Showing papers on "Antigen published in 2003"

An essential role for Scurfin in CD4+CD25+ T regulatory cells.

Abstract: The molecular properties that characterize CD4+CD25+ regulatory T cells (TR cells) remain elusive. Absence of the transcription factor Scurfin (also known as forkhead box P3 and encoded by Foxp3) causes a rapidly fatal lymphoproliferative disease, similar to that seen in mice lacking cytolytic T lymphocyte-associated antigen 4 (CTLA-4). Here we show that Foxp3 is highly expressed by T(R) cells and is associated with T(R) cell activity and phenotype. Scurfin-deficient mice lack T(R) cells, whereas mice that overexpress Foxp3 possess more T(R) cells. In Foxp3-overexpressing mice, both CD4+CD25- and CD4-CD8+ T cells show suppressive activity and CD4+CD25- cells express glucocorticoid-induced tumor-necrosis factor receptor-related (GITR) protein. The forced expression of Foxp3 also delays disease in CTLA-4-/- mice, indicating that the Scurfin and CTLA-4 pathways may intersect and providing further insight into the T(R) cell lineage.

Molecular identification of a danger signal that alerts the immune system to dying cells

Abstract: In infections, microbial components provide signals that alert the immune system to danger and promote the generation of immunity1,2. In the absence of such signals, there is often no immune response or tolerance may develop. This has led to the concept that the immune system responds only to antigens perceived to be associated with a dangerous situation such as infection3,4. Danger signals are thought to act by stimulating dendritic cells to mature so that they can present foreign antigens and stimulate T lymphocytes2,5,6,7. Dying mammalian cells have also been found to release danger signals of unknown identity8,9,10,11. Here we show that uric acid is a principal endogenous danger signal released from injured cells. Uric acid stimulates dendritic cell maturation and, when co-injected with antigen in vivo, significantly enhances the generation of responses from CD8+ T cells. Eliminating uric acid in vivo inhibits the immune response to antigens associated with injured cells, but not to antigens presented by activated dendritic cells. Our findings provide a molecular link between cell injury and immunity and have important implications for vaccines, autoimmunity and inflammation.

Positive and Negative Selection of T Cells

Abstract: A functional immune system requires the selection of T lymphocytes expressing receptors that are major histocompatibility complex restricted but tolerant to self-antigens. This selection occurs predominantly in the thymus, where lymphocyte precursors first assemble a surface receptor. In this review we summarize the current state of the field regarding the natural ligands and molecular factors required for positive and negative selection and discuss a model for how these disparate outcomes can be signaled via the same receptor. We also discuss emerging data on the selection of regulatory T cells. Such cells require a high-affinity interaction with self-antigens, yet differentiate into regulatory cells instead of being eliminated.

Cancer regression and autoimmunity induced by cytotoxic T lymphocyte-associated antigen 4 blockade in patients with metastatic melanoma

Abstract: Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is a critical immunoregulatory molecule (expressed on activated T cells and a subset of regulatory T cells) capable of down-regulating T cell activation. Blockade of CTLA-4 has been shown in animal models to improve the effectiveness of cancer immunotherapy. We thus treated 14 patients with metastatic melanoma by using serial i.v. administration of a fully human anti-CTLA-4 antibody (MDX-010) in conjunction with s.c. vaccination with two modified HLA-A*0201-restricted peptides from the gp100 melanoma-associated antigen, gp100:209-217(210M) and gp100:280-288(288V). This blockade of CTLA-4 induced grade III/IV autoimmune manifestations in six patients (43%), including dermatitis, enterocolitis, hepatitis, and hypophysitis, and mediated objective cancer regression in three patients (21%; two complete and one partial responses). This study establishes CTLA-4 as an important molecule regulating tolerance to "self" antigens in humans and suggests a role for CTLA-4 blockade in breaking tolerance to human cancer antigens for cancer immunotherapy.

Suppression of allogeneic T-cell proliferation by human marrow stromal cells: implications in transplantation.

Abstract: Background Marrow stromal cells (MSC) can differentiate into multiple mesenchymal tissues. To assess the feasibility of human MSC transplantation, we evaluated the in vitro immunogenicity of MSC and their ability to function as alloantigen presenting cells (APC). Methods. Human MSC were derived and used in mixed cell cultures with allogeneic peripheral blood mononuclear cells (PBMC). Expression of immunoregulatory molecules on MSC was analyzed by flow cytometry. An MSC-associated suppressive activity was analyzed using cell-proliferation assays and enzyme-linked immunoassays. Results. MSC failed to elicit a proliferative response when cocultured with allogeneic PBMC, despite provision of a costimulatory signal delivered by an anti-CD28 antibody and pretreatment of MSC with γ-interferon. MSC express major histocompatibility complex (MHC) class I and lymphocyte function-associated antigen (LFA)-3 antigens constitutively and MHC class II and intercellular adhesion molecule (ICAM)-1 antigens upon γ-interferon treatment but do not express CD80, CD86, or CD40 costimulatory molecules. MSC actively suppressed proliferation of responder PBMC stimulated by third-party allogeneic PBMC as well as T cells stimulated by anti-CD3 and anti-CD28 antibodies. Separation of MSC and PBMC by a semipermeable membrane did not abrogate the suppression. The suppressive activity could not be accounted for by MSC production of interleukin-10, transforming growth factor-β1, or prostaglandin E2, nor by tryptophan depletion of the culture medium. Conclusions. Human MSC fail to stimulate allogeneic PBMC or T-cell proliferation in mixed cell cultures. Unlike other nonprofessional APC, this failure of function is not reversed by provision of CD28-mediated costimulation nor γ-interferon pretreatment. Rather, MSC actively inhibit T-cell proliferation, suggesting that allogeneic MSC transplantation might be accomplished without the need for significant host immunosuppression.

Viral Persistence Alters CD8 T-Cell Immunodominance and Tissue Distribution and Results in Distinct Stages of Functional Impairment

Abstract: Chronic viral infections often result in ineffective CD8 T-cell responses due to functional exhaustion or physical deletion of virus-specific T cells. However, how persisting virus impacts various CD8 T-cell effector functions and influences other aspects of CD8 T-cell dynamics, such as immunodominance and tissue distribution, remains largely unknown. Using different strains of lymphocytic choriomeningitis virus (LCMV), we compared responses to the same CD8 T-cell epitopes during acute or chronic infection. Persistent infection led to a disruption of the normal immunodominance hierarchy of CD8 T-cell responses seen following acute infection and dramatically altered the tissue distribution of LCMV-specific CD8 T cells in lymphoid and nonlymphoid tissues. Most importantly, CD8 T-cell functional impairment occurred in a hierarchical fashion in chronically infected mice. Production of interleukin 2 and the ability to lyse target cells in vitro were the first functions compromised, followed by the ability to make tumor necrosis factor alpha, while gamma interferon production was most resistant to functional exhaustion. Antigen appeared to be the driving force for this loss of function, since a strong correlation existed between the viral load and the level of exhaustion. Further, epitopes presented at higher levels in vivo resulted in physical deletion, while those presented at lower levels induced functional exhaustion. A model is proposed in which antigen levels drive the hierarchical loss of different CD8 T-cell effector functions during chronic infection, leading to distinct stages of functional impairment and eventually to physical deletion of virus-specific T cells. These results have implications for the study of human chronic infections, where similar T-cell deletion and functional dysregulation has been observed.

Anatomical basis of tolerance and immunity to intestinal antigens

Abstract: The intestinal immune system has to discriminate between harmful and beneficial antigens. Although strong protective immunity is essential to prevent invasion by pathogens, equivalent responses against dietary proteins or commensal bacteria can lead to chronic disease. These responses are normally prevented by a complex interplay of regulatory mechanisms. This article reviews the unique aspects of the local microenvironment of the intestinal immune system and discuss how these promote the development of regulatory responses that ensure the maintenance of homeostasis in the gut.

T cell anergy

Abstract: T cell anergy is a tolerance mechanism in which the lymphocyte is intrinsically functionally inactivated following an antigen encounter, but remains alive for an extended period of time in a hyporesponsive state. Models of T cell anergy affecting both CD4(+) and CD8(+) cells fall into two broad categories. One, clonal anergy, is principally a growth arrest state, whereas the other, adaptive tolerance or in vivo anergy, represents a more generalized inhibition of proliferation and effector functions. The former arises from incomplete T cell activation, is mostly observed in previously activated T cells, is maintained by a block in the Ras/MAP kinase pathway, can be reversed by IL-2 or anti-OX40 signaling, and usually does not result in the inhibition of effector functions. The latter is most often initiated in naive T cells in vivo by stimulation in an environment deficient in costimulation or high in coinhibition. Adaptive tolerance can be induced in the thymus or in the periphery. The cells proliferate and differentiate to varying degrees and then downregulate both functions in the face of persistent antigen. The state involves an early block in tyrosine kinase activation, which predominantly inhibits calcium mobilization, and an independent mechanism that blocks signaling through the IL-2 receptor. Adaptive tolerance reverses in the absence of antigen. Aspects of both of the anergic states are found in regulatory T cells, possibly preventing them from dominating initial immune responses to foreign antigens and shutting down such responses prematurely.

Defective CD8 T Cell Memory Following Acute Infection Without CD4 T Cell Help

Abstract: The CD8+ cytotoxic T cell response to pathogens is thought to be CD4+ helper T cell independent because infectious agents provide their own inflammatory signals. Mice that lack CD4+ T cells mount a primary CD8 response to Listeria monocytogenes equal to that of wild-type mice and rapidly clear the infection. However, protective memory to a challenge is gradually lost in the former animals. Memory CD8+ T cells from normal mice can respond rapidly, but memory CD8+ T cells that are generated without CD4 help are defective in their ability to respond to secondary encounters with antigen. The results highlight a previously undescribed role for CD4 help in promoting protective CD8 memory development.

Molecular Mechanisms RegulatinG Th1 Immune Responses

Abstract: The T helper lymphocyte is responsible for orchestrating the appropriate immune response to a wide variety of pathogens. The recognition of the polarized T helper cell subsets Th1 and Th2 has led to an understanding of the role of these cells in coordinating a variety of immune responses, both in responses to pathogens and in autoimmune and allergic disease. Here, we discuss the mechanisms that control lineage commitment to the Th1 phenotype. What has recently emerged is a rich understanding of the cytokines, receptors, signal transduction pathways, and transcription factors involved in Th1 differentiation. Although the picture is still incomplete, the basic pathways leading to Th1 differentiation can now be understood in in vitro and a number of infection and disease models.

Biologic activity of cytotoxic T lymphocyte-associated antigen 4 antibody blockade in previously vaccinated metastatic melanoma and ovarian carcinoma patients

Abstract: A large number of cancer-associated gene products evoke immune recognition, but host reactions rarely impede disease progression. The weak immunogenicity of nascent tumors contributes to this failure in host defense. Therapeutic vaccines that enhance dendritic cell presentation of cancer antigens increase specific cellular and humoral responses, thereby effectuating tumor destruction in some cases. The attenuation of T cell activation by cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) further limits the potency of tumor immunity. In murine systems, the administration of antibodies that block CTLA-4 function inhibits the growth of moderately immunogenic tumors and, in combination with cancer vaccines, increases the rejection of poorly immunogenic tumors, albeit with a loss of tolerance to normal differentiation antigens. To gain a preliminary assessment of the biologic activity of antagonizing CTLA-4 function in humans, we infused a CTLA-4 blocking antibody (MDX-CTLA4) into nine previously immunized advanced cancer patients. MDX-CTLA4 stimulated extensive tumor necrosis with lymphocyte and granulocyte infiltrates in three of three metastatic melanoma patients and the reduction or stabilization of CA-125 levels in two of two metastatic ovarian carcinoma patients previously vaccinated with irradiated, autologous granulocyte–macrophage colony-stimulating factor-secreting tumor cells. MDX-CTLA4 did not elicit tumor necrosis in four of four metastatic melanoma patients previously immunized with defined melanosomal antigens. No serious toxicities directly attributable to the antibody were observed, although five of seven melanoma patients developed T cell reactivity to normal melanocytes. These findings suggest that CTLA-4 antibody blockade increases tumor immunity in some previously vaccinated cancer patients.

Pathogenesis of systemic lupus erythematosus

Abstract: The exact patho-aetiology of systemic lupus erythematosus (SLE) remains elusive. An extremely complicated and multifactorial interaction among various genetic and environmental factors is probably involved. Multiple genes contribute to disease susceptibility. The interaction of sex, hormonal milieu, and the hypothalamo–pituitary–adrenal axis modifies this susceptibility and the clinical expression of the disease. Defective immune regulatory mechanisms, such as the clearance of apoptotic cells and immune complexes, are important contributors to the development of SLE. The loss of immune tolerance, increased antigenic load, excess T cell help, defective B cell suppression, and the shifting of T helper 1 (Th1) to Th2 immune responses leads to B cell hyperactivity and the production of pathogenic autoantibodies. Finally, certain environmental factors are probably required to trigger the disease.

IL-10 and TGF-beta cooperate in the regulatory T cell response to mucosal allergens in normal immunity and specific immunotherapy.

Abstract: The regulation of normal and allergic immune responses to airborne allergens in the mucosa is still poorly understood, and the mechanism of specific immunotherapy (SIT) in normalizing the allergic response to such allergens is currently not clear. Accordingly, we have investigated the immunoregulatory mechanism of both normal and allergic responses to the major house-dust mite (HDM) and birch pollen allergens — Dermatophagoides pteroynyssinus (Der p)1 and Bet v 1, respectively — as well as the immunologic basis of SIT to HDM in rhinitis and asthma patients. In normal immunity to HDM and birch pollen, an allergen-specific peripheral T cell suppression to Der p 1 and Bet v 1 was observed. The deviated immune response was characterized by suppressed proliferative T celland Th1 (IFN-γ) and Th2 (IL-5, IL-13) cytokine responses, and increased IL-10 and TGF-β secretion by allergen-specific T cells. Neutralization of cytokine activity showed that T cell suppression was induced by IL-10 and TGF-β during SIT and in normal immunity to the mucosal allergens. In addition, SIT induced an antigen-specific suppressive activity in CD4+ CD25+ T cells of allergic individuals. Together, these results demonstrate a deviation towards a regulatory/suppressor T cell response during SIT and in normal immunity as a key event for the healthy immune response to mucosal antigens.

Cross-priming of CD8 + T cells stimulated by virus-induced type I interferon

Abstract: CD8+ T cell responses can be generated against antigens that are not expressed directly within antigen-presenting cells (APCs), through a process known as cross-priming. To initiate cross-priming, APCs must both capture extracellular antigen and receive specific activation signals. We have investigated the nature of APC activation signals associated with virus infection that stimulate cross-priming. We show that infection with lymphocytic choriomeningitis virus induces cross-priming by a mechanism dependent on type I interferon (IFN-alpha/beta). Activation of cross-priming by IFN-alpha/beta was independent of CD4+ T cell help or interaction of CD40 and CD40 ligand, and involved direct stimulation of dendritic cells. These data identify expression of IFN-alpha/beta as a mechanism for the induction of cross-priming during virus infections.

Prevention of Arthritis by Interleukin 10–producing B Cells

Abstract: In this study we have shown that activation of arthritogenic splenocytes with antigen and agonistic anti-CD40 gives raise to a B cell population that produce high levels of interleukin (IL)-10 and low levels of interferon (IFN)-γ. Transfer of these B cells into DBA/1-TcR-β-Tg mice, immunized with bovine collagen (CII) emulsified in complete Freund's adjuvant inhibited T helper type 1 differentiation, prevented arthritis development, and was also effective in ameliorating established disease. IL-10 is essential for the regulatory function of this subset of B cells, as the B cells population isolated from IL-10 knockout mice failed to mediate this protective function. Furthermore, B cells isolated from arthritogenic splenocytes treated in vitro with anti–IL-10/anti–IL-10R were unable to protect recipient mice from developing arthritis. Our results suggest a new role of a subset of B cells in controlling T cell differentiation and autoimmune disorders.

BTLA is a lymphocyte inhibitory receptor with similarities to CTLA-4 and PD-1.

Abstract: During activation, T cells express receptors for receiving positive and negative costimulatory signals. Here we identify the B and T lymphocyte attenuator (BTLA), an immunoglobulin domain-containing glycoprotein with two immunoreceptor tyrosine-based inhibitory motifs. BTLA is not expressed by naive T cells, but it is induced during activation and remains expressed on T helper type 1 (T(H)1) but not T(H)2 cells. Crosslinking BTLA with antigen receptors induces its tyrosine phosphorylation and association with the Src homology domain 2 (SH2)-containing protein tyrosine phosphatases SHP-1 and SHP-2, and attenuates production of interleukin 2 (IL-2). BTLA-deficient T cells show increased proliferation, and BTLA-deficient mice have increased specific antibody responses and enhanced sensitivity to experimental autoimmune encephalomyelitis. B7x, a peripheral homolog of B7, is a ligand of BTLA. Thus, BTLA is a third inhibitory receptor on T lymphocytes with similarities to cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and programmed death 1 (PD-1).

Aire regulates negative selection of organ-specific T cells

Abstract: Autoimmune polyendocrinopathy syndrome type 1 is a recessive Mendelian disorder resulting from mutations in a novel gene, AIRE, and is characterized by a spectrum of organ-specific autoimmune diseases. It is not known what tolerance mechanisms are defective as a result of AIRE mutation. By tracing the fate of autoreactive CD4+ T cells with high affinity for a pancreatic antigen in transgenic mice with an Aire mutation, we show here that Aire deficiency causes almost complete failure to delete the organ-specific cells in the thymus. These results indicate that autoimmune polyendocrinopathy syndrome 1 is caused by failure of a specialized mechanism for deleting forbidden T cell clones, establishing a central role for this tolerance mechanism.

Human T Cell Receptor γδ Cells Recognize Endogenous Mevalonate Metabolites in Tumor Cells

Abstract: T lymphocytes expressing the T cell receptor (TCR)-γδ recognize unknown antigens on tumor cells. Here we identify metabolites of the mevalonate pathway as the tumor ligands that activate TCR-γδ cells. In tumor cells, blockade of hydroxy-methylglutaryl-CoA reductase (HMGR), the rate limiting enzyme of the mevalonate pathway, prevents both accumulation of mevalonate metabolites and recognition by TCR-γδ cells. When metabolite accumulation is induced by overexpressing HMGR or by treatment with nitrogen-containing bisphosphonate drugs, tumor cells derived from many tissues acquire the capacity to stimulate the same TCR-γδ population. Accumulation of mevalonate metabolites in tumor cells is a powerful danger signal that activates the immune response and may represent a novel target of tumor immunotherapy.

CD46 is a cellular receptor for group B adenoviruses

Abstract: Group B adenoviruses, a subgenus of human Adenoviridae, are associated with a variety of often-fatal illnesses in immunocompromised individuals, including bone marrow transplant recipients and cancer and AIDS patients. Recently, group B adenovirus derivatives have gained interest as attractive gene therapy vectors because they can transduce target tissues, such as hematopoietic stem cells, dendritic cells and malignant tumor cells, that are refractory to infection by commonly used adenoviral vectors. Whereas many adenoviruses infect cells through the coxsackievirus and adenovirus receptor (CAR), group B adenoviruses use an alternate, as-yet-unidentified cellular attachment receptor. Using mass spectrometric analysis of proteins interacting with a group B fiber, we identified human CD46 as a cellular attachment receptor for most group B adenoviruses. We show that ectopic expression of human CD46 rendered nonhuman cells susceptible to infection with group B viruses in vitro and in vivo. In addition, both siRNA-mediated knockdown of CD46 and a soluble form of CD46 blocked infection of human cell lines and primary human cells. The discovery that group B adenoviruses use CD46, a ubiquitously expressed complement regulatory protein, as a cellular attachment receptor elucidates the diverse clinical manifestation of group B virus infections, and bears directly on the application of these vectors for gene therapy.

Phagosomes are competent organelles for antigen cross-presentation

Abstract: The ability to process microbial antigens and present them at the surface of cells is an important aspect of our innate ability to clear infections. It is generally accepted that antigens in the cytoplasm are loaded in the endoplasmic reticulum and presented at the cell surface on major histocompatibility complex (MHC) class I molecules, whereas peptides present in endo/phagocytic compartments are presented on MHC class II molecules. Despite the apparent segregation of the class I and class II pathways, antigens from intracellular pathogens including mycobacteria, Escherichia coli, Salmonella typhimurium, Brucella abortus and Leishmania, have been shown to elicit an MHC class-I-dependent CD8+ T-cell response, a process referred to as cross-presentation. The cellular mechanisms allowing the cross-presentation pathway are poorly understood. Here we show that phagosomes display the elements and properties needed to be self-sufficient for the cross-presentation of exogenous antigens, a newly ascribed function linked to phagocytosis mediated by the endoplasmic reticulum.

ICP34.5 deleted herpes simplex virus with enhanced oncolytic, immune stimulating, and anti-tumour properties.

Abstract: Herpes simplex virus type-1 (HSV1) in which the neurovirulence factor ICP34.5 is inactivated has been shown to direct tumour-specific cell lysis in several tumour models. Such viruses have also been shown to be safe in Phase I clinical trials by intra-tumoral injection in glioma and melanoma patients. Previous work has used serially passaged laboratory isolates of HSV1 which we hypothesized may be attenuated in their lytic capability in human tumour cells as compared to more recent clinical isolates. To produce ICP34.5 deleted HSV with enhanced oncolytic potential, we tested two clinical isolates. Both showed improved cell killing in all human tumour cell lines tested compared to a laboratory strain (strain 17+). ICP34.5 was then deleted from one of the clinical isolate strains (strain JS1). Enhanced tumour cell killing with ICP34.5 deleted HSV has also been reported by the deletion of ICP47 by the up-regulation of US11 which occurs following this mutation. Thus to further improve oncolytic properties, ICP47 was removed from JS1/ICP34.5-. As ICP47 also functions to block antigen processing in HSV infected cells, this mutation was also anticipated to improve the immune stimulating properties of the virus. Finally, to provide viruses with maximum oncolytic and immune stimulating properties, the gene for human or mouse GM-CSF was inserted into the JS1/34.5-/47- vector backbone. GM-CSF is a potent immune stimulator promoting the differentiation of progenitor cells into dendritic cells and has shown promise in clinical trials when delivered by a number of means. Combination of GM-CSF with oncolytic therapy may be particularly effective as the necrotic cell death accompanying virus replication should serve to effectively release tumour antigens to then induce a GM-CSF-enhanced immune response. This would, in effect, provide an in situ, patient-specific, anti-tumour vaccine. The viruses constructed were tested in vitro in human tumour cell lines and in vivo in mice demonstrating significant anti-tumour effects. These were greatly improved compared to viruses not containing each of the modifications described. In vivo, both injected and non-injected tumours showed significant shrinkage or clearance and mice were protected against re-challenge with tumour cells. The data presented indicate that JS1/ICP34.5-/ICP47-/GM-CSF acts as a powerful oncolytic agent which may be appropriate for the treatment of a number of solid tumour types in man.

Delayed Drug Hypersensitivity Reactions

Abstract: Immune reactions to small molecular compounds, such as drugs, can cause a variety of diseases involving the skin, liver, kidney, and lungs. In many drug hypersensitivity reactions, drug-specific CD4+ and CD8+ T cells recognize drugs through their alphabeta T-cell receptors in an MHC-dependent way. Drugs stimulate T cells if they act as haptens and bind covalently to peptides or if they have structural features that allow them to interact with certain T-cell receptors directly. Immunohistochemical and functional studies of drug-reactive T cells in patients with distinct forms of exanthema reveal that distinct T-cell functions lead to different clinical phenotypes. In maculopapular exanthema, perforin-positive and granzyme B-positive CD4+ T cells kill activated keratinocytes, while a large number of cytotoxic CD8+ T cells in the epidermis is associated with formation of vesicles and bullae. Drug-specific T cells also orchestrate inflammatory skin reactions through the release of various cytokines (for example, interleukin-5, interferon) and chemokines (such as interleukin-8). Activation of T cells with a particular function seems to lead to a specific clinical picture (for example, bullous or pustular exanthema). Taken together, these data allow delayed hypersensitivity reactions (type IV) to be further subclassified into T-cell reactions, which through the release of certain cytokines and chemokines preferentially activate and recruit monocytes (type IVa), eosinophils (type IVb), or neutrophils (type IVd). Moreover, cytotoxic functions by either CD4+ or CD8+ T cells (type IVc) seem to participate in all type IV reactions.

Activation of lysosomal function during dendritic cell maturation.

Abstract: In response to a variety of stimuli, dendritic cells (DCs) transform from immature cells specialized for antigen capture into mature cells specialized for T cell stimulation. During maturation, the DCs acquire an enhanced capacity to form and accumulate peptide-MHC (major histocompatibility complex) class II complexes. Here we show that a key mechanism responsible for this alteration was the generalized activation of lysosomal function. In immature DCs, internalized antigens were slowly degraded and inefficiently used for peptide loading. Maturation induced activation of the vacuolar proton pump that enhanced lysosomal acidification and antigen proteolysis, facilitating efficient formation of peptide-MHC class II complexes. Lysosomal function in DCs thus appears to be specialized for the developmentally regulated processing of internalized antigens.

Mechanism of CD1d-restricted natural killer T cell activation during microbial infection

Abstract: CD1d-restricted natural killer T (NKT) cells are important for host defense against a variety of microbial pathogens. How and when these T cells become activated physiologically during infection remains unknown. Our data support a model in which NKT cells use a unique activation mechanism not requiring their recognition of microbial antigens. Instead, weak responses to CD1d-presented self antigens were amplified by interleukin 12 made by dendritic cells in response to microbial products, resulting in potent interferon-gamma secretion. NKT cells were among the first lymphocytes to respond during Salmonella typhimurium infection, and their activation in vivo also depended on interleukin 12 and CD1d recognition. We propose this mechanism of activation as a major pathway responsible for the rapid activation of NKT cells in different microbial infections.

C-Reactive Protein Increases Plasminogen Activator Inhibitor-1 Expression and Activity in Human Aortic Endothelial Cells Implications for the Metabolic Syndrome and Atherothrombosis

Abstract: Background— Inflammation plays a pivotal role in atherosclerosis. In addition to being a risk marker for cardiovascular disease, much recent data suggest that C-reactive protein (CRP) promotes atherogenesis via effects on monocytes and endothelial cells. The metabolic syndrome is associated with significantly elevated levels of CRP. Plasminogen activator inhibitor-1 (PAI-1), a marker of atherothrombosis, is also elevated in the metabolic syndrome and in diabetes, and endothelial cells are the major source of PAI-1. However, there are no studies examining the effect of CRP on PAI-1 in human aortic endothelial cells (HAECs). Methods and Results— Incubation of HAECs with CRP results in a time- and dose-dependent increase in secreted PAI-1 antigen, PAI-1 activity, intracellular PAI-1 protein, and PAI-1 mRNA. CRP stabilizes PAI-1 mRNA. Inhibitors of endothelial NO synthase, blocking antibodies to interleukin-6 and an endothelin-1 receptor blocker, fail to attenuate the effect of CRP on PAI-1. CRP additionally ...

Generation of Tumor-Infiltrating Lymphocyte Cultures for Use in Adoptive Transfer Therapy for Melanoma Patients

Abstract: The generation of T lymphocytes with specific reactivity against tumor antigens is a prerequisite for effective adoptive transfer therapies. Melanoma-specific lymphocyte cultures can be established from tumor infiltrating lymphocytes (TILs) by in vitro culture in high levels of IL-2. We have optimized methods for generating melanoma-reactive TIL cultures from small resected tumor specimens. We report a retrospective analysis of 860 attempted TIL cultures from 90 sequential melanoma biopsy specimens from 62 HLA-A2+ patients. Multiple independent TIL derived from a single tumor often exhibited substantial functional and phenotypic variation. Tumor specific activity was detected in TIL from 29 (81%) of 36 patients screened. TIL cultures selected for high activity were generally capable of large numerical expansion using a single round of a rapid expansion protocol. Limited clonal T-cell populations in an oligoclonal TIL culture could confer specific tumor recognition in these highly selected, highly expanded TIL cultures. These methods were efficient at generating TILs suitable for adoptive transfer therapy.

Hepatic T cells and liver tolerance

Abstract: The T-cell biology of the liver is unlike that of any other organ. The local lymphocyte population is enriched in natural killer (NK) and NKT cells, which might have crucial roles in the recruitment of circulating T cells. A large macrophage population and the efficient trafficking of dendritic cells from sinusoidal blood to lymph promote antigen trapping and T-cell priming, but the local presentation of antigen causes T-cell inactivation, tolerance and apoptosis. These local mechanisms might result from the need to maintain immunological silence to harmless antigenic material in food. The overall bias of intrahepatic T-cell responses towards tolerance might account for the survival of liver allografts and for the persistence of some liver pathogens.