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J Urbain

Publications and source records attributed to J Urbain.

At least 55 records · Page 3Linked to original sources
PubMed1995

Lack of T cell tolerance in mice exposed to a protein antigen through lactation.

Offspring of mother mice treated immediately after delivery with deaggregated human gamma-globulins (dHGG) are unable to produce HGG-specific antibodies when challenged with immunogenic forms of HGG (HGG/CFA) in adulthood. Despite a defective antibody response, animals rendered tolerant to HGG as neonates retain tolerogen-specific T cells able to proliferate and secrete lymphokines. The pattern of IL-2 and IL-4 secretion by T cells isolated from tolerant animals could not be distinguished from the corresponding cells in control mice, suggesting that neonatal exposure to dHGG did not affect T cell reactivity or Th1/Th2 in vivo balance. Moreover, immunization of tolerant animals with haptenated HGG confirmed the presence of tolerogen-specific helper T cells in vivo. Functional T cell depletion by anti-CD3 mAbs during lactation failed to modify induction of B cell tolerance, suggesting that T cells are neither affected nor required to induce the selective tolerance status observed in this model. Based on the finding that antigen-presenting cell functions in secondary organs (spleen, peritoneal cavity) are a late acquisition during ontogeny and reach adult-like levels at weaning, we propose that most soluble proteins elude T cell recognition during lactation due to defective antigen presentation.

Animals↗
PubMed1995

Assessment of a functional role of auto-anti-idiotypes in idiotype dominance.

We have used a well-defined idiotypic system, the cross-reactive idiotype of A strain (CRIA) (Ab1) idiotype generated in A/J mice injected with arsonate coupled to keyhole limpet hemocyanin (ARS-KLH), to determine the frequency of precursors for auto-anti-idiotypic antibodies (auto-Ab2) in naive and immunized A/J mice by limiting dilution analysis after polyclonal activation by lipopolysaccharide. In naive animals, the precursor frequencies of auto-Ab2 B cells were below the limit of sensitivity of the technique in the majority of A/J mice, and could be detected in only 20% of the animals. Upon immunization with ARS-KLH, a large increase in auto-Ab2 precursor frequency was observed. This shift in frequency was not found when A/J mice were injected with KLH alone, or when BALB/c mice, which do not express the CRIA idiotype, were injected with ARS-KLH. To study the functional role of the auto-Ab2 B cells, we injected neonatal A/J mice with polyclonal rabbit Ab3 antibodies directed against a recurrent idiotype of auto-Ab2. Thereafter, these mice were injected with ARS-KLH. Although the anti-arsonate response level was normal, the CRIA Ab1 expression was reduced tenfold. Thus, the suppression of auto-Ab2 affects Ab1 dominance. We further show that the presence of maternal Ab1 can strongly modify the immune response of the offspring by inducing higher levels of the idiotype after immunization. Furthermore, IgM anti-arsonate antibodies were detected before immunization with antigen. From these data, we conclude that the affinity of antigen alone cannot explain the dominance of CRIA. Network selection is important in the shaping of the available repertoire.

Adjuvants, Immunologic↗
PubMed1995

B7.2 provides co-stimulatory functions in vivo in response to staphylococcal enterotoxin B.

Excessive T cell activation induced by bacterial superantigens plays an important role in the pathology associated with Gram-positive bacteremia. To gain insight into the early phases of T cell activation by bacterial enterotoxins in vivo, we investigated the ability of antibodies to well-defined co-stimulatory molecules to inhibit T cell activation and the subsequent toxic shock syndrome induced in BALB/c mice following the injection of staphylococcal enterotoxin B (SEB). We demonstrate here that a single dose of anti-B7.2 antibodies, but not anti-B7.1 antibodies, significantly inhibits T cell activation, as judged by lower systemic IL-2 release, blastogenesis and IL-2 receptor expression, and reduces the lethal effect of SEB in D-galactosamine-sensitized mice. These results demonstrate that co-stimulation through the B7.2 molecule plays an important role in the activation of T cells in response to SEB in vivo and suggest alternative therapies for septic shock caused by bacterial enterotoxins based on blocking antibodies to co-stimulatory molecules.

Animals↗
PubMed1995

Glucocorticoids down-regulate dendritic cell function in vitro and in vivo.

Exogenous glucocorticoid hormones are widely used as therapeutical agents, whereas endogenous glucocorticoids may act as physiological immunosuppressants involved in the control of immune and inflammatory responses. The optimal activation of T lymphocytes requires two distinct signals: the major histocompatibility complex-restricted presentation of the antigen and an additional co-stimulatory signal provided by the antigen-presenting cells. There is ample evidence that, among the cells able to present the antigen, the dendritic cells (DC) have the unique property to activate antigen-specific, naive T cells in vitro and in vivo, and are therefore required for the induction of primary immune responses. In this work, we tested whether glucocorticoids affected the capacity of DC to sensitize naive T cells. Our data show that, in vitro, the steroid hormone analog dexamethasone (Dex) affects the viability of DC, selectively down-regulates the expression of co-stimulatory molecules on viable DC, and strongly reduces their immunostimulatory properties. In vivo, a single injection of Dex results in impaired antigen presenting function, a finding which correlates with reduced numbers of splenic DC. These results show that glucocorticoids regulate DC maturation and immune function in vitro and in vivo and suggest that this mechanism may play a role in preventing overstimulation of the immune system.

Animals↗
PubMed1995

Activation of murine T cells by bacterial superantigens requires B7-mediated costimulation.

Staphylococcus enterotoxins bind class II MHC molecules on antigen-presenting cells (APC) and stimulate T cells expressing appropriate V beta gene products. Although the role of non-TcR-associated costimulatory receptors during antigen-specific T cell stimulation has been clearly established, the involvement of costimulatory activity in T cell activation by superantigens (SAgs) has been the matter of controversy. The aim of this study was to evaluate the role of the costimulatory-receptor ligand molecules CD28/B7 on bacterial SAg-mediated activation of naive murine T cells. We demonstrate in this report that a combination of monoclonal antibodies to murine B7.1 and B7.2 molecules inhibits the in vitro response of naive T cells to SAgs SEA, SEB, and TSST-1. The inhibition of T cell responses required simultaneous blocking of B7.1 and B7.2, suggesting that either B7.1 or B7.2 is sufficient to provide costimulatory signals to naive T cells in response to bacterial exotoxins. Inhibition of T cell activation by antibodies to B7-related molecules can be overcome by antibodies to CD28, a finding in agreement with the hypothesis that CD28-mediated signals participate in T cell activation by bacterial SAgs. These observations suggest that, as demonstrated for conventional antigen, T cell activation by SAgs requires the coordinated participation of TcR- and CD28-derived signals.

Animals↗
PubMed1995

FcR cross-linking on monocytes results in impaired T cell stimulatory capacity.

Presentation of antigen to T lymphocytes without the appropriate co-stimulatory signals results in a state of antigen-specific unresponsiveness. Despite the presumed importance of the B7-CD28 interaction for the initiation and maintenance of T cell-mediated immune responses, relatively few studies have addressed the regulation of B7 expression. We have studied the expression of the CD80 (B7-1) and B7-2 molecules on peripheral blood monocytes following different activation signals, and it was demonstrated that not only IFN-gamma, but also granulocyte macrophage colony stimulating factor can induce CD80 expression on monocytes. In addition, we found that cross-linking of FcR on monocytes strongly inhibits the up-regulation of CD80 and B7-2, with as a functional consequence that the capacity to function as antigen presenting cells (APC) and to stimulate T cell activation is severely impaired. When cultures were prepared in 96-well plates coated with human IgG, stimulation of T cells with allogeneic monocytes resulted only in modest T cell proliferation and no detectable IL-2 secretion as compared with untreated culture plates or plates coated with Fab fragments of human IgG. Under these conditions cross-linking of CD28 on the T cells with specific mAb completely reverted the inhibitory effect observed after culture on IgG-coated plates. Furthermore, FcR cross-linking on monocytes strongly inhibited the capacity of monocytes to induce a specific memory T cell response to viral, bacterial and fungal antigens, whereas the treatment did not impair the capacity of the T cells to respond to pokeweed mitogen, phytohemagglutinin and concanavalin A. We conclude that after FcR cross-linking, the impaired APC function is most likely due to the inability of monocytes to provide the essential co-stimulatory signals to the T cells via the B7-CD28/CTLA-4 interaction.

Antibodies, Monoclonal↗
PubMed1995

Induction of Th2 responses to soluble proteins is independent of B cell tolerance status.

Injection of high doses of monomeric human gamma globulins (dHGG) in naive, adult mice causes antigen-specific tolerance of B cell and Th1 lymphocytes, while inducing the selective expansion of antigen-specific Th2 cells. Several parameters of tolerance induction were analyzed in this work, in order to establish whether B cell tolerance and Th1 unresponsiveness were functionally related in this in vivo model. By varying the antigen form and site of injection, we demonstrate in this work that Th1 unresponsiveness to HGG is not a consequence of peripheral B cell tolerance. In particular, mice pretreated with heat-aggregated antigen (HAHGG) or F(ab')2 HGG were found to develop a strong humoral response while displaying a defective Th1 response. In fact, these animals developed a strong Th2 response in vivo, demonstrating that selective expansion of antigen-specific Th2 cells in this model is not a consequence of B cell tolerance or antigen capture by Fc receptor-expressing cells. We conclude that while B cell tolerance in this model is only observed in response to deaggregated antigen, injection of all forms of adjuvant-free, protein antigens induces T helper precursor cells to differentiate into Th2-type helper cells in vivo irrespectively of the B cell tolerance status.

Animals↗
PubMed1995

Co-stimulation lowers the threshold for activation of naive T cells by bacterial superantigens.

Staphylococcus enterotoxins bind class II MHC molecules on antigen presenting cells (APC) and stimulate T cells expressing appropriate V beta gene products. Although the role of non-TCR associated co-stimulatory receptors during antigen-specific T cell stimulation has been clearly established, the involvement of co-stimulatory activity in T cell activation by superantigens has been the matter of controversy. In this report, we examine the role of co-stimulation provided by selected APC populations in the response to bacterial exotoxins (staphylococcal enterotoxin A, staphylococcal enterotoxin B and toxic shock syndrome type 1). We demonstrate that the APC population able to activate naive T cells to IL-2 production is heterogeneous, comprising both adherent (presumably dendritic) and non-adherent (mostly B lymphocytes) cells. By stimulating naive T cells in the presence of graded doses of superantigens, we have observed that half-maximal IL-2 production was achieved at lower doses of superantigens in the presence of dendritic cells. Similarly, addition of antibodies to CD28 or B7.1-transfected cell lines increased the sensitivity of naive T cells to lower doses of superantigens. These observations indicate therefore that superantigens can be presented to naive T cells by APC displaying distinct levels of co-stimulatory activity, although with different efficacy. Thus, naive T cells are sensitive to CD28-mediated co-stimulation during superantigen-mediated responses but IL-2 production can be induced by high doses of superantigens in the presence of APC expressing weak co-stimulatory activity. These observations are compatible with the hypothesis that CD28-mediated signals participate in T cell activation by lowering T cell sensitivity to TCR ligands.

Animals↗
PubMed1994

Flow cytometric measurement of calcium influx in murine T cell hybrids using Fluo-3 and an organic-anion transport inhibitor.

A method is described to facilitate flow cytometric analysis of calcium mobilization upon stimulation of murine T cell hybrids. In these transformed cell lines, the accuracy of cytometric measurement of free cytoplasmic calcium with Fluo-3 is compromised by the rapid loss of the intracellular dye. We have found that the addition of sulfinpyrazone, a known organic-anion transporter inhibitor in epithelial cells and in macrophages, severely impairs the leakage of the Fluo-3 probe from the cytoplasmic matrix. Under appropriate conditions, sulfinpyrazone has little effect on the cell physiology and permits the detection of calcium influx in a variety of murine T cell hybrids.

Aniline Compounds↗
PubMed1994

T cell long-term hyporesponsiveness follows antigen receptor engagement and results from defective signal transduction.

T cell receptor (TCR)-mediated stimulation of T hybridomas leads to cell activation and lymphokine production that is followed by a long-term hyporesponsiveness. To investigate the biochemical events involved in the induction and maintenance of this antigen receptor hyporesponsiveness or anergy, we have expressed a G protein/PLC beta 1-coupled muscarinic subtype 1 acetylcholine receptor in a murine T cell hybrid. Transfected cells were capable of responding to both muscarinic agonists and TCR ligands by inducing interleukin-2 secretion that was sensitive to cyclosporin A and dexamethasone. Both receptors induced tyrosine kinase (TK) activity, but muscarinic stimulation did not affect tyrosine phosphorylation of PLC gamma 1, nor did the TK inhibitor, herbimycin, block muscarinic receptor-mediated calcium mobilization. These data indicate that in T cells, the muscarinic receptor mediates T cell effector functions by regulating a TK-independent proximal pathway which later converges with the TCR pathway. Using these cells, we have explored the long-term consequences of T cell stimulation via antigen or muscarinic receptors. Our results show that hyporesponsiveness specifically follows TCR engagement and appears to result from a defect in the early signal transduction initiated by TCR cross-linking. A study of TCR-mediated signaling supports this model by showing that tyrosine phosphorylation and calcium mobilization are deficient in hyporesponsive T cells.

Animals↗
PubMed1994

Murine dendritic cells pulsed in vitro with tumor antigen induce tumor resistance in vivo.

The aim of this work is to induce tumor resistance to a B cell lymphoma in BALB/c mice using elements of the immune system. It has indeed been shown by us and by others that antigen-presenting cells (APC) like dendritic cells can induce efficient immune responses and can even substitute for Freund's adjuvant. Here we show that mice immunized with syngeneic dendritic cells pulsed in vitro with tumor antigen (BCL1 idiotype expressed by lymphoma cells) are protected against a subsequent tumor inoculation. The in vivo resistance can be correlated with the induction of a humoral response specific for the idiotype expressed by the tumor. No such protection can be achieved when B cells are used as APC. These data show that effector cells in tumor-bearing animals can be recruited and activated using dendritic cells, providing long-lasting immune surveillance.

Animals↗
PubMed1994

Immunoglobulin isotype regulation by antigen-presenting cells in vivo.

The isotype and magnitude of the B cell response clearly depends on the in vivo activation of T helper (Th) cells which secrete different lymphokines. Since Th are activated by the presentation of the antigen on specialized cells, we wished to test whether the nature of the antigen-presenting cells (APC) influences the isotypic profile of the humoral response. Data are presented showing that antigen-pulsed dendritic cells (DC) and peritoneal macrophages induce the synthesis of specific antibodies when injected in syngeneic animals. By contrast, a single injection of antigen-pulsed resting B cells does not prime the mice in vivo. Moreover, the injection of antigen-pulsed DC induces the synthesis of specific IgG2a and IgG1 antibodies, whereas peritoneal macrophages favor the production of IgG1 and IgE antibodies specific for the antigen. These data show that the isotype and the amplitude of the B cell response can be regulated by the nature of the APC, and indirectly suggest that Th cell differentiation is controlled at the level of antigen presentation.

Animals↗
PubMed1994

In vivo immunosuppression induced by a weakly mitogenic antibody to mouse CD3: evidence that induction of long-lasting in vivo unresponsiveness requires TcR signaling.

The use of anti-CD3 monoclonal antibodies (mAb) to treat allograft rejection has been complicated by the morbidity observed during the first days of treatment, secondary to T cell activation and cytokine release. Available evidence in a mouse model indicates that F(ab')2 fragments of an anti-CD3 mAb are not mitogenic in vitro and can be injected in vivo without apparent toxicity. However, their immunosuppressive capacity is dramatically reduced, suggesting that long-term immunosuppression mediated by anti-CD3 antibodies in vivo may be associated to their mitogenic capacity. This paper demonstrates that a poorly mitogenic anti-CD3 mAb is able to induce potent immunosuppression in vivo with reduced morbidity. This finding suggests that immunosuppression in vivo by anti-CD3 mAbs is not directly related to their activation properties but nevertheless requires signaling capacities. Therefore, immunosuppression in vivo may be best achieved by using antibodies able to deliver an incomplete activation signal to T cells (thus avoiding systemic cytokine release), possibly leading to anergy. The implications of this study for the development of immunosuppressive antibodies are discussed.

Animals↗
PubMed1993

Molecular characterization of monoclonal CRIA-positive anti-arsonate antibodies derived from idiotype-negative mice bearing a light chain polymorphism.

We have elicited anti-arsonate antibodies bearing the major cross-reactive idiotype (CRIA) in a double congenic idiotype-negative strain (C.C58.AL-20) bearing a light chain polymorphism that has previously been shown serologically not to complement idiotype-positive heavy chains. Using the idiotype cascade (Ab1-->Ab2-->Ab3-->-->Ab1'), CRIA-positive antibodies were raised and monoclonal antibodies were isolated and characterized serologically and by nucleotide sequence analysis. Two types of idiotype-positive anti-arsonate antibodies were generated in the C.C58.AL-20 strain. One group of hybridomas used the canonical VH1.8 heavy chain gene segment with V kappa 10 variant light chains. A second group used a VHGAM3.8 heavy chain with V kappa 10 variant light chains. This latter heavy-light pairing has been observed in CRIA-like responses previously in BALB/c mice after idiotypic manipulation (or rarely after antigen alone). These studies demonstrate the plasticity of the immune response when manipulated with idiotype reagents as well as its structural variability. Additionally, they provide important insights into the potentials of idiotype vaccines.

Amino Acid Sequence↗