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Biomedical subjects

M F Bachmann

Publications and source records attributed to M F Bachmann.

At least 91 records · Page 5Linked to original sources
PubMed1996

Dendritic cells process exogenous viral proteins and virus-like particles for class I presentation to CD8+ cytotoxic T lymphocytes.

Previous reports have indicated that both dendritic cells and macrophages have the ability to induce cytotoxic T lymphocyte (CTL) and T helper (Th) cell responses in vivo. Dendritic cells process exogenous antigens conventionally for presentation on major histocompatibility complex (MHC) class II molecules. However, unconventional processing of exogenous antigens in vitro for presentation on MHC class I molecules is still an open question. In this study, we report that a cloned dendritic cell line (D2SC/1) is able to present cell debris-associated exogenous viral proteins to MHC class I-restricted CTL in vitro. The dendritic cell line was very efficient in processing recombinant lymphocytic choriomeningitis virus nucleoprotein (LCMV NP) and presenting the class I-restricted epitope to CTL primed in vivo. Peritoneal macrophages could also process the recombinant LCMV NP for subsequent MHC class I presentation, but were less efficient compared to the dendritic cells. Furthermore, recombinant yeast-derived virus-like particles carrying the HIV-1 V3 loop (V3-VLP), which are protenaceous and do not contain any lipid, were also found to be efficiently processed by the dendritic cell line for presentation of the class I-restricted epitope. These results clearly indicate that viral proteins, in particulate form or associated with cell debris, are processed by dendritic cells for CTL induction.

Amino Acid Sequence↗
PubMed1996

Tumor necrosis factor receptor p55 mediates deletion of peripheral cytotoxic T lymphocytes in vivo.

Cellular death of activated lymphocytes down-regulates immune responses and is involved in maintaining self tolerance. Signals associated with ligation of the membrane molecule Fas lead to lymphocyte apoptosis, but additional, Fas-independent mechanisms have been postulated. Here, we show a marked expansion and prolonged persistence of functional activated cytotoxic T cells in mice lacking the tumor necrosis factor (TNF) receptor p55. In the absence of this receptor, peripheral lymphocyte apoptosis was significantly reduced in vivo. The prolonged thymocyte survival was associated with functional anergy, since the T cells no longer proliferated in vitro when stimulated with peptide antigen. However, specific cytotoxic effector function was easily detected in vitro. We conclude that the TNF receptor p55 is involved in peripheral T cell deletion in vivo.

Animals↗
PubMed1996

Duration of TCR stimulation determines costimulatory requirement of T cells.

Current models suggest that T cells that receive only signal-1 through antigenic stimulation of the T cell receptor (TCR) become anergic, but will mount an immune response when a costimulatory signal-2 is provided. Using mice deficient for an important costimulatory molecule, CD28, we show that a transient signal-1 alone, either through infection with an abortively replicating virus, or through injection of viral peptide, anergizes CD8+ T cells, demonstrating the biological relevance of T cell anergy in vivo. However, in the absence of CD28, continued presence of signal-1 alone, either through prolonged viral replication or repeated injection of peptide, prevents the induction of anergy and generates a functional T cell response in vivo.

Animals↗
PubMed1996

On T cell memory: arguments for antigen dependence.

Memory is a hallmark of the immune system. Considerable progress has been made towards understanding B cell memory, but T cell memory remains poorly understood and its nature is controversial. There is good evidence that B cell memory is driven by antigen, but the antigen dependence of T cell memory is still being debated. For several years we have investigated the nature, duration and antigen dependence of different aspects of CD8+ T cell memory and this review will discuss our findings as well as how and why they differ from some other results. As others, we find that antigen, due to proliferation of antigen-specific T cell clones, induces a shift in the T cell repertoire which remains detectable for years as an elevated cytotoxic T cell precursor frequency (CTLp) in lymphoid organs. Also in the absence of antigen, in vitro assays for T cell memory which invariably isolate memory T cells from these lymphoid organs therefore remain positive. In contrast, immunity against reinfection with a pathogen requires more than just elevated numbers of CTLp in lymphoid organs. Since reinfection usually takes place via peripheral nonlymphoid tissue, these CTLp have to a) efficiently extravasate and patrol through such tissues, and b) be immediately able to exert effector function in case of reinfection. Both functions, require a certain level of activation which critically depends on T cell stimulation by persisting antigen.

Animals↗
PubMed1996

On immunological memory.

Immunological memory is a hallmark of the immune system. Evolution can teach us which effector arms of immunological memory are biologically relevant against which virus. Antibodies appear to be the critical protective mechanism against cytopathic viruses. Since these viruses cause cell damage and disease directly, particularly in the absence of an immune response, mothers protect their offspring during a critical immunoincompetent period (a consequence of MHC- restricted T cell recognition) by passive transfer of neutralizing antibodies. In contrast, CTL appear to be the crucial effector mechanism against noncytopathic viruses. Since MHC polymorphism has made vertical transmission of T cell memory impossible, immunoincompetent offspring are not, and need not be, protected against such noncytopathic viruses. During the primary response and again during secondary infection, the most important function of CTL is to eliminate noncytopathic viruses, which may otherwise cause lethal immunopathology. Increased precursor frequencies of B and T cells appear to remain in the host independent of antigen persistence. However, in order to protect against cytopathic viruses, memory B cells have to produce antibody to maintain protective elevated levels of antibody; B cell differentiation into plasma cells is driven by persisting antigen. Similarly, to protect against infection with a noncytopathic virus, CTL have to recirculate through peripheral organs. Activation and capacity to emigrate into solid tissues as well as cytolytic effector function are also dependent upon, and driven by, persisting antigen. Because no convincing evidence is available yet of the existence of identifiable B or T cells with specialized memory characteristics, the phenotype of immunological memory correlates best with antigen-driven activation of low frequency effector T cells and plasma cells.

Animals↗
PubMed1995

T cell development in CD8-/- mice. Thymic positive selection is biased toward the helper phenotype.

The CD4 and CD8 molecules are involved in T cell differentiation and activation. Nevertheless, efficient thymic maturation of helper T cells has been shown in the absence of the CD4 molecule. These CD4-deficient helper T cells expressed alpha beta-TCR and were able to control Leishmania infections and to mediate Ab class switch. Using mice deficient for the CD8 alpha-chain, we investigated whether a similar cytotoxic T cell population was generated in the absence of the CD8 coreceptor. A CD8-deficient cytotoxic T cell population corresponding to the described CD4-deficient helper T cell population was virtually absent both functionally and physically. These results support the idea that thymic maturation is asymmetrical and strongly biased toward the helper phenotype.

Animals↗
PubMed1995

Fibroblasts as efficient antigen-presenting cells in lymphoid organs.

Only so-called "professional" antigen-presenting cells (APCs) of hematopoietic origin are believed capable of inducing T lymphocyte responses. However, fibroblasts transfected with viral proteins directly induced antiviral cytotoxic T lymphocyte responses in vivo, without involvement of host APCs. Fibroblasts induced T cells only in the milieu of lymphoid organs. Thus, antigen localization affects self-nonself discrimination and cell-based vaccine strategies.

Animals↗
PubMed1995

Early high-affinity neutralizing anti-viral IgG responses without further overall improvements of affinity.

Affinity maturation of IgG antibodies in adaptive immune responses is a well-accepted mechanism to improve effector functions of IgG within 2 weeks to several months of antigen encounter. This concept has been defined mainly for IgG responses against chemically defined haptens. We have evaluated this concept in a viral system and analyzed neutralizing IgG antibody responses against vesicular stomatitis virus (a close relative of rabies virus) with a panel of monoclonal antibodies obtained early (day 6 or 12) and late (day 150) after hyperimmunization. These neutralizing IgG antibodies recognize a single major antigenic site with high affinities (Ka of 10(8)-10(10) liter.mol-1) and with rapid on-rates already on day 6 of a primary response and with no evidence for further antigen dose- and time-dependent overall improvement of affinity. This type of IgG response is probably representative for viruses or bacterial toxins which are crucially controlled by neutralizing antibodies.

Animals↗
PubMed1995

TAP1-independent loading of class I molecules by exogenous viral proteins.

Presentation of peptides derived from endogenous proteins on class I molecules needs functional TAP peptide transporters. To reveal whether class I-associated presentation of exogenous proteins also required the presence of TAP transporters, we assessed in vitro the ability of spleen cells and macrophages from TAP1-deficient mice (TAP1-/-) to present peptides derived from exogenous recombinant viral proteins on their class I molecules. We found that recombinant glyco- and nucleoprotein from lymphocytic choriomeningitis virus and nucleoprotein of vesicular stomatitis virus were presented as efficiently by TAP1-/- cells as by control cells. Peptide regurgitation was not involved. Since particulate, non-replicating antigens can efficiently prime anti-viral cytotoxic T cells in vivo, this new, TAP-independent pathway of class I-associated antigen presentation may be applicable for vaccine strategies.

Animals↗
PubMed1995

Presentation of endogenous viral proteins in association with major histocompatibility complex class II: on the role of intracellular compartmentalization, invariant chain and the TAP transporter system.

Major histocompatibility complex (MHC) class II-associated antigen presentation is mainly linked to processing of exogenous antigens upon cellular uptake by endocytosis, but has also been observed for endogenously synthesized antigens. We have studied the MHC class II-associated presentation of the endogenously synthesized membrane associated glycoprotein (GP) and the cytosolic nucleoprotein (NP) of lymphocytic choriomeningitis virus (LCMV) in professional antigen presenting cells (APC) of mice. Since LCMV is a noncytopathic virus and minimally affects cellular protein synthesis, it is a convenient virus for the study of antigen presentation. In contrast, most other studies assessing class II-associated presentation of endogeneously synthesized viral antigens used cytolytic viruses such as vaccinia, measles and influenza virus, which drastically interfere with host cell functions. In addition, most studies were performed using non-professional APC. We found that class II-associated presentation of endogenously synthesized membrane associated LCMV-GP was efficient and could not be inhibited by chloroquine or leupeptin. Neither the transporter associated with processing (TAP) system nor the invariant chain (Ii) were significantly involved in this process. In contrast, MHC class II-associated presentation of endogenously synthesized cytosolic LCMV-NP was not observed even in Ii-deficient APC. Thus, MHC class II loading of endogenously synthesized LCMV-GP apparently does not require processing in acidic endosomal compartments as defined by chloroquine and leupeptin insensitivity. Furthermore, although the TAP molecules transport peptides of up to 15 amino acids in length, which potentially could bind to MHC class II molecules in the endoplasmic reticulum, such a process apparently does not occur for either the glycoprotein or the nucleoprotein. Therefore, the subcellular localization of an endogenously synthesized protein influences crucially whether or not MHC class II loading can occur independently of the acidic compartments usually involved in MHC class II loading.

ATP-Binding Cassette Transporters↗
PubMed1995

T helper cell-independent neutralizing B cell response against vesicular stomatitis virus: role of antigen patterns in B cell induction?

The neutralizing antibody response against vesicular stomatitis virus (VSV) was studied to analyze conditions necessary for induction of mature B cells. The glycoprotein of VSV (VSV-G) is expressed as repetitive epitopes that are in a rigid densely packed paracristalline form in the virus envelope; in contrast, VSV-G is present in a mobile randomly ordered form on infected cells and in micelles. We found that the rigid, paracristalline form of VSV-G spaced about 5-10 mm on VSV virons induced potent primary and secondary neutralizing B cell responses which were independent of T helper cells, whereas the more randomly distributed, mobile forms of VSV-G induced primary and secondary B cell responses that were more tightly controlled by T helper cells. These data suggest that (i) cross-linking is a critical signal for B cell activation and antibody production, and that this signal alone does not necessarily anergize or delete mature B cells, (ii) the more regularly and rigidly ordered in a distance of 5-10 nm repetitive identical antigenic determinants are, the less are primary and secondary B cell responses controlled by T cells. We therefore propose that B cells take antigen organization as a marker for foreigness.

Animals↗
PubMed1995

Antiviral immune responses in mice deficient for both interleukin-2 and interleukin-4.

Antiviral immune responses of mice lacking interleukin-2 (IL-2) or IL-4 or both IL-2 and IL-4 (IL-2/4) were compared by using different viruses. Primary cytotoxic T-lymphocyte (CTL) responses against lymphocytic choriomeningitis virus (LCMV) were only moderately reduced in mice lacking IL-2 and were normal in mice lacking IL-4. Mice deficient in both interleukins exhibited variable and more strongly reduced but nevertheless in vivo protective LCMV-specific CTL responses. Similar results were obtained with vaccinia virus. Upon virus-specific restimulation in vitro, spleen cells from IL-2- and IL-2/4-deficient mice failed to generate CTL responses against virus-infected target cells, whereas the response of mice deficient in only IL-4 was comparable to that of control mice. The addition of IL-2 during in vitro restimulation completely restored the responses of both IL-2 and IL-2/4-deficient mice. T-helper-cell-independent immunoglobulin M and T-helper-cell-dependent immunoglobulin G antibody responses against vesicular stomatitis virus glycoprotein were within normal ranges for the various mutant mice. After LCMV infection, specific antibody responses against LCMV nucleoprotein were reduced four- to eightfold. These results show that mice lacking IL-2/4 have an overall tendency to exhibit more severely reduced CTL responses than IL-2- or IL-4-deficient mice. Nevertheless, and surprisingly, in vivo protective immune responses were mounted in the absence of IL-2/4, suggesting that besides a minor contribution from IL-4, other interleukins compensate in vivo for the lack of IL-2 in IL-2-deficient mice.

Animals↗
PubMed1994

Free recirculation of memory B cells versus antigen-dependent differentiation to antibody-forming cells.

This study investigated whether or not the localization of persisting Ag influenced the localization of memory B and/or of Ab-forming cells (AFC). As a model Ag, we used vesicular stomatitis virus, which does not measurably replicate extraneuronally in adult mice after peripheral infection. Our results show that memory B cells and AFC are induced at the site where Ag is present; induced memory B cells then recirculate throughout the lymphoid system independently of Ag localization. In contrast, AFC are induced only at the sites of Ag persistence. These triggered Ab producing cells do not recirculate through the lymphoid tissue but migrate to the bone marrow.

Animals↗
PubMed1994

How many specific B cells are needed to protect against a virus?

The size of the Ab repertoire has been estimated to comprise theoretically somewhere between > 10(10) and approximately 10(4) specificities, dependent on the criteria used. In an attempt to estimate the anti-viral protective Ab repertoire of the mouse the B cell and Ab-forming cell (AFC) frequencies and protective neutralizing Ab levels during the course of an infection with vesicular stomatitis virus (VSV) were analyzed. Determination of AFC frequencies, limiting dilution assays, and adoptive transfer experiments to SCID mice revealed that during the acute phase (day 8) of the immune response, more than 50% of all IgG2a-producing AFCs were specific for VSV, most of them recognizing the neutralizing determinant. In a later phase (days 21 or 50), 10 to 20 times fewer VSV-specific AFCs were present, corresponding to a frequency of approximately 1:10(4) spleen cells. Finally, in a protection assay in SCID mice, adoptively transferred protective Ab concentrations were found to be approximately 1 to 10 micrograms Ab/ml mouse serum. Because during the memory phase of the anti-VSV response usually 10(4) AFC/mouse are engaged to maintain a high level of memory IgG against the neutralizing determinant on VSV and if one assumes a total number of about 10(6) AFCs/mouse, these data suggest a rather limited neutralizing anti-viral protective memory-AFC repertoire of 10(2) to 10(4) different specificities.

Animals↗
PubMed1994

Class II major histocompatibility complex-restricted T cell function in CD4-deficient mice.

Previously, we and others have demonstrated that CD4-deficient mice have a normal number of T cells and B cells with a significant population of CD4-8-TcR alpha beta+ T cells. Surprisingly, however, these mice lacking CD4 show in vivo immunoglobulin isotype class switching from IgM to IgG in response to sheep erythrocytes and vesicular stomatitis virus. In this study we have depleted various subpopulations of T cells in vivo and shown that the population of CD4-8-TcR alpha beta+ T cells is responsible for providing "help" in the antibody response of CD4-deficient mice to vesicular stomatitis virus infection. We have used antigen-specific proliferation assays and blocking studies with class I and II major histocompatibility complex (MHC)-specific purified antibodies to show that these cells are class II MHC-restricted in responses against the T cell-dependent antigen keyhole limpet hemocyanin (KLH). Finally, phenotypic analysis of the CD4-CD8- thymocytes in CD4-deficient mice shows that these cells have a more mature phenotype than the CD4-8- thymocytes in wild type mice. These results indicate that CD4 is not absolutely necessary for positive selection or effector function of class II MHC-restricted helper T cells.

Animals↗
PubMed1994

Induction of protective cytotoxic T cells with viral proteins.

Induction of CD8+, class I-restricted T cells by non-infectious, exogenous antigens has been documented for model protein antigens such as ovalbumin and for major histocompatibility complex restricted short peptides in viral and tumor systems. However, the protective capacity of cytotoxic T cells induced by conventional proteins has not been tested in vivo so far. We, therefore, evaluated the induction of protective cytotoxic T cells against three different full-length recombinant viral proteins derived from a baculovirus expression system, i.e. the glycoprotein and nucleoprotein of lymphocytic choriomeningitis virus (LCMV) and the nucleoprotein of vesicular stomatitis virus (VSV). These viral proteins induced cytotoxic T cells in a T helper cell-independent fashion which lysed infected target cells in vitro and protected mice from viral replication, immunopathological disease and growth of a tumor expressing the same antigen as a tumor antigen. These results are surprising, since it had been shown earlier for completely inactivated nonreplicating viral vaccines and again here for beta-propiolactone-inactivated VSV or UV-light inactivated LCMV that nonreplicating viral vaccines were incapable of inducing protective cytotoxic T cells. Our data show that immunization of mice with as little as 10 micrograms of non-infectious viral proteins triggered long-lasting CD8+ T cell-mediated antiviral immunity. It was found that the protein alone was only weakly able to induce cytotoxic T cells, and that association with cellular debris functioned as an adjuvant. These findings may be relevant for our understanding of the phenomenon of cross-priming and have obvious implications for vaccine strategies.

Animals↗