Ena/VASP Protein-Mediated Actin Polymerization Contributes to Naïve CD8+ T Cell Activation and Expansion by Promoting T Cell-APC Interactions In Vivo

Naïve T cell activation in secondary lymphoid organs such as lymph nodes (LNs) occurs upon recognition of cognate antigen presented by antigen presenting cells (APCs). T cell activation requires cytoskeleton rearrangement and sustained interactions with APCs. Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) proteins are a family of cytoskeletal effector proteins responsible for actin polymerization and are frequently found at the leading edge of motile cells. Ena/VASP proteins have been implicated in motility and adhesion in various cell types, but their role in primary T cell interstitial motility and activation has not been explored. Our goal was to determine the contribution of Ena/VASP proteins to T cell–APC interactions, T cell activation, and T cell expansion in vivo. Our results showed that naïve T cells from Ena/VASP-deficient mice have a significant reduction in antigen-specific T cell accumulation following Listeria monocytogenes infection. The kinetics of T cell expansion impairment were further confirmed in Ena/VASP-deficient T cells stimulated via dendritic cell immunization. To investigate the cause of this T cell expansion defect, we analyzed T cell–APC interactions in vivo by two-photon microscopy and observed fewer Ena/VASP-deficient naïve T cells interacting with APCs in LNs during priming. We also determined that Ena/VASP-deficient T cells formed conjugates with significantly less actin polymerization at the T cell–APC synapse, and that these conjugates were less stable than their WT counterparts. Finally, we found that Ena/VASP-deficient T cells have less LFA-1 polarized to the T cell–APC synapse. Thus, we conclude that Ena/VASP proteins contribute to T cell actin remodeling during T cell–APC interactions, which promotes the initiation of stable T cell conjugates during APC scanning. Therefore, Ena/VASP proteins are required for efficient activation and expansion of T cells in vivo.

Ena/VASP protein-mediated actin polymerization contributes to naive CD8+ T cell activation and expansion by promoting T cell-APC interactions in vivo

Naive T cell activation in secondary lymphoid organs such as lymph nodes (LNs) occurs upon recognition of cognate antigens presented by antigen presenting cells (APCs). T cell activation requires cytoskeleton rearrangement and sustained interactions with APCs. Ena/VASP proteins are a family of cytoskeletal effector proteins responsible for actin polymerization and are frequently found at the leading edge of motile cells. Ena/VASP proteins have been implicated in motility and adhesion in various cell types, but their role in primary T cell activation has not been explored. Our goal was to determine the contribution of Ena/VASP proteins to T cell activation and expansion in vivo. Our results showed that naïve T cells from Ena/VASP-deficient mice have a significant reduction in antigen-specific T cell accumulation following Listeria monocytogenes infection. The kinetics of antigen-specific T cell impairment were further confirmed in Ena/VASP-deficient T cells stimulated via dendritic cell immunization. To investigate the cause of this T cell expansion defect, we analyzed T cell-APC interactions in vivo by 2-photon microscopy and observed fewer Ena/VASP-deficient naïve T cells interacting with APCs in LNs during priming. We also found that Ena/VASP-deficient T cells formed conjugates with significantly less actin polymerization at the T cell-APC synapse, and that these conjugates were less stable than their WT counterparts. Thus, we conclude that Ena/VASP proteins contribute to T cell actin remodeling downstream of T-APC interactions required for the initiation of stable T cell conjugates during APC scanning and for efficient activation and expansion of T cells in vivo.

Supported by NIH (R01AI125553; T32AI007405)

Scanning Models of Food Systems Resilience in the Indo-Pacific Region

The Indo-Pacific is a region of the world experiencing rapid growth in population and development. However, it is also exposed to a number of social, economic, geopolitical, and biophysical stressors, which may undermine the region's ability to support its population, ensure food security, and sustain livelihoods. In response to the complex suite of stressors, a number of development initiatives and research programs have been established to build resilience in the region's food systems. These initiatives vary in scope and scale, but also in what they mean by the term resilience and the components of the food system they address. This variation has implications for the outcomes of these efforts and how well they match a theoretical ideal of resilience. This review examines how resilience and food systems are defined, conceptualized, and applied within research studies and projects or initiatives on food systems resilience funded or supported by national, regional, or multilateral government, and non-governmental institutions in the Indo-Pacific region. It also compares how the concepts are treated from an academic or theoretical perspective vs. in practical applications. We take a two-pronged approach: first, identifying organizations engaged in the Indo-Pacific region and developing an inventory of initiatives and projects that have bearing on food systems resilience; and second, carrying out literature searches to record research studies in the region that examine resilience within food systems. We then identify any formalized frameworks or definitions of resilience and/or food systems guiding these projects and studies. The results indicate there is a heavy focus on climate change and natural disasters, and to a lesser extent health-related shocks, in food systems resilience research and practice. Definitions, however, are inconsistently reported, and are often more simplistic than resilience theory depicts, favoring resilience conceptualizations around adaptation and a production-oriented food systems framing. While the specific definitions vary between research and applied projects, the fragmented and ambiguous use of terms presents a challenge for policy applications and coordination. Overall, establishing some clear guiding resilience principles, modified according to contextual factors, could enable more streamlined resilience work in Indo-Pacific food systems.

Autoimmunity in motion: Mechanisms of immune regulation and destruction revealed by in vivo imaging

Autoimmunity arises when mechanisms of immune tolerance fail. Here we discuss mechanisms of T cell activation and tolerance and the dynamics of the autoimmune response at the site of disease. Live imaging of autoimmunity provides the ability to analyze immune cell dynamics at the single-cell level within the complex intact environment where disease occurs. These analyses have revealed mechanisms of T cell activation and tolerance in the lymph nodes, mechanisms of T cell entry into sites of autoimmune disease, and mechanisms leading to pathogenesis or protection in the autoimmune lesions. The overarching conclusions point to stable versus transient T cell antigen presenting cell interactions dictating the balance between T cell activation and tolerance, and T cell restimulation as a driver of pathogenesis at the site of autoimmunity. Findings from models of multiple sclerosis and type 1 diabetes are highlighted, however, the results have implications for basic mechanisms of T cell regulation during immune responses, tumor immunity, and autoimmunity.

Islet Lymphocytes Maintain a Stable Regulatory Phenotype Under Homeostatic Conditions and Metabolic Stress

T cells and B cells have been identified in human and murine islets, but the phenotype and role of islet lymphocytes is unknown. Resident immune populations set the stage for responses to inflammation in the islets during homeostasis and diabetes. Thus, we sought to identify the phenotype and effector function of islet lymphocytes to better understand their role in normal islets and in islets under metabolic stress. Lymphocytes were located in the islet parenchyma, and were comprised of a mix of naïve, activated, and memory T cell and B cell subsets, with an enrichment for regulatory B cell subsets. Use of a Nur77 reporter indicated that CD8 T cells and B cells both received local antigen stimulus, indicating that they responded to antigens present in the islets. Analysis of effector function showed that islet T cells and B cells produced the regulatory cytokine IL-10. The regulatory phenotype of islet T cells and B cells and their response to local antigenic stimuli remained stable under conditions of metabolic stress in the diet induced obesity (DIO) model. T cells present in human islets retained a similar activated and memory phenotype in non-diabetic and T2D donors. Under steady-state conditions, islet T cells and B cells have a regulatory phenotype, and thus may play a protective role in maintaining tissue homeostasis.

Conceptualizing ecosystem services using social-ecological networks

Social-ecological networks (SENs) represent the complex relationships between ecological and social systems and are a useful tool for analyzing and managing ecosystem services. However, mainstreaming the application of SENs in ecosystem service research has been hindered by a lack of clarity about how to match research questions to ecosystem service conceptualizations in SEN (i.e., as nodes, links, attributes, or emergent properties). Building from different disciplines, we propose a typology to represent ecosystem service in SENs and identify opportunities and challenges of using SENs in ecosystem service research. Our typology provides guidance for this growing field to improve research design and increase the breadth of questions that can be addressed with SEN to understand human-nature interdependencies in a changing world.

MERTK on mononuclear phagocytes regulates T cell antigen recognition at autoimmune and tumor sites

Understanding mechanisms of immune regulation is key to developing immunotherapies for autoimmunity and cancer. We examined the role of mononuclear phagocytes during peripheral T cell regulation in type 1 diabetes and melanoma. MERTK expression and activity in mononuclear phagocytes in the pancreatic islets promoted islet T cell regulation, resulting in reduced sensitivity of T cell scanning for cognate antigen in prediabetic islets. MERTK-dependent regulation led to reduced T cell activation and effector function at the disease site in islets and prevented rapid progression of type 1 diabetes. In human islets, MERTK-expressing cells were increased in remaining insulin-containing islets of type 1 diabetic patients, suggesting that MERTK protects islets from autoimmune destruction. MERTK also regulated T cell arrest in melanoma tumors. These data indicate that MERTK signaling in mononuclear phagocytes drives T cell regulation at inflammatory disease sites in peripheral tissues through a mechanism that reduces the sensitivity of scanning for antigen leading to reduced responsiveness to antigen.

Resident mesenchymal vascular progenitors modulate adaptive angiogenesis and pulmonary remodeling via regulation of canonical Wnt signaling

Adaptive angiogenesis is necessary for tissue repair, however, it may also be associated with the exacerbation of injury and development of chronic disease. In these studies, we demonstrate that lung mesenchymal vascular progenitor cells (MVPC) modulate adaptive angiogenesis via lineage trace, depletion of MVPC, and modulation of β-catenin expression. Single cell sequencing confirmed MVPC as multipotential vascular progenitors, thus, genetic depletion resulted in alveolar simplification with reduced adaptive angiogenesis. Following vascular endothelial injury, Wnt activation in MVPC was sufficient to elicit an emphysema-like phenotype characterized by increased MLI, fibrosis, and MVPC driven adaptive angiogenesis. Lastly, activation of Wnt/β-catenin signaling skewed the profile of human and murine MVPC toward an adaptive phenotype. These data suggest that lung MVPC drive angiogenesis in response to injury and regulate the microvascular niche as well as subsequent distal lung tissue architecture via Wnt signaling.

Formin-like 1 mediates effector T cell trafficking to inflammatory sites to enable T cell-mediated autoimmunity

Lymphocyte migration is essential for the function of the adaptive immune system, and regulation of T cell entry into tissues is an effective therapy in autoimmune diseases. Little is known about the specific role of cytoskeletal effectors that mediate mechanical forces and morphological changes essential for migration in complex environments. We developed a new Formin-like-1 (FMNL1) knock-out mouse model and determined that the cytoskeletal effector FMNL1 is selectively required for effector T cell trafficking to inflamed tissues, without affecting naïve T cell entry into secondary lymphoid organs. Here, we identify a FMNL1-dependent mechanism of actin polymerization at the back of the cell that enables migration of the rigid lymphocyte nucleus through restrictive barriers. Furthermore, FMNL1-deficiency impairs the ability of self-reactive effector T cells to induce autoimmune disease. Overall, our data suggest that FMNL1 may be a potential therapeutic target to specifically modulate T cell trafficking to inflammatory sites.

Lymphocytes in autoimmune-resistant mice may protect the islets through IL-10 production

We have identified T cells and B cells in the islets of autoimmune resistant mice, yet the role of these lymphocytes is unknown. In the islets of autoimmune resistant C57BL/6 mice, local antigen receptor signaling was assessed using Nur77-GFP mice. Nur77-GFP expression was increased in islet CD8+ T cells and B cells suggesting that these lymphocyte subsets receive local antigenic stimulus. Islet T cell and B cell populations expressed the regulatory cytokine IL-10, assessed using the B6.TIGER reporter mouse. T cell populations lacked expression of the pro-inflammatory cytokine IFN-γ. These findings indicate that islet T cell populations are likely playing a regulatory role. In addition, cultured whole islets produced IL-10 protein, but not IFN-γ protein. To test the stability of the islet lymphocyte populations under inflammatory conditions, mice were exposed to metabolic stress through a diet-induced obesity (DIO) model. Obesity and type 2 diabetes (T2D) are associated with circulating inflammatory cytokines. In T2D patients, islet lymphocytes have been identified, though the function of these populations is largely unknown. C57BL/6 mice were fed a high fat diet (DIO) or a matched control diet (Control) starting at 5 weeks of age, and then analyzed at 16–25 weeks of age. The number and phenotype of lymphocytes in the islets were similar in DIO and control mice. Notably, under the conditions of obesity-associated systemic inflammation, islet lymphocytes in the DIO mice maintained IL-10 production. From these data, we propose that islet lymphocytes play a regulatory role to protect the islets from systemic inflammation through IL-10 production.

Mononuclear phagocytes drive Mertk-dependent T cell regulation at autoimmune and tumor sites

Understanding mechanisms of immune regulation is key to developing effective immunotherapies for autoimmunity and cancer. We examined the role of mononuclear phagocytes (MNPs) in regulating effector T cells in type 1 diabetes and melanoma. MNPs in the islets impaired T cell responsiveness to antigen by preventing antigen-mediated T cell arrest. MNPs in the autoimmune lesion express the TAM family receptor tyrosine kinase Mertk which functions in efferocytosis. Inhibition or deficiency of Mertk led to a release from T cell regulation characterized by enhanced T cell arrest in pre-diabetic islets and at the tumor site. T cell arrest was accompanied by increased T cell-antigen presenting cell interactions as well as increased antigen experience and effector function by T cells in the islets. Single cell RNA-seq analysis of islet MNPs identified multiple myeloid subsets. Inhibition of Mertk induced the most significant changes in gene expression among the islet resident macrophages including upregulation of inflammatory cytokine and adhesion genes. In the NOD mouse model, inhibition of Mertk-dependent T cell regulation culminated in the rapid acceleration of autoimmune pathology and disease. In human islets, the number of Mertk-expressing cells were increased in remaining insulin-containing islets from type 1 diabetic patients, suggesting that they might have a protective role in human disease. These data indicate that Mertk signaling in MNPs drives T cell regulation that functions specifically at the disease site in peripheral tissues through a mechanism that prevents T cell arrest and response to antigen.

Formin-like-1 mediates effector T cell extravasation through restrictive endothelial barriers enabling T cell entry into peripheral tissues and autoimmunity induction

To perform their functions, T cells migrate from the blood vasculature into tissues by traversing the vascular wall through a process known as transendothelial migration (TEM). While many of the extracellular cues that guide this process have been identified, the role of downstream cytoskeletal effectors that mediate force generation and morphological changes required for TEM remains an area of active research. Formin-like-1 (FMNL1) is a cytoskeletal effector that mediates cytoskeletal remodeling. However, the role of FMNL1 in T cell functions, and migration in particular, is mostly unknown. The goal of our study was to examine the role of FMNL1 in T cell extravasation and trafficking. We generated a new FMNL1 knock-out (KO) mouse and identified a novel role for FMNL1 in promoting T cell migration through restrictive endothelial barriers during TEM. In vitro, FMNL1-deficient T cells had reduced actin polymerization in response to chemokine signaling. Furthermore, FMNL1 KO T cells had a selective impairment in chemotaxis through restrictive 3μm pores vs permissive 5μm pores. Using time-lapse microscopy, we determined that FMNL1-deficient T cells are severely impaired in their capacity to complete TEM through endothelial barriers. In vivo, we found that FMNL1 was dispensable for T cell extravasation through permissive high endothelial venules and homeostatic trafficking to lymphoid organs. Instead, FMNL1 regulated the ability of activated T cells to extravasate into inflamed peripheral tissues and enabled self-reactive T cells to induce autoimmune disease. Overall, our data identify FMNL1 as a key regulator of lymphocyte migration through restrictive barriers and as a potential target for modulating effector T cell trafficking.

Immune cell trafficking to the islets during type 1 diabetes

Inhibition of immune cell trafficking to the pancreatic islets during type 1 diabetes (T1D) has therapeutic potential, since targeting of T cell and B cell trafficking has been clinically effective in other autoimmune diseases. Trafficking to the islets is characterized by redundancy in adhesion molecule and chemokine usage, which has not enabled effective targeting to date. Additionally, cognate antigen is not consistently required for T cell entry into the islets throughout the progression of disease. However, myeloid cells are required to enable T cell and B cell entry into the islets, and may serve as a convergence point in the pathways controlling this process. In this review we describe current knowledge of the factors that mediate immune cell trafficking to pancreatic islets during T1D progression.

CD11c+ Cells Are Gatekeepers for Lymphocyte Trafficking to Infiltrated Islets During Type 1 Diabetes

Type 1 diabetes (T1D) is a T cell mediated autoimmune disease that affects more than 19 million people with incidence increasing rapidly worldwide. For T cells to effectively drive T1D, they must first traffic to the islets and extravasate through the islet vasculature. Understanding the cues that lead to T cell entry into inflamed islets is important because diagnosed T1D patients already have established immune infiltration of their islets. Here we show that CD11c⁺ cells are a key mediator of T cell trafficking to infiltrated islets in non-obese diabetic (NOD) mice. Using intravital 2-photon islet imaging we show that T cell extravasation into the islets is an extended process, with T cells arresting in the islet vasculature in close proximity to perivascular CD11c⁺ cells. Antigen is not required for T cell trafficking to infiltrated islets, but T cell chemokine receptor signaling is necessary. Using RNAseq, we show that islet CD11c⁺ cells express over 20 different chemokines that bind chemokine receptors expressed on islet T cells. One highly expressed chemokine-receptor pair is CXCL16-CXCR6. However, NOD. CXCR6^-/- mice progressed normally to T1D and CXCR6 deficient T cells trafficked normally to the islets. Even with CXCR3 and CXCR6 dual deficiency, T cells trafficked to infiltrated islets. These data reinforce that chemokine receptor signaling is highly redundant for T cell trafficking to inflamed islets. Importantly, depletion of CD11c⁺ cells strongly inhibited T cell trafficking to infiltrated islets of NOD mice. We suggest that targeted depletion of CD11c⁺ cells associated with the islet vasculature may yield a therapeutic target to inhibit T cell trafficking to inflamed islets to prevent progression of T1D.

CD4 T Cells Reactive to Hybrid Insulin Peptides Are Indicators of Disease Activity in the NOD Mouse

We recently established that hybrid insulin peptides (HIPs), formed in islet β-cells by fusion of insulin C-peptide fragments to peptides of chromogranin A or islet amyloid polypeptide, are ligands for diabetogenic CD4 T-cell clones. The goal of this study was to investigate whether HIP-reactive T cells were indicative of ongoing autoimmunity. MHC class II tetramers were used to investigate the presence, phenotype, and function of HIP-reactive and insulin-reactive T cells in NOD mice. Insulin-reactive T cells encounter their antigen early in disease, but they express FoxP3 and therefore may contribute to immune regulation. In contrast, HIP-reactive T cells are proinflammatory and highly diabetogenic in an adoptive transfer model. Because the frequency of antigen-experienced HIP-reactive T cells increases over progression of disease, they may serve as biomarkers of autoimmune diabetes.

Live Imaging of IL-4-Expressing T Follicular Helper Cells in Explanted Lymph Nodes

The generation of class-switched, high-affinity, antibody-producing B cells plays a critical role in the establishment of type 2 immunity to intestinal helminths as well as in the pathogenesis of allergy and asthma. The generation of these high-affinity, antibody-producing B cells occurs in germinal centers (GC) and relies on interactions with follicular dendritic cells (FDCs) and T follicular helper (Tfh) cells. One critical mediator produced by Tfh cells in GCs is interleukin-4 (IL-4). Tfh-derived IL-4 drives class switching to type 2 antibody isotypes IgE and IgG1 and is required for high-affinity IgG1 production. In vivo detection of IL-4-expressing Tfh cells is required to better understand the role of these cells during the GC response. Detection of IL-4-expressing cells has been greatly improved by the generation of the IL-4^4get reporter mice, which read out IL-4 expression as green fluorescent protein (GFP). Much has been learned from these mice with regard to type 2 immunity using flow cytometry and immunohistochemistry. However, these methods do not allow the study of cellular behavior and interactions in real time. In contrast, multi-photon microscopy allows for deep tissue imaging and tracking of multiple cell types in intact tissues over time. Here, we describe a protocol for in vivo detection of IL-4-expressing Tfh cells in an explanted popliteal lymph node by multi-photon microscopy. The dynamics of Tfh cell motility and their interactions with FDC networks in the GCs were analyzed.

Migratory dendritic cells acquire and present lymphatic endothelial cell-archived antigens during lymph node contraction

Antigens derived from viral infection or vaccination can persist within a host for many weeks after resolution of the infection or vaccine responses. We previously identified lymphatic endothelial cells (LEC) as the repository for this antigen archival, yet LECs are unable to present their archived antigens to CD8⁺ T cells, and instead transfer their antigens to CD11c⁺ antigen-presenting cells (APC). Here we show that the exchange of archived antigens between LECs and APCs is mediated by migratory dendritic cells (DC). After vaccination, both migratory basic leucine zipper ATF-like transcription factor 3 (BatF3)-dependent and BatF3-independent DCs are responsible for antigen exchange and cross-presentation. However, exchange of archived viral antigens is mediated only by BatF3-dependent migratory DCs potentially acquiring apoptotic LECs. In conclusion, LEC-archived antigens are exchanged with migratory DCs, both directly and through LEC apoptosis, to cross-present archived antigens to circulating T cells.

Viral infection and vaccination both induce lasting persistence of antigens for protective responses. Here the authors show that migratory dendritic cells, independent of the transcription factor BatF3 for their development, contribute to “archived antigen” exchange with lymphatic endothelial cells.

CD11c+ cells are required for lymphocyte trafficking into previously infiltrated pancreatic islets during type 1 diabetes

Type 1 diabetes (T1D) is a largely T cell mediated autoimmune disease that destroys the beta cells of the pancreatic islets. Inhibition of cell trafficking to an active disease site has been an effective therapy for multiple autoimmune diseases, but the requirements of lymphocyte trafficking to the islets are not fully understood. We show that lymphocyte entry into previously infiltrated islets is dependent on the presence of CD11c+ cells in the islets. T cells and B cells transferred prior to CD11c+ cell depletion were able to enter the islets; whereas, short-term CD11c+ cell depletion rapidly prevented further entry. CD11c+ cells include cells that are highly efficient antigen presenters; however, we show entry of both activated or naïve T cells into previously infiltrated islets was not reliant on antigen. An alternative role for CD11c+ cells in lymphocyte entry into the islets is the production of chemokines and cytokines. These molecules can then either directly recruit lymphocytes through chemoattraction or increased adhesion to the vasculature. Initial experiments show that there are no changes in adhesion to the vasculature after CD11c depletion, suggesting that CD11c+ cells act through recruitment by chemokines following lymphocyte arrest on the vascular endothelium. CD11c+ cells in the islets express high levels of CXCL9, a chemoattractant for T and B lymphocytes. CXCR3, the receptor for CXCL9, is present on both T and B cells in the islets. We hypothesize that CD11c+ cells facilitate the process of extravasation into the islets through chemokine production. Targeting CD11c+ produced chemokine production may be useful therapeutically for the treatment of T1D by preventing T cell entry into remaining or transplanted islets.

Down regulation of macrophage IFNGR1 exacerbates systemic L. monocytogenes infection

Interferons (IFNs) target macrophages to regulate inflammation and resistance to microbial infections. The type II IFN (IFNγ) acts on a cell surface receptor (IFNGR) to promote gene expression that enhance macrophage inflammatory and anti-microbial activity. Type I IFNs can dampen macrophage responsiveness to IFNγ and are associated with increased susceptibility to numerous bacterial infections. The precise mechanisms responsible for these effects remain unclear. Type I IFNs silence macrophage ifngr1 transcription and thus reduce cell surface expression of IFNGR1. To test how these events might impact macrophage activation and host resistance during bacterial infection, we developed transgenic mice that express a functional FLAG-tagged IFNGR1 (fGR1) driven by a macrophage-specific promoter. Macrophages from fGR1 mice expressed physiologic levels of cell surface IFNGR1 at steady state and responded equivalently to WT C57Bl/6 macrophages when treated with IFNγ alone. However, fGR1 macrophages retained cell surface IFNGR1 and showed enhanced responsiveness to IFNγ in the presence of type I IFNs. When fGR1 mice were infected with the bacterium Listeria monocytogenes their resistance was significantly increased, despite normal type I and II IFN production. Enhanced resistance was dependent on IFNγ and associated with increased macrophage activation and antimicrobial function. These results argue that down regulation of myeloid cell IFNGR1 is an important mechanism by which type I IFNs suppress inflammatory and anti-bacterial functions of macrophages.

The Ena/VASP family of cytoskeletal proteins selectively regulates activated T cell trafficking by promoting the diapedesis step of transendothelial migration

Vasodilator-stimulated phosphoprotein (VASP) and Ena-VASP-like (EVL) are cytoskeletal effector proteins that have been implicated in T cell actin cytoskeleton remodeling in response to T cell receptor signaling. However, the role of these proteins in T cell motility, transendothelial migration, and in vivo trafficking remained unknown. We investigated the role of EVL and VASP in T cell trafficking and found that these cytoskeletal effectors are selectively required for activated but not naïve T cell trafficking to the lymph nodes and spleen. Moreover, in a model of Multiple Sclerosis, EVL/VASP deficiency severely impaired activated T cell trafficking to the inflamed central nervous system (CNS) of mice with experimental autoimmune encephalomyelitis (EAE). Deletion of EVL and VASP resulted in impaired Very Late Antigen-4 (VLA-4) expression and function, but unexpectedly did not cause alterations in shear-resistant adhesion and motility of T cells on primary brain microvascular endothelial cells in vitro. Instead, deletion of EVL and VASP caused a significant impairment in the ability of T cells to initiate and complete the diapedesis step of transendothelial migration. Furthermore, upon blockade of VLA-4, T cell diapedesis became equivalent between control and EVL/VASP-deficient T cells. Together, these data suggest that that EVL and VASP selectively regulate activated T cell trafficking by specifically mediating the diapedesis step of transendothelial migration in a VLA-4-dependent manner.

Cutting Edge: Nonobese Diabetic Mice Deficient in Chromogranin A Are Protected from Autoimmune Diabetes

T cells reactive to β cell Ags are critical players in the development of autoimmune type 1 diabetes. Using a panel of diabetogenic CD4 T cell clones derived from the NOD mouse, we recently identified the β cell secretory granule protein, chromogranin A (ChgA), as a new autoantigen in type 1 diabetes. CD4 T cells reactive to ChgA are pathogenic and rapidly transfer diabetes into young NOD recipients. We report in this article that NOD.ChgA(-/-) mice do not develop diabetes and show little evidence of autoimmunity in the pancreatic islets. Using tetramer analysis, we demonstrate that ChgA-reactive T cells are present in these mice but remain naive. In contrast, in NOD.ChgA(+/+) mice, a majority of the ChgA-reactive T cells are Ag experienced. Our results suggest that the presence of ChgA and subsequent activation of ChgA-reactive T cells are essential for the initiation and development of autoimmune diabetes in NOD mice.

CD11c-Expressing B Cells Are Located at the T Cell/B Cell Border in Spleen and Are Potent APCs

In addition to the secretion of Ag-specific Abs, B cells may play an important role in the generation of immune responses by efficiently presenting Ag to T cells. We and other investigators recently described a subpopulation of CD11c(+) B cells (Age/autoimmune-associated B cells [ABCs]) that appear with age, during virus infections, and at the onset of some autoimmune diseases and participate in autoimmune responses by secreting autoantibodies. In this study, we assessed the ability of these cells to present Ag and activate Ag-specific T cells. We demonstrated that ABCs present Ag to T cells, in vitro and in vivo, better than do follicular B cells (FO cells). Our data indicate that ABCs express higher levels of the chemokine receptor CCR7, have higher responsiveness to CCL21 and CCL19 than do FO cells, and are localized at the T/B cell border in spleen. Using multiphoton microscopy, we show that, in vivo, CD11c(+) B cells form significantly more stable interactions with T cells than do FO cells. Together, these data identify a previously undescribed role for ABCs as potent APCs and suggest another potential mechanism by which these cells can influence immune responses and/or the development of autoimmunity.

Antigen recognition in the islets changes with progression of autoimmune islet infiltration

In type 1 diabetes, the pancreatic islets are an important site for therapeutic intervention because immune infiltration of the islets is well established at diagnosis. Therefore, understanding the events that underlie the continued progression of the autoimmune response and islet destruction is critical. Islet infiltration and destruction is an asynchronous process, making it important to analyze the disease process on a single islet basis. To understand how T cell stimulation evolves through the process of islet infiltration, we analyzed the dynamics of T cell movement and interactions within individual islets of spontaneously autoimmune NOD mice. Using both intravital and explanted two-photon islet imaging, we defined a correlation between increased islet infiltration and increased T cell motility. Early T cell arrest was Ag dependent and due, at least in part, to Ag recognition through sustained interactions with CD11c(+) APCs. As islet infiltration progressed, T cell motility became Ag independent, with a loss of T cell arrest and sustained interactions with CD11c(+) APCs. These studies suggest that the autoimmune T cell response in the islets may be temporarily dampened during the course of islet infiltration and disease progression.

Modes and mechanisms of T cell motility: roles for confinement and Myosin-IIA

T cells are charged with surveying tissues for evidence of their cognate foreign antigens. Subsequently, they must navigate to effector sites, which they enter through the process of trans-endothelial migration (TEM). During interstitial migration, T cells migrate according to one of two modes that are distinguished by the strength and sequence of adhesions and the requirement for Myosin-IIA. In contrast during TEM, T cells require Myosin-IIA for the final process of pushing their nucleus through the endothelium. A generalized model emerges with dual roles for Myosin-IIA: This motor protein acts like a tensioning or expansion spring, transmitting force across the cell cortex to sites of surface contact and also optimizing the frictional coupling with substrata by modulating the surface area of the contact. The phosphorylation and deactivation of this motor following TCR engagement can allow T cells to rapidly alter the degree to which they adhere to surfaces and to switch to a mode of interaction with surfaces that is more conducive to forming a synapse with an antigen-presenting cell.

Peripheral tolerance and autoimmunity: lessons from in vivo imaging

Multi-photon microscopy has taken hold as a widely used technique in immunology, allowing for imaging of the kinetics of immune cell motility and cell-cell interactions, but what have we learned from this technique about the processes involved in peripheral tolerance and autoimmunity? Various studies have now looked at the dynamics of several mechanisms of peripheral T cell tolerance and efforts to examine the dynamics of the autoimmune response at the disease site are also under way. Here, we will discuss the findings of studies that use multi-photon microscopy to examine the dynamics of T cell tolerance in the lymph nodes and of the autoimmune processes involved in models of type 1 diabetes and multiple sclerosis. An emerging theme from these studies is that short T cell-antigen presenting cell interactions can lead to tolerance, and that autoreactive T cell restimulation at the disease site can play an important role in autoimmune disease exacerbation.

Evolving immune circuits are generated by flexible, motile, and sequential immunological synapses

The immune system is made up of a diverse collection of cells, each of which has distinct sets of triggers that elicit unique and overlapping responses. It is correctly described as a 'system' because its overall properties (e.g. 'tolerance', 'allergy') emerge from multiple interactions of its components cells. To mobilize a response where needed, the majority of the cells of the system are obligatorily highly motile and so must communicate with one another over both time and space. Here, we discuss the flexibility of the primary immunological synapse (IS) with respect to motility. We then consider the primary IS as an initiating module that licenses 'immunological circuits': the latter consisting of two or more cell-cell synaptic interactions. We discuss how two or three component immunological circuits interact might with one another in sequence and how the timing, stoichiometry, milieu, and duration of assembly of immunological circuits are likely to be key determinants in the emergent outcome and thus the system-wide immune response. An evolving consideration of immunological circuits, with an emphasis on the cell-cell modules that complement T-antigen-presenting cell interaction, provides a fundamental starting point for systems analysis of the immune response.

Real-time analysis of T cell receptors in naive cells in vitro and in vivo reveals flexibility in synapse and signaling dynamics

Real-time imaging defines the dynamics of TCR and T cell motility during early T cell activation in lymph nodes.

The real-time dynamics of the T cell receptor (TCR) reflect antigen detection and T cell signaling, providing valuable insight into the evolving events of the immune response. Despite considerable advances in studying TCR dynamics in simplified systems in vitro, live imaging of subcellular signaling complexes expressed at physiological densities in intact tissues has been challenging. In this study, we generated a transgenic mouse with a TCR fused to green fluorescent protein to provide insight into the early signaling events of the immune response. To enable imaging of TCR dynamics in naive T cells in the lymph node, we enhanced signal detection of the fluorescent TCR fusion protein and used volumetric masking with a second fluorophore to mark the T cells expressing the fluorescent TCR. These in vivo analyses and parallel experiments in vitro show minimal and transient incorporation of TCRs into a stable central supramolecular activating cluster (cSMAC) structure but strong evidence for rapid, antigen-dependent TCR internalization that was not contingent on T cell motility arrest or cSMAC formation. Short-lived antigen-independent TCR clustering was also occasionally observed. These in vivo observations demonstrate that varied TCR trafficking and cell arrest dynamics occur during early T cell activation.

Amplification of autoimmune response through induction of dendritic cell maturation in inflamed tissues

Dendritic cells (DCs) are essential in T cell-mediated destruction of insulin-producing beta cells in the islets of Langerhans in type 1 diabetes. In this study, we investigated T cell induction of intra-islet DC maturation during the progression of the disease in both autoimmune-prone NOD and resistant C57BL/6 mice. We demonstrated steady-state capture and retention of unprocessed beta cell-derived proteins by semimature intra-islet DCs in both mouse strains. T cell-mediated intra-islet inflammation induced an increase in CD40 and CD80 expression and processing of captured Ag by resident DCs without inducing the expression of the p40 subunit of IL-12/23. Some of the CD40(high) intra-islet DCs up-regulated CCR7, and a small number of CD40(high) DCs bearing unprocessed islet Ags were detected in the pancreatic lymph nodes in mice with acute intra-islet inflammation, demonstrating that T cell-mediated tissue inflammation augments migration of mature resident DCs to draining lymph nodes. Our results identify an amplification loop during the progression of autoimmune diabetes, in which initial T cell infiltration leads to rapid maturation of intra-islet DCs, their migration to lymph nodes, and expanded priming of more autoreactive T cells. Therapeutic interventions that intercept this process may be effective at halting the progression of type 1 diabetes.

Real-time imaging of TCR dynamics in vivo reveals rapid TCR clustering and internalization in response to antigen (33.13)

Real-time in vivo imaging has given insight into the cellular dynamics of T cell activation, but less is known about receptor and signaling dynamics in vivo. Live imaging of subcellular signaling complexes has been challenging in living tissues due to low physiological molecular densities, inherent limitations of fluorophores, and strong autofluorescence of tissues. Our goal was to characterize T cell receptor (TCR) dynamics in naïve T cells in the lymph node during their first encounter with dendritic cells (DCs) bearing cognate antigen. To do so we developed a mouse expressing a GFP tagged OT-I TCR to track surface and intracellular TCR, and used image processing facilitated by co-labeling of the T cells to isolate specific fluorescence. In the absence of antigen, the TCR was mainly confined to the cell surface without consistent polarity; however, a small percentage of T cells transiently clustered their TCR. Within 30 min of antigen recognition, many T cells stopped crawling and clustered their TCR. Surprisingly, detectable antigen-dependent TCR clustering duration was short (7.1±5.1 min) and as TCR clustering declined, TCR internalization increased. Thus, naïve T cells in the lymph node can signal through the TCR in response to their first interaction with DCs bearing antigen and these contacts lead to rapid TCR clustering and internalization.

This work was funded by the Larry L. Hillblom Foundation and NIH R21.

T cell trans-endothelial migration and homing to lymph nodes rely on Myosin-IIA mediated acto-myosin contractility (94.25)

T lymphocytes migrate from the vasculature into lymph nodes and tissues scanning for antigenic peptides on cell surfaces. How T cells migrate through different environments and switch between types of motility in response to different stimuli is not fully understood. We have previously shown that in vitro Myosin-IIA has a role in T cell migration by regulating the switch between fast amoeboid-like motility and slower mesenchymal-like motility. Here, using conditional knockout mice, we have studied the role of Myosin-IIA-dependent cytoskeletal contractility in the migration of primary T cells in vivo. While Myosin-IIA depleted T cells in the lymph node were motile, they did not achieve the same fast motility rates of control T cells. In addition, homing of T cells to lymph nodes was inhibited in the absence of Myosin-IIA. This resulted from inefficient trans-endothelial migration (TEM) of Myosin-IIA depleted T cells; specifically, Myosin-IIA contractility was important to squeeze the body of the T cell (containing the nucleus) through the endothelial cell layer. Overall, our results suggest a critical role for Myosin-IIA in promoting TEM and migration through constrictive environments, while migration within more 'permissive' environments is not strictly dependent on the function of this myosin motor.

This work was supported by the NIH (RO1AI052116) and the Leukemia and Lymphoma Society.

Live imaging of peripheral T cell-DC interactions in the islets: An emerging axis of autoimmune infiltration (48.15)

Defining processes of islet infiltration and destruction in Type 1 diabetes (T1D) is important for its prevention and preventing destruction of transplanted islets in diabetic individuals. We hypothesize that T1D onset and persistence is maintained by T cell-dendritic cell (DC) interactions in both the draining pancreatic lymph node (PLN) and the islets. In the steady-state, we found that intra-islet DCs are a uniform semi-mature population that constitutively take up β cell antigens in preparation for antigen presentation. Islet-antigen specific CD8 T cells activated in the PLN trafficked to the islets where they induced maturation of islet DCs. Leukocytic infiltration of the islets and islet DC maturation were dependent on IFN-γ production by T cells. Blockade of antigen processing following T cell activation in the PLN also blocked islet DC maturation but not islet infiltration. This suggests that the DCs require productive antigen-presenting interactions with T cells in the islets for maturation to occur. Through 2-photon imaging of the islets, we visualized sustained interactions of islet-antigen specific CD8 T cells with islet DCs and characterized features of cytotoxicity and dwell-time in this setting. Taken together, these data suggest that directed and synaptic delivery of IFN-γ to intra-islet DCs induces their maturation.

This work was funded by the Larry L. Hillblom Foundation and the Juvenile Diabetes Research Foundation.

Two-photon imaging of the immune system: a custom technology platform for high-speed, multicolor tissue imaging of immune responses

Modern imaging approaches are proving important for addressing contemporary issues in the immune system. These approaches are especially useful for characterizing the complex orchestration of immune responses in vivo. Multicolor, two-photon imaging has been proven to be especially enabling for such studies because of its superior tissue penetration, reduced image degradation by light scattering leading to better resolution, and its high image quality deep inside tissues. Here, we examine the functional requirements of two-photon imaging instruments necessary for such immune studies. These requirements include frame rate, spatial resolution and the number of emission channels. We use this discussion as a starting point to compare commercial systems and to introduce a custom technology platform that meets those requirements. This platform is noteworthy because it is very cost-effective, flexible and experimentally useful. Representative data collected with this instrument is used to demonstrate the utility of this platform. Finally, as the field is rapidly evolving, consideration is given to some of the cutting-edge developments in multiphoton microscopy that will likely improve signal strength, depth penetration and/or the experimental usefulness of this approach.

A synaptic basis for paracrine interleukin-2 signaling during homotypic T cell interaction

T cells slow their motility, increase adherence, and arrest after encounters with antigen-presenting cells (APCs) bearing peptide-MHC complexes. Here, we analyzed the cell-cell communication among activating T cells. In vivo and in vitro, activating T cells associated in large clusters that collectively persisted for >30 min, but they also engaged in more transient interactions, apparently distal to APCs. Homotypic aggregation was driven by LFA-1 integrin interactions. Ultrastructural analysis revealed that cell-cell contacts between activating T cells were organized as multifocal synapses, and T cells oriented both the microtubule-organizing complex and interleukin-2 (IL-2) secretion toward this synapse. T cells engaged in homotypic interactions more effectively captured IL-2 relative to free cells. T cells receiving paracrine synaptic IL-2 polarized their IL-2 signaling subunits into the synaptic region and more efficiently phosphorylated the transcription factor STAT5, likely through a synapse-associated signaling complex. Thus, synapse-mediated cytokine delivery accelerates responses in activating T cells.

Deletional tolerance mediated by extrathymic Aire-expressing cells

The prevention of autoimmunity requires the elimination of self-reactive T cells during their development and maturation. The expression of diverse self-antigens by stromal cells in the thymus is essential to this process and depends, in part, on the activity of the autoimmune regulator (Aire) gene. Here we report the identification of extrathymic Aire-expressing cells (eTACs) resident within the secondary lymphoid organs. These stromally derived eTACs express a diverse array of distinct self-antigens and are capable of interacting with and deleting naïve autoreactive T cells. Using two-photon microscopy, we observed stable antigen-specific interactions between eTACs and autoreactive T cells. We propose that such a secondary network of self-antigen-expressing stromal cells may help reinforce immune tolerance by preventing the maturation of autoreactive T cells that escape thymic negative selection.

Surface-bound chemokines capture and prime T cells for synapse formation

T cell activation in vivo occurs in a lymphoid milieu that presents chemotactic and T cell receptor signals concurrently. Here we demonstrate that T cell zone chemokines such as CCL21 are bound to the surface of lymph node dendritic cells. Contact with antigen-presenting cells bearing chemokines costimulated T cells by a previously unknown two-step contact mechanism. T cells initially formed an antigen-independent 'tethered' adhesion on chemokine-bearing antigen-presenting cells. The formation of those tethers superseded T cell receptor signaling and immunological synapse formation. However, chemokine-tethered T cells were hyper-responsive to subsequent contacts with antigen-presenting cells. Thus, T cells are costimulated 'in trans' and sequentially after initial engagement with their chemokine-rich environment.

Mechanisms of T cell motility and arrest: deciphering the relationship between intra- and extracellular determinants

T lymphocytes are capable of rapid motility in vitro and in vivo. Upon antigen recognition, they may stop crawling and form a stable cell-cell contact called the 'immunological synapse' (IS). However, it is becoming clear that this outcome may not occur with the reliability that was once presumed. T cells, particularly naïve cells, are apparently triggered partly 'on the fly' during short contacts with peptide-MHC (pMHC) bearing antigen-presenting cells (APCs) and are also influenced in both activity and synapse duration by a multitude of external cues. Underlying the emerging issues is a paucity of data concerning the cell biology of T lymphocytes. Here, we review the molecular mechanisms of crawling and adhesion versus the various potential modes of 'stopping' in T lymphocytes. Both motility and arrest involve similar processes: adhesion, actin elongation and internal tension control, but with different coordination. We will attempt to integrate this with the known and potential external cues that signal for T cell motility versus stopping to form a synapse in vivo. Finally, we discuss how this interplay may give rise to unexpectedly complex motile and morphological behavior.

Identification of naturally processed CD8 T cell epitopes from prostein, a prostate tissue-specific vaccine candidate

Prostein is a prostate tissue-specific protein that is uniquely and abundantly expressed in normal and cancerous prostate tissues. Due to this expression profile, we examined the immunogenicity of prostein as a potential vaccine candidate for prostate cancer. To determine the presence of CD8 T cells specific for naturally processed prostein-derived epitopes in healthy individuals, we developed and applied an in vitro stimulation protocol. Using this protocol, we identified CD8 T cells specific for prostein in the peripheral blood of a male and a female donor. Prostein-specific CD8 T cell clones specifically recognized prostein-expressing targets, including prostate tumor cell lines expressing the relevant HLA alleles. CD8 T cell clones isolated from the male donor were significantly less effective in recognizing target cells compared to cells isolated from the female donor and appeared to recognize subdominant epitopes. The identification of a prostein-specific CD8 T cell repertoire supports the development of prostein in vaccination strategies against prostate cancer. Furthermore, the naturally processed peptide epitopes identified provide tools for the development of peptide-based vaccination strategies against prostate cancer and for monitoring of prostein-specific responses in vaccinated patients.

Molecular and Immunological Evaluation of the Transcription Factor SOX-4 as a Lung Tumor Vaccine Antigen

The developmental transcription factor SOX-4 has been shown to be highly and differentially overexpressed in primary small cell lung carcinomas (SCLC). To examine the potential of SOX-4 for broad use as a lung cancer vaccine, we have evaluated the expression of SOX-4 in a panel of primary adenocarcinoma, squamous, and large cell tumor samples as well as in a panel of established small cell and non-small cell lung carcinoma tumor cell lines. SOX-4 mRNA is shown to be overexpressed in a substantial fraction of each of these lung tumor types. To examine the immunological potential of SOX-4, we have evaluated the presence of SOX-4-specific CD4 and CD8 T cells in PBMC of healthy donors and the presence of SOX4-specific Abs in sera from SCLC patients. We demonstrate the presence of both CD4 and CD8 T cells that recognize naturally processed epitopes derived from SOX-4 as well as the presence of SOX-4-specific Abs in sera from SCLC patients, but not in sera from healthy donors. The lung tumor-specific overexpression and demonstration of a comprehensive Ag-specific immune response specific for SOX-4 support the use of this molecule in the development of whole gene-, peptide-, or protein-based vaccination strategies against lung cancer. Furthermore, the identification of naturally processed T cell and Ab epitopes from SOX-4 provides valuable tools for the development of peptide-based vaccination strategies against lung cancer as well as to monitor SOX-4-specific responses in vaccinated patients.

Identification of naturally processed CD4 T cell epitopes from the prostate-specific antigen kallikrein 4 using peptide-based in vitro stimulation

Kallikrein (KLK)4 is a recently described member of the tissue kallikrein gene family that is specifically expressed in normal and prostate tumor tissues. The tissue-specific expression profile of this molecule suggests that it might be useful as a vaccine candidate against prostate cancer. To examine the presence of CD4 T cells specific for KLK4 in PBMC of normal individuals, a peptide-based in vitro stimulation protocol was developed that uses overlapping KLK4-derived peptides spanning the majority of the KLK4 protein. Using this methodology, three naturally processed CD4 epitopes derived from the KLK4 sequence are identified. These epitopes are restricted by HLA-DRB1*0404, HLA-DRB1*0701, and HLA-DPB1*0401 class II alleles. CD4 T cell clones specific for these epitopes are shown to efficiently and specifically recognize both recombinant KLK4 protein and lysates from prostate tumor cell lines virally infected to express KLK4. CD4 T cells specific for these KLK4 epitopes are shown to exist in PBMC from multiple male donors that express the relevant class II alleles, indicating that a CD4 T cell repertoire specific for KLK4 is present and potentially expandable in prostate cancer patients. The demonstration that KLK4-specific CD4 T cells exist in the peripheral circulation of normal male donors and the identification of naturally processed KLK4-derived CD4 T cell epitopes support the use of KLK4 in whole gene-, protein-, or peptide-based vaccine strategies against prostate cancer. Furthermore, the identification of naturally processed KLK4-derived epitopes provides valuable tools for monitoring preexisting and vaccine-induced responses to this molecule.

The effects of promotion and prevention cues on creativity

This study tested whether cues associated with promotion and prevention regulatory foci influence creativity. The authors predicted that the "risky," explorative processing style elicited by promotion cues, relative to the risk-averse, perseverant processing style elicited by prevention cues, would facilitate creative thought. These predictions were supported by two experiments in which promotion cues bolstered both creative insight (Experiment 1) and creative generation (Experiment 2) relative to prevention cues. Experiments 3 and 4 provided evidence for the process account of these findings. suggesting that promotion cues, relative to prevention cues, produce a riskier response bias (Experiment 3) and bolster memory search for novel responses (Experiment 4). A final experiment provided evidence that individual differences in regulatory focus influence creative problem solving in a manner analogous to that of incidental promotion and prevention cues.

The effects of promotion and prevention cues on creativity

This study tested whether cues associated with promotion and prevention regulatory foci influence creativity. The authors predicted that the "risky," explorative processing style elicited by promotion cues, relative to the risk-averse, perseverant processing style elicited by prevention cues, would facilitate creative thought. These predictions were supported by two experiments in which promotion cues bolstered both creative insight (Experiment 1) and creative generation (Experiment 2) relative to prevention cues. Experiments 3 and 4 provided evidence for the process account of these findings. suggesting that promotion cues, relative to prevention cues, produce a riskier response bias (Experiment 3) and bolster memory search for novel responses (Experiment 4). A final experiment provided evidence that individual differences in regulatory focus influence creative problem solving in a manner analogous to that of incidental promotion and prevention cues.

Induction of human immunodeficiency virus (HIV)-specific CD8 T-cell responses by Listeria monocytogenes and a hyperattenuated Listeria strain engineered to express HIV antigens

Induction of cell-mediated immunity may be essential for an effective AIDS vaccine. Listeria monocytogenes is an attractive bacterial vector to elicit T-cell immunity to human immunodeficiency virus (HIV) because it specifically infects monocytes, key antigen-presenting cells, and because natural infection originates at the mucosa. Immunization with recombinant L. monocytogenes has been shown to protect mice from lymphocytic choriomeningitis virus, influenza virus, and tumor inoculation. L. monocytogenes expressing HIV gag elicits sustained high levels of Gag-specific cytotoxic T lymphocytes (CTLs) in mice. We have examined the ability of Listeria to infect human monocytes and present HIV antigens to CD8 T lymphocytes of HIV-infected donors to induce a secondary T-cell immune response. Using this in vitro vaccination protocol, we show that L. monocytogenes expressing the HIV-1 gag gene efficiently provides a strong stimulus for Gag-specific CTLs in HIV-infected donor peripheral blood mononuclear cells. Listeria expressing Nef also elicits a secondary in vitro anti-Nef CTL response. Since L. monocytogenes is a pathogen, before it can be seriously considered as a human vaccine vector, safety concerns must be addressed. We therefore have produced a highly attenuated strain of L. monocytogenes that requires D-alanine for viability. The recombinant bacteria are attenuated at least 10(5)-fold. We show that when these hyperattenuated bacteria are engineered to express HIV-1 Gag, they are at least as efficient at stimulating Gag-specific human CTLs in vitro as wild-type recombinants. These results suggest that attenuated Listeria is an attractive candidate vaccine vector to induce T-cell immunity to HIV in humans.

The effects of approach and avoidance motor actions on the elements of creative insight

The authors propose that the nonaffective bodily feedback produced by arm flexion and extension informs individuals about the processing requirements of the situation, leading to the adoption of differential processing styles and thereby influencing creativity. Specifically, the authors predicted that arm flexion would elicit a heuristic processing strategy and bolster insight processes, whereas arm extension would elicit a systematic processing strategy and impair insight processes. To test these predictions, the authors assessed the effects of these motor actions on 3 central elements of creative insight: contextual set-breaking, restructuring, and mental search. As predicted, in 6 experiments, arm flexion, relative to arm extension, facilitated insight-related processes. In a 7th experiment, arm extension, relative to arm flexion, facilitated analytical reasoning, supporting a cognitive tuning interpretation of the findings.

CD3zeta and CD28 down-modulation on CD8 T cells during viral infection

Down-modulation of CD3zeta expression on CD8 T lymphocytes occurs, independently of other T-cell receptor (TCR)-CD3 components, in tumor-infiltrating lymphocytes, human immunodeficiency virus infection, and autoimmune disease. These associations suggest that it might be related to chronic antigenic stimulation. CD3zeta down-modulation was found, however, in CD8 T cells that proliferate in response to acute viral infections. In 3 otherwise healthy donors with acute gastroenteritis, infectious mononucleosis, and Epstein-Barr virus/cytomegalovirus/mononucleosis, 30% to 60% of circulating CD8 T cells had down-modulated CD3zeta to below the level of detection. The CD3zeta-T cells were also CD28- but expressed the activation markers HLA-DR and CD57. CD3zeta-CD28- T cells are effector CTL because they express perforin and produce IFN-gamma, but not IL-2, on activation and contain the viral-specific cytotoxic T lymphocyte (CTL). However, CD3zeta-CD28-T cells generally do not express CD25 after anti-CD3 and anti-CD28 stimulation and are not cytotoxic until they are cultured with IL-2 overnight. Cytotoxicity coincides with the re-expression of CD3zeta but not CD28. Down-modulation of CD3zeta and CD28 on effector CTL may control CTL triggering and proliferation to prevent immunopathogenesis.

Expansion of CD57 and CD62L-CD45RA+ CD8 T lymphocytes correlates with reduced viral plasma RNA after primary HIV infection

OBJECTIVE

CD8 T cells, expressing cell surface molecules distinct from those on resting and naive T cells, are increased in HIV infection. The association of increased CD38 and human leukocyte antigen DR (HLA-DR) CD8 T cells with poor prognosis has suggested that activated CD8 T cells may aggravate HIV infection. We examined whether other immunological parameters might influence the viral setpoint.

DESIGN

Peripheral T cells from nine untreated patients, obtained after primary HIV infection when plasma HIV had stabilized, were examined for proteins expressed in activated versus resting, memory versus naive, and cytolytic versus non-cytolytic T cells.

METHODS

The proportion of CD8 T cells that stain for CD38 and HLA-DR, CD28 and CD57 was compared with plasma viraemia and CD4 cell count. These parameters were also compared with the proportion of CD4 and CD8 T cells that express CD62L and CD45RA, present on naive cells and down-modulated in memory cells. Internal staining for the cytotoxic protein granzyme A was also examined.

RESULTS

An increase in CD38 and CD38 HLA-DR CD8 T cells correlated with increased plasma viral RNA (P < 0.00002, P < 0.03, respectively). An increase in CD8 T cells expressing granzyme A was associated with lower CD4 cell counts (P < 0.04). However, the expansion of CD57 and CD62L CD45RA+ CD8 T cells was associated with a lower viral setpoint (P < 0.01, P < 0.02, respectively).

CONCLUSION

Phenotypically defined activated CD8 T cells may have different functions in HIV infection. Activated CD8 T cells that are CD57 or CD62L(-)CD45RA+ may be beneficial, because their expansion in untreated patients correlates with a reduced viral setpoint after primary infection.

A role for heat shock protein 27 in CTL-mediated cell death

CTL exocytosis of granules containing perforin and granzyme proteases induces apoptotic cell death. Either granzyme A or B can act with perforin to trigger apoptosis. Granzyme B activates a ubiquitous apoptotic cascade induced by caspase cleavage, but the granzyme A pathway is largely unknown. Using affinity chromatography with recombinant mutant inactive granzyme A, we previously isolated two granzyme A-binding proteins, PHAP (putative HLA-associated protein) I and II. PHAP II, a substrate of granzyme A, is degraded within minutes of CTL attack. Two additional cytoplasmic proteins of 27 and 53 kDa bind strongly to the mutant granzyme A column, requiring 6 M urea to elute. Sequencing identified these as the monomer and dimer of hsp27, a small heat shock protein up-regulated by stress and cellular activation. Hsp27 coprecipitates with granzyme A from cytoplasmic lysates and is not a substrate of the enzyme. Hsp27 translocates to the detergent-insoluble fraction of target cells and relocalizes from diffuse cytoplasmic staining to long filamentous fibers, especially concentrated in a perinuclear region, within minutes of CTL attack. Hsp27 may participate in morphologic changes during granule-mediated lysis. Low or absent levels of hsp27 expression in T lymphocytes, even after heat shock, may play a role in CTL resistance to granule-mediated lysis.

A Role for Heat Shock Protein 27 in CTL-Mediated Cell Death

CTL exocytosis of granules containing perforin and granzyme proteases induces apoptotic cell death. Either granzyme A or B can act with perforin to trigger apoptosis. Granzyme B activates a ubiquitous apoptotic cascade induced by caspase cleavage, but the granzyme A pathway is largely unknown. Using affinity chromatography with recombinant mutant inactive granzyme A, we previously isolated two granzyme A-binding proteins, PHAP (putative HLA-associated protein) I and II. PHAP II, a substrate of granzyme A, is degraded within minutes of CTL attack. Two additional cytoplasmic proteins of 27 and 53 kDa bind strongly to the mutant granzyme A column, requiring 6 M urea to elute. Sequencing identified these as the monomer and dimer of hsp27, a small heat shock protein up-regulated by stress and cellular activation. Hsp27 coprecipitates with granzyme A from cytoplasmic lysates and is not a substrate of the enzyme. Hsp27 translocates to the detergent-insoluble fraction of target cells and relocalizes from diffuse cytoplasmic staining to long filamentous fibers, especially concentrated in a perinuclear region, within minutes of CTL attack. Hsp27 may participate in morphologic changes during granule-mediated lysis. Low or absent levels of hsp27 expression in T lymphocytes, even after heat shock, may play a role in CTL resistance to granule-mediated lysis.

Performance incentives and means: how regulatory focus influences goal attainment

Study 1 demonstrated that as individuals' promotion-related ideal strength increases, performance on an anagram task is greater for a monetary task incentive framed in terms of gains and nongains (i.e., promotion framed) than one framed in terms of losses and nonlosses (i.e., prevention framed), whereas the reverse is true as individuals' prevention-related ought strength increases. Study 2 further demonstrated that with promotion-framed task incentives, individuals' ideal' strength increases motivation for promotion-related goal attainment means (gaining points), whereas with prevention-framed task incentives, individuals' ought strength increases motivation for prevention-related means (avoiding losing points). These results suggest that motivation and performance are greater when the regulatory focus of task incentives and means match (vs. mismatch) the chronic regulatory focus of the performers.