Historical carbon footprinting and implications for sustainability planning: a case study of the Pittsburgh region

This study estimates fossil-based CO(2) emissions and energy use from 1900-2000 for Allegheny County, PA. Total energy use and emissions increased from 1900 to 1970, reflecting the significant industrial, economic, and population growth that occurred in Allegheny County. From 1970 to 2000, Allegheny County experienced a 30% decrease in total emissions and energy use from peak values, primarily because of a decline in industrial activity (40% decrease in value added) and the loss of a quarter of its population. Despite these dramatic economic and demographic transitions, per capita emissions remained stable from 1970 to 2000, buoyed by relatively stable or slightly increasing emissions in the commercial and transportation sectors. Allegheny County's history suggests the scale of change needed to achieve local emissions reductions may be significant; given years of major technological, economic, and demographic changes, per capita emissions in 1940 were nearly the same in 2000. Most local governments are planning emissions reductions rates that exceed 1% per year, which deviate significantly from historical trends. Our results suggest additional resources and improved planning paradigms are likely necessary to achieve significant emissions reductions, especially for areas where emissions are still increasing.

Identifying quantitative trait loci for resistance to Sclerotinia head rot in two USDA sunflower germplasms

Sclerotinia head rot is a major disease of sunflower in the world, and quantitative trait loci (QTL) mapping could facilitate understanding of the genetic basis of head rot resistance and breeding in sunflower. One hundred twenty-three F2:3 and F2:4 families from a cross between HA 441 and RHA 439 were studied. The mapping population was evaluated for disease resistance in three field experiments in a randomized complete block design with two replicates. Disease incidence (DI) and disease severity (DS) were assessed. A genetic map with 180 target region amplification polymorphism, 32 simple sequence repeats, 11 insertion-deletion, and 2 morphological markers was constructed. Nine DI and seven DS QTL were identified with each QTL explaining 8.4 to 34.5% of phenotypic variance, suggesting the polygenic basis of the resistance to head rot. Five of these QTL were identified in more than one experiment, and each QTL explained more than 12.9% of phenotypic variance. These QTL could be useful in sunflower breeding. Although a positive correlation existed between the two disease indices, most of the respective QTL were located in different chromosomal regions, suggesting a different genetic basis for the two indices.

Species- and strain-specific control of a complex, flexible regulon by Bordetella BvgAS

The Bordetella master virulence regulatory system, BvgAS, controls a spectrum of gene expression states, including the virulent Bvg(+) phase, the avirulent Bvg(-) phase, and at least one Bvg-intermediate (Bvg(i)) phase. We set out to define the species- and strain-specific features of this regulon based on global gene expression profiling. Rather than functioning as a switch, Bvg controls a remarkable continuum of gene expression states, with hundreds of genes maximally expressed in intermediate phases between the Bvg(+) and Bvg(-) poles. Comparative analysis of Bvg regulation in B. pertussis and B. bronchiseptica revealed a relatively conserved Bvg(+) phase transcriptional program and identified previously uncharacterized candidate virulence factors. In contrast, control of Bvg(-)- and Bvg(i)-phase genes diverged substantially between species; regulation of metabolic, transporter, and motility loci indicated an increased capacity in B. bronchiseptica, compared to B. pertussis, for ex vivo adaptation. Strain comparisons also demonstrated variation in gene expression patterns within species. Among the genes with the greatest variability in patterns of expression, predicted promoter sequences were nearly identical. Our data suggest that the complement of transcriptional regulators is largely responsible for transcriptional diversity. In support of this hypothesis, many putative transcriptional regulators that were Bvg regulated in B. bronchiseptica were deleted, inactivated, or unregulated by BvgAS in B. pertussis. We propose the concept of a "flexible regulon." This flexible regulon may prove to be important for pathogen evolution and the diversification of host range specificity.

Listeria monocytogenes as a vaccine vector: virulence attenuation or existing antivector immunity does not diminish therapeutic efficacy

The bacterium L. monocytogenes is a proposed vaccine carrier based upon the observation that this pathogen replicates within the intracytoplasmic environment facilitating delivery of Ag to the endogenous Ag processing and presentation pathway with subsequent stimulation of peptide specific MHC class I-restricted CD8(+) effector cells. In this report, we evaluate virulence-attenuated strains of Listeria monocytogenes as vaccine vectors and examine whether existing antivector (antilisterial) immunity limits or alters its efficacy as a therapeutic cancer vaccine. Following immunization with virulence-attenuated mutants, we found that the effectiveness of L. monocytogenes as a recombinant cancer vaccine remains intact. In addition, we found that antibiotic treatment initiated 24 or 36 h following therapeutic immunization with recombinant L. monocytogenes allows full development of the antitumor response. We also demonstrate that the vaccine vector potential of L. monocytogenes is not limited in animals with existing antilisterial immunity. For these latter studies, mice previously immunized with wild-type L. monocytogenes were infused with melanoma cells and then 5 days later challenged with recombinant tumor Ag expressing L. monocytogenes. Collectively, these results add additional support for the use of L. monocytogenes as a vaccine vector and underscore its potential to be used repeatedly for stimulation of recall responses concomitant with primary cell-mediated responses to newly delivered heterologous tumor-associated epitopes.

Construction of mini-Tn5cyaA' and its utilization for the identification of genes encoding surface-exposed and secreted proteins in Bordetella bronchiseptica

A mini-Tn5 transposon derivative, mini-Tn5cyaA', has been constructed. It contains a promoter-less and ribosome binding site-deficient reporter gene, encoding the catalytic domain of Bordetella pertussis adenylate cyclase toxin (CyaA'). We used this system to mutagenize B. bronchiseptica and we developed a screen for identification of mutants containing cyaA' translational fusions. This system was used to identify B. bronchiseptica genes that encode surface-exposed and secreted proteins.

Mechanisms of Bordetella pathogenesis

Bordetella are Gram negative bacteria that cause respiratory tract infections in humans and animals. While at least five different species of Bordetella are known to exist, this review focuses on B. pertussis, B. bronchiseptica and B. parapertussis subspecies. In their virulent phase, all of these bacteria produce a nearly identical set of virulence factors which include adhesins such as filamentous hemagglutinin (FHA), fimbriae and pertactin, as well as toxins such as a bifunctional adenylate cyclase/hemolysin, dermonecrotic toxin, tracheal cytotoxin, a B. pertussis specific pertussis toxin and B. bronchiseptica specific type III secreted proteins. Expression of nearly all of these virulence factors is positively regulated by the products of the bvgAS locus. BvgA and BvgS comprise a two-component signal transduction system that mediates transition between at least three identifiable phases---a virulent (Bvg+) phase, an avirulent (Bvg-) phase and an intermediate (Bvg(i)) phase---in response to specific environmental signals. Bordetella colonize the ciliated respiratory mucosa, a surface designed to eliminate foreign particles, thereby making the adherence and persistence mechanisms of these bacteria crucial. The development of relevant animal models for B. bronchiseptica has enabled us to study Bordetella pathogenesis in the context of natural host-pathogen interactions. In addition, evolutionary studies across the various Bordetella species and detailed analysis of differential regulation of Bvg-activated/repressed genes has greatly enhanced our understanding of the mechanisms of Bordetella pathogenesis.

Immune self-tolerance mechanisms

Tolerance of both T and B cells to self-antigens can be achieved through a great variety of different routes, at the level of the primary lymphoid organs (thymus and bone marrow) and throughout the secondary lymphoid tissues. Whether self-reactive lymphocytes ignore their target autoantigen, or are tolerized by the various mechanisms discussed, depends on the circumstances.

Diversity in the Bordetella virulence regulon: transcriptional control of a Bvg-intermediate phase gene

The BvgAS signal transduction system controls the expression of at least three distinct phenotypic phases that lie along a continuum of gene expression states. The Bvg+ phase is characterized by the expression of adhesins and toxins, whereas the Bvg- phase is characterized by motility in Bordetella bronchiseptica and the expression of vrg loci in Bordetella pertussis. The Bvg-intermediate (Bvgi) phase is characterized by the absence of Bvg-repressed phenotypes, the expression of some, but not all, Bvg-activated virulence factors and the presence of a recently discovered set of antigens and phenotypes that are unique to this phase. We report here the transcriptional regulation of bipA, the first-identified Bvgi phase gene. We have mapped the bipA promoter and identified numerous BvgA binding sites in the transcriptional control region. Based on these data, we present a model in which phase-dependent expression of bipA results from the spatial distribution and relative affinities of multiple BvgA binding sites relative to the start site of transcription.

Kidney protection against autoreactive CD8(+) T cells distinct from immunoprivilege and sequestration

BACKGROUND

The kidney tubulointerstitium has been reported to be protected from T-cell--mediated damage by sequestration from the T-cell compartment. We examined the ability of autoreactive T cells to infiltrate the kidney in a transgenic mouse model.

METHODS

RIP-mOVA transgenic mice express the model autoantigen, membrane-bound ovalbumin (mOVA), in kidney proximal tubular cells and pancreatic beta cells. OVA-specific CD8(+) T cells (OT-I cells) were transferred into these recipient mice and their immune response against pancreas and kidney tissue was compared.

RESULTS

When OVA-specific CD8(+) T cells (OT-I cells) were injected into RIP-mOVA mice, they were activated in the renal and pancreatic lymph nodes by cross-presentation. These in vivo-activated OT-I cells caused the destruction of pancreatic islets leading to autoimmune diabetes, but did not infiltrate the kidney. Neither CD95--CD95 ligand interactions, which have been proposed to induce apoptosis in T cells infiltrating immunologically privileged sites, nor CD30 signaling was responsible for the lack of kidney infiltration. When OT-I cells were activated in vitro prior to injection, they could infiltrate the kidney and caused acute renal failure when injected in high numbers.

CONCLUSIONS

A mechanism distinct from previously described organ-specific protective mechanisms such as sequestration of antigen or CD95-mediated immunoprivilege contributes to the protection of the kidney tubulointerstitium from infiltration by autoreactive CD8(+) T cell.

Ligand density determines the efficiency of negative selection in the thymus

To study the influence of antigen density on the efficiency of negative selection in the thymus, MHC class I (H-2K(b), K(b)) transgenic mice were generated, which expressed a K(b) transgene under the control of its natural promoter at 33% (K(b-lo)) or 150% (K(b-hi)) the surface density of Kb in C57BL/6 (B6, H-2(b)) mice. These mice were crossed to anti-K(b) T-cell receptor (Des-TCR) transgenic mice. In Des-TCRxK(b-hi) double transgenic mice, Des-TCR bearing T cells were completely eliminated during thymocyte maturation. In contrast, in Des-TCRxK(b-lo) double transgenic mice, two populations of Des-TCR T cells were evident, which either expressed the Des-TCR at intermediate density in the absence of CD8 (Des-TCR(int)CD8(-)) or expressed both the Des-TCR and CD8 at low density (Des-TCRloCD8lo). In the thymus of both types of double transgenic mice, no Des-TCR(+)CD4(+)CD8(+) thymocytes were detected, suggesting that deletion of Des-TCR cells occurred before the CD4(+)CD8(+) stage. Because only very few Des-TCR(+) thymocytes were found in Des-TCRxK(b-hi) transgenic mice, deletion of these T cells apparently occurred upon expression of the Des-TCR. By contrast, Des-TCRxK(b-lo) transgenic mice showed distinct populations of Des-TCR(int)CD4-8- and Des-TCR(lo)CD8(lo) thymocytes, suggesting that expression of the CD8 coreceptor was required to allow negative selection to proceed. Functional analyses showed that sublethally irradiated Des-TCRxK(b-lo) double transgenic mice were protected from lethal graft-versus-host disease by injected Des-TCR lymph node cells.

Mice lacking the orphan G protein-coupled receptor G2A develop a late-onset autoimmune syndrome

Mice with a targeted disruption of the gene encoding a lymphoid-expressed orphan G protein-coupled receptor, G2A, demonstrate a normal pattern of T and B lineage differentiation through young adulthood. As G2A-deficient animals age, they develop secondary lymphoid organ enlargement associated with abnormal expansion of both T and B lymphocytes. Older G2A-deficient mice (>1 year) develop a slowly progressive wasting syndrome, characterized by lymphocytic infiltration into various tissues, glomerular immune complex deposition, and anti-nuclear autoantibodies. G2A-deficient T cells are hyperresponsive to TCR stimulation, exhibiting enhanced proliferation and a lower threshold for activation. Our findings demonstrate that G2A plays a critical role in controlling peripheral lymphocyte homeostasis and that its ablation results in the development of a novel, late-onset autoimmune syndrome.

Effect of localized cytokine dysregulation: accelerated rejection of IL-2-expressing skin grafts

Transgenic mice were created in which a sheep keratin promoter directed the expression of IL-2 into the dermis. These KIL-2 transgenic mice were used to investigate the effects of localized IL-2 dysregulation on immune responses. Peripheral tolerance to skin antigens was not broken by in situ IL-2 expression because syngeneic KIL-2 skin grafts were not rejected. However, MHC Class I-disparate skin grafts from KIL-2 donors were rejected faster (median survival time (MST) 12 days) than grafts of non-transgenic littermate skin (MST 18 days). In contrast, the kinetics of KIL-2 H-Y-disparate skin graft rejection (MST 14 days) did not differ significantly from controls (MST 16 days), suggesting that upregulation of IL-2 at the effector site could affect CD4+ T cell- independent, but not CD4+ T cell-dependent, responses. No effect on rejection kinetics was observed when wild type allogeneic skin was grafted onto transgenic mice that expressed bcl2 constitutively in their lymphocytes (MST of 14 days, both sets), indicating that this was not simply due to increased longevity of T cells within the IL-2 expressing graft. We therefore suggest that aberrant expression of IL-2 can accelerate helper-independent CD8+ T cell responses by increasing proliferation and/or differentiation of cytolytic T cells at the effector site.

Betahistine effects on cochlear blood flow: from the laboratory to the clinic

The development of laser Doppler flowmetry techniques has contributed greatly to the study of cochlear blood flow (CBF). In animal models, intravenous betahistine dihydrochloride clearly increased CBF in a dose-dependent manner. This effect was greater in the cochlear vasculature than in the systemic vascular bed. The effects of betahistine were blocked by the alpha 2-antagonist idazoxan, thus suggesting an interaction between histaminergic and presynaptic adrenergic receptors. This was further supported by studies investigating the effects of electrical stimulation on CBF. Local (round window membrane) application of betahistine did not affect CBF, but had a non-specific effect on cochlear electrophysiology. This indicates that the receptors for betahistine vascular effects in the inner ear are most likely located in the modiolar artery. More recently, laser Doppler flowmetry techniques have been applied to human subjects. It has been shown that intratympanic application of adrenaline affects CBF and that this blood flow is under vigorous sympathetic control. Electrical stimulation has also been used to obtain measures of dynamic responsiveness in human subjects. This results in an increase in CBF, which is dependent on the intensity of the stimulation. Preliminary evidence indicates that this procedure can provide a standardized measure of the dynamic properties of CBF and may provide a means to differentially identify patients with compromised vasculature.

Spinal interneurons that receive input from muscle afferents are differentially modulated by dorsolateral descending systems

The possibility that descending systems have differential actions on the spinal interneurons that receive input from muscle afferents was investigated. Prolonged, physiological inputs were generated by stretch of the triceps surae muscles. The resulting firing patterns of 25 lumbosacral interneurons were recorded before and during a reversible cold block of the dorsolateral white matter at the thoracic level in nonparalyzed, decerebrate preparations. The strength of group I muscle afferent input was assessed from the response to sinusoidal tendon vibration, which activated muscle spindle Ia afferents directly and tendon organ Ib afferents via the resulting reflex force. The stretch-evoked responses of interneurons with strong responses to vibration were markedly suppressed by dorsal cold block, whereas the stretch-evoked responses of interneurons with weak vibration input were enhanced. The cells most strongly activated by vibration received their primary input from Ia afferents and all of these cells were inhibited by the cold block. These results suggest that a disruption of the descending system, such as occurs in spinal cord injury, will lead to a suppression of the interneuronal pathways with group Ia input while enhancing excitability within interneuronal pathways transmitting actions from higher threshold afferents. One possible consequence of this suppression would be a decreased activity among the Ia inhibitory interneurons that mediate reciprocal inhibition, resulting in abnormal reciprocal relations between antagonists and promoting anomalous muscle cocontraction.

Identification and characterization of BipA, a Bordetella Bvg-intermediate phase protein

The Bordetella BvgAS sensory transduction system has traditionally been viewed as controlling a transition between two distinct phenotypic phases: the Bvg(+) or virulent phase and the Bvg(-) or avirulent phase. Recently, we identified a phenotypic phase of Bordetella bronchiseptica that displays reduced virulence in a rat model of respiratory infection concomitant with increased ability to survive nutrient deprivation. Characterization of this phase, designated Bvg-intermediate (Bvg(i)), indicated the presence of antigens that are maximally, if not exclusively, expressed in this phase and therefore suggested the existence of a previously unidentified class of Bvg-regulated genes. We now report the identification and characterization of a Bvg(i) phase protein, BipA (Bvg-intermediate phase protein A), and its structural gene, bipA. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis indicates that bipA is expressed maximally under Bvgi phase conditions and thus represents the first identified Bvgi phase gene. bipA encodes a 1578-amino-acid protein that shares amino acid sequence similarity at its N-terminus with the proposed outer membrane localization domains of intimin (Int) of enteropathogenic and enterohaemorrhagic Escherichia coli and invasin (Inv) of Yersinia spp. Although not apparent at the amino acid level, BipA is also similar to Int and Inv in that the proposed membrane-spanning domain is followed by several 90-amino-acid repeats and a distinct C-terminal domain. Localization studies using an antibody directed against the C-terminus of BipA indicated that its C-terminus is exposed on the bacterial cell surface. Western blot analysis with this same antibody indicated that BipA homologues are expressed in Bvg(i) phase Bordetella pertussis and Bordetella parapertussis. Comparison of a Delta bipA strain with wild-type B. bronchiseptica indicated that BipA is not required for Bvg(i) phase-specific aggregative adherence to rat lung epithelial cells in vitro or for persistent colonization of the rabbit respiratory tract in vivo. However, our data are consistent with the hypothesis that BipA, and the Bvg(i) phase in general, play an important role in the Bordetella infectious cycle, perhaps by contributing to aerosol transmission.

Multiple roles for Bordetella lipopolysaccharide molecules during respiratory tract infection

Bordetella pertussis, Bordetella parapertussis, and Bordetella bronchiseptica are closely related subspecies that cause respiratory tract infections in humans and other mammals and express many similar virulence factors. Their lipopolysaccharide (LPS) molecules differ, containing either a complex trisaccharide (B. pertussis), a trisaccharide plus an O-antigen-like repeat (B. bronchiseptica), or an altered trisaccharide plus an O-antigen-like repeat (B. parapertussis). Deletion of the wlb locus results in the loss of membrane-distal polysaccharide domains in the three subspecies of bordetellae, leaving LPS molecules consisting of lipid A and core oligosaccharide. We have used wlb deletion (Deltawlb) mutants to investigate the roles of distal LPS structures in respiratory tract infection by bordetellae. Each mutant was defective compared to its parent strain in colonization of the respiratory tracts of BALB/c mice, but the location in the respiratory tract and the time point at which defects were observed differed significantly. Although the Deltawlb mutants were much more sensitive to complement-mediated killing in vitro, they displayed similar defects in respiratory tract colonization in C5(-/-) mice compared with wild-type (wt) mice, indicating that increased sensitivity to complement-mediated lysis is not sufficient to explain the in vivo defects. B. pertussis and B. parapertussis Deltawlb mutants were also defective compared to wt strains in colonization of SCID-beige mice, indicating that the defects were not limited to interactions with adaptive immunity. Interestingly, the B. bronchiseptica Deltawlb strain was defective, compared to the wt strain, in colonization of the respiratory tracts of BALB/c mice beginning 1 week postinoculation but did not differ from the wt strain in its ability to colonize the respiratory tracts of B-cell- and T-cell-deficient mice, suggesting that wlb-dependent LPS modifications in B. bronchiseptica modulate interactions with adaptive immunity. These data show that biosynthesis of a full-length LPS molecule by these three bordetellae is essential for the expression of full virulence for mice. In addition, the data indicate that the different distal structures modifying the LPS molecules on these three closely related subspecies serve different purposes in respiratory tract infection, highlighting the diversity of functions attributable to LPS of gram-negative bacteria.

Characterization of the ovalbumin-specific TCR transgenic line OT-I: MHC elements for positive and negative selection

The present report provides the first extensive characterization of the OT-I TCR transgenic line, which produces MHC class I-restricted, ovalbumin-specific, CD8+ T cells (OT-I cells). These cells are shown to be positively selected in vivo in H-2b C57BL/6 mice and in bm5 mice, which express the Kbm5 mutant molecule. In contrast, OT-I cells were not selected by mutant Kb molecules in bm1, bm3, bm8, bm10, bm11 or bm23 mice. Interestingly, however, when positive selection was examined in vitro in foetal thymic organ culture (FTOC), bm1 and bm8 were still poorly selective, but the bm3 haplotype now selected as efficiently as B6. The ability to select in vitro correlated with the capacity to present the ovalbumin (OVA) peptide to OT-I cells, as measured by induction of an OVA-specific proliferative response. These results suggest that a lower affinity TCR:MHC interaction may be necessary for positive selection in FTOC compared with selection in situ.

Role of Bordetella bronchiseptica fimbriae in tracheal colonization and development of a humoral immune response

Fimbriae are filamentous, cell surface structures which have been proposed to mediate attachment of Bordetella species to respiratory epithelium. Bordetella bronchiseptica has four known fimbrial genes: fim2, fim3, fimX, and fimA. While these genes are unlinked on the chromosome, their protein products are assembled and secreted by a single apparatus encoded by the fimBCD locus. The fimBCD locus is embedded within the fha operon, whose genes encode another putative adhesin, filamentous hemagglutinin (FHA). We have constructed a Fim(-) B. bronchiseptica strain, RB63, by introducing an in-frame deletion extending from fimB through fimD. Western blot analysis showed that RB63 is unable to synthesize fimbriae but is unaffected for FHA expression. Using this mutant, we assessed the role of fimbriae in pathogenesis in vitro and in vivo in natural animal hosts. Although RB63 was not significantly defective in its ability to adhere to various tissue culture cell lines, including human laryngeal HEp-2 cells, it was considerably altered in its ability to cause respiratory tract infections in rats. The number of DeltafimBCD bacteria recovered from the rat trachea at 10 days postinoculation was significantly decreased compared to that of wild-type B. bronchiseptica and was below the limit of detection at 30 and 60 days postinoculation. The number of bacteria recovered from the nasal cavity and larynx was not significantly different between RB63 and the wild-type strain at any time point. The ability of fimbriae to mediate initial attachment to tracheal tissue was tested in an intratracheal inoculation assay. Significantly fewer RB63 than wild-type bacteria were recovered from the tracheas at 24 h after intratracheal inoculation. These results demonstrate that fimbriae are involved in enhancing the ability of B. bronchiseptica to establish tracheal colonization and are essential for persistent colonization at this site. Interestingly, anti-Bordetella serum immunoglobulin M (IgM) levels were significantly lower in animals infected with RB63 than in animals infected with wild-type B. bronchiseptica at 10 days postinoculation. Even at 30 days postinoculation, RB63-infected animals had lower serum anti-Bordetella antibody titers in general. This disparity in antibody profiles suggests that fimbriae are also important for the induction of a humoral immune response.

Modulation of host immune responses, induction of apoptosis and inhibition of NF-kappaB activation by the Bordetella type III secretion system

Bordetella bronchiseptica establishes respiratory tract infections in laboratory animals with high efficiency. Colonization persists for the life of the animal and infection is usually asymptomatic in immunocompetent hosts. We hypothesize that this reflects a balance between immunostimulatory events associated with infection and immunomodulatory events mediated by the bacteria. We have identified 15 loci that are part of a type III secretion apparatus in B. bronchiseptica and three secreted proteins. The functions of the type III secretion system were investigated by comparing the phenotypes of wild-type bacteria with two strains that are defective in type III secretion using in vivo and in vitro infection models. Type III secretion mutants were defective in long-term colonization of the trachea in immunocompetent mice. The mutants also elicited higher titres of anti-Bordetella antibodies upon infection compared with wild-type bacteria. Type III secretion mutants also showed increased lethal virulence in immunodeficient SCID-beige mice. These observations suggest that type III-secreted products of B. bronchiseptica interact with components of both innate and adaptive immune systems of the host. B. bronchiseptica induced apoptosis in macrophages in vitro and inflammatory cells in vivo and type III secretion was required for this process. Infection of an epithelial cell line with high numbers of wild type, but not type III deficient B. bronchiseptica resulted in rapid aggregation of NF-kappaB into large complexes in the cytoplasm. NF-kappaB aggregation was dependent on type III secretion and aggregated NF-kappaB did not respond to TNFalpha activation, suggesting B. bronchiseptica may modulate host immunity by inactivating NF-kappaB. Based on these in vivo and in vitro results, we hypothesize that the Bordetella type III secretion system functions to modulate host immune responses during infection.

Manipulating the host to study bacterial virulence

The ability to manipulate animal hosts as well as bacterial pathogens greatly expands the utility of in vivo models of infection. For example, the construction of mice that harbor human tissues or express specific transgenes can provide ligand-receptor interactions that are essential for pathogenesis. Interactions between virulence factors and specific host defenses can sometimes be resolved by challenging selectively immuno deficient mice with bacteria containing virulence gene mutations. Transgenic animals expressing inducible reporters can be used to conveniently identify cells in which specific response pathways have been activated during infection. These and other approaches promise to improve the quality of information obtainable from in vivo assessments of pathogenesis.

Information characteristics and the structure of landscapes

Various techniques for statistical analysis of the structure of fitness landscapes have been proposed. An important feature of these techniques is that they study the ruggedness of landscapes by measuring their correlation characteristics. This paper proposes a new information analysis of fitness landscapes. The underlying idea is to consider a fitness landscape as an ensemble of objects that are related to the fitness of neighboring points. Three information characteristics of the ensemble are defined and studied. They are termed: information content, partial information content, and information stability. The information characteristics of a range of landscapes with known correlation features are analyzed in an attempt to reveal the advantages of the information analysis. We show that the proposed analysis is an appropriate tool for investigating the structure of fitness landscapes.

Pregenomic comparative analysis between bordetella bronchiseptica RB50 and Bordetella pertussis tohama I in murine models of respiratory tract infection

We describe here a side-by-side comparison of murine respiratory infection by Bordetella pertussis and Bordetella bronchiseptica strains whose genomes are currently being sequenced (Tohama I and RB50, respectively). B. pertussis and B. bronchiseptica are most appropriately classified as subspecies. Their high degree of genotypic and phenotypic relatedness facilitates comparative studies of pathogenesis. RB50 and Tohama I differ in their abilities to grow in the nose, trachea, and lungs of BALB/c mice and to induce apoptosis, lung pathology, and an antibody response. To focus on the interactions between the bacteria and particular aspects of the host immune response, we used mice with specific immune defects. Mice lacking B cells and T cells were highly susceptible to B. bronchiseptica and were killed by intranasal inoculation with doses as low as 500 CFU. These mice were not killed by B. pertussis, even when doses as high as 10(5) CFU were delivered to the lungs. B. bronchiseptica, which was highly resistant to naive serum in vitro, caused bacteremia in these immunodeficient mice, while B. pertussis, which was highly sensitive to naive serum, did not cause bacteremia. B. bronchiseptica was, however, killed by immune serum in vitro, and adoptive transfer of anti-Bordetella antibodies protected SCID-beige mice from B. bronchiseptica lethal infection. Neutropenic mice were similarly killed by B. bronchiseptica but not B. pertussis infection, suggesting neutrophils are critical to the early inflammatory response to the former but not the latter. B. bronchiseptica was dramatically more active than B. pertussis in mediating the lysis of J774 cells in vitro and in inducing apoptosis of inflammatory cells in mouse lungs. This side-by-side comparison describes phenotypic differences that may be correlated with genetic differences in the comparative analysis of the genomes of these two highly related organisms.

CD8 T cell ignorance or tolerance to islet antigens depends on antigen dose

There are two major mechanisms reported to prevent the autoreactivity of islet-specific CD8(+) T cells: ignorance and tolerance. When ignorance is operative, naïve autoreactive CD8(+) T cells ignore islet antigens and recirculate without causing damage, unless activated by an external stimulus. In the case of tolerance, CD8(+) T cells are deleted. Which factor(s) contributes to each particular outcome was previously unknown. Here, we demonstrate that the concentration of self antigen determines which mechanism operates. When ovalbumin (OVA) was expressed at a relatively low concentration in the pancreatic islets of transgenic mice, there was no detectable cross-presentation, and the CD8(+) T cell compartment remained ignorant of OVA. In mice expressing higher doses of OVA, cross-presentation was detectable and led to peripheral deletion of OVA-specific CD8(+) T cells. When cross-presentation was prevented by reconstituting the bone marrow compartment with cells incapable of presenting OVA, deletional tolerance was converted to ignorance. Thus, the immune system uses two strategies to avoid CD8(+) T cell-mediated autoimmunity: for high dose antigens, it deletes autoreactive T cells, whereas for lower dose antigens, it relies on ignorance.

A central role for thymic emigrants in peripheral T cell homeostasis

After initial seeding by thymic emigrants, homeostatic regulation of the T cell pool has been thought to occur entirely within the periphery. Here we report that the degree of thymic emigration directly affects the number and the CD4/CD8 ratio of peripheral T cells. We demonstrate that the increase in T cell pool size caused by the engraftment of 2, 6, or 9 thymic lobes correlates almost exactly with the number of emigrants exported from those grafts in the previous 3 weeks, regardless of how long the graft has been in place. The extent of the increase supports the concept of a 3-week period after thymic export in which emigrant T cells are exempt from peripheral T cell homeostasis. This apparent exclusion of recent thymic emigrants from the niche-based regulation of peripheral T cell numbers ensures repertoire turnover throughout adult life and provides the basis of a direct and previously unrecognized role for the thymus in the regulation of peripheral T cell homeostasis.

A comparison of T cell memory against the same antigen induced by virus versus intracellular bacteria

Cytotoxic T cell (CTL) memory was analyzed after infection with lymphocytic choriomeningitis virus (LCMV) and recombinant Listeria monocytogenes (rLM) expressing the complete nucleoprotein of LCMV (rLM-NP(actA)) or only the immunodominant epitope of H-2(d) mice (rLM-NP(118-126)). Immunization with LCMV and rLM induced a long-lived increased CTL precursor (CTLp) frequency specific for the viral (NP(118-126)) and for the bacterial (LLO(91-99)) epitope, respectively. However, after infection with rLM memory, CTLs were less protective against an intravenous LCMV challenge infection than a comparable number of LCMV-induced memory T cells. LCMV, but not recombinant Listeria-induced memory T cells were able to protect against lethal choriomeningitis by LCMV or a subsequent peripheral infection with recombinant vaccinia virus expressing LCMV-NP. The protective memory after viral and after rLM immunization was paralleled by evidence of LCMV but not rLM antigen persistence on day 15 and 30 after vaccination. These results document a striking difference in protective T cell memory between viral and bacterial vaccines and indicate that rapid T cell-dependent immune protection correlates with antigen persistence.

Discovering the origins of immunological competence

Work done in the late 1950s and in the 1960s revealed the role of the thymus in virus-induced leukemia in mice. Thymectomizing mice at birth to test whether the virus first multiplied in thymus tissue and then spread elsewhere ultimately led to the conclusion that the thymus was essential to the normal development of the immune system. Subsequent testing to try to understand how the thymus contributes to the pool of immunocompetent lymphocytes opened a new chapter in immunology and required a reappraisal of many immunological phenomena and an understanding of the molecular interactions that take place during cell-to-cell interactions.

CD30 prevents T-cell responses to non-lymphoid tissues

Self antigens can induce T-cell tolerance via a mechanism termed cross-tolerance. This involves the transfer of peripheral tissue antigens to professional APC for presentation in the draining lymph nodes. In this site, CD8+ T cells are activated, proliferate, and are slowly deleted by a CD95-dependent mechanism. Prior to their deletion, some activated cells leave the lymph nodes and encounter antigens on peripheral parenchymal tissues. Without functional CD30, these cells proliferate extensively and cause substantial tissue damage. Thus, CD30 limits autoreactivity, acting as a 'brake' on T-cell proliferation after recognition of autoantigens on parenchymal tissues.

Signalling through CD30 protects against autoimmune diabetes mediated by CD8 T cells

Autoantigens found on pancreatic islets can move to draining lymph nodes, where they are able to cause the activation and consequent deletion of autoreactive T cells by a mechanism termed cross-tolerance. This deletion depends on signalling through CD95 (also known as Fas), a member of the superfamily of tumour-necrosis-factor receptors. Here we describe a new mechanism that protects against autoimmunity: this mechanism involves another member of this superfamily, CD30, whose function was largely unknown. CD30-deficient islet-specific CD8-positive T cells are roughly 6,000-fold more autoaggressive than wild-type cells, with the transfer of as few as 160 CD30-deficient T cells leading to the complete destruction of pancreatic islets and the rapid onset of diabetes. We show that, in the absence of CD30 signalling, cells activated but not yet deleted by the CD95-dependent cross-tolerance mechanism gain the ability to proliferate extensively upon secondary encounter with antigen on parenchymal tissues, such as the pancreatic islets. Thus, CD30 signalling limits the proliferative potential of autoreactive CD8 effector T cells and protects the body against autoimmunity.

Probing the function of Bordetella bronchiseptica adenylate cyclase toxin by manipulating host immunity

We have examined the role of adenylate cyclase-hemolysin (CyaA) by constructing an in-frame deletion in the Bordetella bronchiseptica cyaA structural gene and comparing wild-type and cyaA deletion strains in natural host infection models. Both the wild-type strain RB50 and its adenylate cyclase toxin deletion (DeltacyaA) derivative efficiently establish persistent infections in rabbits, rats, and mice following low-dose inoculation. In contrast, an inoculation protocol that seeds the lower respiratory tract revealed significant differences in bacterial numbers and in polymorphonuclear neutrophil recruitment in the lungs from days 5 to 12 postinoculation. We next explored the effects of disarming specific aspects of the immune system on the relative phenotypes of wild-type and DeltacyaA bacteria. SCID, SCID-beige, or RAG-1(-/-) mice succumbed to lethal systemic infection following high- or low-dose intranasal inoculation with the wild-type strain but not the DeltacyaA mutant. Mice rendered neutropenic by treatment with cyclophosphamide or by knockout mutation in the granulocyte colony-stimulating factor locus were highly susceptible to lethal infection by either wild-type or DeltacyaA strains. These results reveal the significant role played by neutrophils early in B. bronchiseptica infection and by acquired immunity at later time points and suggest that phagocytic cells are a primary in vivo target of the Bordetella adenylate cyclase toxin.

Existing antilisterial immunity does not inhibit the development of a Listeria monocytogenes-specific primary cytotoxic T-lymphocyte response

Infection of BALB/c mice with Listeria monocytogenes stimulates an antilisterial immune response evident by the appearance of H2-Kd-restricted CD8(+) cytotoxic T lymphocytes (CTLs) specific for the nanomer peptides amino acids (aa) 91 to 99 of listeriolysin O (LLO 91-99) and aa 217 to 225 of the p60 molecule (p60 217-225). We have introduced point mutations at anchor residues within LLO 91-99 (92F) or p60 217-225 (218F), and BALB/c mice infected with L. monocytogenes strains containing these point mutations do not develop CTLs specific for LLO 91-99 or p60 217-225, respectively. We have used these strains to test whether primary CTL responses against L. monocytogenes-derived determinants can be stimulated within an environment of existing antilisterial immunity. We found that the development of a primary L. monocytogenes-specific CTL response is not altered by existing immunity to L. monocytogenes. For example, primary immunization with the p60 218F strain of L. monocytogenes followed by a secondary immunization with wild-type L. monocytogenes results in stimulation of p60 217-225-specific CTLs at primary response levels and LLO 91-99-specific effectors at levels consistent with a memory CTL response. Similarly, primary immunization with the 92F strain of L. monocytogenes followed by a secondary immunization with wild-type L. monocytogenes results in stimulation of LLO 91-99-specific CTLs at primary response levels and p60 217-225-specific effectors at levels consistent with a memory CTL response. These results provide additional support for the use of L. monocytogenes as a recombinant vaccine vector and show that antivector immunity does not inhibit the development of a primary CTL response when the epitope is delivered by L. monocytogenes as the vaccine strain.

Antibody-directed enzyme prodrug therapy with the T268G mutant of human carboxypeptidase A1: in vitro and in vivo studies with prodrugs of methotrexate and the thymidylate synthase inhibitors GW1031 and GW1843

Antibody-directed enzyme prodrug therapy (ADEPT) is a technique to increase antitumor selectivity in cancer chemotherapy. Our approach to this technology has been to design a mutant of human carboxypeptidase A (hCPA1-T268G) which is capable of hydrolyzing in vivo stable prodrugs of MTX and targeting this enzyme to tumors on an Ep-CAM1-specific antibody, ING1. Through the use of this >99% human enzyme which is capable of catalyzing a completely nonhuman reaction, we hope to increase ADEPT selectivity while decreasing overall immunogenicity of the enzyme-antibody conjugate. In the current report, prodrugs of the thymidylate synthase inhibitors GW1031 and GW1843 and the dihydrofolate reductase inhibitor methotrexate were studied for their wild-type and mutant hCPA enzyme hydrolysis, their in vivo stability, and their use in therapy. Prodrugs with high kcat/Km ratios for mutated versus wild-type hCPA1 were examined in vitro for their stability in human pancreatic juice, and in vivo for their stability in mouse plasma and tissues. In addition, targeting and in vivo enzyme activity studies were performed with an ING1 antibody conjugate of the mutant enzyme (ING1-hCPA1-T268G). Finally, in vivo therapy studies were performed with LS174T tumors to demonstrate proof of principle. Results indicate that prodrugs can be synthesized that are selective and efficient substrates of hCPA1-T268G and not substrates of the endogenous CPA activities; this leads to excellent in vivo stability for these compounds. In vivo conjugate targeting studies showed that the antibody-enzyme conjugate was targeted to the tumor and enzyme was initially active in vivo at the site. Unfortunately therapeutic studies did not demonstrate tumor reduction. Experiments to determine reasons for the lack of antitumor activity showed that the enzyme activity decreased as a result of enzyme instability. The results offer encouragement for additional novel mutant enzyme improvements and additional in vivo studies on this unique approach to ADEPT.

B cells directly tolerize CD8(+) T cells

This report investigates the response of CD8(+) T cells to antigens presented by B cells. When C57BL/6 mice were injected with syngeneic B cells coated with the Kb-restricted ovalbumin (OVA) determinant OVA257-264, OVA-specific cytotoxic T lymphocyte (CTL) tolerance was observed. To investigate the mechanism of tolerance induction, in vitro-activated CD8(+) T cells from the Kb-restricted, OVA-specific T cell receptor transgenic line OT-I (OT-I cells) were cultured for 15 h with antigen-bearing B cells, and their survival was determined. Antigen recognition led to the killing of the B cells and, surprisingly, to the death of a large proportion of the OT-I CTLs. T cell death involved Fas (CD95), since OT-I cells deficient in CD95 molecules showed preferential survival after recognition of antigen on B cells. To investigate the tolerance mechanism in vivo, naive OT-I T cells were adoptively transferred into normal mice, and these mice were coinjected with antigen-bearing B cells. In this case, OT-I cells proliferated transiently and were then lost from the secondary lymphoid compartment. These data provide the first demonstration that B cells can directly tolerize CD8(+) T cells, and suggest that this occurs via CD95-mediated, activation-induced deletion.

N-(2-Benzoylphenyl)-L-tyrosine PPARgamma agonists. 1. Discovery of a novel series of potent antihyperglycemic and antihyperlipidemic agents

We have identified a novel series of antidiabetic N-(2-benzoylphenyl)-L-tyrosine derivatives which are potent, selective PPARgamma agonists. Through the use of in vitro PPARgamma binding and functional assays (2S)-3-(4-(benzyloxy)phenyl)-2-((1-methyl-3-oxo-3-phenylpropenyl)+ ++amin o)propionic acid (2) was identified as a structurally novel PPARgamma agonist. Structure-activity relationships identified the 2-aminobenzophenone moiety as a suitable isostere for the chemically labile enaminone moiety in compound 2, affording 2-((2-benzoylphenyl)amino)-3-(4-(benzyloxy)phenyl)propionic acid (9). Replacement of the benzyl group in 9 with substituents known to confer in vivo potency in the thiazolidinedione (TZD) class of antidiabetic agents provided a dramatic increase in the in vitro functional potency and affinity at PPARgamma, affording a series of potent and selective PPARgamma agonists exemplified by (2S)-((2-benzoylphenyl)amino)-3-¿4-[2-(methylpyridin-2-ylamino+ ++)ethoxy ]phenyl¿propionic acid (18), 3-¿4-[2-(benzoxazol-2-ylmethylamino)ethoxy]phenyl¿-(2S)-((2- benzoylph enyl)amino)propanoic acid (19), and (2S)-((2-benzoylphenyl)amino)-3-¿4-[2-(5-methyl-2-phenyloxazol-4-y l)e thoxy]phenyl¿propanoic acid (20). Compounds 18 and 20 show potent antihyperglycemic and antihyperlipidemic activity when given orally in two rodent models of type 2 diabetes. In addition, these analogues are readily prepared in chiral nonracemic fashion from L-tyrosine and do not show a propensity to undergo racemization in vitro. The increased potency of these PPARgamma agonists relative to troglitazone may translate into superior clinical efficacy for the treatment of type 2 diabetes.

Filamentous hemagglutinin of Bordetella bronchiseptica is required for efficient establishment of tracheal colonization

Adherence to ciliated respiratory epithelial cells is considered a critical early step in Bordetella pathogenesis. For Bordetella pertussis, the etiologic agent of whooping cough, several factors have been shown to mediate adherence to cells and cell lines in vitro. These putative adhesins include filamentous hemagglutinin (FHA), fimbriae, pertactin, and pertussis toxin. Determining the precise roles of each of these factors in vivo, however, has been difficult, due in part to the lack of natural-host animal models for use with B. pertussis. Using the closely related species Bordetella bronchiseptica, and by constructing both deletion mutation and ectopic expression mutants, we have shown that FHA is both necessary and sufficient for mediating adherence to a rat lung epithelial (L2) cell line. Using a rat model of respiratory infection, we have shown that FHA is absolutely required, but not sufficient, for tracheal colonization in healthy, unanesthetized animals. FHA was not required for initial tracheal colonization in anesthetized animals, however, suggesting that its role in establishment may be dedicated to overcoming the clearance action of the mucociliary escalator.

Cross-presentation of self antigens to CD8+ T cells: the balance between tolerance and autoimmunity

Upon encounter with foreign antigen, tissue-associated antigen-presenting cells (APCs) migrate to draining lymph nodes to prime specific T cells. Using the transgenic RIP-mOVA model, we recently demonstrated that self antigens derived from peripheral tissues are constitutively transported to draining lymph nodes, and can be presented in association with MHC class I molecules by a bone marrow-derived APC population. This form of class I-restricted presentation of exogenous antigen has been referred to as cross-presentation and can induce activation and proliferation of antigen-specific CD8+ T cells. In the absence of CD4+ T cell help, activation of CD8+ T cells is inefficient, and cross-presentation leads to peripheral deletion of autoreactive CD8+ T cells, acting as a mechanism to maintain self-tolerance. If CD4+ T cell help is available, CD8+ T cell responses to self antigens can be rendered immunogenic, leading to autoreactive responses. Whether autoimmunity results from such responses also depends on the tissue location of the antigen. In RIP-mOVA mice, which express the model antigen mOVA (a membrane-bound form of ovalbumin) in the pancreatic beta cells and kidney proximal tubules, OVA-specific CD8+ T cells, activated by cross-presentation, infiltrated the pancreas and caused B cell destruction. Interestingly, however, these cells did not infiltrate the kidney, suggesting that proximal tubular cells are to some extent protected from immune destruction. Analysis of the role of antigen concentration indicates that high doses were required for efficient cross-presentation, suggesting that this pathway is directed towards immune responses to high-dose antigens, such as may be present during viral infection.

Induction of peripheral CD8+ T-cell tolerance by cross-presentation of self antigens

There is now convincing evidence that CD8+ T cells can be activated by professional antigen-presenting cells which present antigens derived from non-lymphoid tissues in association with MHC class I molecules in the draining lymph nodes. This mechanism, referred to as cross-presentation, enables the immune system to respond to those microorganisms that infect only non-lymphoid tissues. Consistent with this view, cross-presentation was found to focus on antigens expressed in high concentrations and those released from dying cells, which can be expected to result from viral infections. Recent evidence, however, demonstrates that high dose self antigens can be cross-presented constitutively, resulting in the activation of autoreactive CD8+ T cells. This does not lead to auto immunity under physiologic conditions, but to CD95-mediated deletion of the T cells. Cross-presentation can thus engage a well-defined pathway of antigen-induced T-cell death and purge the immune system of autoreactive CD8+ T cells. Low dose self antigens are not cross-presented and are consequently ignored. The immune system therefore uses two strategies to avoid CD8+ T-cell-mediated autoimmunity in the periphery: deletion of autoreactive CD8+ T cells responding to high dose self antigens and ignorance of self antigens expressed at low concentrations.

Human but not ovine isolates of Bordetella parapertussis are highly clonal as determined by PCR-based RAPD fingerprinting

The DNA fingerprints of 170 human isolates and ten ovine isolates of Bordetella parapertussis were examined by arbitrarily-primed PCR/RAPD with 29 primers. Based on this technique, all the human isolates appear highly genetically homogeneous. The ovine isolates could be distinguished from human isolates and they showed diversity among themselves. Therefore, human isolates of B. parapertussis are a highly clonal group adapted to infect humans and they are distinct from polymorphic ovine isolates.

Fas (CD95)-dependent cell-mediated immunity to Listeria monocytogenes

Two distinct and complementary pathways, one mediated by perforin and the other dependent upon CD95 (Fas), effect cell-mediated cytotoxicity. We examined the relative roles of these pathways in host defenses against the intracellular bacterial pathogen Listeria monocytogenes by using murine listeriosis as a model system. Mice which lacked both perforin and Fas (P0L0) were generated, and their responses to primary and secondary listeriosis were compared to those of wild-type (WT), Fas-deficient (L0), and perforin knockout (P0) mice. Relative to WT mice during primary listeriosis, P0 mice exhibited a reduced capacity to clear the infection from their spleens but not their livers whereas L0 mice had elevated bacterial titers in their livers and a modestly increased titer in their spleens. In contrast, bacterial titers in P0L0 mice were increased approximately 50- to 560-fold in their spleens and 230- to 1, 000-fold in their livers; eventual clearance of listeriae from both organs was significantly delayed. Furthermore, the resistance of P0L0 mice to secondary listeriosis was significantly reduced in their spleens and livers compared to that of WT, P0, or L0 mice. In vitro experiments indicated that immune cytotoxic T lymphocytes (CTL) lysed L. monocytogenes-infected hepatocytes primarily via a Fas-dependent, perforin-independent mechanism. The absence of Fas severely abrogated the lysis of infected hepatocytes by immune CD8(+) CTL. Taken together, these results provide the first evidence for Fas-dependent CTL-mediated lysis of L. monocytogenes-infected hepatocytes and demonstrate complementary roles for Fas and perforin in host defenses against an intracellular bacterial pathogen.

Major histocompatibility complex class I-restricted cross-presentation is biased towards high dose antigens and those released during cellular destruction

Naive T cells recirculate mainly within the secondary lymphoid compartment, but once activated they can enter peripheral tissues and perform effector functions. To activate naive T cells, foreign antigens must traffic from the site of infection to the draining lymph nodes, where they can be presented by professional antigen presenting cells. For major histocompatibility complex class I-restricted presentation to CD8+ T cells, this can occur via the cross-presentation pathway. Here, we investigated the conditions allowing antigen access to this pathway. We show that the level of antigen expressed by peripheral tissues must be relatively high to facilitate cross-presentation to naive CD8+ T cells. Below this level, peripheral antigens did not stimulate by cross-presentation and were ignored by naive CD8+ T cells, although they could sensitize tissue cells for destruction by activated cytotoxic T lymphocytes (CTLs). Interestingly, CTL-mediated tissue destruction facilitated cross-presentation of low dose antigens for activation of naive CD8+ T cells. This represents the first in vivo evidence that cellular destruction can enhance access of exogenous antigens to the cross-presentation pathway. These data indicate that the cross-presentation pathway focuses on high dose antigens and those released during tissue destruction.

The peripheral deletion of autoreactive CD8+ T cells induced by cross-presentation of self-antigens involves signaling through CD95 (Fas, Apo-1)

Recently, we demonstrated that major histocompatibility complex class I-restricted cross-presentation of exogenous self-antigens can induce peripheral T cell tolerance by deletion of autoreactive CD8+ T cells. In these studies, naive ovalbumin (OVA)-specific CD8+ T cells from the transgenic line OT-I were injected into transgenic mice expressing membrane-bound OVA (mOVA) under the control of the rat insulin promoter (RIP) in pancreatic islets, kidney proximal tubules, and the thymus. Cross-presentation of tissue-derived OVA in the renal and pancreatic lymph nodes resulted in activation, proliferation, and then the deletion of OT-I cells. In this report, we investigated the molecular mechanisms underlying this form of T cell deletion. OT-I mice were crossed to tumor necrosis factor receptor 2 (TNFR2) knockout mice and to CD95 (Fas, Apo-1) deficient mutant lpr mice. Wild-type and TNFR2-deficient OT-I cells were activated and then deleted when transferred into RIP-mOVA mice, whereas CD95-deficient OT-I cells were not susceptible to deletion by cross-presentation. Furthermore, cross-presentation led to upregulation of the CD95 molecule on the surface of wild-type OT-I cells in vivo, consistent with the idea that this is linked to rendering autoreactive T cells susceptible to CD95-mediated signaling. This study represents the first evidence that CD95 is involved in the deletion of autoreactive CD8+ T cells in the whole animal.