Mechanism of action of cyclosporine A in vivo. II. T cell priming in vivo to alloantigen can be mediated by an IL-2-independent cyclosporine A-resistant pathway

Cyclosporine A (CsA) inhibits T lymphocyte activation in vitro by blocking at a pretranslational level the production of IL-2 and other cytokines. It is widely assumed that the effectiveness of CsA as an immunosuppressive drug is secondary to a similar mechanism of action in vivo. We have previously demonstrated that certain parameters of T cell activation in the draining popliteal lymph node in response to the injection of alloantigen in the footpad were either completely resistant or enhanced by the administration of CsA. In the present study, we have shown that the mechanism of action of CsA in vivo is identical to that seen in vitro as CsA completely suppressed the induction of IL-2 mRNA as detected in a nuclease protection assay in lymph node cells from alloantigen-primed animals. Nevertheless, T cells from CsA-treated animals appeared to have undergone both priming and differentiation. Thus, upon culture in vitro in the presence of CsA, cells from CsA-treated animals manifested a vigorous proliferative response that could not be inhibited by the addition of a large panel of anti-cytokine mAb. Furthermore, cells from CsA-treated animals demonstrated an enhanced secondary response to the priming alloantigen, which suggests that they had undergone clonal expansion in vivo. Although CTL activity was markedly suppressed in cells from CsA-treated animals, after a 36-h culture in the absence of CsA, CTL activity equivalent to that detected in cells from nontreated animals was present. Collectively, these data support the existence of an alternative IL-2-independent, CsA-resistant pathway of T cell activation/differentiation that may play a prominent role in the generation of certain T effector functions in vivo.

Mechanism of action of cyclosporine A in vivo. II. T cell priming in vivo to alloantigen can be mediated by an IL-2-independent cyclosporine A-resistant pathway

Cyclosporine A (CsA) inhibits T lymphocyte activation in vitro by blocking at a pretranslational level the production of IL-2 and other cytokines. It is widely assumed that the effectiveness of CsA as an immunosuppressive drug is secondary to a similar mechanism of action in vivo. We have previously demonstrated that certain parameters of T cell activation in the draining popliteal lymph node in response to the injection of alloantigen in the footpad were either completely resistant or enhanced by the administration of CsA. In the present study, we have shown that the mechanism of action of CsA in vivo is identical to that seen in vitro as CsA completely suppressed the induction of IL-2 mRNA as detected in a nuclease protection assay in lymph node cells from alloantigen-primed animals. Nevertheless, T cells from CsA-treated animals appeared to have undergone both priming and differentiation. Thus, upon culture in vitro in the presence of CsA, cells from CsA-treated animals manifested a vigorous proliferative response that could not be inhibited by the addition of a large panel of anti-cytokine mAb. Furthermore, cells from CsA-treated animals demonstrated an enhanced secondary response to the priming alloantigen, which suggests that they had undergone clonal expansion in vivo. Although CTL activity was markedly suppressed in cells from CsA-treated animals, after a 36-h culture in the absence of CsA, CTL activity equivalent to that detected in cells from nontreated animals was present. Collectively, these data support the existence of an alternative IL-2-independent, CsA-resistant pathway of T cell activation/differentiation that may play a prominent role in the generation of certain T effector functions in vivo.

CD4 and CD8 molecules can physically associate with the same T-cell receptor

The expression of the cell-surface glycoproteins CD4 and CD8 on functionally mature T cells is usually mutually exclusive and correlates with class II and class I major histocompatibility complex (MHC) restriction, respectively. CD4 and CD8 function by binding to class II and class I MHC molecules on the antigen-presenting cell (APC), thereby increasing the adhesion between the T cell and the APC. From antibody-blocking studies and from cocapping and comodulation experiments, CD4 and CD8 come into close physical contact with their appropriately restricted T-cell receptor (TCR) at the time of antigen recognition. By the use of affinity chromatography followed by two-dimensional diagonal gel electrophoresis, we have identified a Mr 43,000 disulfide-bonded heterodimer copurifying with CD4. This protein was identified as the TCR by its removal after preclearing with the anti-TCR antibody F23.1 and by its generation after protease digestion of the same peptides as the TCR from this clone. When CD4 and CD8 were similarly isolated from an unusual CD4+ CD8+ class II-restricted T-cell clone, the TCR was identified as associating with either accessory molecule in the absence of activation. Therefore, CD4 and CD8 do not distinguish between class I- and class II-restricted TCRs in their ability to form membrane complexes, indicating a need for both the TCR and its associated accessory molecule to recognize the same individual MHC molecule on the APC to optimize TCR triggering.

The bvgA gene of Bordetella pertussis encodes a transcriptional activator required for coordinate regulation of several virulence genes

The bvg region of the respiratory pathogen Bordetella pertussis coordinately regulates the expression of several unlinked virulence determinants in response to environmental signals. The DNA sequence of the bvg region contains three genes (bvgA, bvgB, and bvgC). Transcription of a single-copy fusion consisting of the upstream region of a bvg-activated B. pertussis gene (fhaB) attached to the promoterless lac operon in Escherichia coli requires the entire bvgABC region in trans. Activation of the fhaB::lacZYA fusion is sensitive to the same environmental stimuli in E. coli that modulate the expression of bvg-activated genes in B. pertussis. Our data show that overexpression of the bvgA gene from a strong heterologous promoter results in transcriptional activation of the fhaB::lacZYA fusion even in the absence of the bvgB and bvgC products. Activation of fhaB transcription by bvgA overexpression in E. coli is no longer repressed by environmental conditions. The bvgA product has been identified by maxicell analysis as a 23-kilodalton protein. A B. pertussis mutant containing an in-frame deletion in bvgA was constructed. This mutant was nonhemolytic and no longer produced filamentous hemagglutinin and pertussis toxin. The mutation in this strain was complemented by returning the bvgA gene in trans. Transcriptional chloramphenicol acetyltransferase fusions to the fhaB and ptx promoter regions were returned to both the B. pertussis bvgA deletion mutant and its parental wild-type strain. Analysis of these strains indicated that the deletion mutant was defective in transcription of both ptx and fhaB. We conclude from these data that bvgA, bvgB, and bvgC comprise an operon encoding the components essential for coordinate regulation and sensory transduction. The BvgA protein is a transcriptional regulatory factor. The bvgB and bvgC products may be important in regulating the activity of BvgA in response to the changing environmental stimuli that B. pertussis encounters during the diseases whooping cough.

Transformation of Actinobacillus pleuropneumoniae and analysis of R factors by electroporation

An efficient method for DNA transfer is essential for the genetic manipulation of any organism. Such a capacity will be required for the genetic analysis of Actinobacillus pleuropneumoniae as a swine pathogen, as well as for its manipulation for vaccination purposes. For this reason, the use of electroporation as a means of plasmid DNA introduction into this species was examined. The multiple antibiotic-resistant strain 80-8141 of Actinobacillus pleuropneumoniae harbors 3 plasmids: pYG10, pYG15, and pYG12 of 5.0, 2.7, and 2.5 kb, respectively. Electroporation of A pleuropneumoniae strain 4074 with a plasmid extract of strain 80-8141 showed that pYG10 encodes chloramphenicol resistance and that pYG12 encodes ampicillin resistance. Electrical pulse conditions for efficient electroporation of strain 4074 were examined by use of pYG10 DNA isolated from a 4074 transformant. Efficiency, expressed as transformants per microgram of plasmid DNA, increased directly with pulse amplitude. However, high efficiencies were only observed in a narrow window of pulse duration (tau = 12 to 22 ms at 6.25 kV/cm). Longer pulse durations resulted in cell death. Electroporation efficiencies increased with cell density. Yield of transformants increased directly with DNA concentration. Results indicate that electroporation can be used to efficiently transform A pleuropneumoniae and that pYG10 and pYG12 are suitable plasmid vectors for use in the genetic manipulation of this organism.

Analysis of Bordetella pertussis virulence gene regulation by use of transcriptional fusions in Escherichia coli

The virulence regulon of Bordetella pertussis includes a trans-acting regulatory locus, bvg, that is required for expression of several virulence factors. The virulence control system also responds to environmental signals. We have reconstructed a bvg-dependent regulatory system in Escherichia coli by using bacteriophage lambda vectors carrying transcriptional fusions to lacZYA. Single-copy lacZYA fusions to the B. pertussis fhaB locus, which encodes the attachment factor filamentous hemagglutinin, were activated nearly 400-fold by pBR322 replicons carrying sequences that included bvg. In contrast, bvg had no effect on the pertussis toxin operon (ptxA-E) promoter in E. coli as measured by ptxA-lacZ expression. Environmental signals that modulate expression of virulence genes in B. pertussis had a pronounced effect on bvg-mediated activation of fhaB-lacZ. MgSO4, nicotinic acid, and low temperature resulted in decreases in beta-galactosidase activities of 175-, 115-, and 45-fold respectively. Sensory transduction and transcriptional activation were tightly coupled, and both required an intact bvg locus as determined by 5' and 3' deletions that eliminated both activities.

Expression of class I histocompatibility antigens in defined tissues: effects on T cell function

We have generated transgenic mice by introducing into fertilized eggs the major histocompatibility complex class I gene, H-2Kb, linked to various promoters that target gene expression to particular tissues. In one system the gene was expressed in the medullary epithelial cells of the thymus; these were unable to impose tolerance on differentiating T lymphocytes. These findings, together with those of other workers who showed that epithelial thymus grafts can impose tolerance, provide clear evidence of functional heterogeneity among thymus epithelial cells. In other transgenic models the gene was expressed in nonlymphoid tissues, such as the pancreatic islet beta cells or the hepatocytes, exocrine pancreas and kidney tubules. In all these cases the tissues were not subjected to autoimmune attack and the animals were specifically tolerant of H-2Kb-bearing cells in vivo, although some could generate cytotoxic T lymphocytes in vitro. Hence, although the intrathymic environment may be the dominant site for negative selection, it is clear that ancillary mechanisms exist in the periphery to ensure that tolerance is achieved to antigens not synthesized in the thymus.

Sequences required for expression of Bordetella pertussis virulence factors share homology with prokaryotic signal transduction proteins

The bvg locus of Bordetella pertussis is required for coordinate regulation of several factors associated with virulence. The control system is modulated by various environmental signals, including low temperature, MgSO4, and nicotinic acid. The nucleotide sequence of the bvg region has been determined and three open reading frames, bvgA, bvgB, and bvgC, are present. Twelve-base-pair linker insertion mutations in any of these open reading frames result in a Bvg- phenotype. The predicted protein products of bvgA and bvgC share homology with a family of prokaryotic regulatory proteins that respond to environmental stimuli and are members of two-component sensory transduction systems. We propose a model in which BvgB and the N-terminal portion of BvgC are localized in the periplasm. Environmental signals are recognized, transduced to the cytoplasmic portion of BvgC, and then transmitted to BvgA, a positive regulator of transcription.

MHC molecules and beta-cell destruction. Immune and nonimmune mechanisms

Hyperexpression of major histocompatibility complex (MHC) molecules by islet cells is a prominent, early feature of islet pathology in insulin-dependent diabetes mellitus and concomitant with beta-cell failure after exposure of islets to specific cytokines or viruses. The transgenic expression of a class I MHC gene (H-2Kb) in the beta-cells of either syngeneic or allogeneic mice leads to beta-cell failure by a nonimmune mechanism. Several class II MHC transgenes, with one exception, have the same effect, but the expression of other transgenes that have products that are membrane proteins is not necessarily detrimental. Class I MHC molecules have been shown to interact directly with other membrane proteins. The inappropriate expression of MHC molecules could therefore interfere with key cellular functions. We postulate that the hyperexpression of MHC molecules in the beta-cell, e.g. in response to viruses, is a primary, nonimmune mechanism of beta-cell failure that precedes a secondary autoimmune response.

Tolerance of class I histocompatibility antigens expressed extrathymically

Although convincing evidence has been obtained for the imposition of self-tolerance by the intrathymic deletion of self-reactive T cells, the development of tolerance to antigens which are expressed only in the periphery is not so well understood. We have approached this question by creating transgenic mice which carry a class I major histocompatibility complex (MHC) gene (H-2Kb) linked to the rat insulin promoter. Mice expressing the transgene develop diabetes, but do not appear to mount an immune response against the transgene-expressing pancreatic beta-cells, even when the transgene is allogeneic with respect to the endogenous host H-2 antigens. We have now explored the mechanism of this tolerance further. We find that spleen cells from pre-diabetic transgenic (RIP-Kb) mice do not kill targets bearing H-2Kb, whereas thymus cells from the same mice do. The unresponsiveness of these spleen cells can be reversed in vitro by providing recombinant interleukin-2 (rIL-2). In older, diabetic mice, responsiveness develops as the pancreatic beta-cells are lost. Our results point to an extrathymic mechanism of tolerance induction, dependent on the continuous presence of antigen and the lack of IL-2 in the local environment of potentially reactive T cells.

Purification and characterization of glia maturation factor beta: a growth regulator for neurons and glia

A protein has been isolated from bovine brains by using a modification of the procedure used to purify glia maturation factor. The method consists of ammonium sulfate precipitation, chromatography with DEAE-Sephacel, Sephadex G-75, and hydroxylapatite columns, passage through a heparin-Sepharose column, and finally fractionation by reverse-phase HPLC with a C4 column. The isolated protein reacts strongly with the mouse monoclonal antibody G2-09 and has a molecular weight of approximately 17,000 and an isoelectric point of pH 4.9. The N terminus is blocked, but tryptic digestion releases 28 peptides, 8 of which have been sequenced. The total known residues add up to more than two-thirds of the entire 140-residue protein, estimated from amino acid composition, and show no sequence homology with any known protein. Reversible thermal renaturation greatly enhances its biological activity. The purified protein stimulates differentiation of normal neurons as well as glial cells. It inhibits the proliferation of the N-18 neuroblastoma line and the C6 glioma line while promoting their phenotypic expression. We designate this protein glia maturation factor beta.

Expression in transgenic mice of class I histocompatibility antigens controlled by the metallothionein promoter

To study the effects of increased expression of major histocompatibility complex class I molecules on the development of self-tolerance, transgenic mice were produced that expressed the H-2Kb gene under the control of the metallothionein promoter. Administration of zinc enhanced transgene expression in liver, kidney and exocrine pancreas. No evidence suggestive of an autoimmune response was found in transgene-expressing tissues in mice otherwise allogeneic to H-2Kb. Despite this lack of responsiveness in vivo, T cells could be stimulated in vitro to lyse H-2Kb-bearing target cells. No infiltration was detected in transgenic mice after irradiation and reconstitution with bone marrow cells. When spleen cells were used for reconstitution, however, dense lymphocytic infiltration was seen, particularly in the portal tracts of the liver, and this was accompanied by piecemeal necrosis and apoptosis of periportal hepatocytes. This aggressive response progressively diminished with time, and by 12 weeks after reconstitution many of the portal tracts were free of infiltration while the others showed no accompanying necrosis. The picture at this stage was similar to that seen in chronic persistent hepatitis. These results suggest that, in addition to negative selection in the thymus, peripheral mechanisms not involving clonal deletion or permanent clonal anergy can prevent immune responses to self molecules.

Development of atherosclerosis in genetically hyperlipidemic rabbits during chronic fish-oil ingestion

The evidence for a reduction in cardiovascular mortality from fish oil is based on epidemiologic observations. To test whether fish-oil supplementation influences the development of atherosclerosis, we treated Watanabe heritable hyperlipidemic rabbits (WHHL), an inbred strain that spontaneously develops atherosclerosis, with 2.5 ml of MaxEPA fish-oil concentrate daily and compared them to a control group fed unsupplemented rabbit chow. Serial cholesterol and triglyceride levels were monitored as were plasma lipid hydroperoxides. The animals were given fish oil from the time of weaning until 1 year of age, when they were sacrificed and their aortas were compared for the extent of atherosclerosis. No significant differences in the cholesterol or triglyceride levels were noted between the two groups. Fatty acid hydroperoxide levels were also similar and were noted to increase from weaning (1.0 +/- 0.7 microM) to the time of sacrifice (1.8 +/- 1.5 microM, p less than 0.01). Fish oil had no influence on the extent of aortic atherosclerosis (25% +/- 14% surface area for controls vs. 28% +/- 19% for treated, p = NS), plaque thickness, or plaque volume after 1 year. We conclude that fish oil does not reduce the levels of serum cholesterol, lipid hydroperoxides, or aortic atherosclerosis in WHHL rabbits. The hypothesis that fish oil protects against atherosclerosis was not supported by this study.

In vivo studies of DnaA binding to the origin of replication of Escherichia coli

We have shown that DnaA, a protein required for initiation of DNA replication in Escherichia coli, binds to three of four DnaA binding sequences in the replicative origin oriC (boxes R1, R2 and R4). Protein-oriC DNA interactions in minichromosomes carried by wild-type and dnaA mutant strains were demonstrated by in vivo footprinting using dimethylsulfate treatment of intact cells. The same characteristic enhancement/protection pattern was seen in wild-type minichromosomes or mutants defective in oriC function but carrying the four DnaA boxes. Minichromosomes in dnaA (Ts) mutants showed no protein binding at non-permissive temperatures and reduced binding even at permissive temperatures. In vivo footprints of the wild-type strain were identical to those obtained in vitro using purified DnaA proteins and oriC DNA. Transcription into oriC affected the binding of DnaA protein to the DnaA boxes. These findings suggest that the protein causing the in vivo footprints at oriC is DnaA.

Coordinate regulation and sensory transduction in the control of bacterial virulence

Genes and operons that encode bacterial virulence factors are often subject to coordinate regulation. These regulatory systems are capable of responding to various environmental signals that may be encountered during the infectious cycle. For some pathogens, proteins that mediate sensory transduction and virulence control are similar to components of other bacterial information processing systems. Understanding the molecular mechanisms governing global regulation of pathogenicity is essential for understanding bacterial infectious diseases.

Immunological tolerance: new approaches using transgenic mice

Transgenic technology allows the introduction into the germline of an animal of a known gene coding for a normally foreign antigen, and by means of a specific promoter, the direction of its expression to specific tissues. The antigen is therefore synthesized by the animal as an authentic self molecule, at a particular stage in development, and in a particular site. In this review, J.F.A.P. Miller and colleagues discuss this radically new approach to the investigation of the mechanism of acquired immunological tolerance to self components.

Hope-inspiring strategies of the critically ill

Sixty persons who had been critically ill were studied to determine what mechanisms they used to maintain or increase their hope while confronting a life-threatening event. Patients were interviewed 2 to 4 days after discharge from a critical care unit. Responses to the interviews were categorized into nine hope-inspiring themes. The findings provide direction for developing strategies to inspire hope in the critically ill.