Biomedical subjects

M F Bachmann

Publications and source records attributed to M F Bachmann.

103 records · Page 6Linked to original sources

PubMed1994

Regulation of IgG antibody titers by the amount persisting of immune-complexed antigen.

Antigens normally induce an immunoglobulin (Ig)G response which stays at an elevated level for several weeks or months, constituting an important part of the immunological memory. This study investigated factors influencing the level of neutralizing IgG titers against a virus and shows that within the range tested it was independent of the number of initially available and potentially responding T helper and B cells, but was regulated by the amount of specific IgG-immune complexes forming depots of persisting antigen. These findings support the notion that the efficiency of vaccines in inducing long-lasting protective IgG is regulated predominantly by the amount of persisting (and presumably follicular dendritic cell-associated) antigen-antibody complexes.

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PubMed1994

T helper cell unresponsiveness: rapid induction in antigen-transgenic and reversion in non-transgenic mice.

T cell tolerance is usually established by clonal deletion of self-specific T cells in the thymus, or some times, in the periphery. Alternatively, tolerance may also be achieved by induction of clonal T cell unresponsiveness by a poorly understood mechanism called "anergy". We found that transgenic mice expressing a soluble form of vesicular stomatitis virus (VSV) glycoprotein (G) predominantly in liver and kidney exhibited normal B cell responses. VSV-G-specific T help-independent neutralizing IgM responses were within normal ranges, but no T help-dependent neutralizing IgG antibodies were generated upon immunization with recombinant VSV-G protein and recombinant vaccinia virus expressing VSV-G. This demonstrated absence of B cell tolerance but presence of T helper cell unresponsiveness. After adoptive transfer of transgenic spleen cells into thymectomized immuno-incompetent hosts, the unresponsive T helper cells regained function and switched the neutralizing IgM response to IgG, comparably to control T helper cells, within 7 days. Conversely, when naive non-transgenic spleen cells were transferred into transgenic mice, VSV-G-specific T helper cells became unresponsive within 3-4 days. These results suggest that VSV-G-specific T helper cells are rendered unresponsive within a few days in the VSV-G transgenic host also outside of the thymus and that this unresponsiveness was reversed by transfer into antigen-free recipients.

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PubMed1994

Immunization with recombinant protein: conditions for cytotoxic T cell and/or antibody induction.

Safe vaccines should optimally induce both cell-mediated and humoral immunity. Recently, it has been shown that protective cytotoxic T cells (CTLs) can be induced not only with live vaccines, but also with recombinant viral proteins. This report shows in C57BL/6 (H-2b) mice that the recombinant nucleoprotein (N) of vesicular stomatitis virus (VSV) induced protective CTLs but no neutralizing antibodies in mice, whereas the recombinant glycoprotein (G) of VSV alone induced neutralizing antibodies but no CTLs. If the N and G of VSV were coinjected, both CTLs and a long-lasting neutralizing IgG response was measurable, demonstrating that mixed vaccines can be used to induce protective CTLs and antibodies with an efficiency comparable to live virus. In an attempt to define optimal conditions for CTL priming, the intravenous, intraperitoneal and subcutaneous route of injection were compared. Intravenous injection of recombinant VSV-N induced up to 30 times higher responses than the latter two routes. Finally, we tried to define conditions inducing only CTLs and no antibodies binding to the native protein form, or vice versa, only antibodies and no CTLs. Intravenous injection of boiled VSV-N induced a CTL response but no antibodies specific for the native VSV-N, whereas VSV-N injected subcutaneously in incomplete Freund's adjuvant induced high amounts of anti-VSV-N antibodies but virtually no CTLs. The conditions defined here permit vaccines to be designed which would function along selected and defined immunological effector pathways.

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PubMed1994

Immunogenicity of a viral model vaccine after different inactivation procedures.

Various strategies for the production of safe vaccines have been used. This study compared three different inactivation procedures, i.e. treatment with formaldehyde, beta-propiolactone or UV-light using vesicular stomatitis virus (VSV) as a model antigen. All three inactivation procedures drastically impaired induction of neutralizing IgG responses, confirming previous observations [Bachmann et al. (1993) J Virol 67:3917-3922]. This reduction could be overcome using higher doses for all three preparations. Both formaldehyde and beta-propiolactone completely abrogated the induction of VSV-specific cytotoxic T cells (CTLs), whereas UV-inactivated virus was able to induce significant and long-lasting CTL responses. These results may be of practical relevance since induction of neutralizing antibodies alone is often not sufficient for protection and sometimes may even enhance immunopathological responses of vaccinees.

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PubMed1994

In vivo versus in vitro assays for assessment of T- and B- cell function.

As mice deficient in a particular gene provide an increasing number of novel in vivo models, in vivo assays that examine immune function are becoming a central issue. We found that the sensitivities of in vivo and in vitro assays are strikingly different. These differences have important implications for the interpretation and biological relevance of results.

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PubMed1994

Vesicular stomatitis virus Indiana glycoprotein as a T-cell-dependent and -independent antigen.

The neutralizing immunoglobulin M (IgM) response to vesicular stomatitis virus (VSV) has been shown to be largely T-cell independent in several T-cell-deficient models of mice. By using different antigen froms of VSV, VSV antigen doses could be graded in vivo (infectious > > UV inactivated > formalin inactivated). The present study reveals a T-cell-dependent component of the neutralizing IgM response in nude mice given intravenous injections of low doses of noninfectious UV-inactivated VSV serotype Indiana (VSV-IND) only if the mice are transfused with VSV-IND-specific helper T cells. Instead, nude mice immunized with infectious VSV, which leads to greater antigen doses in vivo, were able to mount an IgM response in the absence of T cells. These results indicate that the IgM response to low doses of VSV-IND glycoprotein (G) is T-cell dependent. Nude mice immunized with infectious VSV also made a variable but low VSV-IND-neutralizing IgG response. A VSV-IND matrix (M)-specific helper T-cell line rendered this response more consistent, much higher, and longer lasting. Thus (i) VSV-G induces a mostly T-cell-independent but partially T-cell-dependent IgM (the latter can be visualized best at low doses of antigen) and (ii) the antibody response to VSV in nude mice proceeds through steps, i.e., IgM and IgG, that are dose dependent. The results suggest that the predominant role of helper T cells may be to expand and maintain the individual steps of differentiating B cells.

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PubMed1993

The influence of antigen organization on B cell responsiveness.

The influence of antigen epitope density and order on B cell induction and antibody production was assessed with the glycoprotein of vesicular stomatitis virus serotype Indiana [VSV-G (IND)]. VSV-G (IND) can be found in a highly repetitive form the envelope of VSV-IND and in a poorly organized form on the surface of infected cells. In VSV-G (IND) transgenic mice, B cells were unresponsive to the poorly organized VSV-G (IND) present as self antigen but responded promptly to the same antigen presented in the highly organized form. Thus, antigen organization influences B cell tolerance.

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PubMed1993

Immune responses in interleukin-2-deficient mice.

The role of costimulatory signals in T cell induction was evaluated in mice lacking the interleukin-2 (IL-2) gene. In vitro secondary antiviral T cell responses were absent unless IL-2 was added, confirming the crucial role of IL-2 in vitro. In vivo, primary and secondary cytotoxic T cell responses against vaccinia and lymphocytic choriomeningitis virus were within normal ranges. B cell reactivity to vesicular stomatitis virus was not impaired. T helper cell responses were delayed but biologically functional. Natural killer cell activity was markedly reduced but inducible. These normal in vivo immune responses in IL-2-deficient mice question the importance of IL-2 as defined by in vitro studies.

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PubMed1993

Comparison of the sensitivity of in vivo and in vitro assays for detection of antiviral cytotoxic T cell activity.

Sensitivities of in vitro and in vivo assays for the detection of lymphocytic choriomeningitis virus (LCMV)-specific CTL were compared. Measurement of primary cytotoxicity was the least sensitive of all the tested assays. However, when the same 51Cr release assays were performed after in vitro restimulation, this in vitro method was found to be more sensitive than all of the five in vivo assays tested. Assessment of CTL-mediated protection against LCMV replication in spleens was most sensitive among the in vivo tests, followed by CTL-mediated resistance to intracerebral or intraperitoneal challenge infections with vaccinia-LCMV-recombinant virus. Inhibition of LCMV-induced choriomeningitis and of the footpad swelling reaction were least sensitive in detecting LCMV-specific CTL. As discussed, the presented sensitivity gradient may most probably be generalized.

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PubMed1993

Peripheral T cells in mice lacking p56lck do not express significant antiviral effector functions.

Mutant mice lacking p56lck, the T cell-specific protein tyrosine kinase, have a profound thymic atrophy and possess only an immature thymocyte population. Only 5 to 10% of normal levels of mature T cells (TCR-alpha beta+, CD4+, or CD8+) are present in these mice. These T cells, but also B cells of mutant mice, can be activated by mitogens, and T cells proliferate upon stimulation with IL-2 or mAb against the TCR. Thus, it appears that selected T cells can mature without lck and that they may have circumvented the need for this enzyme. This study evaluated the capacity of these mice to generate antiviral immune responses: 1) mutant mice failed to generate virus-specific CTL after acute infection with lymphocytic choriomeningitis virus (LCMV) or vaccinia virus. 2) LCMV was not cleared from the spleen on day 10 after infection. 3) Infection of LCMV into footpads of mutant mice did not induce a T cell-dependent swelling reaction. 4) Intracerebral inoculation with LCMV did not induce in mutant mice any clinical signs of sickness. 5) Vesicular stomatitis virus (VSV)-primed mutant mice could not eliminate nucleoprotein of VSV recombinant vaccinia virus upon intracerebral infection. 6) VSV infection of mutant mice elicited normal, specific T cell-independent IgM responses, but no significant switch to IgG. These results show that, despite the presence of in vitro activatable CD8+ and CD4+ T cells in the mutant mice, no biologically relevant functions can be detected. Therefore, these data indicate that p56lck is directly or indirectly crucially involved in in vivo Ag-induced T cell responses.

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PubMed1993

Nonimmunogenic tumor cells may efficiently restimulate tumor antigen-specific cytotoxic T cells.

Induction of immunity to a viral protein that had been transfected into a tumor cell line was studied. The nucleoprotein (NP) of vesicular stomatitis virus (VSV) was used as a model tumor-associated Ag after transfection into EL-4, and H-2b thymoma originating from C57BL/6 mice. The NP-transfected cell line (EL-4NP) was lysed by NP-specific CTL and was found to restimulate NP-specific CTL in vitro as efficiently as did VSV-infected macrophages. Despite both of these in vitro characteristics, C57BL/6 mice inoculated with EL-4NP did not mount a measurable NP-specific CTL response and developed a lethal tumor as rapidly as did mice given control EL-4. This lack of immunogenicity could not be explained by down-regulation of MHC class I molecules or by loss of NP; even EL-4NP cells metastasizing to the spleen kept their high restimulatory capacity and excellent target characteristics. However, once mice were immunized with VSV or with a vaccinia-VSV-NP recombinant virus they were protected against tumor growth of EL-4NP by CD8+ CTL but not by CD4+ T cells. Taken together, the failure of the tumor-associated Ag to induce a protective T cell response in vivo despite its excellent capacity to restimulate CTL in vitro may encourage adjuvant immunotherapy in cancer; even the effects of weakly immunizing tumor vaccines, e.g., recombinant viruses, may be efficiently amplified by tumor cells.

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PubMed1993

Fewer protective cytotoxic T-cell epitopes than T-helper-cell epitopes on vesicular stomatitis virus.

Cytotoxic T-lymphocyte (CTL) and T-helper-cell responses in various mouse strains were monitored. Protective CTL responsiveness against three proteins of vesicular stomatitis virus was H-2 linked and inducible only in half of the 15 combinations tested (each of five H-2 haplotypes combined with each of three viral proteins), whereas biologically relevant T-helper-cell responses were inducible in all. This suggests that vesicular stomatitis virus exhibits more T-helper-cell than CTL epitopes.

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PubMed1993

Formalin inactivation of vesicular stomatitis virus impairs T-cell- but not T-help-independent B-cell responses.

The effects of formalin on the infectivity and immunogenicity of vesicular stomatitis virus (VSV) serotype Indiana were investigated. We found that formalin inactivation of VSV prevents infection of Vero cells in a concentration- and time-dependent manner, as shown by fluorometric cell analysis and inhibition of plaque formation. Inactivated VSV failed to induce significant cytotoxic T-lymphocyte responses in vivo or after restimulation in vitro. In contrast, the early immunoglobulin M (IgM) response, which is T help independent in the VSV system, was unaltered, suggesting normal antigenicity for and induction of B cells. However, no switch to IgG occurred, demonstrating failure of induction of T help. If cross-reactive T help was provided by previous infection with a second serotype of VSV (New Jersey), the IgG response was almost completely restored, confirming that the absence of IgG was due to lack of T help. A formalin-treated preparation of glycoprotein of VSV led to a delayed but otherwise normal IgG response, whereas treatment of VSV with UV light or beta-propiolactone reduced IgG titers to the same extent as did formalin. These results suggest that loss of infectivity and the ensuing lack of amplification of viral antigens of formaldehyde-inactivated VSV is the major factor impairing induction of specific T-helper cell responses.

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