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B Stockinger

Publications and source records attributed to B Stockinger.

16 recordsLinked to original sources
PubMed1992

Capacity of antigen uptake by B cells, fibroblasts or macrophages determines efficiency of presentation of a soluble self antigen (C5) to T lymphocytes.

Self antigens in the body fluids must be taken up, processed and presented by antigen-presenting cells (APC) in order to induce T cell tolerance. For self antigens like the fifth component of complement (C5) which is not picked up by APC via antigen-specific receptors, presentation has to rely on uptake by nonspecific means. C5 was used as a model soluble self antigen to study the capacity of different APC (B lymphoma cells, fibroblasts and macrophages) of taking up, processing and presenting low concentrations of soluble C5 to C5 specific T cell hybrids. Under conditions of limiting antigen amounts macrophages and fibroblasts exhibited similar presentation capacity for soluble C5 while B cells did not. C5 presentation by macrophages was enhanced in the presence of C5-specific antibody and augmented further if antigen was added in the form of particulate latex-antigen-antibody complexes indicating enhanced uptake via Fc receptor-mediated endocytosis or phagocytosis. B cells presented soluble C5 only in the presence of C5-specific antibody. Uptake of C5 under these conditions occurred via Fc receptors type II. This pathway of antigen uptake did not operate with other antigens which were presented efficiently after nonspecific endocytosis. In light of these findings it seems reasonable to propose that nonspecific endocytosis of serum proteins like C5 by B cells is normally limited in order to avoid interference with their critical role in antigen receptor-mediated uptake and presentation for the initiation of an antibody response. It seems likely that presentation of soluble self antigens present in the circulation may normally be the task of dendritic cells and macrophages depending on the physical shape of the antigen.

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PubMed1991

Mouse macrophage clones immortalized by retroviruses are functionally heterogeneous.

Murine macrophage clones were generated from thymus, spleen, brain, and bone marrow by in vitro immortalization with recombinant retroviruses carrying an avian v-myc oncogene. The cloned cell lines express F4/80 molecules, exert phagocytosis, have nonspecific esterase activity, and express class II molecules after interferon gamma activation. The macrophage clones are diploid and their karyotypes have remained stable for greater than 3 years in culture. After the macrophage clones were activated, their pattern of cytokine production was investigated. Functional heterogeneity in cytokine transcription was demonstrated: one of six liposaccharide-activated macrophages was unable to transcribe interleukin 1 alpha, whereas all of the liposaccharide-activated clones were able to transcribe tumor necrosis factor alpha. Interleukin 6 production was detected in three of six clones. The production of nitrite and tumor necrosis factor alpha as effector molecules of cytotoxicity was detected in all clones, thus showing that a single macrophage can exert more than one cytotoxic mechanism. The results indicate that immortalized and cloned macrophages have a differentially regulated expression of cytokine genes, adding further evidence for the existence of functional heterogeneity among cloned macrophages. This heterogeneity seems to derive from differentiation-related mechanisms rather than from external constraints.

Animals↗
PubMed1991

Molecules that modify antigen recognition.

MHC class II molecules assemble in the presence of invariant chains. These probably serve not only to protect the peptide-binding site on MHC class II molecules from endogenous peptides, but also to sort MHC class II molecules from the Golgi complex to endosomes and there to retain the class II polypeptides to allow binding of peptides generated from exogenous antigens.

Animals↗
PubMed1991

Novel pathways of antigen presentation for the maintenance of memory.

Follicular dendritic cells (FDC) store native antigen for long periods in lymphoid follicles and so provide a source of continued stimulation for specific B cells. The expression of MHC class II by FDC suggested they might act as antigen-presenting cells for MHC class II-restricted T cells. We show here, however, that the MHC class II molecules found on their surface are not synthesized by the FDC but are picked up from surrounding B cells in germinal centres. Although FDC by themselves cannot present native antigen to T cells, acquired MHC class II-peptide complexes can be recognized by T cells. The true physiological role of FDC seems to be as long-term antigen depots. We demonstrate that antigen localized onto FDC in vivo can be retrieved by antigen-specific B cells, which in turn process and present it to T cells. These presentation pathways are likely to be crucial in both the maintenance of long-term immune responses and the continued survival of memory cells.

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PubMed1990

Analysis of T lymphocyte reactivity to complex antigen mixtures by the use of proteins coupled to latex beads.

This report describes a suitable model for analysing heterogeneous T cell responses to complex foreign antigens using coated polystyrene beads. The advantage of this technique is that it allows the simple removal of detergents from bound antigen so that biochemically separated antigens or crude antigen mixtures can be used. Furthermore, due to the enhanced uptake of latex-bound antigens by phagocytic antigen-presenting cells (APC), very small amounts of antigen will suffice for activation of T cells in vitro. The potential use of this technique to analyse relevant T cell responses to antigens which are difficult to obtain purified in bulk quantities, is discussed.

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PubMed1989

A role of Ia-associated invariant chains in antigen processing and presentation.

Most native antigens require processing in a cellular compartment for efficient presentation to T helper cells. The cellular elements that permit processing are not known. We investigated a possible role of the class II MHC-associated invariant chains in antigen processing. Fibroblast cells that were transfected with class II genes were compared with fibroblasts supertransfected with the invariant chain gene for their capacity to present the fifth component of complement (C5) to C5-specific class II restricted T cell clones or influenza virus protein to a virus-specific T cell clone. Only fibroblasts supertransfected with the invariant chain gene were able to present native antigen, even at very low antigen concentration, whereas both fibroblast types could present cyanogen bromide-fragmented C5 or the virus peptide. Presentation of intact antigen but not of fragmented antigen was totally abrogated by treatment of fibroblasts with chloroquine. The invariant chain gene encodes two polypeptides, li31 and li41. Expression of either li31 or li41 was sufficient to render class II-expressing fibroblasts capable of presenting intact antigen.

Animals↗
PubMed1989

T cell immunity or tolerance as a consequence of self antigen presentation.

In this study we investigated the basis for immunity or tolerance to a mouse serum protein, the fifth component of complement (C5). In C5-deficient mice this protein is absent from serum and therefore they are not tolerized. Immunization of C5-deficient mice with C5-sufficient serum generates CD4+ T cells, which recognize C5 presented in the context of class II. No C5-specific responses were observed in T cells from C5-sufficient mice. We show that this self protein is processed and presented with class II by cells from C5-sufficient tolerant mice and can be recognized by C5-specific T cell clones and hybrids in the absence of exogenously added antigen. The stimulation of C5-specific T cells by C5-sufficient antigen-presenting cells is not a consequence of C5 secretion and subsequent processing in vitro but rather employs C5 peptide/class II complexes generated in vivo. We conclude that this self antigen is presented in normal mice in a form recognizable by T cells to induce and maintain immunological tolerance.

Animals↗
PubMed1989

An intracellular self protein synthesized in macrophages is presented but fails to induce tolerance.

Mice deficient for the fifth component of murine complement (C5), unlike normal mice, do not possess the secreted form of C5 in their body fluids and can be readily immunized to serum-derived normal C5. Although macrophages from C5-deficient mice do not secrete C5, they synthesize the precursor form (pro-C5). Therefore contact of T cells with autologous pro-C5 presented by macrophages is theoretically possible. We show that macrophages from C5-deficient mice can indeed stimulate a class II restricted C5-specific T cell clone without addition of exogenous C5. Immunization of C5-deficient mice with autologous pro-C5 induces vigorous C5-specific T cell proliferation and pro-C5 is recognized by C5-specific T cells in vitro, demonstrating that this protein fails to induce tolerance under physiological conditions. Thus, intracellular pro-C5 is processed and presented by C5-deficient macrophages and can activate T cell clones in vitro, yet is neither immunogenic nor tolerogenic for T cells in vivo.

Animals↗
PubMed1988

Purification of the fifth component of murine complement from ascites fluid.

The murine complement component C5 was purified on an affinity column using a monoclonal anti-mouse C5 antibody. We describe in this paper that ascites fluid from normal (C5-sufficient) mice contains almost as much C5 protein as mouse serum. Since ascites fluid is much easier to obtain in large quantities it is a convenient source for the purification of this mouse serum protein.

Animals↗
PubMed1988

Induction of an immune response to a self antigen.

The question has been addressed whether the endogenous B cell population of a mouse can be induced to secrete antibodies specific for a self antigen present in serum. The antigen studied was the fifth component of mouse complement (C5). Nude BALB/c mice which are C5 sufficient were used as a source of potentially C5-reactive B cells and endogenous serum C5 provided the antigenic stimulus. We purposely avoided immunization with C5 in adjuvant. T cells from C5-deficient mice which lack this component in serum and are therefore not tolerant of C5 were injected into nude mice as a source of T cell help for anti-C5 reactive B cells. Control groups received T cells from C5-sufficient euthymic donors, which are tolerant of C5. Initiation of a response to C5 was monitored by testing the hemolytic function of serum. Reduction of C5-dependent hemolysis was observed in sera of mice which had received T cells from C5-deficient donors. Recipients of T cells from C5-sufficient donors maintained normal hemolytic complement levels throughout the test period of 45 days. Reduction of functional complement levels correlated with the presence of immune complexes of anti-C5/C5. C5-specific antibodies were mainly IgG1 and carried the IgG1 allotype of BALB/c providing unequivocal evidence that they were derived from the endogenous B cell population of the C5-sufficient host.

Animals↗
PubMed1987

Generation of a monoclonal antibody to mouse C5 application in an ELISA assay for detection of anti-C5 antibodies.

We have generated a monoclonal antibody with specificity for the fifth component of mouse complement (C5). This antibody precipitates the two chains of C5 from normal mouse serum and inhibits C5-dependent hemolysis in a functional complement test. In this study we describe its application in an enzyme-linked immunoadsorbent assay (ELISA assay) for the detection of anti-C5 antibodies in serum. Monoclonal anti-C5 coupled to wells of an ELISA plate specifically binds C5 from unfractionated normal mouse serum. This subsequently serves as antigen to bind anti-C5 serum antibodies. By this approach we have circumvented the need for extensive purification of C5 from serum which would be required if C5 was directly coupled to ELISA plates as antigen. Serum antibodies from C5-immunized mice bound with high avidity to wells containing normal serum as antigen source in amounts representing 1 microgram to 250 ng C5. There was no antibody binding to wells containing C5-deficient serum as antigen source. The immune reaction was detected by development with enzyme-coupled goat-anti mouse Ig antibodies specific for various mouse Ig subclasses. This method allows the qualitative characterization of immune responses to mouse C5 which is an ideal model for a natural self antigen in studies of immunological tolerance.

Animals↗
PubMed1986

Adsorption on B cell hybridomas removes suppressor cells from spleen cells of neonatally tolerized mice.

Spleen cells from CBA mice neonatally tolerized to Dd MHC (major histocompatibility complex) determinants were adsorbed on monolayers of Dd-specific B cell hybridomas. Adsorption on 4 different Dd-specific hybridomas but not on a Kd-specific hybridoma removed suppressor cells and resulted in generation of cytotoxic T lymphocyte (CTL) effector cells against the tolerogen. Responses of normal CBA CTL against Dd as well as anti-third party responses were not influenced by adsorption. Successful adsorption was also achieved on monolayers of fixed hybridoma cells. Monolayers of Dd-specific hybridomas specifically removed suppressor cells from CBA mice tolerant to Dd; they failed to adsorb suppressor cells from AKR mice tolerant to H-2b. Immunofluorescence analysis with antibodies specific for determinants on tolerizing cells showed the presence of donor-derived F1 cells on the monolayer. Under the experimental circumstances described suppressor cells are most likely removed by recognition of their MHC determinants by the monolayer population. These data suggest that neonatal tolerance is actively maintained by donor-derived suppressor cells.

Animals↗
PubMed1979

On the feedback regulation of humoral immune response. I. Evidence for 'B suppressor cells'.

Evidence has been presented that complete and antigen-specific immune inhibition can be obtained by 'B suppressor cells'. Transfer of spleen cells from twice-immunized (SRBC) donors to untreated syngeneic recipients resulted in antigen-specific inhibition of the hosts' immune response. The cell responsible for this phenomenon could be shown to be the 7S-producing B cell; participation of T cells and macrophages could be excluded. After a second immunization of the donors, these B cells remained inhibitory for more than 20 weeks in the donors as well as in the recipients after transfer. Passively administered specific IgG antibody caused a similar inhibition of the hosts' immune response, which, however, lasted for less than 9 weeks only. The extent of inhibition caused by transfer of hyperimmune cells was parallel to the number of transferred 7S producing cells. Since it could be demonstrated that memory cells were present at times when the transferred cell material had lost its inhibitory potency, we concluded that inhibition is not caused by the mere presence of these cells. Since the transferred cells regained their inhibitory capacity after non-specific activation with LPS, we concluded that a product of such activated cells--most likely the specific 7S antibody--was responsible for the observed inhibition. Thus, it is demonstrated that B cells may serve as 'suppressor cells' in appropriate transfer experiments. It is, however, concluded that this effect is basically mediated by produced IgG and may in its mechanism be identical to the phenomenon of antibody-mediated regulation of humoral immune response.

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