Biomedical subjects

M F Bachmann

Publications and source records attributed to M F Bachmann.

At least 19 recordsLinked to original sources

PubMed1998

Normal responsiveness of CTLA-4-deficient anti-viral cytotoxic T cells.

CTLA-4 has been proposed to negatively regulate immune responses, and mice deficient for CTLA-4 expression succumb to a lymphoproliferative disorder within a few weeks after birth. This study assessed the responsiveness of CTLA-4-deficient T cells expressing a class I-restricted TCR specific for lymphocytic choriomeningitis virus (LCMV). The kinetics of T cell proliferation were studied in vitro after stimulation of T cells with full and partial T cell agonists. No gross abnormalities in CTLA-4-deficient T cells could be detected. Using adoptive transfer experiments, T cell responses were also measured in vivo after infection with LCMV. Low dose infection with LCMV leads to strong expansion of specific T cells followed by a reduction in T cells that parallels the elimination of Ag. The kinetics of T cell expansion and elimination after low dose LCMV infection were not affected by the absence of CTLA-4. High dose infection of mice with LCMV leads to a transient expansion of T cells followed by T cell exhaustion, where all specific T cells are eliminated. T cell exhaustion also occurred in the absence of CTLA-4. Thus, surprisingly, the absence of CTLA-4 did not interfere with T cell activation, down-regulation of ongoing T cell responses after the elimination of Ag, or the exhaustion of T cell responses in the presence of excessive amounts of Ag.

Abatacept↗

PubMed1998

Virus-specific MHC-class II-restricted TCR-transgenic mice: effects on humoral and cellular immune responses after viral infection.

A transgenic mouse expressing MHC class II-restricted TCR with specificity for a lymphocytic choriomeningitis virus (LCMV) glycoprotein-derived T helper cell epitope was developed to study the role of LCMV-specific CD4+ T cells in virus infection in vivo. The majority of CD4+ T cells in TCR transgenic mice expressed the transgenic receptor, and LCMV glycoprotein-specific TCR transgenic CD4+ T cells efficiently mediated help for the production of LCMV glycoprotein-specific isotype-switched antibodies. In contrast, LCMV glycoprotein-specific TCR transgenic mice exhibited a drastically reduced ability to provide help for the generation of antibody responses specific for the virus-internal nucleoprotein, indicating that intramolecular/intrastructural help is limited to antigens that are accessible to B cells on the viral surface. Antiviral cellular immunity was studied with noncytopathic LCMV and recombinant cytopathic vaccinia virus expressing the LCMV glycoprotein. TCR transgenic mice failed to efficiently control LCMV infection, demonstrating that functional LCMV-specific CD4+ T cells--even if activated and present at extremely high frequencies--cannot directly mediate protective immunity against LCMV. Despite the fact that LCMV-primed CD4+ T cells from TCR transgenic mice as well as from control mice showed low MHC class II-restricted cytotoxic activity in vivo, this did not correlate with protection against LCMV replication in vivo. In contrast, CD4+ T cells from TCR-transgenic mice mediated efficient protection against infection with recombinant vaccinia virus. These results further support the need for different immune effector functions for protective immunity against different viral infections.

Adoptive Transfer↗

PubMed1998

The role of germinal centers for antiviral B cell responses.

Germinal centers (GCs) are crucially involved in T cell-dependent B cell responses. B cells rapidly proliferate within GCs and their Ig variable region genes undergo hypermutation. Cognate T helper cells and antigen presented in native form on follicular dendritic cells (FDCs) select B cells expressing high-affinity Igs, leading to affinity maturation and the generation of memory B cells. In addition to these well-established functions of GCs, this article presents evidence that they also play a crucial role for the maintenance of specific memory Ig titers and for the prevention of viral antibody escape mutants.

Animals↗

PubMed1998

Absence of TNFRp55 influences virus-induced autoimmunity despite efficient lymphocytic infiltration.

Tumor necrosis factor (TNF)-alpha is a multipotent cytokine associated with many cellular functions, including inflammation and anti-viral defense. Many studies have implicated TNF-alpha in the pathogenesis of autoimmune diseases. TNF-alpha responses are mediated through binding to specific cell surface receptors, TNFRp55 and TNFRp75. The objective of the present study was to investigate the contribution of the TNFRp55 in the inflammatory response associated with autoimmune diabetes development in a viral transgenic model. In this model, the animals express lymphocytic choriomeningitis virus (LCMV)-glycoprotein (gp) in the beta cells of the pancreas under the control of the rat insulin promoter (RIP-gp). Diabetes is induced following LCMV infection due to beta cell destruction by LCMV-specific CD8+ cytotoxic T lymphocytes. TNFRp55-deficient RIP-gp animals were examined to assess the importance of the TNFRp55. The kinetics and onset of lymphocytic infiltration into the pancreatic islets and hyperglycemia was not altered in the absence of TNFRp55 after LCMV infection. Animals were evaluated following recombinant LCMV-gp vaccinia virus infection to test whether properties of the infectious agent influence autoimmunity. Interestingly, the kinetics were accelerated and the frequency of diabetes was increased in TNFRp55-deficient mice compared with control animals. This accelerated onset of diabetes is likely a result of increased viral replication in the TNFRp55-deficient host. Thus, these data demonstrate that TNFRp55 is not essential for producing the local inflammatory effects which contribute to organ-specific autoimmunity in this transgenic model. However, the absence of TNFRp55 altered the kinetics and incidence of the disease in a pathogen-dependent fashion.

Animals↗

PubMed1997

Altered peptide ligands trigger perforin- rather than Fas-dependent cell lysis.

CTLs lyse Fas-expressing target cells by the concomitant action of a perforin- and a Fas-dependent mechanism. This study analyzed whether target cells pulsed with T cell antagonists and other altered peptide ligands (APLs) were susceptible selectively to only one of these two mechanisms. In vivo and in vitro activated T cells from transgenic mice expressing a TCR specific for lymphocytic choriomeningitis virus were used as effector cells. To distinguish between perforin- and Fas-dependent cytotoxicity, T cells from normal or perforin-deficient mice were used to lyse peptide-pulsed Fas-positive or Fas-negative target cells. In contrast to previous reports that have shown that APLs selectively induce the Fas-dependent pathway of cytotoxicity, our results demonstrate that target cells pulsed with T cell antagonists and other APLs are lysed predominantly by the perforin-dependent pathway. The contribution of Fas-mediated cytotoxicity was similar for the full agonist and the APLs. Thus, full agonists, partial agonists, and antagonists trigger similar and not distinct pathways of cytotoxicity.

Animals↗

PubMed1997

Self antigens expressed by solid tumors Do not efficiently stimulate naive or activated T cells: implications for immunotherapy.

Induction and maintenance of cytotoxic T lymphocyte (CTL) activity specific for a primary endogenous tumor was investigated in vivo. The simian virus 40 T antigen (Tag) expressed under the control of the rat insulin promoter (RIP) induced pancreatic beta-cell tumors producing insulin, causing progressive hypoglycemia. As an endogenous tumor antigen, the lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) was introduced also under the control of the RIP. No significant spontaneous CTL activation against GP was observed. However, LCMV infection induced an antitumor CTL response which efficiently reduced the tumor mass, resulting in temporarily normalized blood glucose levels and prolonged survival of double transgenic RIP(GP x Tag2) mice (137 +/- 18 d) as opposed to control RIP-Tag2 mice (88 +/- 8 d). Surprisingly, the tumor-specific CTL response was not sustained despite the facts that the tumor cells continued to express MHC class I and LCMV-GP-specific CTLs were present and not tolerized. Subsequent adoptive transfer of virus activated spleen cells into RIP(GP x Tag2) mice further prolonged survival (168 +/- 11 d), demonstrating continued expression of the LCMV-GP tumor antigen and MHC class I. The data show that the tumor did not spontaneously induce or maintain an activated CTL response, revealing a profound lack of immunogenicity in vivo. Therefore, repetitive immunizations are necessary for prolonged antitumor immunotherapy. In addition, the data suggest that the risk for induction of chronic autoimmune diseases is limited, which may encourage immunotherapy against antigens selectively but not exclusively expressed by the tumor.

Adoptive Transfer↗

PubMed1997

Similar ligand densities required for restimulation and effector function of cytotoxic T cells.

This study compared ligand densities on antigen-presenting cells (APCs) needed for in vitro restimulation of in vivo primed T cells and for in vitro assessed T cell effector function. Spleen cells of lymphocytic choriomeningitis virus (LCMV)-primed mice were restimulated in vitro with graded amounts of virus-derived peptides using macrophages or a cloned dendritic cell line as APCs. To test for effector function of these cytotoxic T cells, the same APCs pulsed with graded amounts of the peptides were used as target cells in an in vitro 51Cr release assay. The same peptide concentration that rendered an APC restimulatory for primed cytotoxic T lymphocytes (CTLs) also rendered it susceptible for lysis by the same CTLs. In addition, the same peptide concentrations that made macrophages susceptible for CTL-mediated lysis induced proliferative responses in vitro of in vivo primed memory CTLs. Thus, restimulation of in vivo primed T cells--measured by either proliferation or cytotoxic effector function--or sensibilization of target cells for lysis requires similar ligand densities on APCs and is therefore, contrary to expectations, governed by similar overall avidity thresholds. These results have implications for CTL memory.

Amino Acid Sequence↗

PubMed1997

The role of antibody concentration and avidity in antiviral protection.

Neutralizing antibodies are necessary and sufficient for protection against infection with vesicular stomatitis virus (VSV). The in vitro neutralization capacities and in vivo protective capacities of a panel of immunoglobulin G monoclonal antibodies to the glycoprotein of VSV were evaluated. In vitro, neutralizing activity correlated with avidity and with neutralization rate constant, a measure of on-rate. However, in vivo, protection was independent of immunoglobulin subclass, avidity, neutralization rate constant, and in vitro neutralizing activity; above a minimal avidity threshold, protection depended simply on a minimum serum concentration. These two biologically defined thresholds of antibody specificity offer hope for the development of adoptive therapy with neutralizing antibodies.

Animals↗

PubMed1997

Functional in vivo MHC class II loading by endogenously synthesized glycoprotein during viral infection.

MHC class II presentation of antigenic peptides derived from soluble proteins is usually preceded by antigenic uptake via (nonreceptor-mediated) endocytosis by professional APCs, followed by processing in endosomal compartments. Although in vitro alternative pathways for MHC class II loading have been described for certain intracellularly synthesized proteins, the importance of these pathways has not been assessed in vivo. We have shown previously that endogenously produced membrane-associated glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV), a noncytopathic virus, can be presented in vitro on MHC class II molecules in the absence of the invariant chain (Ii), whereas the cytosolic LCMV nucleoprotein (LCMV-NP) failed to be presented under the same conditions. Taking advantage of this system, we analyzed presentation of LCMV-GP and LCMV-NP in vivo in Ii-deficient mice and followed the induced Th cell and B cell responses. At early time points after LCMV infection of li-deficient mice, we found in vivo MHC class II loading exclusively by the endogenously synthesized LCMV-GP, whereas no MHC class II loading by LCMV-NP could be detected. As a direct consequence, LCMV-specific Th cells exhibited initially only LCMV-GP specificity. In contrast, both LCMV-GP- and LCMV-NP-derived epitopes were presented in comparable amounts on APCs upon LCMV infection of normal mice, and LCMV-GP- as well as LCMV-NP-specific Th cells were comparably induced in vivo. Thus, cell internal MHC class II loading pathways are functional in vivo and may become dominant if the usual Ag presentation pathways are hampered.

Animals↗

PubMed1997

Correlation of tolerogenicity of a viral antigen with its immunogenicity.

Induction of B cell tolerance or activation was analyzed with vesicular stomatitis virus (VSV) glycoprotein (G) expressed as a neo-self Ag. A membrane form of VSV-G expressed in all tissues, including the bone marrow, induced unresponsiveness at both the Th and B cell level, whereas a soluble form of VSV-G expressed peripherally in liver and kidney did not tolerize B cells and only reversibly anergized Th cells. Interestingly, a similar correlation was found for activation of mature lymphocytes. When mature normal spleen cells were transferred into the two transgenic mouse lines, the membrane form of VSV-G was strongly immunogenic for both Th and B cells, and high VSV-G-specific IgG Ab titers were induced in these transgenic mice. In contrast, spleen cells transferred into mice expressing the soluble form of VSV-G were not activated, and no VSV-G specific Abs were induced. These results indicate that highly immunogenic Ags are strongly tolerogenic for both immature B and T cells.

Animals↗

PubMed1997

TNF receptor p55 controls early acute graft-versus-host disease.

Allogeneic bone marrow transplantation is frequently associated with graft-vs-host disease (GVHD). To understand the effector mechanisms of GVHD, we investigated the role of the TNF receptor p55 (TNFRp55), which is known to be important in inflammation and cytotoxicity. After the transplantation of allogeneic bone marrow and spleen cells to lethally irradiated mice, all wild-type recipients developed early lethal GVHD within 1 wk, whereas TNFRp55-deficient recipients had much reduced GVHD and survived for at least 3 wk. No defect in alloantigen presentation was found, since T cell proliferation and cytotoxicity were similar to allogeneic wild-type and TNFRp55-deficient stimulator and target cells. Also, TNF alpha release did not differ significantly between the two types of recipients. Therefore, early acute GVHD in wild-type mice was primarily due to TNFRp55-mediated tissue damage. Interestingly, lethal GVHD was not entirely dependent upon the TNFRp55. In experimental conditions using sublethal irradiation and high donor spleen cell numbers, TNFRp55-deficient recipient mice developed lethal GVHD with similar kinetics and frequency as the control mice. These data suggest that the effector mechanisms leading to organ damage in murine acute GVHD can be dissected in a cytokine pathway through the TNFRp55, as demonstrated here, and in a cellular pathway through direct interaction of cytotoxic lymphocytes with target tissues involving perforin and Fas/Fas ligand, as reported previously.

Animals↗

PubMed1997

Role of repetitive antigen patterns for induction of antibodies against antibodies.

Antibody responses against antibodies, such as rheumatoid factors, are found in several immunopathological diseases and may play a role in disease pathogenesis. Experience shows that they are usually difficult to induce experimentally. Antibodies specific for immunoglobulin constant regions (anti-allotypic) or for variable regions (anti-idiotypic) have been investigated in animal models; the latter have even been postulated to regulate antibody and T cell responses via network-like interactions. Why and how such anti-antibodies are induced during autoimmune diseases, has remained largely unclear. Because repetitively arranged epitopes in a paracrystalline structure of a viral envelope cross-link B cell receptors efficiently to induce a prompt T-independent IgM response, this study used immune complexes containing viruses or bacteria to evaluate the role of antigen pattern for induction of anti-antibody responses. We present evidence that antibodies bound to strictly ordered, but not to irregularly arranged, antigens dramatically enhance induction of anti-antibodies, already after a single immunization and without using adjuvants. The results indicate a novel link between anti-antibody responses and infectious agents, and suggest a similar role for repetitive self-antigens such as DNA or collagen involved in chronic immunopathological diseases.

Animals↗

PubMed1997

Acute graft-versus-host disease without costimulation via CD28.

T lymphocyte activity is enhanced by costimulatory signals mediated through CD28 binding to B7-1/B7-2 on antigen-presenting cells. Several recent studies have shown that graft-versus-host disease (GVHD) can be inhibited by in vivo treatment with CTLA4Ig, which blocks CD28-B7 interactions. These findings prompted us to investigate the role of CD28 in acute GVHD, using gene-targeted mice. We performed the experiments in the context of strong allogeneic MHC stimulation (H2(b) anti-H2(d)) and weak stimulation (H2(d) anti-H2(b)). In both directions, efficient in vitro T-cell cytotoxicity and acute lethal GVHD were induced by CD28-deficient lymphocytes, which was only partially delayed when compared with wild-type mice. We conclude that lethal GVHD can develop without costimulation via CD28.

Abatacept↗

PubMed1997

Crucial role of interferon consensus sequence binding protein, but neither of interferon regulatory factor 1 nor of nitric oxide synthesis for protection against murine listeriosis.

Listeria monocytogenes is widely used as a model to study immune responses against intracellular bacteria. It has been shown that neutrophils and macrophages play an important role to restrict bacterial replication in the early phase of primary infection in mice, and that the cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) are essential for protection. However, the involved signaling pathways and effector mechanisms are still poorly understood. This study investigated mouse strains deficient for the IFN-dependent transcription factors interferon consensus sequence binding protein (ICSBP), interferon regulatory factor (IRF) 1 or 2 for their capacity to eliminate Listeria in vivo and in vitro and for production of inducible reactive nitrogen intermediates (RNI) or reactive oxygen intermediates (ROI) in macrophages. ICSBP-/- and to a lesser degree also IRF2-/- mice were highly susceptible to Listeria infection. This correlated with impaired elimination of Listeria from infected peritoneal macrophage (PEM) cultures stimulated with IFN-gamma in vitro; in addition these cultures showed reduced and delayed oxidative burst upon IFN-gamma stimulation, whereas nitric oxide production was normal. In contrast, mice deficient for IRF1 were not able to produce nitric oxide, but they efficiently controlled Listeria in vivo and in vitro. These results indicate that (a) the ICSBP/IRF2 complex is essential for IFN-gamma-mediated protection against Listeria and that (b) ROI together with additional still unknown effector mechanisms may be responsible for the anti-Listeria activity of macrophages, whereas IRF1-induced RNI are not limiting.

Adoptive Transfer↗

PubMed1997

Protection against immunopathological consequences of a viral infection by activated but not resting cytotoxic T cells: T cell memory without "memory T cells"?

Immunological memory is a key characteristic of specific immune responses. Persistence of increased levels of precursor T cells is antigen-independent and is often used as an indicator of T cell memory. This study documents that, depending on the chosen readout, cytotoxic T lymphocyte (CTL) memory against lymphocytic choriomeningitis virus (LCMV) appears long- or short-lived in the absence of persisting antigen. To study T cell memory in the absence of persisting antigen, either short-lived antigens were used for immunization or adoptive transfer methods were used to eliminate possibly persisting antigen. These experiments revealed that increased specific precursor frequencies and CTL-mediated protection against an i.v. infection with LCMV were long-lived. In contrast, CTL-mediated protection against a peripheral infection of the skin with LCMV, or of the ovary with recombinant vaccinia virus, was short-lived. These results show that maintenance of increased specific CTL precursor frequencies and central T cell memory in lymphoid tissue (where preexisting neutralizing antibodies usually provide protection anyway) is long-lived and antigen-independent. In contrast, in protection against peripheral viral infections, where the relative kinetics of virus growth and virus elimination by T cells are of key importance, T cell memory is short-lived in the absence of antigen. This indicates that peripheral T cell memory in antibody-inaccessible tissues is mediated by antigen-activated effector T cells and apparently not by specialized memory T cells.

Adoptive Transfer↗

PubMed1997

T-cell-independent antiviral B cell responses in CD45-deficient mice.

CD45 is expressed on all B cells and has been reported to be essential for their B cell receptor mediated stimulation. The present study addressed T-cell-independent B cell responses in CD45-deficient mice using the glycoprotein (G) of vesicular stomatitis virus (VSV) as a model antigen. VSV-G exists in two forms exhibiting different degrees of repetitiveness. In mice, the two forms of VSV-G induce either a type 1 or a type 2 T-cell-independent B cell response. We found that CD45-deficient mice mounted T-cell-independent B cell responses to both forms of VSV-G. This demonstrates that the B cell receptor complex is able to generate a functional signal in the absence of CD45, provided the cross-linking stimulus is sufficiently strong.

Animals↗

PubMed1997

Normal thymic selection, normal viability and decreased lymphoproliferation in T cell receptor-transgenic CTLA-4-deficient mice.

CTLA-4 is a T cell surface receptor essential for the negative regulation of T cell activation. In the CTLA-4-deficient mouse, a dramatic accumulation of activated peripheral T cells effects extensive damage to host tissues, resulting in mortality within 5 weeks of age. To determine whether the accumulation of activated T cells in CTLA-4(-/-) mice is due to a defect in thymic selection, we examined negative selection in CTLA-4(-/-) mice using two transgenic T cell receptor (TCR) models of thymic selection. Neither the H-Y-specific TCR nor the lymphocytic choriomeningitis virus (LCMV)-specific TCR transgenic models revealed a defect in positive or negative selection in CTLA-4(-/-) mice in vivo or in vitro. In fact, the negatively selecting phenotype of male H-YTCR-transgenic mice greatly mitigated the accumulation of activated peripheral T cells. Further, peripheral CTLA-4(-/-) T cells expressing a single LMCV-specific transgenic TCR did not have an activated phenotype, indicating that CTLA-4(-/-) T cells require specific antigen for proliferation. These results demonstrate that specific antigen is required for the lymphoproliferation observed in CTLA-4(-/-) mice, and that CTLA-4 deficiency does not lead to a gross defect in negative selection.

Abatacept↗

PubMed1997

Peptide-induced T cell receptor down-regulation on naive T cells predicts agonist/partial agonist properties and strictly correlates with T cell activation.

Recent experiments defining T cell agonists, partial agonists and antagonists have suggested that the T cell can discriminate between subtle differences in interactions leading to T cell activation. To further understand the complexities of T cell activation, we have analyzed the requirements for the induction of a variety of effector functions using naive T cells and a variety of altered peptide ligands. Using a strong agonist peptide, massive T cell receptor (TCR) down-regulation correlated with a wide range of effector functions that were all induced above the same threshold peptide concentration. Interestingly, the kinetics of TCR down-regulation correlated with the concentration of the peptide, whereas the maximal degree of TCR down-regulation correlated with the induction of all monitored effector functions. A selected group of altered peptide ligands was also examined that were able to render target cells susceptible for lysis by effector cytotoxic T lymphocytes. The extent of TCR down-regulation induced by these peptides corresponded to the induction of a subset of effector functions. These studies have shown that the extent of TCR down-regulation defines the strength of TCR-mediated "signal 1" which correlates with the spectrum of effector functions activated within the T cell. Thus, activation of different T cell functions requires the triggering of distinct numbers of TCR. The different parameters that influence TCR down-regulation define important distinctions between our results and previously reported findings with T cell clones and may outline decisive parameters for the consequences of T cell activation in vivo.

Animals↗