only 15 min after stimulation, when standard RNA-seq does not detect differentially expressed genes. Transcription of enhancers that are primed for activation by nucleosome depletion can occur immediately and simultaneously with transcription of target gene promoters. Our results indicate that enhancer transcription is a good proxy for enhancer regulatory activity in target gene activation, and establish TT-seq as a tool for monitoring the dynamics of enhancer landscapes and transcription programs during cellular responses and differentiation.

The T cell receptor resides in ordered plasma membrane nanodomains that aggregate upon patching of the receptor

Two related models for T cell signalling initiation suggest either that T cell receptor (TCR) engagement leads to its recruitment to ordered membrane domains, often referred to as lipid rafts, where signalling molecules are enriched or that ordered TCR-containing membrane nanodomains coalesce upon TCR engagement. That ordered domains form upon TCR engagement, as they do upon lipid raft marker patching, has not been considered. The target of this study was to differentiate between those three options. Plasma membrane order was followed in live T cells at 37 °C using laurdan to report on lipid packing. Patching of the TCR that elicits a signalling response resulted in aggregation, not formation, of ordered plasma membrane domains in both Jurkat and primary T cells. The TCR colocalised with actin filaments at the plasma membrane in unstimulated Jurkat T cells, consistent with it being localised to ordered membrane domains. The colocalisation was most prominent in cells in G1 phase when the cells are ready to commit to proliferation. At other cell cycle phases the TCR was mainly found at perinuclear membranes. Our study suggests that the TCR resides in ordered plasma membrane domains that are linked to actin filaments and aggregate upon TCR engagement.

Multiple infusions of CD20-targeted T cells and low-dose IL-2 after SCT for high-risk non-Hodgkin's lymphoma: a pilot study

A pilot phase I clinical trial involving 15 infusions of anti-CD3 × anti-CD20 bispecific Ab (CD20Bi)-armed anti-CD3-activated T cells (aATC) and low-dose IL-2 was conducted in three non-Hodgkin's lymphoma (NHL) patients (two high-risk and one refractory) after autologous SCT. The feasibility of T-cell expansion, safety of aATC infusions, cytotoxic immune responses and trafficking of aATC were evaluated. Three NHL patients received 15 infusions of 5 × 10(9) aATC (three infusions/week for 3 weeks and one infusion/week for 6 weeks) between days 1 and 65 after SCT with IL-2. There were no dose-limiting toxicities. Chills, fever, hypotension and malaise were the common side effects. Engraftment was delayed in one patient with a low stem cell dose. CD20Bi aATC infusions induced specific cytotoxicity directed at lymphoma targets. Endogenous peripheral blood mononuclear cells from two patients mediated anti-lymphoma cytotoxicity above preSCT background (P<0.001). (111)In labeled aATC trafficked to the lungs at 1 h and accumulated in the liver and bone marrow after 24 h. aATC infusions given over 69 days in combination with IL-2 were safe, did not inhibit engraftment, and induced endogenous cytotoxic responses directed at lymphoma targets.

CD20-targeted T cells after stem cell transplantation for high risk and refractory non-Hodgkin's lymphoma

A phase I trial of infusing anti-CD3 × anti-CD20 bispecific antibody (CD20Bi) armed activated T cells (aATC) was conducted in high-risk/refractory non-Hodgkin's lymphoma patients to determine whether aATC infusions are safe, affect immune recovery, and induce an antilymphoma effect. Ex vivo expanded ATC from 12 patients were armed with anti-CD20 bispecific antibody, cryopreserved, and infused after autologous stem cell transplantation (SCT). Patients underwent SCT after high-dose chemotherapy, and aATC infusions were started on day +4. The patients received 1 infusion of aATC per week for 4 weeks after SCT with doses of 5, 10, 15, and 20 × 10(9). aATC infusions were safe and did not impair engraftment. The major side effects were chills, fever, hypotension, and fatigue. The mean number of IFN-γ Enzyme-linked Immunosorbent Spots (ElSpots) directed at CD20 positive lymphoma cells (DAUDI, P = .0098) and natural killer cell targets (K562, P < .0051) and the mean specific cytotoxicity directed at DAUDI (P = .037) and K562 (P = .002) from pre-SCT to post-SCT were significantly higher. The increase in IFN-γ EliSpots from pre-SCT to post-SCT in patients who received armed ATC after SCT were significantly higher than those in patients who received SCT alone (P = .02). Serum IL-7, IL-15, Macrophage inflammatory protein (MIP)-1 beta, IP-10, MIP-1α, and Monokine induced by gamma interferone increased within hours after infusion. Polyclonal and specific antibodies were near normal 3 months after SCT. aATC infusions were safe and increased innate and specific antilymphoma cell immunity without impairing antibody recovery after SCT.

B7-H4 Treatment of T Cells Inhibits ERK, JNK, p38, and AKT Activation

B7-H4 is a newly identified B7 homolog that plays an important role in maintaining T-cell homeostasis by inhibiting T-cell proliferation and lymphokine-secretion. In this study, we investigated the signal transduction pathways inhibited by B7-H4 engagement in mouse T cells. We found that treatment of CD3(+) T cells with a B7-H4.Ig fusion protein inhibits anti-CD3 elicited T-cell receptor (TCR)/CD28 signaling events, including phosphorylation of the MAP kinases, ERK, p38, and JNK. B7-H4.Ig treatment also inhibited the phosphorylation of AKT kinase and impaired its kinase activity as assessed by the phosphorylation of its endogenous substrate GSK-3. Expression of IL-2 is also reduced by B7-H4. In contrast, the phosphorylation state of the TCR proximal tyrosine kinases ZAP70 and lymphocyte-specific protein tyrosine kinase (LCK) are not affected by B7-H4 ligation. These results indicate that B7-H4 inhibits T-cell proliferation and IL-2 production through interfering with activation of ERK, JNK, and AKT, but not of ZAP70 or LCK.

B7-H4 Treatment of T Cells Inhibits ERK, JNK, p38, and AKT Activation

B7-H4 is a newly identified B7 homolog that plays an important role in maintaining T-cell homeostasis by inhibiting T-cell proliferation and lymphokine-secretion. In this study, we investigated the signal transduction pathways inhibited by B7-H4 engagement in mouse T cells. We found that treatment of CD3(+) T cells with a B7-H4.Ig fusion protein inhibits anti-CD3 elicited T-cell receptor (TCR)/CD28 signaling events, including phosphorylation of the MAP kinases, ERK, p38, and JNK. B7-H4.Ig treatment also inhibited the phosphorylation of AKT kinase and impaired its kinase activity as assessed by the phosphorylation of its endogenous substrate GSK-3. Expression of IL-2 is also reduced by B7-H4. In contrast, the phosphorylation state of the TCR proximal tyrosine kinases ZAP70 and lymphocyte-specific protein tyrosine kinase (LCK) are not affected by B7-H4 ligation. These results indicate that B7-H4 inhibits T-cell proliferation and IL-2 production through interfering with activation of ERK, JNK, and AKT, but not of ZAP70 or LCK.

The DTH effector response and IL-2 are unaffected by cyclosporine A in autoimmune B6D2F1 mice

Delayed-type hypersensitivity (DTH) is classically defined as inflammation involving activated Th1 cells and cytokine production. DTH paw swelling, along with the cytokines IL-2, IFNγ, MCP-1 and TNFα, were inhibited in Balb/c mice by cyclosporine A (CsA). Surprisingly, the DTH response in the B6D2F1 mice was unaffected by CsA, despite a decrease in TNFα and IFNγ levels. IL-2 levels, however, were not decreased. To determine if the IL-2 production in the B6D2F1 strain is occurring through CD28-mediated costimulation, both CsA and CTLA-4Ig were administered. Paw swelling and IL-2 levels were decreased, indicating a role for costimulation. Co-administration of temsirolimus and CsA also reduced DTH and IL-2 levels in B6D2F1 mice, demonstrating involvement of the mTORC1 pathway. These results indicate that the cell activation pathways responsible for DTH differ with mouse strain. It is important to understand these differences in order to accurately interpret the results using potential therapeutic agents.

Organization of proximal signal initiation at the TCR:CD3 complex

The series of events leading to T-cell activation following antigen recognition has been extensively investigated. Although the exact mechanisms of ligand binding and transmission of this extracellular interaction into a productive intracellular signaling sequence remains incomplete, it has been known for many years that the immunoreceptor tyrosine activation motifs (ITAMs) of the T-cell receptor (TCR):CD3 complex are required for initiation of this signaling cascade because of the recruitment and activation of multiple protein tyrosine kinases, signaling intermediates, and adapter molecules. It however remains unclear why the TCR:CD3 complex requires 10 ITAMs, while many other ITAM-containing immune receptors, such as Fc receptors (FcRs) and the B cell receptor (BCR), contain far fewer ITAMs. We have recently demonstrated that various parameters of T cell development and activation are influenced by the number, as well as location and type, of ITAMs within the TCR:CD3 complex and hence propose that the TCR is capable of 'scalable signaling' that facilitates the initiation and orchestration of diverse T-cell functions. While many of the underlying mechanisms remain hypothetical, this review intends to amalgamate what we have learned from conventional biochemical analyses regarding initiation and diversification of T-cell signaling, with more recent evidence from molecular and fluorescent microscopic analyses, to propose a broader purpose for the TCR:CD3 ITAMs. Rather than simply signal initiation, individual ITAMs may also be responsible for the differential recruitment of signaling and regulatory molecules which ultimately affects T-cell development, activation and differentiation.

T cell activation

This year marks the 25th anniversary of the first Annual Review of Immunology article to describe features of the T cell antigen receptor (TCR). In celebration of this anniversary, we begin with a brief introduction outlining the chronology of the earliest studies that established the basic paradigm for how the engaged TCR transduces its signals. This review continues with a description of the current state of our understanding of TCR signaling, as well as a summary of recent findings examining other key aspects of T cell activation, including cross talk between the TCR and integrins, the role of costimulatory molecules, and how signals may negatively regulate T cell function.Acronyms and DefinitionsAdapter protein: cellular protein that functions to bridge molecular interactions via characteristic domains able to mediate protein/protein or protein/lipid interactions Costimulation: signals delivered to T cells by cell surface receptors other than the TCR itself that potentiate T cell activation cSMAC: central supramolecular activation cluster Immunoreceptor tyrosine-based activation motif (ITAM): a short peptide sequence in the cytoplasmic tails of key surface receptors on hematopoietic cells that is characterized by tyrosine residues that are phosphorylated by Src family PTKs, enabling the ITAM to recruit activated Syk family kinases Inside-out signaling: signals initiated by engagement of immunoreceptors that lead to conformational changes and clustering of integrins, thereby increasing the affinity and avidity of the integrins for their ligands NFAT: nuclear factor of activated T cells PI3K: phosphoinositide 3-kinase PKC: protein kinase C PLC: phospholipase C pMHC: peptide major histocompatibility complex (MHC) complex pSMAC: peripheral supramolecular activation cluster PTK: protein tyrosine kinase Signal transduction: biochemical events linking surface receptor engagement to cellular responses TCR: T cell antigen receptor

The cytoplasmic domain of Fas ligand costimulates TCR signals

Productive T cell activation generally requires costimulation in addition to a signal delivered through the TCR. Although FasL is well-characterized for its capacity to deliver a death signal through Fas, this TNF family member can also transmit a reverse signal to enhance Ag-driven T cell proliferation. In this study, we define this reverse signal through FasL as costimulation by showing it requires TCR coengagement and is CD28 independent. We demonstrate that FasL-mediated costimulation drives FasL recruitment into lipid rafts and association with select Src homology 3 (SH3)-containing proteins. We further show that the proline-rich intracellular domain of FasL is sufficient to costimulate by enhancing the phosphorylation of Akt, ERK1/2, JNK, and FasL itself, by activating the transcription factors NFAT and AP-1, and by enhancing IFN-gamma production. These results elucidate the pathway of costimulation through the death inducer FasL, and comprise the first mechanistic analysis of a newly emerging group of costimulators, the TNF family.

Capric acid and hydroxypropylmethylcellulose increase the immunogenicity of nasally administered peptide vaccines

Immunization by the nasal route is an established method for the induction of mucosal and systemic humoral and cell-mediated antigen-specific responses. However, the effectiveness of nasal immunization is often hampered by the need for increased doses of antigen. Bioadhesives and absorption enhancers were investigated for their ability to enhance immune responses in mice after nasal immunization with model HIV-1 peptide and protein immunogens. Two additives, hydroxypropylmethylcellulose (HPMC) and capric acid, consistently enhanced antigen-specific serum IgG endpoint titers under conditions in which antigen dose was limiting. Nasal immunization of mice with 20 microg of an HIV-1 peptide immunogen plus cholera toxin (CT) as adjuvant induced serum antipeptide IgG titers of 1:9.5log2 after four immunizations while the addition of CA or HPMC to the vaccine formulation increased serum antipeptide IgG titers to 1:15.4log2 and 1:17.6log2, respectively. When 5 microg recombinant HIV-1 gp41 was used as the immunogen, the addition of CA or HPMC to the vaccine formulation increased serum anti-gp41 IgG titers to 1:11.6log2 and 1:8.8log2, respectively, compared to 1:5.2log2 after three nasal immunizations with 5 microg gp41 + CT alone. Thus, HPMC and capric acid may be useful additives that increase the immunogenicity of nasally administered vaccines and permit less antigen to be used with each immunization.

Increased serum vascular endothelial growth factor levels in microscopic poly angiitis with pulmonary involvement

Microscopic polyangiitis (MPA) is a systemic necrotizing vasculitis that affects small vessels, resulting in a wide spectrum of organ involvement including the lungs. However, there are little serological markers that predict its prognosis or severity of pulmonary involvement. Vascular endothelial growth factor (VEGF) is an angiogenic mediator, which has been reported to be elevated in systemic vasculitis. In this study, we measured serum VEGF levels in 22 MPA patients with pulmonary involvement. We also investigated VEGF expression in pulmonary cells using flow cytometry analysis. We found that serum VEGF levels in MPA patients were significantly higher than those in respiratory or urinary tract infection. The serum VEGF levels decreased in parallel with the improvement of MPA symptoms. The serum VEGF levels in MPA patients who died within 5 years were significantly higher than those who survived more than 5 years. The sensitivity of VEGF levels to distinguish MPA patient with poor prognosis from those with good prognosis was 90.9%, and specificity was 81.8% (cutoff value = 802.5 pg/ml). The serum VEGF levels showed significant positive correlation with the composite physiological index, which indicates the severity of pulmonary lesion. In flow cytometry analysis, CD11b positive bronchoalveolar lavage fluid cells expressed VEGF. Immunohistochemically, alveolar macrophages, tissue infiltrating inflammatory cells and alveolar epithelial cells stained positive for VEGF. Measurement of serum VEGF levels in MPA might become one of the markers for prognosis and the severity of pulmonary involvement in MPA. VEGF might contribute to the development of pulmonary lesion of MPA.

Characterization of surface interleukin-2 receptor expression on gated populations of peripheral blood mononuclear cells from manatees, Trichechus manatus latirostris

An in vitro system to determine surface interleukin-2 receptor (IL-2R) expression on mitogen-stimulated peripheral blood mononuclear cells (PBMC) from free-ranging manatees, Trichechus manatus latirostris was developed. Human recombinant IL-2, conjugated with a fluorescein dye was used in conjunction with flow cytometric analysis to determine changes in surface expression of IL-2R at sequential times over a 48-h period of in vitro stimulation. Surface expression of IL-2R was detected on manatee PBMC, which also cross-reacted with an anti-feline pan T-cell marker. An expression index (EI) was calculated by comparing mitogen-activated and non-activated PBMC. Based on side- and forward-scatter properties, flow cytometric analysis showed an increase in the number of larger, more granular "lymphoblasts" following concanavalin A (Con A) stimulation. The appearance of lymphoblasts was correlated with an increase in their surface expression of IL-2 receptors. Surface IL-2R expression, in Con A-stimulated PBMC, was detected at 16 h, peaked at 24-36 h, and began to decrease by 48 h. Characterization of the IL-2R expression should provide additional information on the health status of manatees, and the effect of their sub lethal exposure to brevetoxin.

Signaling through MHC in transgenic mice generates a population of memory phenotype cytolytic cells that lack TCR

We constructed a chimeric molecule, composed of the T-cell receptor (TCR)-zeta chain fused to the extracellular domains of a prototypical allogeneic major histocompatibility complex (MHC) class I molecule, Dd, to assess whether such a construct could affect Dd allospecific responses in vitro and in vivo. To generate cytotoxic T lymphocytes (CTLs) expressing the construct, Dd-zeta was targeted to lymphocyte populations in transgenic mice by placing its expression under control of the CD2 promoter. In response to ligation of Dd, lymphocytes from transgenic mice expressing high levels of Dd-zeta are activated to proliferate and kill cells binding to Dd, despite the near total loss of CD8+ T cells in these mice. Thus, the Dd-zeta cytolytic cell was found not to be a conventional CD8+ CTL, but rather an unusual T lineage cell (CD3-CD5+Thy1.1+) that lacked alphabeta or gammadelta TCRs, as well as CD4 and CD8 coreceptors, but expressed surface markers strikingly similar to memory CTLs, including CD44, Ly-6C, and CD122. These cells originate in the thymus and potently veto responses to Dd in vitro. Lacking TCRs, these veto cells are unlikely to mediate graft-versus-host disease (GVHD) and thus may be useful as a cellular therapy for therapeutic deletion of alloreactive T cells in the settings of graft rejection and GVHD.

BAX and BAK regulation of endoplasmic reticulum Ca2+: a control point for apoptosis

BAX and BAK are "multidomain" proapoptotic proteins that initiate mitochondrial dysfunction but also localize to the endoplasmic reticulum (ER). Mouse embryonic fibroblasts deficient for BAX and BAK (DKO cells) were found to have a reduced resting concentration of calcium in the ER ([Ca2+]er) that results in decreased uptake of Ca2+ by mitochondria after Ca2+ release from the ER. Expression of SERCA (sarcoplasmic-endoplasmic reticulum Ca2+ adenosine triphosphatase) corrected [Ca2+]er and mitochondrial Ca2+ uptake in DKO cells, restoring apoptotic death in response to agents that release Ca2+ from intracellular stores (such as arachidonic acid, C2-ceramide, and oxidative stress). In contrast, targeting of BAX to mitochondria selectively restored apoptosis to "BH3-only" signals. A third set of stimuli, including many intrinsic signals, required both ER-released Ca2+ and the presence of mitochondrial BAX or BAK to fully restore apoptosis. Thus, BAX and BAK operate in both the ER and mitochondria as an essential gateway for selected apoptotic signals.

Implication of three isoforms of PLA(2) in human T-cell proliferation

We observed that human (Jurkat) T-cells constitutively expressed the mRNA, encoding for the four isoforms of phospholipase A(2) (PLA(2)), i.e. two secretory (type IB and type V), and two cytosolic (type IV, Ca(2+)-dependent and type VI, Ca(2+)-independent). In order to assess whether these PLA(2) isoforms are active, we labeled Jurkat T-cells with [(3)H]arachidonic acid ([(3)H]AA) and determined its release into the extracellular medium in the presence of phorbol 12-myristate 13-acetate (PMA) and ionomycin. The three PLA(2) isoforms seem functional as aristolochic acid and bromoenol lactone (BEL), the respective inhibitors of type IB/type V and type VI PLA(2)s, significantly inhibited the release of free [(3)H]AA. On the other hand, arachidonyl trifluoromethyl ketone (AACOCF(3)), an inhibitor of type IV PLA(2), failed to curtail significantly the release of free [(3)H]AA into the extracellular medium. We assessed the implication of these PLA(2) isoforms in transcription of the interleukin-2 (IL-2) gene, involved in T-cell proliferation. Hence, aristolochic acid and BEL, but not AACOCF(3), significantly inhibited the PMA and ionomycin-induced induction of mRNA of IL-2. Similarly, aristolochic acid and BEL, but not AACOCF(3), significantly inhibited the PMA and ionomycin-induced secretion of IL-2 in the culture supernatants. Together these results suggest that human Jurkat T-cells possess two secretory and two cytosolic PLA(2) isoforms and only three of them (type IB, type V and type VI) are implicated in T-cell proliferation.

T-cell tolerance and autoimmune diabetes

Herein we describe the major signaling events that occur in T-cells upon T-cell receptor (TCR) engagement, and the mechanisms responsible for the induction of T-cell anergy that may ultimately lead to the development of immunospecific therapies in T-cell mediated autoimmune diseases. A new type of antigen presenting molecule (dimeric MHC class-II/peptide, DEF) endowed with antigen-specific immunomodulatory effects such as induction of Th2 polarization and T-cell anergy is also described as a potential antidiabetogenic agent. According to our preliminary results, the MHC II/peptide-based approach may provide rational grounds for further development of antigen-specific immunotherapeutic agents such as human-like MHC lI/peptide chimeras endowed with efficient down-regulatory effects in CD4 T-cell-mediated autoimmune diseases such as Type 1 diabetes, multiple sclerosis, primary biliary cirrhosis, and rheumatoid arthritis.

The CD3 gamma leucine-based receptor-sorting motif is required for efficient ligand-mediated TCR down-regulation

TCR down-regulation plays an important role in modulating T cell responses both during T cell development and in mature T cells. At least two distinct pathways exist for down-regulation of the TCR. One pathway is activated following TCR ligation and is dependent on tyrosine phosphorylation. The other pathway is dependent on protein kinase C (PKC)-mediated activation of the CD3 gamma di-leucine-based receptor-sorting motif. Previous studies have failed to demonstrate a connection between ligand- and PKC-induced TCR down-regulation. Thus, although an apparent paradox, the dogma has been that ligand- and PKC-induced TCR down-regulations are not interrelated. By analyses of a newly developed CD3 gamma-negative T cell variant, freshly isolated and PHA-activated PBMC, and a mouse T cell line, we challenged this dogma and demonstrate in this work that PKC activation and the CD3 gamma di-leucine-based motif are indeed required for efficient ligand-induced TCR down-regulation.

SF20/IL-25, a novel bone marrow stroma-derived growth factor that binds to mouse thymic shared antigen-1 and supports lymphoid cell proliferation

Using a forward genetic approach and phenotype-based complementation screening to search for factors that stimulate cell proliferation, we have isolated a novel secreted bone marrow stroma-derived growth factor, which we termed SF20/IL-25. This protein signals cells to proliferate via its receptor, which we have identified as mouse thymic shared Ag-1 (TSA-1). Enforced expression of TSA-1 in IL-3-dependent Ba/F3 cells that do not express endogenous TSA-1 rendered cells to proliferate in a dose-dependent manner when stimulated with SF20/IL-25. FDCP2, a factor-dependent hemopoietic cell line that expresses endogenous TSA-1, could also be stimulated to proliferate with SF20/IL-25. Binding of SF20 to TSA-1 was blocked by anti-TSA-1 Ab and SF20-induced proliferation of TSA-1-expressing cells was inhibited by anti-TSA-1. In vitro assay revealed that SF20/IL-25 has no detectable myelopoietic activity but supports proliferation of cells in the lymphoid lineage.

Immune modulation in cancer patients after adoptive transfer of anti-CD3/anti-CD28-costimulated T cells-phase I clinical trial

Anti-CD3/anti-CD28 monoclonal antibody-coactivated T cells (COACTs) proliferate, secrete tumoricidal cytokines, and mediate non-major histocompatibility complex (MHC)-restricted cytotoxicity. This phase I study was done to determine the safety, maximum tolerated dose, technical limits of expansion, and modulation of immune functions in cancer patients given COACTs. Coactivated T cells were produced by stimulating peripheral blood mononuclear cells (PBMCs) with OKT3 anti-CD3 and 9.3 (anti-CD28)-coated beads in the presence of 100 IU interleukin (IL)-2 per milliliter for 14 days. The beads were removed after 4 days of culture. Ten courses of COACTs were given to eight patients with renal cell (1), ovarian (2), breast (1), and colorectal (4) carcinomas; two patients received two courses of COACTs. Patients were given up to 10 x 10 9 COACTs twice a week for 3 weeks without dose-limiting toxicities. Patients at the first and second dose levels received a mean total of 17.6 and 42.4 x 10 9 COACTs, respectively. After 14 days of culture, the COACTs contained a mean of 57.5% CD4+ cells and 42.5% CD8+ cells, exhibited non-MHC-restricted cytotoxicity, and produced significant amounts of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and granulocyte macrophage colony-stimulating factor (GM-CSF). Infusions were safe and induced measurable serum levels of IFNgamma, TNFalpha, and IL-4 in two patients. Peripheral blood mononuclear cells from patients who received COACTs secreted higher amounts of IFNgamma and GM-CSF on in vitro anti-CD3/anti-CD28 restimulation than PBMCs obtained before immunotherapy. The detection of cytokines in patient sera and enhanced in vitro production of cytokines by anti-CD3/anti-CD28-stimulated patient PBMCs after COACT infusions suggest that COACTs were modulating immune responses in cancer patients.

Calcium signaling mechanisms in T lymphocytes

Elevation of intracellular free Ca(2+) is one of the key triggering signals for T-cell activation by antigen. A remarkable variety of Ca(2+) signals in T cells, ranging from infrequent spikes to sustained oscillations and plateaus, derives from the interactions of multiple Ca(2+) sources and sinks in the cell. Following engagement of the T cell receptor, intracellular channels (IP3 and ryanodine receptors) release Ca(2+) from intracellular stores, and by depleting the stores trigger prolonged Ca(2+) influx through store-operated Ca(2+) (CRAC) channels in the plasma membrane. The amplitude and dynamics of the Ca(2+) signal are shaped by several mechanisms, including K(+) channels and membrane potential, slow modulation of the plasma membrane Ca(2+)-ATPase, and mitochondria that buffer Ca(2+) and prevent the inactivation of CRAC channels. Ca(2+) signals have a number of downstream targets occurring on multiple time scales. At short times, Ca(2+) signals help to stabilize contacts between T cells and antigen-presenting cells through changes in motility and cytoskeletal reorganization. Over periods of minutes to hours, the amplitude, duration, and kinetic signature of Ca(2+) signals increase the efficiency and specificity of gene activation events. The complexity of Ca(2+) signals contains a wealth of information that may help to instruct lymphocytes to choose between alternate fates in response to antigenic stimulation.

Targeting of p300 to the interleukin-2 promoter via CREB-Rel cross-talk during mitogen and oncogenic molecular signaling in activated T-cells

In this report, we explore the mechanisms of targeting of p300 to the interleukin-2 (IL-2) promoter in response to mitogenic and oncogenic molecular signals. Recruitment of p300 by cAMP-responsive element-binding protein-Rel cross-talk at the composite CD28 response element (CD28RE)-TRE element of the IL-2 promoter is essential for promoter inducibility during T-cell activation, and CD28RE-TRE is the exclusive target of the human T-cell lymphotropic virus type I oncoprotein Tax. The intrinsic histone acetyltransferase activity of p300 is dispensable for activation of the IL-2 promoter, and the N-terminal 743 residues contain the minimal structural requirements for synergistic transactivation of the CD28RE-TRE, the IL-2 promoter, and endogenous IL-2 gene expression. Mutational analysis of p300 reveals differential structural requirements for the N-terminal p300 module by individual cis-elements within the IL-2 promoter. These findings provide evidence that p300 assembles at the IL-2 promoter to form an enhanceosome-like signal transduction target that is centrally integrated at the CD28RE-TRE element of the IL-2 promoter through specific protein module-targeted associations in activated T-cells.

cDNA cloning, sequencing and characterization of bovine pim-1

The cDNA clone of bovine pim-1 has been isolated from phorbol-12-myristate-13-acetate (PMA) and concanavalin A (ConA)-activated peripheral blood lymphocytes (PBLs). The full-length cDNA contains a 411bp 5' untranslated region (5'-UTR), followed by a 939bp coding region and a 3' untranslated region (3'-UTR) that contains 1403bp. Comparison of the bovine pim-1 coding sequence with the human, rat, mouse, frog and zebrafish counterparts reveals 94, 90, 89, 67 and 40% homology at the nucleotide level, respectively. The predicted amino acid sequence of bovine Pim-1 shares 98.7, 97.1, 93.3, 68.8, and 52.4% similarity with the sequences of human, rat, mouse, frog, and zebrafish, respectively. The 5'-UTR of bovine pim-1 shares high sequence similarity to the human and mouse counterparts and is G/C-rich (75%) which may promote a high degree of secondary structure. The 3'-UTR of bovine pim-1 contains two potential polyadenylation sites and an A/T-rich motif which has been shown to decrease the stability of polyA mRNA molecules. Southern blot results indicate that a single copy of the gene exists in the bovine genome. Northern blot results show that PMA stimulation of PBLs increases the expression of the pim-1 mRNA. In addition, examination of Pim-1 protein expression in PBLs stimulated with a variety of mitogens including ConA, PMA, anti-CD3 and purified protein derivative (PPD) from Mycobacterium tuberculosis, reveals two different types of expression patterns during the course of a 24h period of stimulation. ConA and PPD gave a biphasic pattern of expression while PMA and anti-CD3 gave single transient pattern of expression suggesting that expression is controlled by more than one signaling pathway.

Role of two conserved cytoplasmic threonine residues (T410 and T412) in CD5 signaling

CD5 is a transmembrane coreceptor that modulates activation and differentiation signals mediated by the Ag-specific receptor present on both T and B1a lymphocytes. CD5 lacks intrinsic catalytic activity, and its immunomodulatory properties result from intracellular interactions mediated by the CD5 cytoplasmic tail. The nature of these interactions is currently a matter of investigation. Here, we present a selective mutagenesis analysis of two conserved threonine residues (T410 and T412) located at the membrane-proximal cytoplasmic region of CD5. These residues are contained within consensus phosphorylation motifs for protein kinase C and are shown here to be critical for in vivo protein kinase C-mediated phosphorylation of CD5. Functional studies revealed that the integrity of T410 and T412 is also critical for CD5-mediated phosphatidylcholine-specific phospholipase C (PC-PLC) activation and phorbol ester-mediated inhibition of Ab-induced internalization of CD5. These results strongly argue in favor of a role for T410 and T412 in the signaling mediated by CD5.

T cells in mice expressing a transgenic human TCR beta chain get positively selected but cannot be activated in the periphery by signaling through TCR

TCR-CD3 complex-mediated signaling is crucial for both developmental selection and antigenic activation of T cells. We report that mice expressing a recombined human TCRbeta chain (Tg), which have normal development of T cells, mounted very weak responses to immunization with protein antigens as well as the HA307-319 peptide recognized by the human T cell clone HA1.7 from which the transgene is derived. An anti-CD3epsilon mAb triggered equivalent proliferation from Tg and non-Tg T cells, but an anti-human TCRbeta mAb induced proliferation poorly in Tg T cells in contrast to human T cells or HA1.7. In Tg mice, T cells expressing endogenous TCR were CD44(high), whereas most transgene-expressing T cells remained CD44(low), suggesting that transgene-expressing cells are not activated in the periphery to participate in immune responses. However, anti-human TCRbeta could induce some activation markers on T cells and cross-linking of the Tg TCR by plate-coated anti-human TCRbeta efficiently induced T cell proliferation. Human TCRbeta-mediated Tg T cell activation could be rescued by exogenous IL-2, as well as by the calcium ionophore A23187, but not by phorbol esters. Thus, this human TCRbeta chain functions efficiently for positive selection of mouse T cells, but not for their peripheral activation, probably because of a lack of oligomerization leading to defects in signaling for calcium flux and IL-2 induction. The data thus suggest an early point of separation of signaling pathways between positive selection and peripheral activation of T cells.

Distinct mRNAs that encode La autoantigen are differentially expressed and contain internal ribosome entry sites

Analysis by reverse transcription-polymerase chain reaction has suggested the existence of at least two La autoantigen-encoding mRNAs that contain different 5' noncoding regions (NCRs) linked to the same La coding region (Troster, H., Metzger, T. E., Semsei, I., Schwemmle, M., Winterpacht, A., Zabel, B., and Bachmann, M. (1994) J. Exp. Med. 180, 2059-2067). La-encoding transcripts La1 and La1' contain 115- and 483-nucleotide 5' NCRs, respectively. To determine whether the various La transcripts are functional mRNAs, the expression and polysomal association of natural La1 and La1' RNAs were examined. Although La1 transcripts were ubiquitously expressed in human tissues, La1' transcripts were predominantly expressed in peripheral blood leukocytes, especially in B, T, and natural killer cells. Both La1 and La1' transcripts associated with polysomes in natural killer cells, suggesting that these transcripts were functional mRNAs. Upon activation of B cells with the mitogens phorbol 12-myristate 13-acetate and ionomycin, the amount of La1' mRNA, but not La1, declined. In contrast, after chemical activation of T cells, the amount of La 1 mRNA, but not La1', declined. The mechanism by which the La1 and La1' 5' NCRs initiate translation initiation was tested in cultured human HeLa cells and in two different in vitro translation systems. It was found that both 5' NCRs can mediate translation initiation by internal initiation. These findings indicate that the constitutive expression of La1 mRNA and the tissue-specific expression of La1' mRNA can both allow La protein synthesis under conditions when cap-dependent translation is compromised, such as inflammation, apoptosis, or certain viral infections.

Apoptosis and the cell cycle in Xenopus laevis: PHA and PMA exposure of splenocytes

T cell receptor (TCR) ligation and protein kinase C (PKC) activation stimulate proliferation and modulate apoptosis in both mammalian and amphibian lymphocytes. The potential relationship between apoptosis and the cell cycle in mature Xenopus laevis splenic lymphocytes is addressed by monitoring apoptosis and DNA synthesis over time, using incorporation of propidium iodide (PI) and flow cytometry. Aliquots of the same populations of cells are followed after exposure in vitro to phytohemagglutinin (PHA) or phorbol 12-myristate 13-acetate (PMA). Significant increases in apoptosis preceed those in DNA synthesis by 12 to 16 h following exposure to both reagents. Since apoptosis preceeds DNA synthesis, these dying cells clearly do not need to enter the S phase of the cell cycle before becoming apoptotic, in contrast to mammalian T cells. Another striking difference is that the reagent with weaker mitogenic properties in this species, PHA, is significantly a more potent apoptogen, than the strong mitogen, PMA. The two phenomena then appear to be inversely related in Xenopus cells. Data on DNA synthesis suggest independence of the two phenomena, as DNA synthesis is stimulated in direct proportion to the strength of each reagent as a mitogen. Mature mammalian T-cells undergo apoptosis only when previously activated. The Xenopus lymphocytes examined were not deliberately activated by exposure to antigen or lectin. PMA, a cancer promoter in mammals, usually 'rescues' mammalian cells from apoptosis, but stimulates apoptotic increases in Xenopus cells. Thus, mature Xenopus lymphocytes may be more readily stimulated to die by cancer inducing agents than mammalian lymphocytes. This could make them less susceptible to transformation into immortalized cancer cells. This characteristic may considerably contribute to the observed resistance to spontaneous and chemically-induced neoplasia in wild type, non-isogeneic or non-inbred Xenopus.

CD45-induced tumor necrosis factor alpha production in monocytes is phosphatidylinositol 3-kinase-dependent and nuclear factor-kappaB-independent

The pro-inflammatory cytokine tumor necrosis factor (TNF)-alpha plays a pivotal role in the pathogenesis of rheumatoid arthritis. The mechanisms involved in regulating monocyte/macrophage TNFalpha production are not yet fully understood but are thought to involve both soluble factors and cell/cell contact with other cell types. Ligation of certain cell surface receptors, namely CD45, CD44, and CD58, can induce the production of TNFalpha in monocytes. In this paper, we investigate further the signaling pathways utilized by cell surface receptors (specifically CD45) to induce monocyte TNFalpha and compare the common/unique pathways involved with that of lipopolysaccharide. The results indicate that monocyte TNFalpha induced upon CD45 ligation or lipopolysaccharide stimulation is differentially modulated by phosphatidylinositol 3-kinase and nuclear factor-kappaB but similarly regulated by p38 mitogen-activated protein kinase. These results demonstrate that both common and unique signaling pathways are utilized by different stimuli for the induction of TNFalpha. These observations may have a major bearing on approaches to inhibiting TNFalpha production in disease where the cytokine has a pathogenic role.

Impact of extremely low frequency electromagnetic fields on CD4 expression in peripheral blood mononuclear cells

There is increasing evidence suggesting that extremely low frequency electromagnetic fields (ELF-EMF) may influence several cell functions. Here the effects of ELF-EMF were studied on the expression of CD4+ cell surface receptors of human peripheral blood mononuclear cells (PBMC) using fluorescence-activated cell sorter (FACScan). The expression of CD4+ in ELF-EMF exposed (24, 48 and 72 h) and not exposed PBMC were not statistically significant. In addition, a flow cytometric analysis was determined by using a fluorescent labeled antibody, at 24 and 72 h incubations. The amount of bound antibody was distributed with a slight difference in the ELF-EMF-exposed PBMC compared to the not exposed cells. Moreover, DNA CD4+ expression in PBMC strongly increased in exposed cells, resting and activated with Phytohaemaglutinin (PHA). When polymerase chain reaction was performed on CD4+ mRNA of PBMC an increase of CD4+ mRNA expression was found after the resting cells were exposed to ELF-EMF at 24 h compared to not exposed cells, while at 48 and 72 h no difference was found. In the cell cycle progression analysis, the PBMC exposed to ELF-EMF presented a significant increase of percentage expression of cell cycle progression in the S phase compared to not exposed cells; while in G1 and G2 phases, there were no differences. Our results provide new evidence that ELF-EMF can affect CD4+ expression in PBMC and describe an additional biological activity for ELF-EMF affecting CD4+ transcription and translation protein and the increase of the percentage expression of the cell cycle progression of the S phase.

Effect of electromagnetic fields on several CD markers and transcription and expression of CD4

We carried out flow cytometric analysis for multiparametric evaluation of cell surface markers related to cellular functions. Specifically, we studied the expression of CD4, CD8, CD3, CD16, CD19, HLA-DR, and CD14 macrophage receptors expression and cell cycle progression on cells exposed to ELF-EMF. In addition, we tested the effects of ELF-EMF on CD4 mRNA protein transcription and translation and the cell-cycle progression using an immunofluorescence method. Our data show that same CD surface marker expression are weakly influenced by electromagnetic fields, with no differences between cells exposed or not exposed to ELF-EMFs. However, when the CD4 protein generation was studied, an indication of protein production was found in lymphocytes exposed to ELF-EMF, as evidenced by immunofluorescence, Western blotting and RT-PCR analysis. CD16 and CD14 expression were affected by EMF exposure at all times studied (24, 48, 72 h). The results obtained with cell cycle analysis show that after 48 h of exposure to ELF-EMF, PHA-activated and not activated cells in S phase increase with respect to non-exposed cells. The findings from this study demonstrate that under our defined experimental conditions there is evidence that ELF-EMF has a slight effect on CD4, CD14 and CD16 receptor expression, while the other CD receptors are not affected.

The dynamics of T cell receptor signaling: complex orchestration and the key roles of tempo and cooperation

T cells constantly sample their environment using receptors (TCR) that possess both a germline-encoded low affinity for major histocompatibility complex (MHC) molecules and a highly diverse set of CDR3 regions contributing to a range of affinities for specific peptides bound to these MHC molecules. The decision of a T cell "to sense and to respond" with proliferation and effector activity rather than "to sense, live on, but not respond" is dependent on TCR interaction with a low number of specific foreign peptide:MHC molecule complexes recognized simultaneously with abundant self peptide-containing complexes. Interaction with self-complexes alone, on the other hand, generates a signal for survival without a full activation response. Current models for how this distinction is achieved are largely based on translating differences in receptor affinity for foreign versus self ligands into intracellular signals that differ in quality, intensity, and/or duration. A variety of rate-dependent mechanisms involving assembly of molecular oligomers and enzymatic modification of proteins underlie this differential signaling. Recent advances have been made in measuring TCR:ligand interactions, in understanding the biochemical origin of distinct proximal and distal signaling events resulting from TCR binding to various ligands, and in appreciating the role of feedback pathways. This new information can be synthesized into a model of how self and foreign ligand recognition each evoke the proper responses from T cells, how these two classes of signaling events interact, and how pathologic responses may arise as a result of the underlying properties of the system. The principles of signal spreading and stochastic resonance incorporated into this model reveal a striking similarity in mechanisms of decision-making among T cells, neurons, and bacteria.

Mutant p53: epigenetic mutator of the T-cell receptor via induction of methylation

The mechanism and effects of epigenetic alterations in human carcinogenesis are not well understood, except that cancers often have alterations in the methylation status of their genomes. Additionally, human cancers, including aggressive T-cell leukemias and lymphomas, have a high frequency of p53 mutations, particularly missense mutations, which raises the possibility of gain-of-new-function proteins, but the new proteins' oncogenic functions are mechanistically ill-defined. To investigate the mechanisms behind the high prevalence of p53 tumor suppressor gene mutations in aggressive or relapsed T-cell leukemias, we transfected Jurkat cells null for p53 protein with a temperature-sensitive p53 mutant. We showed that this mutant p53 abrogated expression of the T-cell antigen receptor (TCR) by affecting the methylation of an at least 20-kb region of DNA, 5'to the TCR beta-chain gene enhancer region, which includes TCRbetaC1 and betaC2. Expression of the TCR is restored when the temperature is reduced to 32 degrees C, at which temperature the mutant p53 regains wild-type function. The TCR, a common site of dysfunction in T-cell malignancies, is the principal signal transduction moiety controlling both T-cell activation and activation-induced apoptosis. These results suggest a new role for mutant p53-as an epigenetic mutator, bridging p53, methylation, and transcriptional silencing-and suggest novel mechanisms in immunosuppression and cancer progression.

Immunosuppressant PG490 (triptolide) inhibits T-cell interleukin-2 expression at the level of purine-box/nuclear factor of activated T-cells and NF-kappaB transcriptional activation

PG490 (triptolide) is a diterpene triepoxide with potent immunosuppressive and antiinflammatory properties. PG490 inhibits interleukin(IL)-2 expression by normal human peripheral blood lymphocytes stimulated with phorbol 12-myristate 13-acetate (PMA) and antibody to CD3 (IC50 of 10 ng/ml), and with PMA and ionomycin (Iono, IC50 of 40 ng/ml). In Jurkat T-cells, PG490 inhibits PMA/Iono-stimulated IL-2 transcription. PG490 inhibits the induction of DNA binding activity at the purine-box/antigen receptor response element (ARRE)/nuclear factor of activated T-cells (NF-AT) target sequence but not at the NF-kappaB site. PG490 can completely inhibit transcriptional activation at the purine-box/ARRE/NF-AT and NF-kappaB target DNA sequences triggered by all stimuli examined (PMA, PMA/Iono, tumor necrosis factor-alpha). PG490 also inhibits PMA-stimulated activation of a chimeric transcription factor in which the C-terminal TA1 transactivation domain of NF-kappaB p65 is fused to the DNA binding domain of GAL4. In 16HBE human bronchial epithelial cells, IL-8 expression is regulated predominantly by NF-kappaB, and PG490 but not cyclosporin A can completely inhibit expression of IL-8. The mechanism of PG490 inhibition of cytokine gene expression differs from cyclosporin A and involves nuclear inhibition of transcriptional activation of NF-kappaB and the purine-box regulator operating at the ARRE/NF-AT site at a step after specific DNA binding.

Sodium arsenite reduces proliferation of human activated T-cells by inhibition of the secretion of interleukin-2

Arsenic (As) is a common metalloid which contaminates drinking water in several regions of the world and chronic exposure is associated with skin, lung, bladder, and kidney cancer. Previous studies suggest that arsenic exposure leads to a diminution of phytohemaglutinin (PHA) stimulated T cell proliferation in humans. In order to understand the mechanism of this suppression, the effect of As was evaluated on the expression of CD25, and IL-2 secretion in human peripheral blood mononuclear cells (PBMC). Inhibition of proliferation was observed in all donors studied. Most of the donors did not show any change in the expression of CD25, but IL-2 secretion was inhibited in 6 of the 7 donors tested. Proliferative inhibition was due to a suboptimal levels of IL-2 secreted by lymphocytes, since the addition of recombinant IL-2 to the cultures reversed in a dose-dependent fashion the inhibitory effect of As. The determination of the mRNA of IL-2 and the intracellular IL-2 levels demonstrated that the inhibition is not at the transcriptional level. Electron microscopy studies revealed that cellular ultrastructure in Golgi apparatus, mitochondria, cytoskeleton, and perinuclear membrane were altered. These alterations suggest that due to sodium arsenite effects on cytoskeleton, the intracellular secretion of proteins is affected, including the one of IL-2, leading to an impaired proliferation of the T cells when stimulated with PHA.

Effects of single intravenous doses of recombinant human interleukin-10 on subsets of circulating leukocytes in humans

Recombinant human interleukin-10 (rhIL-10) is a potent and specific immunomodulatory agent which inhibits endotoxin-stimulated pro-inflammatory cytokine production by monocytes, blocks T-lymphocyte activation by antigen presenting cells, and modulates T(H)1/T(H)2 balance in immune responses. In previous clinical trials, rhIL-10 administered to healthy volunteers induced rapid and transient elevations of neutrophil and monocyte counts and reductions of lymphocyte counts in addition to suppression of endotoxin-stimulated whole blood cytokine synthesis. We sought to better characterize the effects of rhIL-10 on immunophenotypically defined subsets of circulating leukocytes that could be relevant to its immunomodulatory effects. Healthy volunteers were given single doses of 10 microg/kg rhIL-10 (n = 8) or equivalent placebo (n = 4) by intravenous injection. Significant changes of circulating leukocytes included transiently increased neutrophils and monocytes with parallel increases of CD33+ and CD14+ cells. Total lymphocytes as well as total CD3+, CD3+/CD4+ and CD3+/CD8+ cells transiently decreased. Mean fluorescence intensity of CD11a (integrin alpha-chain subunit of lymphocyte function antigen-1, LFA-1) on lymphocytes transiently but significantly decreased, suggesting a mechanism for transient alteration of lymphocyte trafficking. In addition, mean fluorescence intensity of HLA-DR (major histocompatibility class II) on CD14+ cells (predominantly monocytes) transiently but significantly decreased, implying a possible alteration of antigen presenting function. Further study will be required to elucidate the immunomodulatory roles and potential clinical significance of these hematologic changes in therapeutic trials of rhIL-10 in patients with chronic inflammatory and autoimmune diseases.

Activation of human T lymphocytes by ganglioside-containing liposomes

We investigated the in vitro stimulatory effect of ganglioside (GM3, GD1a, GD1b, GT1b, or GQ1b)-containing liposomes on human immune cells. The effect of ganglioside-containing liposomes on the concentration of cytoplasmic free calcium ions ([Ca2+]i) in human immunocytes was examined using the confocal laser fluorescence microscopic method. The GD1a- and GT1b-containing liposomes significantly increased [Ca2+]i of human T lymphocytes compared with the GM3-, GD1b- and GQ1b-containing ones. The response of CD8+ and CD4+ cells was significantly higher than that of CD20+ cells. Our results show that the increase in [Ca2+]i may be caused by not the number of sialic acids contained in the gangliosides but the conformation of the sialic acid moiety to protrude exteriorly from the liposomal membrane surface, and that a sort of receptor recognizing the sialic acid moiety exists on human T lymphocytes (both CD8+ and CD4+ cells), which may be involved in the activation of the cells. The present results are almost the same as those obtained for the rat T lymphocyte system previously reported. This clearly confirms that a sort of ganglioside surely stimulates T lymphocytes directly, which is not species-specific but conserved in humans and rats among animal species.

Analysis of peripheral blood leukocytes in patients with cyclosporine A-induced gingival hyperplasia

BACKGROUND

Gingival overgrowth is one of the major adverse effects of the immunosuppressive drug cyclosporine A (CsA). Although several studies have attempted to determine the immunological mechanisms of gingival hyperplasia (GO) due to CsA therapy, the pathogenesis remains unclear. In this study, the distribution of the peripheral blood leukocytes in a group of renal transplant patients undergoing CsA therapy was analyzed and possible correlations of periodontal and pharmacological variables to lymphocyte subpopulations, natural killer cells, and monocytes investigated.

METHODS

Thirty-six patients were classified into 2 groups of 18 each according to the degree of gingival overgrowth. The periodontal evaluation included plaque index (PI), gingival index (GI), gingival overgrowth (GO), calculus index (CI), and probing depth (PD). The pharmacological variables of current doses of the therapeutic serum levels of CsA were investigated. The peripheral blood leukocytes were studied by 2-color flow cytometric analysis using anti-human CD2, CD3, CD4, CD8, CD11b, CD11c, CD16, CD19, HLA-DR, and CD3+HLA-DR+ monoclonal antibodies.

RESULTS

Statistical evaluation revealed that none of the pharmacological variables varied between the 2 groups. Responders (GO >30%) had significantly higher GI, PD, and GO scores compared to nonresponders (GO < or =30%). Of the immunological parameters studied, only CD2 was higher in the responder group. None of the clinical parameters correlated to the immunological values.

CONCLUSIONS

The results of this study may be useful in explaining the underlying mechanisms of drug-induced gingival overgrowth. Several previously unsuspected cells and accessory activation mechanisms for T lymphocytes could play a role in the pathogenesis.

Recombinant human G protein-coupled lysophosphatidic acid receptors mediate intracellular calcium mobilization

Mobilization of intracellular Ca2+ is a critical cellular response to lysophosphatidic acid (LPA) in many cell types. Recent identification of endothelial differentiation gene (Edg) 2 and Edg4 as subtypes of G protein-coupled receptors for LPA allowed examination of the Ca2+ mobilization mediated specifically by each subtype. To reduce endogenous background levels while enhancing recombinant receptor-specific signals, the aequorin luminescence method was used to quantify cytoplasmic Ca2+ levels. In TAg-Jurkat T cells transiently co-transfected with apoaequorin and human Edg2 or Edg4 cDNA, LPA dose-dependently increased light emission triggered by increased Ca2+ bound to aequorin. N-Palmitoyl-L-serine-phosphoric acid and N-palmitoyl-L-tyrosine-phosphoric acid, which had been previously shown to be antagonists for Xenopus laevis LPA receptors, did not antagonize the Ca2+-mobilizing effects of Edg2 and Edg4. Surprisingly, they acted as agonists or partial agonists for Edg2 and Edg4. The Ca2+ mobilization by Edg2 and Edg4 was further characterized in stable transfectants of rat HTC4 hepatoma cells. By using the fura-2 fluorescence method, a difference in the kinetics of Ca2+ flux with Edg2 and Edg4 was observed. With Edg2, but not Edg4, the initial increase in the Ca2+ concentration was followed by a sustained influx of extracellular Ca2+. The coincident production of inositol phosphates and the inhibition of Ca2+ mobilization by the phospholipase C inhibitor U73122 strongly suggested that Edg2 and Edg4 mobilize Ca2+ through inositol trisphosphate generated by phospholipase C activation. Pertussis toxin almost completely blocked LPA-induced Ca2+ mobilization by Edg2 but only partially blocked that by Edg4, which suggests that Edg2 transduces Ca2+ mobilization largely through pertussis toxin-sensitive Gi proteins, whereas Edg4 requires both Gi and Gq.

Functional analysis of the T-cell-restricted protein tyrosine kinase Txk

T lymphocytes express a range of tyrosine kinases that are involved in signalling processes driving cell activation, proliferation and differentation. Two tyrosine kinases expressed only in T cells, the Itk/Emt and Txk gene products, are members of the Tec family of kinases. The role of Tec kinases in cellular function is poorly understood, although a Tec kinase specific to B cells, Btk, is essential for B-cell development. To explore the contribution of the T-cell-specific Tec kinases to lymphocyte function, we have expressed human Txk in the baculovirus system and conducted the first characterization of its activity. We find that Txk exhibits a substrate preference in vitro quite distinct from that of the major T-cell kinases Lck and ZAP70, suggesting that Tec-family kinases might act on a distinct range of substrates. We also investigated the interactions of Txk with the cytoplasmic domains of the key signalling molecules CD3zeta, CD28 and CTLA4 and find that none of these are phosphorylated by Txk, nor are they ligands for the SH2 or SH3 domains of Txk. We conclude that it is unlikely that Txk has a role in the early signal transduction events associated with these key pathways controlling T-cell activation.

Biology of the interleukin-2 receptor

Studies of the biology of the IL-2 receptor have played a major part in establishing several of the fundamental principles that govern our current understanding of immunology. Chief among these is the contribution made by lymphokines to regulation of the interactions among vast numbers of lymphocytes, comprising a number of functionally distinct lineages. These soluble mediators likely act locally, within the context of the microanatomic organization of the primary and secondary lymphoid organs, where, in combination with signals generated by direct membrane-membrane interactions, a wide spectrum of cell fate decisions is influenced. The properties of IL-2 as a T-cell growth factor spawned the view that IL-2 worked in vivo to promote clonal T-cell expansion during immune responses. Over time, this singular view has suffered from increasing appreciation that the biologic effects of IL-2R signals are much more complex than simply mediating T-cell growth: depending on the set of conditions, IL-2R signals may also promote cell survival, effector function, and apoptosis. These sometimes contradictory effects underscore the fact that a diversity of intracellular signaling pathways are potentially activated by IL-2R. Furthermore, cell fate decisions are based on the integration of multiple signals received by a lymphocyte from the environment; IL-2R signals can thus be regarded as one input to this integration process. In part because IL-2 was first identified as a T-cell growth factor, the major focus of investigation in IL-R2 signaling has been on the mechanism of mitogenic effects in cultured cell lines. Three critical events have been identified in the generation of the IL-2R signal for cell cycle progression, including heterodimerization of the cytoplasmic domains of the IL-2R beta and gamma(c) chains, activation of the tyrosine kinase Jak3, and phosphorylation of tyrosine residues on the IL-2R beta chain. These proximal events led to the creation of an activated receptor complex, to which various cytoplasmic signaling molecules are recruited and become substrates for regulatory enzymes (especially tyrosine kinases) that are associated with the receptor. One intriguing outcome of the IL-2R signaling studies performed in cell lines is the apparent functional redundancy of the A and H regions of IL-2R beta, and their corresponding downstream pathways, with respect to the proliferative response. Why should the receptor complex induce cell proliferation through more than one mechanism or pathway? One possibility is that this redundancy is an unusual property of cultured cell lines and that primary lymphocytes require signals from both the A and the H regions of IL-2R beta for optimal proliferative responses in vivo. An alternative possibility is that the A and H regions of IL-2R beta are only redundant with respect to proliferation and that each region plays a unique and essential role in regulating other aspects of lymphocyte physiology. As examples, the A or H region could prove to be important for regulating the sensitivity of lymphocytes to AICD or for promoting the development of NK cells. These issues may be resolved by reconstituting IL-2R beta-/-mice with A-and H-deleted forms of the receptor chain and analyzing the effect on lymphocyte development and function in vivo. In addition to the redundant nature of the A and H regions, there remains a large number of biochemical activities mediated by the IL-2R for which no clear physiological role has been identified. Therefore, the circumstances are ripe for discovering new connections between molecular signaling events activated by the IL-2R and the regulation of immune physiology. Translating biochemical studies of Il-2R function into an understanding of how these signals regulate the immune system has been facilitated by the identification of natural mutations in IL-2R components in humans with immunodeficiency and by the generation of mice with targeted mutations in these gen

Cyclosporin A-Resistant Transactivation of the IL-2 Promoter Requires Activity of Okadaic Acid-Sensitive Serine/Threonine Phosphatases

Expression of the IL-2 gene requires activation of T cells through stimulation of the TCR and costimulation through accessory receptors. We have found recently that okadaic acid-sensitive Ser/Thr phosphatases are involved in a cyclosporin A-insensitive pathway that selectively transmits costimulatory signals. In this study, we analyzed whether activities of these phosphatases are necessary for the expression of the IL-2 gene. In both activated peripheral blood T lymphocytes and activated tumorigenic T cell lines, IL-2 gene expression was blocked at the transcriptional level by okadaic acid. The transcription factors active at the IL-2 promoter were differentially influenced: upon down-modulation of okadaic acid-sensitive phosphatases, transactivation by octamer, NF-κB, and NF of activated T cells proteins was abrogated, while transactivation by AP-1 proteins was even enhanced.

Mice with a fluorescent marker for interleukin 2 gene activation

Production of interleukin (IL)-2 by T lymphocytes is one of the earliest events during immune response. A mutant mouse strain was generated by replacing the IL-2 gene with a cDNA encoding green fluorescent protein (GFP). In this model, GFP fluorescence is readily detectable upon T cell activation and is mostly coexpressed with IL-2 at the single cell level. Thus, individual activated T cells can express the IL-2 gene biallelically. Upon stimulation through the T cell antigen receptor, CD4+ cells separate into distinct GFP+ and GFP- populations, both of which are capable of differentiating into either Th1 or Th2 effectors. These mice allow noninvasive detection of IL-2 production by single cells and analysis of the subsequent differentiative fate of these cells as an immune response develops.

Alterations in early biochemical events following T cell activation in leprosy patients

The early events of activation and cytokine profiles (IL-2, 4, and 6) were studied in lymphocytes of paucibacillary (TT/BT) and multibacillary (BL/LL) leprosy patients after stimulation with PMA/A23187 and Mycobacterium leprae antigen (PGL-1). Lymphocytes from BT/TT patients showed proliferation in response to both PMA/A23187 and PGL-1 compared to BL/LL. The levels of early activation signaling molecules such as IP3, calcium, and protein kinase C (PKC) in the particulate fraction were found to be elevated in BT/TT and BL/LL patients and showed a further significant increase after stimulation with PMA/A23187 in BT/TT patients. PGL-1 marginally increased the IP3 levels in BT/TT patients, whereas in BL/LL patients, it had no effect. The levels of IL-2 were enhanced in lymphocytes of BT/TT leprosy patients and were further augmented by PPD and PGL-1, while the levels of IL-4 and IL-6 were increased in LL/BL lymphocytes and further augmented by PGL-1. Thus PGL-1 seems to be a major culprit in inducing the TH2-type cytokine response observed in lepromatous leprosy patients.

Dimethyldithiocarbamate inhibits in vitro activation of primary human CD4+ T lymphocytes

Dithiocarbamates (DTC), a diverse group of industrial and therapeutic chemicals, have been reported to inhibit, enhance or have no effect on the immune system. These apparent inconsistencies reflect the complexity of the DTCs biological activities and are probably due in part to differences in dose, route of exposure, animal species used and/or specific compound tested. The studies described herein were undertaken to investigate the immunotoxicity of one member of this family, dimethyldithiocarbamate (DMDTC). We demonstrate that 0.1-0.5 microM DMDTC inhibits TNF-alpha-induced activation of NF-kappaB in primary human CD4+ T cells. This inhibition is not accompanied by a loss in viability, and DMDTC-treated T cells retain other active signaling pathways throughout the exposure duration. The inhibition of NF-kappaB is apparently permanent as DMDTC-treated T cells did not regain normal TNF-alpha activation, even after 72 h in culture. DMDTC does not appear to alter NF-kappaB directly as pre-incubation of nuclear extracts with DMDTC does not diminish binding activity of this protein. We further demonstrate that 0.1-0.5 microM DMDTC inhibits intracellular IL-2 production and decreases surface expression of CD25 (the alpha subunit of the IL-2 receptor) in T cells stimulated with phorbol ester. These data demonstrate that DMDTC is a potent immunosuppressive compound in vitro.