PubMed Health⌕ Search

Biomedical subjects

C H June

Publications and source records attributed to C H June.

At least 73 records · Page 4Linked to original sources
PubMed1996

Antiviral effect and ex vivo CD4+ T cell proliferation in HIV-positive patients as a result of CD28 costimulation.

Because stimulation of CD4+ lymphocytes leads to activation of human immunodeficiency virus-type 1 (HIV-1) replication, viral spread, and cell death, adoptive CD4+ T cell therapy has not been possible. When antigen and CD28 receptors on cultured T cells were stimulated by monoclonal antibodies (mAbs) to CD3 and CD28 that had been immobilized, there was an increase in the number of polyclonal CD4+ T cells from HIV-infected donors. Activated cells predominantly secreted cytokines associated with T helper cell type 1 function. The HIV-1 viral load declined in the absence of antiretroviral agents. Moreover, CD28 stimulation of CD4+ T cells from uninfected donors rendered these cells highly resistant to HIV-1 infection. Immobilization of CD28 mAb was crucial to the development of HIV resistance, as cells stimulated with soluble CD28 mAb were highly susceptible to HIV infection. The CD28-mediated antiviral effect occurred early in the viral life cycle, before HIV-1 DNA integration. These data may facilitate immune reconstitution and gene therapy approaches in persons with HIV infection.

Antibodies, Monoclonal↗
PubMed1996

Regulated expression of telomerase activity in human T lymphocyte development and activation.

Telomerase, a ribonucleoprotein that is capable of synthesizing telomeric repeats, is expressed in germline and malignant cells, and is absent in most normal human somatic cells. The selective expression of telomerase has thus been proposed to be a basis for the immortality of the germline and of malignant cells. In the present study, telomerase activity was analyzed in normal human T lymphocytes. It was found that telomerase is expressed at a high level in thymocyte subpopulations, at an intermediate level in tonsil T lymphocytes, and at a low to undetectable level in peripheral blood T lymphocytes. Moreover, telomerase activity is highly inducible in peripheral T lymphocytes by activation through CD3 with or without CD28 costimulation, or by stimulation with phorbol myristate acetate (PMA)/ionomycin. The induction of telomerase by anti-CD3 plus anti-CD28 (anti-CD3/CD28) stimulation required RNA and protein synthesis, and was blocked by herbimycin A, an inhibitor of S pi protein tyrosine kinases. The immunosuppressive drug cyclosporin A selectively inhibited telomerase induction by PMA/ionomycin and by anti-CD3, but not by anti-CD3/CD28. Although telomerase activity in peripheral T lymphocytes was activation dependent and correlated with cell proliferation, it was not cell cycle phase restricted. These results indicate that the expression of telomerase in normal human T lymphocytes is both developmentally regulated and activation induced. Telomerase may thus play a permissive role in T cell development and in determining the capacity of lymphoid cells for cell division and clonal expansion.

Antigens, CD↗
PubMed1996

Protection against lethal toxic shock by targeted disruption of the CD28 gene.

Toxic shock syndrome (TSS) is a multi system disorder resulting from superantigen-mediated cytokine production. Nearly 90% of the clinical cases of TSS arise due to an exotoxin, toxic shock syndrome toxin-1 (TSST-1), elaborated by toxigenic strains of Staphylococcus aureus. It is clearly established that besides antigen-specific signals a variety of costimulatory signals are required for full T cell activation. However, the nature and potential redundancy of costimulatory signals are incompletely understood, particularly with regards to superantigen-mediated T cell activation in vivo. Here we report that CD28-deficient mice (CD28-/-) are completely resistant to TSST-1-induced lethal TSS while CD28 (+/-) littermate mice were partially resistant to TSST-1. The mechanism for the resistance of the CD28 (-/-) mice was a complete abrogation of TNF-alpha accumulation in the serum and a nearly complete (90%) impairment of IFN-gamma secretion in response to TSST-1 injection. In contrast, the serum level of IL-2 was only moderately influenced by the variation of CD28 expression. CD28 (-/-) mice retained sensitivity to TNF-alpha as demonstrated by equivalent lethality after cytokine injection. These findings establish an essential requirement for CD28 costimulatory signals in TSST-1-induced TSS. The hierarchy of TSST-1 resistance among CD28 wild-type (CD28+/+), CD28 heterozygous (CD28+/-), and CD28-/- mice suggests a gene-dose effect, implying that the levels of T cell surface CD28 expression critically regulate superantigen-mediated costimulation. Finally, as these results demonstrate the primary and non-redundant role of CD28 receptors in the initiation of the in vivo cytokine cascade, they suggest therapeutic approaches for superantigen-mediated immunopathology.

Animals↗
PubMed1996

Intact antigen receptor-mediated calcium signals in patients with early stage HIV-1 infection.

A variety of deficiencies in T cell activation have been described in HIV-1 infection. To determine whether one component of Ag receptor signal transduction might be impaired and contribute to the immunopathology of HIV infection, we tested CD4 cells from patients with early to mid-stage HIV infection for TCR-induced calcium mobilization. There was no detectable difference between patients and controls in the mean CD4 cell calcium response or in the fraction of responding CD4 cells after cross-linking the TCR with OKT3 Ab. In addition, in HIV-infected patients, there was no correlation between calcium mobilization and the CD4 cell count. These results indicate that there are no intrinsic impairments of Ag receptor calcium signaling in circulating CD4 cells from HIV-infected patients with more than 400 CD4 cells/mm3, although abnormalities in patients with later stage infections cannot be excluded.

Adult↗
PubMed1996

CD28-deficient mice generate an impaired Th2 response to Schistosoma mansoni infection.

Engagement of CD28 on T cells provides a co-stimulatory signal necessary for T cell activation and differentiation. Recent findings suggest that priming of T helper (Th)2 cells is more dependent on CD28 activation that Th1 cells. The present study examines whether mice that lack expression of CD28 as a result of gene targeting are capable of generating a Th2 response characteristic during infection with the intravascular trematode parasite Schistosoma mansoni. Mutant and control mice were either inoculated in the footpad with S. mansoni eggs (a potent inducer of a Th2 response) or infected percutaneously with the parasite. Draining lymph nodes (after footpad injection) or spleen cells (after natural infection) were harvested at 12 days and 8 weeks, respectively, and examined for cytokine responses to egg antigens. CD28-deficient mice (-/-) generated diminished egg antigen-driven interleukin (IL)-4 and IL-5 production (by 5- to 17-fold, respectively) compared to CD28-expressing (+/+) littermates. In contrast, lymphocyte proliferation and interferon (IFN)-gamma production to egg antigens were equivalent for mutant and control mice. Infected CD28-/- mice also had reduced immunoglobulin secretion. Serum levels of parasite antigen-specific IgG1 and polyclonal IgE were significantly diminished in CD28-/- compared to CD28+/+ mice. Lack of CD28 expression had no effect on granuloma formation around eggs trapped in the liver, but increased susceptibility of mice to primary schistosomiasis infection. These studies indicate that CD28 activation contributes to T cell priming required for generation of a Th2 response to an intravascular dwelling helminth parasite.

Abatacept↗
PubMed1996

Opposing effects of CTLA4-Ig and anti-CD80 (B7-1) plus anti-CD86 (B7-2) on experimental allergic encephalomyelitis.

The roles of the B7 receptors, CD80 and CD86, during actively induced experimental allergic encephalomyelitis were examined with specific monoclonal antibodies and CTLA4-Ig. Injection of CTLA4-Ig on day 2 post-immunization resulted in decreased incidence and severity of resultant disease. Anti-CD80 injection on day 2 blocked development of the first disease episode. Subsequent relapses were unaffected. In contrast, injection of anti-CD86 alone had no effect. Surprisingly, combined anti-CD80 + anti-CD86 monoclonal antibody injection on day 2 resulted in marked exacerbation of disease. Examination of cytokine production in the draining lymph node cells demonstrated a reduction in both interferon (IFN)-gamma and interleukin (IL)-2 producing cells, but a dramatic increase in tumor necrosis factor (TNF)-alpha secretion in animals receiving both monoclonal antibodies. These results suggest distinct roles for CD80 and CD86 in the initiation of EAE, resulting in the diverse clinical outcomes observed in this model of EAE.

Abatacept↗
PubMed1996

Primary porcine endothelial cells express membrane-bound B7-2 (CD86) and a soluble factor that co-stimulate cyclosporin A-resistant and CD28-dependent human T cell proliferation.

Increasing evidence suggests that endothelial cells can directly activate syngeneic, allogeneic and xenogeneic T cells. In this study we demonstrate that unstimulated, paraformaldehyde-fixed primary porcine aortic endothelial cells (PAEC) and microvascular endothelial cells (PMVEC) can provide co-stimulation for human T cell IL-2 secretion and proliferation. EC-mediated co-stimulation has both cyclosporin A (CsA)-sensitive and CsA-resistant components. The CsA-resistant component is completely suppressed either by blocking with anti-CD28 F(ab) fragments or CTLA-4-Ig. Northern blot analysis of unstimulated PAEC and PMVEC with porcine-specific probes reveals constitutive expression of B7-2 mRNA while B7-1 message was not detected. hCTLA-4-Ig and anti-B7-2 mAb immunoprecipitates a single 79 kDa PMVEC surface protein. Surprisingly, PMVEC conditioned media also has soluble co-stimulatory activity that is blocked by anti-CD28 F(ab) fragments or anti-B7-2 mAb. These findings demonstrate that primary unstimulated porcine EC can co-stimulate CsA-resistant human T cell proliferation through binding of membrane bound, constitutively expressed EC B7-2 (CD86) to human T cell CD28, providing one of the first demonstrations of functional B7-2 on cells outside the immune system. In addition, PMVEC secrete or shed a soluble factor that mediates CD28-dependent human T cell proliferation, demonstrating the existence of soluble mediators of CD28 activation.

Animals↗
PubMed1996

Signal transduction properties of the T cell activation monoclonal antibody panel: ubiquitous increase in cellular substrate tyrosine phosphorylation in the absence of detectable calcium mobilization.

A panel of coded monoclonal antibodies (mAbs) submitted to the T cell section of the Vth International Workshop and Conference on Human Leukocyte Differentiation Antigens was examined for the ability to induce cellular activation. Intracellular calcium levels were examined by loading resting T cells with the Ca(+2)-specific dye Indo-1, incubating the cells with Ab, cross-linking with goat anti-mouse Ab and analyzing by flow cytometry. Only 11 out of 68 Abs induced a detectable rise in Ca+2; two of these Abs induced a substantial rise in Ca+2. In resting T cells, 63 of 68 Abs induced increased tyrosine phosphorylation of substrates compared to negative control. Approximately half of the Abs that induced tyrosine phosphorylation induced substrates different from those seen following treatment of cells with anti-CD3 Ab. All mAbs that induced a rise in Ca+2 also induced increased tyrosine phosphorylation. These experiments show a distinct difference in the ability of cross-linked Ab to induce changes in tyrosine phosphorylation and intracellular free Ca+. Furthermore, these results indicate that transient increases in cellular substrate phosphorylation may have questionable biologic significance in T cells.

Animals↗
PubMed1995

Human naive and memory T lymphocytes differ in telomeric length and replicative potential.

The present study has assessed the replicative history and the residual replicative potential of human naive and memory T cells. Telomeres are unique terminal chromosomal structures whose length has been shown to decrease with cell division in vitro and with increased age in vivo for human somatic cells. We therefore assessed telomere length as a measure of the in vivo replicative history of naive and memory human T cells. Telomeric terminal restriction fragments were found to be 1.4 +/- 0.1 kb longer in CD4+ naive T cells than in memory cells from the same donors, a relationship that remained constant over a wide range of donor age. These findings suggest that the differentiation of memory cells from naive precursors occurs with substantial clonal expansion and that the magnitude of this expansion is, on average, similar over a wide range of age. In addition, when replicative potential was assessed in vitro, it was found that the capacity of naive cells for cell division was 128-fold greater as measured in mean population doublings than the capacity of memory cells from the same individuals. Human CD4+ naive and memory cells thus differ in in vivo replicative history, as reflected in telomeric length, and in their residual replicative capacity.

Adult↗
PubMed1995

Acute graft-versus-host reaction can be aborted by blockade of costimulatory molecules.

Injection of parental lymphocytes into an unirradiated adult F1 host results in an acute GVH reaction characterized by immune deficiency, attack on host lymphohematopoietic tissues, and repopulation with donor-derived cells. All of these events result from the initial activation of donor lymphocytes by host alloantigens. Interaction of pairs of host and donor costimulatory molecules, in particular CD28/CTLA4 and B7-1/B7-2, play a crucial role in this initial activation of donor T cells. We demonstrate here that in vivo treatment of the host with high doses of CTLA4-Ig solely during the initial period of donor alloactivation can completely abort the subsequent development of GVH reaction. Although donor T cells are retained, CTLA4-Ig treatment reduces the initial endogenous cytokine production and arrests the subsequent expansion of donor T cells, the differentiation of anti-host effectors, and the development of severe immune deficiency. This result is consistent with the establishment of host-specific tolerance in the donor population, while maintaining host immune competence.

Abatacept↗
PubMed1995

Growth factors can enhance lymphocyte survival without committing the cell to undergo cell division.

Growth factors have been defined by their ability to promote the proliferative expansion of receptor-bearing cells. For example, antigen-activated T cells expressing the alpha beta gamma form of the interleukin 2 (IL-2) receptor will proliferate in response to IL-2. In contrast, resting T cells, which express the IL-2 receptor beta and gamma chains, do not proliferate in response to IL-2. We demonstrate that the survival of resting T cells following gamma irradiation is greatly enhanced by pretreatment with IL-2. The radioprotective effect of IL-2 is dose dependent, does not result from the induction of cell proliferation, and does not require expression of the IL-2 receptor alpha chain. Thus, the beta gamma IL-2 receptor expressed on resting T cells can transduce signals that promote cell survival without committing the T cell to undergo cell division. IL-4 and IL-7, but not IL-1, IL-3, or IL-6, were also found to enhance the survival of quiescent T cells following gamma irradiation. Thus, certain growth factor-receptor interactions can serve to maintain cell viability in a manner that is independent of their ability to initiate or maintain cell proliferation. These data may have important implications for the use of growth factors in patients being treated with radiation and/or chemotherapy.

Apoptosis↗
PubMed1995

Role of B7:CD28/CTLA-4 in the induction of chronic relapsing experimental allergic encephalomyelitis.

T cell activation requires both Ag/MHC recognition and costimulatory signals. The present studies were designed to test whether the loss of tolerance to myelin basic protein (MBP) requires costimulation by members of the B7 receptor family. CTLA-4Ig, a fusion protein ligand for B7-1 and B7-2, was used to assess the role of B7-mediated costimulation in chronic relapsing experimental allergic encephalomyelitis (EAE) induced by the transfer of MBP specific T cell lines. In adoptively transferred EAE, administering CTLA-4Ig to donor mice or during in vitro activation of MBP specific-T cells resulted in diminution of clinical disease. The presence of CTLA-4Ig during both the immunization and in vitro activation stages was most effective in preventing clinical signs of disease. This diminution in clinical disease was paralleled by a decreased proliferative response and reduced production of IL-2 and IL-4, but not IFN-gamma, after antigenic stimulation of encephalitogenic T cells in vitro. In contrast, CTLA-4Ig treatment of recipient animals after the transfer of MBP-activated T cells affected neither disease course nor severity. These results indicate that additional costimulatory pathways may be involved in established EAE, or that some cells are independent of costimulation or, alternatively, that CTLA-4Ig does not enter brain parenchyma in therapeutic concentrations. Thus, we conclude that costimulation provided by B7 molecules plays a major role in the development of encephalitogenic T cells and in the establishment of chronic relapsing EAE, a prototypic CD4+ T cell-mediated autoimmune disease.

Abatacept↗
PubMed1995

Distinct signal transduction in mouse CD4+ and CD8+ splenic T cells after CD28 receptor ligation.

Current evidence suggests that recognition of Ag/MHC by the TCR alone is insufficient to lead to T cell proliferation or effector function. For a Th cell to produce sufficient IL-2 to allow autocrine-driven clonal expansion, there is a requirement for so-called "costimulatory" or "accessory" signals in addition to TCR ligation by Ag/MHC. Although the first signal delivered by TCR ligation has been well characterized, information regarding the biochemical nature of second signals is limited. In the present report, using a newly generated mAb specific for CD28, signal transduction by the CD28 receptor has been studied in mouse splenic T cells. When freshly isolated splenic T cells were assessed, cross-linking of CD28 by mAb did not induce increases in intracellular calcium concentration were assessed, cross-linking of CD28 by mAb did not induce increases in intracellular calcium concentration whereas TCR cross-linking was able to induce calcium mobilization. In contrast, when T cells were activated by phorbol ester treatment or by in vitro culture, CD28 ligation was able to induce calcium mobilization in 60 to 70% of splenic T cells. Unexpectedly, the CD28-induced calcium response was mainly limited to T cells of the CD4+ subset, whereas both CD4+ and CD8+ T cell subsets showed increases in [Ca2+]i of similar magnitude after CD3 epsilon ligation. The temporal nature of the CD28-induced signal was also different from TCR-induced calcium mobilization. CD28-induced signals were delayed in onset and sustained in duration in contrast to TCR signals that had short latency and brief duration. Differential expression of CD28 on the surface of activated CD4+ or CD8+ T cells did not appear to account for the differences in signal transduction between the two T cell subsets. The preferential responsiveness of the CD4+ T cell population to CD28-induced signaling was also observed in downstream events such as the induction of IL-2R, CD69 expression, and in cellular proliferation. These results indicate that the costimulatory signal delivered by CD28 may have fundamentally different biochemical properties in CD4 and CD8 T cell subsets, and therefore the functional role of CD28 may differ in these T cell subsets.

Animals↗
PubMed1995

Analysis of antigen receptor signaling in B cells from mice with a retrovirus-induced acquired immunodeficiency syndrome.

MAIDS is a retrovirus-induced immunodeficiency syndrome in mice that has similarities to human AIDS. Because the functional defects in B cells from retroviral immunodeficiency syndromes have not been characterized in detail, we examined early and late parameters of B cell responses to IgM cross-linking in B cells from MAIDS and normal mice. Splenic B cells from mice with MAIDS have defective in vitro proliferative responses to LPS and anti-IgM-mediated stimuli, as well as to PMA plus calcium ionophore, indicating a generalized defect in proliferative response potential independent of specific receptor-mediated signaling. When early signaling parameters were analyzed in response to IgM cross-linking, it was found that calcium flux in B cells from MAIDS mice was significantly reduced; this reduction was not accounted for by quantitative differences in cell-surface IgM expression and therefore indicates a defect in early signal transduction through the IgM receptor. The tyrosine phosphorylation response to IgM cross-linking was also markedly deficient; tyrosine phosphorylation of Ig-alpha, Ig-beta, and an undefined protein of 80 kDa was detected in MAIDS B cells after anti-IgM stimulation, at levels substantially less than those observed in normal B cells. Multiple other tyrosine phosphorylation events observed in normal B cells, including phosphorylation of GTPase-activating protein, P13-kinase, and syk kinase, were not detected in MAIDS B cells in response to IgM cross-linking. The defect in tyrosine phosphorylation seemed to correlate with reduced surface IgM levels on a subpopulation of MAIDS B cells. B cells from mice expressing the MAIDS retrovirus-induced immunodeficiency thus reflect defects in early signaling through the Ag-specific IgM receptor as well as a generalized defect in proliferative responsiveness.

Animals↗
PubMed1995

CD28 activation promotes Th2 subset differentiation by human CD4+ cells.

Ligation of CD28 provides a costimulatory signal to T cells necessary for their activation resulting in increased interleukin (IL)-2 production in vitro, but its role in IL-4 and other cytokine production and functional differentiation of T helper (Th) cells remains uncertain. We studied the pattern of cytokine production by highly purified human adult and neonatal CD4+ T cells activated with anti-CD3, phorbol 12-myristate 13-acetate (PMA) and ionomycin, or phytohemagglutinin (PHA) in the presence or absence of anti-CD28 in repetitive stimulation-rest cycles. Initial stimulation of CD4+ cells with anti-CD3 (or the mitogens PHA or PMA+ionomycin) and anti-CD28 monoclonal antibodies induced IL-4, IL-5 and interferon-gamma (IFN-gamma) production and augmented IL-2 production (6- to 11-fold) compared to cells stimulated with anti-CD3 or mitogen alone. The anti-CD28-induced cytokine production corresponded with augmented IL-4 and IL-5 mRNA levels suggesting increased gene expression and/or mRNA stabilization. Most striking, however, was the progressively enhanced IL-4 and IL-5 production and diminished IL-2 and IFN-gamma production with repetitive consecutive cycles of CD28 stimulation. The enhanced Th2-like response correlated with an increased frequency of IL-4-secreting cells; up to 70% of the cells produced IL-4 on the third round of stimulation compared to only 5% after the first stimulation as determined by ELISPOT. CD28 activation also promoted a Th2 response in naive neonatal CD4+ cells, indicating that Th cells are induced to express a Th2 response rather than preferential expansion of already established Th2-type cells. This CD28-mediated response was IL-4 independent, since enhanced IL-5 production with repetitive stimulation cycles was not affected in the presence of neutralizing anti-IL-4 antibodies. These results indicate that CD28 activation may play an important role in the differentiation of the Th2 subset in humans.

Animals↗
PubMed1995

Potential roles of the B7 and CD28 receptor families in autoimmunity and immune evasion.

Recognition of self major histocompatability complex (MHC)-presented antigen (MHC:Ag) by the T cell antigen receptor (TCR) is by itself not sufficient to induce T cell proliferation. Rather, to be fully activated T cells require both a TCR-generated signal and a "costimulatory" signal. This important costimulatory signal is not completely understood. Recent evidence suggests that this costimulatory signal is generated by the interaction of the T cell CD28 receptor with the B7 counterreceptor found on antigen-presenting cells. Regulation of costimulation may well prove to be more complex than was previously imagined based on the discovery that CD28 and B7 are each members of larger gene families. The present review highlights recent advances in the understanding of the CD28 and B7 receptor families with an emphasis on controversies in the field. Certain forms of immunopathology that might result from the aberrant regulation of CD28 and/or B7 expression are also discussed.

Animals↗
PubMed1995

B7-mediated costimulation can either provoke or prevent clinical manifestations of experimental allergic encephalomyelitis.

T-cell activation requires signalling provided by ligation of the T-cell receptor for antigen (TCR) and a second antigen (Ag) nonspecific signal, known as costimulation. The B7 receptors, CD80 (B7-1) and CD86 (B7-2), on the Ag-presenting cell (APC), interact with T-cell CD28 or CTLA-4 to deliver a costimulatory signal, which is particularly important for Th1 activation. Experimental allergic encephalomyelitis (EAE) is an autoimmune disorder, induced by Th1 cells directed against myelin antigens that provides an in vivo model for studying the role of B7-mediated costimulation in the induction of a pathological immune response. Using a soluble fusion protein ligand for the B7 receptors, as well as specific monoclonal antibodies specific for either CD80 or CD86, it has been demonstrated that B7 costimulation plays a prominent role in determining clinical disease outcome in EAE. Here we review recent data indicating that a paradoxical exacerbation of disease as well as the expected amelioration of disease can occur with costimulatory receptor blockade.

Abatacept↗