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J Urbain

Publications and source records attributed to J Urbain.

At least 37 records · Page 2Linked to original sources
PubMed1998

Carrier-induced, hapten-specific suppression: a problem of antigen presentation?

Prior immunity against a carrier protein has been shown to modulate the serologic response to injected haptens attached to the same carrier. In particular, a carrier/hapten-carrier immunization protocol induces marked suppression for IgG2a anti-hapten Ab production but does not interfere with anti-carrier Ab responses. Although the phenomenon of epitopic suppression has been amply demonstrated, the mechanism underlying the suppression remains unknown. The selective deficiency in IgG2a secretion suggests that IFN-gamma-producing Th1 cells are not properly activated. We and others have shown that the nature of the APCs present during the first encounter with the Ag influences the development of selected Th populations in vivo; dendritic cells (DCs) seem to be required for the induction of primary, Th1-type responses. Since carrier priming induces the clonal expansion of specific B cells that appear to efficiently capture the Ag, we hypothesized that the hapten-carrier conjugate may be presented by B cells in preimmunized animals. Therefore, we immunized mice to the conjugate by injecting syngeneic DCs pulsed in vitro with the Ag. Our data show that an injection of DCs and IL-12 prevents epitopic suppression, suggesting that it may result from defective Ag presentation.

Animals↗
PubMed1998

Dendritic cells fused with mastocytoma cells elicit therapeutic antitumor immunity.

Characterization of the spontaneous immune response that frequently occurs in tumor-bearing animals, as well as immunization using dendritic cells pulsed with tumor antigens, suggests that a limiting factor of the tumor-specific immune response may be a defect in the co-stimulatory signal that is required for optimal activation of T cells. In this work, we describe a new approach to improve the antigen-presenting capacity of tumor cells, which does not require a source of purified tumor-associated antigen. We fused P815 mastocytoma cells with bone marrow-derived dendritic cells. We obtained one hybrid that displayed the phenotypic and functional properties of dendritic cells and expressed mRNA coding for the tumor-associated antigen P815 A/B. Injections of irradiated hybrid cells prevented the growth of preimplanted mastocytoma and induced long-lasting tumor resistance.

Animals↗
PubMed1998

Regulation of T helper cell differentiation in vivo by soluble and membrane proteins provided by antigen-presenting cells.

The aim of this study was to test whether the nature of the antigen-presenting cell (APC) can influence the Th1/Th2 balance in vivo. Our data show that dendritic cells (DC), pulsed extracorporeally with antigen, induced the development of cells secreting IL-2, IFN-gamma and IL-4 upon antigen rechallenge in vitro. Priming with peritoneal macrophages sensitized cells that produced IL-4 but not IFN-gamma. To identify the factors involved in T helper development, mice were primed with APC with or without treatment with neutralizing antibodies to costimulatory molecules or cytokines. Our results indicate that priming with DC or macrophages is strictly dependent on the CD28-CTLA4/B7 interaction. Of note, CD86 provides the initial signal to induce naive T cells to become IL-4 producers, whereas CD80 is a more neutral differentiation signal. IL-12, released by the DC, appears as a potent and obligatory inducer of differentiation for IFN-gamma-producing cells. IL-6, although produced by both APC populations, is necessary to direct activation of the Th2-type response by macrophages but not by DC.

Animals↗
PubMed1998

The immune response induced in vivo by dendritic cells is dependent on B7-1 or B7-2, but the inhibition of both signals does not lead to tolerance.

Dendritic cells (DC) can be used as physiological adjuvant in vivo. Indeed, a single injection of DC, pulsed in vitro with antigen, induces activation of specific T and B lymphocytes in syngeneic mice. The unique capacity of DC to sensitize naive T lymphocytes correlates with elevated expression of MHC antigens as well as co-stimulatory molecules. The aim of this work was to evaluate the functional role of the individual CD28 ligands in the induction of primary humoral and cellular responses, and to characterize the nature of the immune response induced in the presence of selected co-stimulatory molecules. Our data show that the primary response is strictly B7 dependent, and that B7-1 and B7-2 mediate overlapping co-stimulatory functions, as either molecule alone is sufficient to initiate an immune reaction. Inhibition of B7-1 and B7-2, however, does not lead to tolerance as predicted by the two-signal hypothesis. Rather, recognition of antigen in the absence of B7 appears as a null event, since subsequent immunogenic stimulation results in a primary response. Blockade of B7-2 co-stimulatory molecules significantly inhibits antigen-specific IgG1 but not IgG2a production, suggesting that B7-2 may direct the development of Th2 cells. These data emphasize the critical role of the CD28/B7 pathway in the induction of the immune response by DC, which appear to be the initiating antigen-presenting cells in situ.

Abatacept↗
PubMed1998

Murine dendritic cells pulsed in vitro with Toxoplasma gondii antigens induce protective immunity in vivo.

The activation of a predominant T-helper-cell subset plays a critical role in disease resolution. In the case of Toxoplasma gondii, the available evidence indicates that CD4(+) protective cells belong to the Th1 subset. The aim of this study was to determine whether T. gondii antigens (in T. gondii sonicate [TSo]) presented by splenic dendritic cells (DC) were able to induce a specific immune response in vivo and to protect CBA/J mice orally challenged with T. gondii cysts. CBA/J mice immunized with TSo-pulsed DC exhibited significantly fewer cysts in their brains after oral infection with T. gondii 76K than control mice did. Protected mice developed a strong humoral response in vivo, with especially high levels of anti-TSo immunoglobulin G2a antibodies in serum. T. gondii antigens such as SAG1 (surface protein), SAG2 (surface protein), MIC1 (microneme protein), ROP2 through ROP4 (rhoptry proteins), and MIC2 (microneme protein) were recognized predominantly. Furthermore, DC loaded with TSo, which synthesized high levels of interleukin-12 (IL-12), triggered a strong cellular response in vivo, as assessed by the proliferation of lymph node cells in response to TSo restimulation in vitro. Cellular proliferation was associated with gamma interferon and IL-2 production. Taken together, these results indicate that immunization of CBA/J mice with TSo-pulsed DC can induce both humoral and Th1-like cellular immune responses and affords partial resistance against the establishment of chronic toxoplasmosis.

Adoptive Transfer↗
PubMed1997

Purification and characterization of bovine dendritic cells from peripheral blood.

Optimal activation of T lymphocytes depends on TCR interaction with peptide/MHC complexes in conjunction with costimulatory signals, which are delivered by specialized cells called antigen-presenting-cells (APC). The population of APC is heterogeneous and includes dendritic cells, B cells and macrophages. The family of dendritic cells (DC) is widely distributed in tissues and plays a major role in the induction of primary T-dependent immune responses. The aim of this paper was to isolate and characterize dendritic cells from cattle. Two methods are described that have been used to isolate dendritic cells from bovine peripheral blood. One method involves sequential depletion of other cells, adherence and isolation of low buoyant density cells on Metrizamide column. The second involves enrichment of cells displaying receptors for plasma fibronectin, followed by adherence and separation on Metrizamide. Both preparations were characterized morphologically by flow cytometry and functionally. Both procedures produced enriched populations that did not express molecules typical of T cells (CD3, CD4, CD8, WC1), B cells (sIg, CD21) and monocytes (CD14, Fc gamma 2R). Procedure 2 yielded cells with a typical veiled DC morphology that were highly effective at stimulating allogeneic T cells. Procedure 1 yielded cells that did not have the veiled morphology and were less effective in the MLR which may represent a more immature stage.

Animals↗
PubMed1997

Staphylococcal enterotoxin B induces an early and transient state of immunosuppression characterized by V beta-unrestricted T cell unresponsiveness and defective antigen-presenting cell functions.

Staphylococcal enterotoxin B (SEB) is a bacterial enterotoxin able to simultaneously bind to class II molecules on APCs and to selected V beta regions (including V beta 8) of the TCR complex. Administration of SEB to adult BALB/c mice results in clonal activation of T cells bearing V beta 8 receptors, leading to an excessive release of proinflammatory cytokines. This initial immune response is followed by a long-lasting state of V beta 8-specific unresponsiveness, thought to benefit both the host (as it contributes to the down-regulation of the inflammatory response) and the bacterium (through ligand-specific T cell anergy). However, it is not clear how this type of restricted unresponsiveness can effectively impair the generation of an antibacterial response. To gain insight into the mechanism by which Gram-positive bacteria subvert the host immune response, we have investigated the immune competence of SEB-treated mice 48 h following SEB administration. We demonstrate in this report that in vivo, SEB induces a transient but profound state of unresponsiveness affecting both T and Ag-presenting cell functions. Although in vivo activation by SEB appears to be V beta-restricted under our experimental conditions, SEB-treated mice displayed an early (lasting 48 to 72 h postinjection) and V beta-unrestricted unresponsive state characterized by the inability to produce IL-2 in response to polyclonal TCR mitogens including third party bacterial superantigens (staphylococcal enterotoxin A and toxic shock syndrome toxin 1, SEA and TSST-1, respectively), Abs to non-SEB reactive V beta regions (V beta 6), anti-CD3 epsilon Abs, and a lectin (Con A). Spleen cell populations from SEB-treated mice also displayed defective APC functions, possibly related to a selective decrease in splenic dendritic cells numbers. Taken together, these observations indicate that SEB induces an early and transient state of immunodeficiency in vivo, representing a potential mechanism for escaping host immune surveillance.

Animals↗
PubMed1997

Effect of interleukin-10 on dendritic cell maturation and function.

The main function of dendritic cells (DC) is to induce the differentiation of naive T lymphocytes into helper cells producing a large array of lymphokines, including interleukin (IL)-2; interferon-gamma (IFN-gamma), IL-4, IL-5 and IL-10. The potent immunostimulatory properties of DC develop during a process of maturation that occurs spontaneously in vitro. Since IL-10 has been shown to inhibit Th1 responses, we determined its effect on DC maturation and accessory function. Our data show that DC that have undergone maturation in vitro in the presence of IL-10, have an impaired capacity to induce a Th1-type response in vivo, leading to the development of Th2 lymphocytes. Their inability to promote the synthesis of IFN-gamma seems to correlate with a decreased production of IL-12, an heterodimeric cytokine necessary for optimal generation of Th1-type cells. These results suggest that IL-10 skews the Th1/Th2 balance to Th2 in vivo by selectively blocking IL-12 synthesis by the antigen-presenting cells that play a role of adjuvant of the primary immune response. The cytokines present in the environment at the presentation step may, therefore, determine the class of the immune response induced by DC in vivo, i.e. Th0, Th1 and/or Th2.

Animals↗
PubMed1996

Regulation of dendritic cell numbers and maturation by lipopolysaccharide in vivo.

Dendritic cells (DC) are described as "nature's adjuvant," since they have the capacity to sensitize T cells in vivo upon first encounter with the antigen. The potent accessory properties of DC appear to develop sequentially. In particular, the ability to process antigens and to sensitize native T cells develops in sequence, a process termed "maturation" that is well described in vitro. Here, we obtain evidence for maturation in vivo in response to the bacterial product lipopolysaccharide (LPS). Before LPS treatment, many DC are found at the margin between the red and white pulp. These cells lack the M342 and DEC-205 markers, but process soluble proteins effectively. 6 h after LPS, DC with the M342 and DEC-205 markers are found in increased numbers in the T cell areas. These cells have a reduced capacity to process proteins, but show increases in the B7 costimulator and T cell stimulatory capacity. 48 h after LPS, the number of DC in the spleen is reduced markedly. We interpret these findings to mean that LPS can cause DC in the marginal zone to mature and to migrate into and then out of the T cell areas.

Animals↗
PubMed1996

Dexamethasone inhibits the early steps of antigen receptor signaling in activated T lymphocytes.

Glucocorticoids are very effective in inhibiting inflammatory and immune responses. In particular, the synthetic analogue dexamethasone has been shown to inhibit T cell proliferation and IL-2 production by interfering with the transcriptional activation of the IL-2 gene. The experiments described in this report were performed to determine whether dexamethasone treatment affects the early steps of TCR signal transduction in T cell hybrids. Incubation of murine T cell hybrids in the presence of dexamethasone prevents the intracellular calcium increase that normally follows TCR/CD3 aggregation. Accordingly, dexamethasone treatment decreases inositol phosphates production and phospholipase-Cgamma1 tyrosine phosphorylation induced after TCR/CD3 stimulation. Dexamethasone has no effect on cell surface expression of TCR-associated structures nor does it inhibit calcium responses induced by a heterologous G protein-coupled muscarinic receptor, suggesting that this hormone analogue specifically inhibits the TCR signaling pathway at a postreceptor stage. We also show that inhibition of membrane proximal events by dexamethasone requires binding to the intracellular glucocorticoid receptor and de novo protein synthesis. When splenic T cells were assayed, only activated but not resting T cells were found to be sensitive to this new immunomodulatory effect of dexamethasone. These findings indicate that in addition to their previously described inhibitory effects on cytokine gene transcription, glucocorticoids block IL-2 production in activated T cells by interfering with an early step of the signal transduction cascade initiated by TCR/CD3 cross-linking.

Animals↗
PubMed1996

Induction of T cell unresponsiveness by anti-CD3 antibodies occurs independently of co-stimulatory functions.

Antibodies to the T cell receptor (TcR)-associated CD3 molecules represent potent immunosuppressive agents in vivo in both human and animals models, in spite of their well-characterized mitogenic properties. We demonstrate in this report that antibodies to the B7.2 molecule inhibit IL-2 production in vivo caused by anti-CD3 administration, suggesting that anti-CD3 monoclonal antibodies (mAb) stimulate naive T cells in vivo in a co-stimulation-dependent fashion. To characterize better the mechanisms by which antibodies to CD3 induce antigen unresponsiveness in naive T cells, we developed a model of activation-induced T cell unresponsiveness in vitro. Our data indicate that following interaction with mitogenic anti-CD3 mAb in vitro, naive purified CD4+ T cells become refractory to a further stimulus. This unresponsive state develops independently of co-stimulatory functions, as neither B7-expressing antigen-presenting cells nor anti-CD28 mAb are able to prevent anergy induction in this model. We therefore conclude that induction of unresponsiveness in naive T cells by anti-CD3 mAb is not a consequence of co-stimulus-deficient stimulation, but may develop following a productive response both in vivo and in vitro. Unresponsive T cells display a defective calcium mobilization upon TcR triggering, suggesting that anergy is maintained in these cells through receptor desensitization. The potential role of co-stimulation-independent TcR desensitization in the down-regulation of immune responses in vivo is briefly discussed.

Adjuvants, Immunologic↗
PubMed1996

Costimulation regulates the kinetics of interleukin-2 response to bacterial superantigens.

The aim of this study was to investigate the mechanisms by which B7-related costimulatory molecules (CD80, CD86) increase T-cell responsiveness to extracellular ligands. As a model study, the in vitro response of purified splenic CD4+ T cells to a bacterial superantigen, SEB, was characterized. Previous analysis of this experimental model led us to conclude that expression of B7-related molecules is strictly required in order to activate CD4+ T cells in the presence of bacterial superantigens. In the present report, we demonstrate that antigen-presenting cell-derived costimulatory signals regulate the kinetics of interleukin-2 (IL-2) production by SEB-activated splenic CD4+ T cells. Indeed, experiments performed with purified subpopulations of antigen-presenting cells and using B7-transfected cell lines indicated that increased levels of CD80 and/or CD86 cell surface expression is associated with a faster kinetics of IL-2 production in response to SEB. Accordingly, blocking of CD80 or CD86-derived signals by specific monoclonal antibodies led to a slower kinetics of IL-2 production in response to SEB. Thus these data demonstrate that similar strength of signal through the T-cell receptor can lead to immune responses displaying distinct kinetics depending on the level of costimulatory ligands on APC.

Animals↗
PubMed1996

Idiotype vaccination strategies against a murine B-cell lymphoma: dendritic cells loaded with idiotype and bispecific idiotype x anti-class II antibodies can protect against tumor growth.

Three strategies were used to evaluate 38C13 B-cell lymphoma-specific idiotype immunization to protect against subsequent lymphoma challenge in C3H/He mice. It was observed that tumor-specific immunity could be induced by immunization with (i) KLH-conjugated 38C13 B-cell lymphoma idiotype in complete Freund's adjuvants (survival rate 80%), (ii) dendritic cells pulsed in vitro with native idiotype protein (survival rate 80%), and (iii) bispecific antibodies composed of B-lymphoma-related idiotype and an MHC class II binding moiety (survival rate 40%). Presentation of idiotype determinants by dendritic cells or bispecific antibody resulted in lymphoma-specific immunity and obviated the requirement for carrier protein or adjuvant. Moreover, primed dendritic cells induced predominant development of a tumor-specific T-cell response. Each of these immunization strategies resulted in long-term survival without the emergence of idiotype variants or the induction of tumor dormancy.

Animals↗