L-Arginine modulates CD3zeta expression and T cell function in activated human T lymphocytes

Engagement of the T cell receptor (TCR) by antigen or anti-CD3 antibody results in a cycle of internalization and re-expression of the CD3zeta. Following internalization, CD3zeta is degraded and replaced by newly synthesized CD3zeta on the cell surface. Here, we provide evidence that availability of the amino acid L-arginine modulates the cycle of internalization and re-expression of CD3zeta and cause T cell dysfunction. T cells stimulated and cultured in presence of L-arginine, undergo the normal cycle of internalization and re-expression of CD3zeta. In contrast, T cells stimulated and cultured in absence of L-arginine, present a sustained down-regulation of CD3zeta preventing the normal expression of the TCR, exhibit a decreased proliferation, and a significantly diminished production of IFNgamma, IL5, and IL10, but not IL2. The replenishment of L-arginine recovers the expression of CD3zeta. The decreased expression of CD3zeta is not caused by a decreased CD3zeta mRNA, an increased CD3zeta degradation or T cell apoptosis.     

L-arginine consumption by macrophages modulates the expression of CD3 zeta chain in T lymphocytes

L-Arginine plays a central role in the normal function of several organs including the immune system. It is metabolized in macrophages by inducible nitric oxide synthase to produce nitric oxide, important in the cytotoxic mechanisms, and by arginase I (ASE I) and arginase II (ASE II) to synthesize L-ornithine and urea, the first being the precursor for the production of polyamines needed for cell proliferation. L-Arginine availability can modulate T cell function. Human T cells stimulated and cultured in the absence of L-arginine lose the expression of the TCR zeta-chain (CD3zeta) and have an impaired proliferation and a decreased cytokine production. The aim of this work was to test whether activated macrophages could modulate extracellular levels of L-arginine and alter T cell function, and to determine which metabolic pathway was responsible for this event. The results show that macrophages stimulated with IL-4 + IL-13 up-regulate ASE I and cationic amino acid transporter 2B, causing a rapid reduction of extracellular levels of L-arginine and inducing decreased expression of CD3zeta and diminished proliferation in normal T lymphocytes. Competitive inhibitors of ASE I or the addition of excess L-arginine lead to the re-expression of CD3zeta and recovery of T cell proliferation. In contrast, inducible nitric oxide synthase or ASE II failed to significantly reduce the extracellular levels of L-arginine and modulate CD3zeta expression. These results may provide new insights into the mechanisms leading to T cell dysfunction and the down-regulation of CD3zeta in cancer and chronic infectious diseases.     

TCR dynamics in human mature T lymphocytes lacking CD3 gamma

The contribution of CD3gamma to the surface expression, internalization, and intracellular trafficking of the TCR/CD3 complex (TCR) has not been completely defined. However, CD3gamma is believed to be crucial for constitutive as well as for phorbol ester-induced internalization. We have explored TCR dynamics in resting and stimulated mature T lymphocytes derived from two unrelated human congenital CD3gamma-deficient (gamma(-)) individuals. In contrast to gamma(-) mutants of the human T cell line Jurkat, which were selected for their lack of membrane TCR and are therefore constitutively surface TCR negative, these natural gamma(-) T cells constitutively expressed surface TCR, mainly through biosynthesis of new chains other than CD3gamma. However, surface (but not intracellular) TCR expression in these cells was less than wild-type cells, and normal surface expression was clearly CD3gamma-dependent, as it was restored by retroviral transduction of CD3gamma. The reduced surface TCR expression was likely caused by an impaired assembly or membrane transport step during recycling, whereas constitutive internalization and degradation were apparently normal. Ab binding to the mutant TCR, but not phorbol ester treatment, caused its down-modulation from the cell surface, albeit at a slower rate than in normal controls. Kinetic confocal analysis indicated that early ligand-induced endocytosis was impaired. After its complete down-modulation, TCR re-expression was also delayed. The results suggest that CD3gamma contributes to, but is not absolutely required for, the regulation of TCR trafficking in resting and Ag-stimulated mature T lymphocytes. The results also indicate that TCR internalization is regulated differently in each case.     

TCR activation of human T cells induces the production of exosomes bearing the TCR/CD3/zeta complex

We show in this study that human T cells purified from peripheral blood, T cell clones, and Jurkat T cells release microvesicles in the culture medium. These microvesicles have a diameter of 50-100 nm, are delimited by a lipidic bilayer membrane, and bear TCR beta, CD3epsilon, and zeta. This microvesicle production is regulated because it is highly increased upon TCR activation, whereas another mitogenic signal, such as PMA and ionomycin, does not induce any release. T cell-derived microvesicles also contain the tetraspan protein CD63, suggesting that they originate from endocytic compartments. They contain adhesion molecules such as CD2 and LFA-1, MHC class I and class II, and the chemokine receptor CXCR4. These transmembrane proteins are selectively sorted in microvesicles because CD28 and CD45, which are highly expressed at the plasma membrane, are not found. The presence of phosphorylated zeta in these microvesicles suggests that the CD3/TCR found in the microvesicles come from the pool of complexes that have been activated. Proteins of the transduction machinery, tyrosine kinases of the Src family, and c-Cbl are also observed in the T cell-derived microvesicles. Our data demonstrate that T lymphocytes produce, upon TCR triggering, vesicles whose morphology and phenotype are reminiscent of vesicles of endocytic origin produced by many cell types and called exosomes. Although the exact content of T cell-derived exosomes remains to be determined, we suggest that the presence of TCR/CD3 at their surface makes them powerful vehicles to specifically deliver signals to cells bearing the right combination of peptide/MHC complexes.     

Down-regulation of zeta chain and zeta-associated protein 70 (Zap 70) expression in circulating T lymphocytes in laryngeal squamous cell carcinoma

OBJECTIVE: To evaluate zeta chain and Zap 70 expression in T lymphocytes of patients with laryngeal cancer in relation to surgical treatment. STUDY DESIGN: This study investigated, by dual-color flow cytometry, zeta chain and Zap 70 expression in the circulating T lymphocytes of 13 patients with laryngeal cancer patients before and after surgical treatment. RESULTS: Patients exhibited a significant lower expression of both zeta chain and Zap 70 compared to healthy normal controls; no statistical differences were observed after surgical treatment. CONCLUSION: The results of this investigation seem to indicate that both the zeta chain and the Zap 70 expression in circulating T lymphocytes are down-regulated in patients with laryngeal cancer and that these changes do not immediately return to normal after surgery. Flow cytometry analysis may represent an easy-to-use procedure for monitoring the immune status of patients with laryngeal cancer.     

A1/Bfl-1 expression is restricted to TCR engagement in T lymphocytes

We analyzed regulation of the prosurvival Bcl-2 homologue A1, following T-cell receptor (TCR) or cytokine receptor engagement. Activation of CD4(+) or CD8(+) T cells by antigenic peptides induced an early but transient IL-2-independent expression of A1 and Bcl-xl mRNA and proteins, whereas expression of Bcl-2 was delayed and required IL-2. Cytokines such as IL-2, IL-4, IL-7 or IL-15 prevented apoptosis of activated T cells that effect being associated with the maintenance of Bcl-2, but not of A1 expression. However, restimulation of activated or posteffector T cells with antigenic peptide strongly upregulated A1 mRNA and maintained A1 protein expression. IL-4, IL-7 or IL-15 also prevented cell death of naive T cells. In those cells, cytokines upregulated Bcl-2, but not A1 expression. Therefore, in naive, activated and posteffector T cells, expression of A1 is dependent on TCR but not on cytokine receptor engagement, indicating that A1 is differently regulated from Bcl-xl and Bcl-2.     

Stimulation through the TCR/CD3 complex up-regulates the CD2 surface expression on human T lymphocytes.

Despite the well known interrelationship between the CD2- and CD3-mediated signal transduction pathways, it is not well established whether the CD2 surface expression can be regulated by triggering of TCR/CD3 complex. In this study we show that the stimulation of human PBMC with the Cris-7 (CD3) mAb, both in soluble and particulate form, results in hyperexpression of the CD2 surface Ag, as assessed by immunofluorescence and semi-quantitative immunoprecipitation assays. Similar effects on CD2 surface expression were obtained when different CD3 mAb (OKT3, RW2-8C8 and Leu-4) were tested. The CD3-mediated CD2 up-regulation was suppressed by cycloheximide and actinomycin D, indicating that it requires de novo protein and RNA synthesis. In agreement with this, increased CD2 RNA levels were observed after 3 h of stimulation, reaching a plateau at 24 h that was maintained for 72 h. The CD2 up-regulation was concomitant to other CD3-induced activation-related events such as induction of surface CD25 and CD71 and high RNA levels for c-myc, IL-2R alpha- and beta-chains, CD71, and IFN-gamma. CD2 up-regulation appeared to be elicited by a protein kinase C-dependent mechanism because it was abrogated by staurosporine, a potent protein kinase C inhibitor. Moreover, IL-2-dependent events may also help in enhancing CD2 hyper-expression because it was only partially inhibitable by cyclosporine, dexamethasone, or Mar-108 (CD25) mAb. In conclusion, our data suggest that CD2 up-regulation can be a relevant event in T cell activation triggered by the physiologic engagement of the TCR/CD3 complex.     

Surface expression of the IFN-gamma R2 chain is regulated by intracellular trafficking in human T lymphocytes

The surface and cytoplasmic expressions of the transducing chain (IFN-gamma R2) of the heterodimeric IFN-gamma receptor on human T lymphocytes have been investigated. We show that its surface expression is low, whereas high cytoplasmic levels are found in both resting and PHA-activated T lymphocytes. This low expression does not prevent activated T cells from responding to IFN-gamma, because it induces IFN-regulatory factor 1 expression. Low surface IFN-gamma R2 expression appears to be due to recycling between cytoplasmic stores and the cell surface, which does not depend on signals mediated by endogenous IFN-gamma, because IFN-gamma R2 surface expression is low, and its internalization is equally observed in patients with inherited IFN-gamma R1 gene deficiency and in healthy donors. Moreover, IFN-gamma R2 internalization in T lymphoblasts from healthy donors was not affected by the presence of anti-IFN-gamma-neutralizing or anti-IFN-gamma R1-blocking mAb. In conclusion, these data illustrate a new mechanism whereby human T cells limit the surface expression of IFN-gamma R2 in a ligand-independent manner.     

Functional and morphologic characterization of human T lymphocytes expressing the TCR gamma /delta

A minor subset of T lymphocytes express a TCR composed of gamma and delta chains. This subset differs from conventional T cells for a number of phenotypic and functional characteristics. TCR gamma/delta+ cells simultaneously lack both CD4 and CD8 antigens. Cloning of CD4-8- peripheral blood lymphocytes, under limiting dilution conditions, revealed that they are homogeneously composed of cytolytic cells which efficiently lyse tumor target cells. Formal proofs have been provided that TCR gamma/delta+ cells are able to recognize antigens. For example, they proliferated in response to allogeneic mixed lymphocyte culture (MLC); in addition, MLC-derived TCR gamma/delta+ cells specifically lysed PHA-induced blast cells bearing the stimulating alloantigens. The selection of monoclonal antibodies specific for TCR gamma/delta molecules allowed to identify two distinct subsets of TCR gamma/delta+ cells. Both of these mABs, termed BB3 and delta TCS-1 respectively, induced specific activation of cloned cells expressing the corresponding antigenic determinants (as assessed by measurements of intracellular Ca++ and/or lymphokine production or cytolytic activity). Analysis of the distribution of subsets expressing different forms of TCR gamma/delta, showed that the BB3-reactive form is prevalent in the peripheral blood. In contrast, delta-TCS-1-reactive cells are relatively unfrequent in peripheral blood but represent the majority of TCR gamma/delta+ cells in tissues.     

Effect of trichostatin A on human T cells resembles signaling abnormalities in T cells of patients with systemic lupus erythematosus: a new mechanism for TCR zeta chain deficiency and abnormal signaling

Trichostatin A (TSA) is a potent reversible inhibitor of histone deacetylase, and it has been reported to have variable effects on the expression of a number of genes. In this report, we show that TSA suppresses the expression of the T cell receptor zeta chain gene, whereas, it upregulates the expression if its homologous gene Fc(epsilon) receptor I gamma chain. These effects are associated with decreased intracytoplasmic-free calcium responses and altered tyrosine phosphorylation pattern of cytosolic proteins. Along with these effects, we report that TSA suppresses the expression of the interleukin-2 gene. The effects of TSA on human T cells are predominantly immunosuppressive and reminiscent of the signaling aberrations that have been described in patients with systemic lupus erythematosus.     

Helicobacter pylori arginase inhibits T cell proliferation and reduces the expression of the TCR zeta-chain (CD3zeta)

Helicobacter pylori infects approximately half the human population. The outcomes of the infection range from gastritis to gastric cancer and appear to be associated with the immunity to H. pylori. Patients developing nonatrophic gastritis present a Th1 response without developing protective immunity, suggesting that this bacterium may have mechanisms to evade the immune response of the host. Several H. pylori proteins can impair macrophage and T cell function in vitro through mechanisms that are poorly understood. We tested the effect of H. pylori extracts and live H. pylori on Jurkat cells and freshly isolated human normal T lymphocytes to identify possible mechanisms by which the bacteria might impair T cell function. Jurkat cells or activated T lymphocytes cultured with an H. pylori sonicate had a reduced proliferation that was not caused by T cell apoptosis or impairment in the early T cell signaling events. Instead, both the H. pylori sonicate and live H. pylori induced a decreased expression of the CD3zeta-chain of the TCR. Coculture of live H. pylori with T cells demonstrated that the wild-type strain, but not the arginase mutant rocF(-), depleted L-arginine and caused a decrease in CD3zeta expression. Furthermore, arginase inhibitors reversed these events. These results suggest that H. pylori arginase is not only important for urea production, but may also impair T cell function during infection.