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Results for “CD3 Complex”

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PubMed1993

Mononuclear cell infiltration and its relation to the expression of major histocompatibility complex antigens and adhesion molecules in pancreas biopsy specimens from newly diagnosed insulin-dependent diabetes mellitus patients.

We examined pancreas biopsy specimens from 18 newly diagnosed insulin-dependent diabetes mellitus (IDDM) patients to elucidate the mechanism underlying beta cell destruction. Pancreas islets were seen in all patients and insulitis in eight patients. Infiltrating mononuclear cells consisted of CD4+T, CD8+T, B lymphocytes, and macrophages. Among them, CD8+T lymphocytes were predominant and macrophages followed. The expression of MHC class I antigens was increased in islet and endothelial cells in nine patients. MHC class II expression was increased in endothelial cells of the same patients. The expression of intercellular adhesion molecule-1 was increased in endothelial cells in two of the nine patients with MHC hyperexpression; in one of them, lymphocyte function-associated antigen-3 expression was also increased. Out of the eight patients with insulitis, seven showed MHC class I hyper-expression, whereas 2 of the 10 patients without insulitis showed the phenomenon (P < 0.05). The relation between insulitis and the hyperexpression of adhesion molecules was not evident. In conclusion, we revealed the close relation between CD8+T lymphocyte-predominant insulitis and MHC class I hyperexpression in islet cells. This suggests that infiltrating CD8+T lymphocytes recognize islet autoantigens in association with increased MHC class I molecules and act as major effector cells in autoimmune response against islet cells in IDDM pancreases. The role of adhesion molecules in the pathogenesis of IDDM still remains to be elucidated.

Adolescent↗

PubMed1987

Differential expression of nuclear proto-oncogenes in T cells triggered with mitogenic and nonmitogenic T3 and T11 activation signals.

The relationship between induction of nuclear proto-oncogenes and cellular proliferation is not fully understood. To better define this relationship, we have studied c-fos, c-myc, and c-myb mRNA induction in T lymphocytes where early and late activation events have been clearly delineated. In T cells, initial activation from G0 to G1 results from stimulation of either the antigen/major histocompatibility complex receptor (T3-Ti) or the T11 structure; further cycle progression and proliferation follow interaction of interleukin 2 (IL-2) with the IL-2 receptor. These events can be dissected with monoclonal antibodies to T3 or T11 which cause early activation but differ in their ability to initiate IL-2-dependent cycle progression and proliferation. In T lymphocytes triggered through either T3-Ti or T11, c-fos is induced with a nonmitogenic activation signal whereas c-myb is only induced with a mitogenic signal capable of triggering IL-2 and IL-2 receptor expression. Furthermore, c-myc induction is biphasic and associated with both early and late activation events. Early c-myc, like c-fos, is induced with a nonmitogenic signal. In contrast, induction of late c-myc, like that of c-myb, requires a mitogenic signal. Thus, appearance of c-fos and initial c-myc mRNA seem to be early responses to membrane signaling whereas late c-myc and c-myb are more directly associated with actual cellular proliferation. That nonmitogenic stimulation of T cells via T3-Ti not only abrogates T11-mediated proliferation but also eliminates late c-myc and c-myb transcription further supports this notion.

Antigens, Surface↗

PubMed2000

Human immunodeficiency virus-specific circulating CD8 T lymphocytes have down-modulated CD3zeta and CD28, key signaling molecules for T-cell activation.

Although human immunodeficiency virus (HIV)-infected subjects without AIDS have a high frequency of HIV-specific CD8 T lymphocytes, cellular immunity is unable to control infection. Freshly isolated lymphocytes often do not lyse HIV-infected targets in 4-h cytotoxicity assays. A large fraction of circulating CD8 T cells from HIV-infected donors down-modulate CD3zeta, the signaling component of the T-cell receptor complex, which is reexpressed in vitro coincident with the return of cytotoxic function. To investigate further the link between CD3zeta down-modulation and possible CD8 T-cell functional defects, we used flow cytometry to characterize further the properties of the CD3zeta-down-modulated subset. HIV-specific CD8 T cells, identified by tetramer staining, are CD3zeta(-). CD8 T cells with down-modulated CD3zeta also do not express the key costimulatory receptor CD28 and have the cell surface phenotype of activated or memory T cells (HLA-DR(+) CD62L(-)). After T-cell activation, CD3zeta-down-modulated cells express the activation marker CD69 but not the high-affinity interleukin 2 (IL-2) receptor alpha-chain CD25 and produce gamma interferon but not IL-2. Therefore HIV-specific CD8 T cells have down-modulated key signaling molecules for T-cell activation and costimulation and require exogenous cytokine stimulation. The typical impairment of HIV-specific CD4 T helper cells, which would normally provide specific CD8 T-cell stimulation, means that in vivo CTL function in vivo is compromised in most HIV-infected individuals. In AIDS patients, the functional defect is more severe, since CD3zeta is not reexpressed even after IL-2 exposure.

CD28 Antigens↗

PubMed1994

Non-responsiveness to hepatitis B vaccination in haemodialysis patients: association with impaired TCR/CD3 antigen receptor expression regulating co-stimulatory processes in antigen presentation and recognition.

The study was undertaken to evaluate the relationship between non-responsiveness to hepatitis B (HBV) vaccination in haemodialysed patients and HBs antigen (Ag) presentation and recognition depending on TCR/CD3 receptors expression. We have found that the cause of the blunted response to HBV vaccination is multifactorial and seems to be associated with the following: (1) A reduced number of TCR/CD3 antigen receptor complexes on freshly isolated uraemic CD4 T cells, especially in non-responders. (2) The blunted proliferative response of uraemic CD4 T cells isolated from non-responders and stimulated for 6 days by autologous monocytes presenting HBsAg was associated with the decreased density of the TCR/CD3 receptors. (3) Moreover, in uraemic non-responders the expression of adhesion and accessory molecules on monocytes (intercellular adhesion molecule-1/ICAM-1, HLA-DR/Ia/) was significantly decreased following the culture with autologous monocytes serving as HBsAg-presenting cells. CD4 molecules and lymphocyte function antigen-1 beta/LFA-1 beta/ on helper-inducer T cells were increased before and after the culture. (4) These findings were also associated with a diminished binding capacity of IL-1 beta and IL-6 to their receptors on helper-inducer T cells. (5) IL-2, IFN-gamma and IL-4 production was decreased in uraemic non-responders, especially after 72 h of the culture. (6) Inhibited proliferation of helper-inducer T cells in uraemic non-responders was only partially reversible in the presence of exogenous IL-1 beta, IL-6, IL-2 and IFN-gamma. (7) HLA typing of uraemic non-responders was associated with extended haplotype: HLA A1,B8,DR3,DR7,DQ2.

Adult↗

PubMed1998

Permanent CD8(+) T cell depletion prevents proteinuria in active Heymann nephritis.

Active Heymann nephritis (HN) is a rat model of human idiopathic membranous nephropathy in which injury is thought to be mediated by membrane attack complex of complement (MAC) activated by antibody (Ab) to glomerular epithelial cells. Recent work has shown that HN develops in C6-deficient rats which cannot assemble MAC, and that infiltration of activated cytotoxic CD8(+) T cells and macrophages into glomeruli coincides with proteinuria. This study examined the role of CD8(+) T cells in mediating glomerular injury in HN by permanent CD8(+) cytotoxic T cell depletion via adult thymectomy (ATx) and anti-CD8 mAb. Groups of rats were depleted of CD8(+) T cells either before immunization for HN or 6 wk after immunization when Ab responses and glomerular IgG deposition were well established. These were compared with groups of HN, ATx/HN, and complete Freund's adjuvant (CFA) controls. Neither group of CD8(+) T cell-depleted rats developed proteinuria, although there was normal development and deposition of Ab. CD8(+) T cell-depleted rats developed neither T cell or macrophage infiltrates nor their effector cytokines, which are present in glomeruli of rats with HN. Examination of lymph node (LN) draining sites of immunization showed these findings were not explained by altered immune events within these LNs. It was concluded that CD8(+) cytotoxic T cells are essential to the mediation of glomerular injury in HN and may be relevant to the pathogenesis and treatment of membranous nephropathy.

Animals↗

PubMed1987

Molecular cloning of the cDNA encoding the T3 gamma subunit of the mouse T3/T cell antigen receptor complex.

Complementary DNA (cDNA) clones encoding the T3 gamma subunit of the mouse T3/T cell antigen receptor complex were isolated from a cDNA library prepared from a cytochrome C-specific, I-E (class II antigen)-restricted murine T cell clone. The cDNA hybridized to a single mRNA transcript of 1 kb in size the expression of which was restricted to T lymphocytes. The 182-amino acid sequence deduced from the cDNA revealed a signal peptide, a 89-amino acid extracellular domain with one N-glycosylation site, a hydrophobic domain with a centrally located glutamic acid residue, and a 44-amino acid intracellular domain. Comparative analysis of the mouse T3 gamma sequence with those of the human T3 gamma chain and the related human and mouse T3 delta chains revealed that the regions incorporating the extracellular cysteine residues were highly conserved. More importantly, the mouse T3 gamma subunit retained the potential serine phosphorylation site (Ser 126) unique to the human T3 gamma subunit, in the membrane-proximal region of the intracellular domain. The 16-amino acid region flanking Ser 126 was totally conserved (100%) in the gamma subunits, yet showed little homology (38 to 44%) with the corresponding region in the delta subunits, in spite of the otherwise high degree of conservation (61 to 68%) between the remainder of the cytoplasmic domains of the gamma and delta chains.

Amino Acid Sequence↗

PubMed1986

Exon/intron organization of the genes coding for the delta chains of the human and murine T-cell receptor/T3 complex.

Genomic DNA clones containing the gene coding for the 20-kDa T3 glycoprotein of the T-cell receptor/T3 complex (T3-delta chain) of human and mouse were isolated and characterized. The human T3-delta gene is approximately equal to 4 kilobases (kb) long and contains five exons: a 151-base-pair (bp) exon containing the 5' untranslated and the coding sequences of the signal peptide, one exon of 219 bp, which contains most of the extracellular segment of the T3-delta chain, one 130-bp-long exon coding mainly for the transmembrane portion of the molecule, and two exons of 44 bp and 156 bp encoding the cytoplasmic domain and 3' untranslated region of the T3-delta chain, respectively. The murine T3-delta gene, which has a similar organization, contains 5 kb, because the first intron is approximately equal to 1 kb larger than in the human gene. Two major mRNA initiation sites within a small area approximately equal to 100 nucleotides 5' of the AUG codon were determined by S1 nuclease analysis and primer-extension studies. The remarkably high level of conservation of nucleotide sequences in this region suggests that this segment may be important for the regulation of T-cell-specific transcription of the T3-delta gene. The T3-delta gene does not contain the "TATA box" found in many eukaryotic promoters.

Animals↗

PubMed1984

Lymphocyte mitogenesis induced by monoclonal antibodies to the T3 complex. Differential modulation by human IgG.

Murine monoclonal antibodies OKT3 (IgG2), 64.1 (IgG2), and Leu 4 (IgG1) react with a common membrane antigen on human T cells and induce potent mitogenesis at concentrations of 1 ng/ml, 10 ng/ml, and 100 ng/ml, respectively. Human serum inhibits the mitogenic effect of antibodies OKT3 and 64.1, but not that of Leu 4. The inhibitor in serum has been identified as immunoglobulin G (IgG) as evidenced by the ability of anti-human IgG-Sepharose affinity columns to retain the inhibitory activity. Various immunoglobulin classes and subclasses obtained from human myelomas differ in their ability to inhibit the OKT3-induced activation. The best inhibition is obtained with the IgG subclasses IgG1 and IgG3, followed by IgG2; IgG4, IgM, and IgA have little if any effect. None of the IgG subclasses inhibit the Leu 4-induced mitogenesis. Indomethacin as well as supernatants containing interleukin 2 (IL-2) can reverse the inhibitory effects of IgG. Prostaglandins (PGE1 and PGE2) inhibit both the OKT3- and Leu 4-induced mitogenesis, thus lacking the selectivity seen with IgG. Since stimulation by the monoclonal antibodies requires the participation of monocytes, an interpretation consistent with the present data is that IgG stimulates monocytes via its Fc portion to release prostaglandins and/or other suppressor factors via an indomethacin-sensitive pathway. The inability of IgG to inhibit Leu 4-induced mitogenesis may therefore relate to an inability of the monocyte subpopulation, which mediates the Leu 4 response, to secrete suppressor factors. These data suggest a potential value of the mitogenic monoclonal antibodies as probes in studying monocyte heterogeneity and T-cell-monocyte interactions.

Antibodies, Monoclonal↗

PubMed1992

Interferon-alpha suppresses the capacity of T cells to help antibody production by human B cells.

This study was designed to analyze the effect of interferon-alpha (IFN-alpha) on the potential of T cells to help B-cell differentiation in vitro. Human splenic T cells preactivated via the T-cell receptor (TCR)/CD3 complex, as well as murine EL4 thymoma T cells preactivated with phorbol esters, stimulated human B cells via a species cross-reactive physical interaction to differentiate into antibody-producing cells. If the human or murine T cells were activated in the presence of IFN-alpha, normal proliferation and interleukin-2 (IL-2) production occurred, but the cells did not acquire any B-cell helper potential. Therefore, IFN-alpha modulates the B-cell stimulatory potential of T cells by interfering with the T-cell activation process. In contrast, IFN-alpha neither acted on B cells directly nor on already activated T cells, because it did not suppress B-cell differentiation induced by T cells preactivated in the absence of IFN-alpha. IFN-alpha did not induce the production of inhibitory T-cell factor(s), since T cells preactivated in the presence of IFN-alpha did not inhibit the interaction of B cells with T cells optimally preactivated in the absence of IFN-alpha. Taken together the data indicate that IFN-alpha suppresses the potential of T cells to stimulate B-cell differentiation by interfering with the T-cell activation process, but acts neither on B cells directly nor on already activated T cells.

Animals↗

PubMed2001

CD28 co-stimulates TCR/CD3-induced phosphoinositide turnover in human T lymphocytes.

Upon engagement of TCR with peptide-MHC complexes displayed on the surface of antigen-presenting cells, T lymphocytes undergo a sustained elevation of intracellular Ca(2+) concentration([Ca(2+)](i)), which is required for cytokine production. In the present work, we investigate how inositol lipid metabolism can be activated for a prolonged time to ensure a sustained link between receptor triggering and downstream signaling effectors. Four lines of evidence indicate that an extensive phosphoinositide turnover induced by TCR and CD28 engagement allows this task to be accomplished: (i) continuous phosphoinositide breakdown is required for a sustained [Ca(2+)](i )increase in antigen-stimulated T cells; (ii) TCR triggering results in a continuous release of inositol phosphates from the cell membrane paralleled by a massive and sustained phosphoinositide re-synthesis due to free inositol re-incorporation; (iii) TCR-induced phosphoinositide turnover is strongly increased by CD28 ligation; and (iv) CD28 engagement augments and sustains the TCR-induced [Ca(2+)](i )increase. Our results show that the T cell pool of phosphoinositides is continuously re-formed during T cell-APC cognate interaction, thereby explaining how sustained receptor triggering can transduce an equally sustained [Ca(2+)](i) increase. Importantly, our data identify a novel step in the signaling cascade where co-stimulation converges with TCR-generated signals to sustain and amplify the activation process.

CD28 Antigens↗

PubMed1990

A novel model for antigen-dependent activation of normal human T cells. Transmembrane signaling by crosslinkage of the CD3/T cell receptor-alpha/beta complex with the cluster determinant 2 antigen.

Transmembrane signaling of normal human T cells was explored with mAbs directed at TCR, CD2, CD4, CD5, or CD8 antigens and highly purified CD4+ T cells and CD8+ T cells. Our experiments explicitly show that: (a) crosslinkage of TCR with the CD2 antigen, and not independent crosslinking of TCR and of CD2 antigen or crosslinking of either protein with the CD4 or CD8 antigen induces significant proliferation independent of co-stimulatory signals (e.g., accessory cells, recombinant lymphokines, or tumor promoter), (b) F(ab')2 fragments of mAb directed at the TCR and F(ab')2 anti-CD2, crosslinked with F(ab')2 fragments of rabbit anti-mouse IgG, promote the proliferation of highly purified T cells, (c) a prompt and sustained increase in intracellular free Ca2+ concentration results from crosslinkage of TCR with the CD2 antigen, (d) T cell proliferation induced by this novel approach is curtailed by EGTA and by direct or competitive inhibitors of PKC, (e) crosslinkage of TCR with the CD2 antigen results in the transcriptional activation and translation of the gene for IL-2 and in the expression of IL-2 receptor alpha (CD25), (f) anti-CD25 mAbs inhibit T cell proliferation initiated by crosslinkage of TCR with the CD2 antigen, and recombinant IL-2 restores the proliferative response. Our first demonstration that crosslinkage of TCR with the CD2 antigen induces proliferation of normal human CD4+ T cells and CD8+ T cells, in addition to revealing a novel activation mechanism utilizable by the two major subsets of T cells, suggest that the CD2 antigen might be targeted for the regulation of antigen-specific T cell immunity (e.g., organ transplantation).

Antibodies, Monoclonal↗

PubMed2001

Prolonged exposure of T cells to TNF down-regulates TCR zeta and expression of the TCR/CD3 complex at the cell surface.

A role for TNF-alpha in the pathogenesis of chronic inflammatory disease is now firmly established. Paradoxically, TNF also has potent immunomodulatory effects on CD4(+) T lymphocytes, because Ag-specific proliferative and cytokine responses are suppressed following prolonged exposure to TNF. We explored whether TNF attenuated T cell activation by uncoupling proximal TCR signal transduction pathways using a mouse T cell hybridoma model. Chronic TNF exposure induced profound, but reversible, T cell hyporesponsiveness, with TNF-treated T cells requiring TCR engagement with higher peptide concentrations for longer periods of time for commitment to IL-2 production. Subsequent experiments revealed that chronic TNF exposure led to a reversible loss of TCRzeta chain expression, in part through a reduction in gene transcription. Down-regulation of TCRzeta expression impaired TCR/CD3 assembly and expression at the cell surface and uncoupled membrane-proximal tyrosine phosphorylation events, including phosphorylation of the TCRzeta chain itself, CD3epsilon, ZAP-70 protein tyrosine kinase, and linker for activation of T cells (LAT). Intracellular Ca(2+) mobilization was also suppressed in TNF-treated T cells. We propose that TNF may contribute to T cell hyporesponsiveness in chronic inflammatory and infectious diseases by mechanisms that include down-regulation of TCRzeta expression. We speculate that by uncoupling proximal TCR signals TNF could also interrupt mechanisms of peripheral tolerance that are dependent upon intact TCR signal transduction pathways.

Acetylcysteine↗

PubMed1997

Regulation of the interleukin-2 CD28-responsive element by NF-ATp and various NF-kappaB/Rel transcription factors.

The CD28 costimulatory signal enhances antigen-mediated induction of interleukin-2 (IL-2) gene transcription through activation of an enhancer termed the CD28-responsive element (CD28RE). Although various nuclear proteins have been shown to bind to CD28RE, their in vivo functions in the regulation of this enhancer remain elusive. In this report, we show that CD28RE binds distinct transcription factors in cells treated with different mitogenic stimuli. Stimulation of the T-cell receptor (TCR) complex in the absence of a CD28 costimulatory signal induces a member of the nuclear factor of the activated T cells, NF-ATp; however, this treatment fails to activate the CD28RE enhancer activity. Significant activation of CD28RE was detected when the cells were treated with both the TCR stimulators and an anti-CD28 monoclonal antibody (anti-CD28), which induces the NF-kappaB/Rel enhancer binding proteins in addition to NF-ATp. The costimulatory activity of anti-CD28 can be further enhanced by a phorbol ester. Kinetic analyses demonstrate that activation of endogenous IL-2 gene transcription is correlated with the binding of CD28RE by NF-ATp and different NF-kappaB/Rel species. Transient-transfection studies reveal that expression of either NF-ATp or the p50-RelA NF-kappaB heterodimer leads to the potent transactivation of both the CD28RE enhancer and the intact IL-2 promoter in mitogen-stimulated cells. Remarkably, coexpression of these two families of enhancer-binding proteins in Jurkat T cells results in the transactivation of the CD28RE enhancer even in the absence of any cellular stimuli. Together, these results suggest that activation of IL-2 gene transcription by the TCR- and CD28-mediated signals involves the interaction of CD28RE with NF-ATp and various NF-kappaB/Rel transcription factors.

CD28 Antigens↗

PubMed2006

Transfection of drug-specific T-cell receptors into hybridoma cells: tools to monitor drug interaction with T-cell receptors and evaluate cross-reactivity to related compounds.

In the context of drug hypersensitivity, our group has recently proposed a new model based on the structural features of drugs (pharmacological interaction with immune receptors; p-i concept) to explain their recognition by T cells. According to this concept, even chemically inert drugs can stimulate T cells because certain drugs interact in a direct way with T-cell receptors (TCR) and possibly major histocompatibility complex molecules without the need for metabolism and covalent binding to a carrier. In this study, we investigated whether mouse T-cell hybridomas transfected with drug-specific human TCR can be used as an alternative to drug-specific T-cell clones (TCC). Indeed, they behaved like TCC and, in accordance with the p-i concept, the TCR recognize their specific drugs in a direct, processing-independent, and dose-dependent way. The presence of antigen-presenting cells was a prerequisite for interleukin-2 production by the TCR-transfected cells. The analysis of cross-reactivity confirmed the fine specificity of the TCR and also showed that TCR transfectants might provide a tool to evaluate the potential of new drugs to cause hypersensitivity due to cross-reactivity. Recombining the alpha- and beta-chains of sulfanilamide- and quinolone-specific TCR abrogated drug reactivity, suggesting that both original alpha- and beta-chains were involved in drug binding. The TCR-transfected hybridoma system showed that the recognition of two important classes of drugs (sulfanilamides and quinolones) by TCR occurred according to the p-i concept and provides an interesting tool to study drug-TCR interactions and their biological consequences and to evaluate the cross-reactivity potential of new drugs of the same class.

Animals↗

PubMed1996

Murine gamma/delta-expressing T cells affect alloengraftment via the recognition of nonclassical major histocompatibility complex class Ib antigens.

T cells with antidonor specificities have been isolated from human recipients experiencing graft rejection after allogeneic bone marrow transplantation (BMT). Partial T-cell depletion of unrelated BM grafts with an anti- T-cell receptor (TCR) monoclonal antibody (MoAb) directed against the TCR alpha/beta heterodimer have shown that the incidence of graft-versus-host disease is low and that the incidence of durable engraftment is high. These studies suggest either that the number of residual TCR alpha/beta+ cells was sufficient to permit alloengraftment or that the preservation of cells other than TCR alpha/beta+ cells was beneficial for engraftment. With respect to the latter, one such candidate cell is the TCR gamma/delta+ T cell. Because no studies have specifically examined whether TCR gamma/delta+ cells might be capable of eliminating BM-derived hematopoietic cells, we established a new graft rejection model system in which transgenic (Tg) H-2d mice (termed G8), known to express gamma/delta heterodimers on high proportion of peripheral T cells, were used as BMT recipients. These Tg TCR gamma/delta+ cells respond vigorously to target cells that express the nonclassical major histocompatibility complex (MHC) class lb region gene products encoded in H-2T region of H-2T(b)+ strains. G8 Tg mice were used as recipients for C57BL/6 (B6: H-2(b); H-2T(b)) T-cell-depleted (TCD) donor BM. We show that G8 Tg (H-2(d), H-2T(d)) mice are potent mediators of B6 BM graft rejection and that the rejection process was inhibited by anti-TCR gamma/delta MoAbs. In contrast, BM from a B6 congenic strain that expresses the H-2T(a) allele, B6.A-Tl(a)/BoyEg, was readily accepted, suggesting that H-2T antigens on repopulating donor BM cells are the targets of host graft rejecting T cells that express the TCR gamma/delta heterodimer. PB chimerism studies were performed at > or = 1.5 months post-BMT using TCD BM from severe combined immunodeficient allogeneic donors, which is highly susceptible to rejection by the host. The addition of donor G8 TCR gamma/delta+ cells to TCD donor BM was shown to significantly increase alloengraftment in B6 recipients. These results show that (1) host TCR gamma/delta+ cells can reject repopulating donor cells, presumably by responding to nonclassical MHC class lb gene products expressed on BM-derived hematopoietic progenitor cells; and (2) donor TCR gamma/delta+ cells can facilitate the alloengraftment of rigorously TCD donor BM.

Animals↗

PubMed2003

Reconstitution of deficient T cell receptor zeta chain restores T cell signaling and augments T cell receptor/CD3-induced interleukin-2 production in patients with systemic lupus erythematosus.

OBJECTIVE: T cells from a majority of patients with systemic lupus erythematosus (SLE) display antigen receptor-mediated signaling aberrations associated with defective T cell receptor (TCR) zeta chain, a subunit of the TCR/CD3 complex. This study was undertaken to explore the possibility that forced expression of TCR zeta chain may reverse the known signaling abnormalities and defective interleukin-2 (IL-2) production in SLE T cells. METHODS: Freshly isolated SLE T cells were transfected with TCR zeta chain construct in a eukaryotic expression vector at high efficiency, by a recently developed nucleoporation technique. Restoration of TCR/CD3-mediated signaling was studied in the zeta chain-transfected cells. RESULTS: In SLE T cells transfected with TCR zeta chain, surface expression of TCR chain was increased and the TCR/CD3-induced increased free intracytoplasmic calcium concentration response was normalized, as was hyperphosphorylation of cellular substrates. Simultaneously, the previously noted increased expression of the Fc receptor gamma chain was diminished in SLE T cells transfected with the zeta chain expression vector, and the surface membrane clusters of cell signaling molecules were redistributed to a more continuous pattern. TCR zeta chain replacement also augmented the expression of diminished TCR/CD3-mediated IL-2 production in SLE T cells, associated with increased expression of the p65 subunit of nuclear factor kappaB in the nuclear fractions of these T cells. CONCLUSION: These results suggest that reconstitution of deficient TCR zeta chain can reverse the TCR/CD3-mediated signaling abnormalities as well as the defective IL-2 production in T cells of patients with SLE.

Adult↗

PubMed2006

Direct stimulation of T lymphocytes by immunosomes: virus-like particles decorated with T cell receptor/CD3 ligands plus costimulatory molecules.

Many infectious viruses coevolved with the vertebrate immune system. During the assembly of enveloped viruses, lipid ordered domains of the host cell plasma membrane, called lipid rafts, frequently function as a natural meeting point for viral proteins. The role of lipid rafts in the organization of complex combinations of immune receptors during antigen presentation and T cell signaling is widely recognized. In our studies, we determined whether lipid rafts, virus budding, and molecular interactions during T cell activation could be brought into a novel context to create artificial antigen-presenting particles. We show here that cell-free virus-like particles (VLP) expressing a surrogate TCR/CD3 ligand (OKT3scFv) and the costimulator CD80 polyclonally activate human T cells independently of accessory cells. VLP expressing the glycoprotein epitope 33-41 of the lymphocytic choriomeningitis virus in the context of H-2D(b) activate and expand naïve, antigen-specific CD8(+) T lymphocytes and differentiate them into cytotoxic effector cells. Efficient targeting of T cell ligands to lipid rafts and ultimately to VLP is achieved by C-terminal introduction of glycosyl phosphatidyl inositol acceptor sequences, replacing transmembrane and intracellular domains. In this work, basic functions of immunostimulatory molecules meet virus biology and translate into a reductionist antigen-specific T lymphocyte-stimulating vehicle, which we refer to as immunosomes. A large variety of agonistic and antagonistic accessory molecules on genuine antigen-presenting cells may complicate the predictable manipulation of T cells as well as the analysis of selected receptor combinations, making immunosomes potentially useful reagents for such purposes in the future.

Animals↗

PubMed2004

Tyrosine-mediated inhibitory signals contribute to CTLA-4 function in vivo.

The ability of CTLA-4 to inhibit T cell activation may be either negatively or positively regulated by a critical tyrosine at position 201 (Y201) within the CTLA-4 cytoplasmic domain. By binding to the clathrin-associated adaptor complex AP-2 and inducing endocytosis, Y201 reduces the amount of CTLA-4 on the cell surface, thereby down-regulating CTLA-4 inhibitory function. Alternatively, Y201 may function to transmit CTLA-4 inhibitory signals, perhaps through binding to intracellular proteins that oppose TCR- and/or CD28-induced signal transduction. Results from studies performed in vitro have cast doubt on whether this second mechanism contributes significantly to CTLA-4 function. In order to determine if a role existed for Y201 in mediating CTLA-4 inhibitory signaling in vivo, we studied lymphocyte activation and homeostasis in CTLA-4(-/-) mice that were reconstituted with a transgenic CTLA-4 receptor in which Y201 was mutated to valine (Y201V/CTLA-4(-/-)). We found that despite augmented levels of CTLA-4 on the cell surface of T cells, Y201V/CTLA-4(-/-) mice developed a lymphoproliferative syndrome characterized by lymphadenopathy and the accumulation of T cells that secreted IL-4. Mutant T cells exhibited increased cell division when treated with suboptimal doses of mitogenic stimuli in vitro. These results demonstrate that in addition to down-modulating CTLA-4 expression on the cell surface of T cells, the Y201 residue also functions to transmit CTLA-4 inhibitory signals in vivo. Elucidating the biochemical pathways downstream of Y201 will be important for a full understanding of the molecular basis for CTLA-4 function.

Age Factors↗