Antigen decoding by T lymphocytes: from synapses to fate determination

Metabolic Profiling to Assess Response to Targeted and Immune Therapy in Melanoma

There is currently no consensus to determine which advanced melanoma patients will benefit from targeted therapy, immunotherapy, or a combination of both, highlighting the critical need to identify early-response biomarkers to advanced melanoma therapy. The goal of this review is to provide scientific rationale to highlight the potential role of metabolic imaging to assess response to targeted and/or immune therapy in melanoma cancer. For that purpose, a brief overview of current melanoma treatments is provided. Then, current knowledge with respect to melanoma metabolism is described with an emphasis on major crosstalks between melanoma cell metabolism and signaling pathways involved in BRAF-targeted therapy as well as in immune checkpoint inhibition therapies. Finally, preclinical and clinical studies using metabolic imaging and/or profiling to assess response to melanoma treatment are summarized with a particular focus on PET (Positron Emission Tomography) imaging and 13C-MRS (Magnetic Resonance Spectroscopy) methods.

Direct antigen presentation is the canonical pathway of cytomegalovirus CD8 T-cell priming regulated by balanced immune evasion ensuring a strong antiviral response

CD8 T cells are important antiviral effectors in the adaptive immune response to cytomegaloviruses (CMV). Naïve CD8 T cells can be primed by professional antigen-presenting cells (pAPCs) alternatively by "direct antigen presentation" or "antigen cross-presentation". In the case of direct antigen presentation, viral proteins are expressed in infected pAPCs and enter the classical MHC class-I (MHC-I) pathway of antigen processing and presentation of antigenic peptides. In the alternative pathway of antigen cross-presentation, viral antigenic material derived from infected cells of principally any cell type is taken up by uninfected pAPCs and eventually also fed into the MHC class-I pathway. A fundamental difference, which can be used to distinguish between these two mechanisms, is the fact that viral immune evasion proteins that interfere with the cell surface trafficking of peptide-loaded MHC-I (pMHC-I) complexes are absent in cross-presenting uninfected pAPCs. Murine cytomegalovirus (mCMV) models designed to disrupt either of the two presentation pathways revealed that both are possible in principle and can substitute each other. Overall, however, the majority of evidence has led to current opinion favoring cross-presentation as the canonical pathway. To study priming in the normal host genetically competent in both antigen presentation pathways, we took the novel approach of enhancing or inhibiting direct antigen presentation by using recombinant viruses lacking or overexpressing a key mCMV immune evasion protein. Against any prediction, the strongest CD8 T-cell response was elicited under the condition of intermediate direct antigen presentation, as it exists for wild-type virus, whereas the extremes of enhanced or inhibited direct antigen presentation resulted in an identical and weaker response. Our findings are explained by direct antigen presentation combined with a negative feedback regulation exerted by the newly primed antiviral effector CD8 T cells. This insight sheds a completely new light on the acquisition of viral immune evasion genes during virus-host co-evolution.

Functional DNA as a Molecular Tool in Regulating Immunoreceptor-Ligand Interactions

During immune responses, activating ligands would trigger dynamic spatiotemporal organization of immunoreceptors at the cell interface, governing the fate and effector functions of immune cells. To understand the biophysical mechanisms of immunoreceptor signaling, diverse tools, including DNA technologies, have been developed to manipulate receptor-ligand interactions during the immune activation process. With great capability in the controllable assembly of biomolecules, functional DNA-based precise arrangement of immune molecules at cell interfaces has provided a powerful means in revealing the principles of immunoreceptor triggering, even at the single-molecule level. In addition, precisely regulating immunoreceptor-ligand interactions with functional DNA has been applied in immunotherapies of major diseases. This Perspective will focus on the recent advances in exploring immunoreceptor signaling with functional DNA as the molecular tool as well as the applications of functional DNA mediated regulation of immunoreceptor activation. We also outline the challenges and opportunities of applying functional DNA in immune modulation and immunotherapy.

Activation of Cellular Players in Adaptive Immunity via Exogenous Delivery of Tumor Cell Lysates

Tumor cell lysates (TCLs) are a good immunogenic source of tumor-associated antigens. Since whole necrotic TCLs can enhance the maturation and antigen-presenting ability of dendritic cells (DCs), multiple strategies for the exogenous delivery of TCLs have been investigated as novel cancer immunotherapeutic solutions. The TCL-mediated induction of DC maturation and the subsequent immunological response could be improved by utilizing various material-based carriers. Enhanced antitumor immunity and cancer vaccination efficacy could be eventually achieved through the in vivo administration of TCLs. Therefore, (1) important engineering methodologies to prepare antigen-containing TCLs, (2) current therapeutic approaches using TCL-mediated DC activation, and (3) the significant sequential mechanism of DC-based signaling and stimulation in adaptive immunity are summarized in this review. More importantly, the recently reported developments in biomaterial-based exogenous TCL delivery platforms and co-delivery strategies with adjuvants for effective cancer vaccination and antitumor effects are emphasized.

Polysialic Acid in the Immune System

Polysialic acid (polySia) is a highly regulated polymer of sialic acid (Sia) with such potent biophysical characteristics that when expressed drastically influences the interaction properties of cells. Although much of what is known of polySia in mammals has been elucidated from the study of its role in the central nervous system (CNS), polySia is also expressed in other tissues, including the immune system where it presents dynamic changes during differentiation, maturation, and activation of different types of immune cells of the innate and adaptive response, being involved in key regulatory mechanisms. At least six polySia protein carriers (CCR7, ESL-1, NCAM, NRP2, ST8Sia 2, and ST8Sia 4) are expressed in different types of immune cells, but there is still much to be explored in regard not only to the regulatory mechanisms that determine their expression and the structure of polySia chains but also to the identification of the cis- and trans- ligands of polySia that establish signaling networks. This review summarizes the current knowledge on polySia in the immune system, addressing its biosynthesis, its tools for identification and structural characterization, and its functional roles and therapeutic implications.

Clustering of Major Histocompatibility Complex-Class I Molecules in Healthy and Cancer Colon Cells Revealed from Their Nanomechanical Properties

The activation of the T cell mediated immune response relies on the fine interaction between the T cell receptor on the immune cell and the antigen-presenting major histocompatibility complex (MHC) molecules on the membrane surface of antigen-presenting cells. Both the distribution and quantity of MHC/peptide complexes and their adequate morphological presentation affect the activation of the immune cells. In several types of cancer the immune response is down-regulated due to the low expression of MHC-class I (MHC-I) molecules on the cell's surface, and in addition, the mechanical properties of the membrane seem to play a role. Herein, we investigate the distribution of MHC-I molecules and the related nanoscale mechanical environment on the cell surface of two cell lines derived from colon adenocarcinoma and a healthy epithelial colon reference cell line. Atomic force microscopy (AFM) force spectroscopy analysis using an antibody-tagged pyramidal probe specific for MHC-I molecules and a formula that relates the elasticity of the cell to the energy of adhesion revealed the different population distributions of MHC-I molecules in healthy cells compared to cancer cells. We found that MHC-I molecules are significantly less expressed in cancer cells. Moreover, the local elastic modulus is significantly reduced in cancer cells. We speculate that these results might be related to the proven ability of cancer cells to evade the immune system, not only by reducing MHC-I cell surface expression but also by modifying the local mechanical properties affecting the overall morphology of MHC-I synapse presentation to immune cells.

Immune Response to SARS-CoV-2 Infection in Obesity and T2D: Literature Review

In December 2019, a novel coronavirus known as SARS-CoV-2 was first detected in Wuhan, China, causing outbreaks of the coronavirus disease COVID-19 that has now spread globally. For this reason, The World Health Organization (WHO) declared COVID-19 a public health emergency in March 2020. People living with pre-existing conditions such as obesity, cardiovascular diseases, type 2 diabetes (T2D), and chronic kidney and lung diseases, are prone to develop severe forms of disease with fatal outcomes. Metabolic diseases such as obesity and T2D alter the balance of innate and adaptive responses. Both diseases share common features characterized by augmented adiposity associated with a chronic systemic low-grade inflammation, senescence, immunoglobulin glycation, and abnormalities in the number and function of adaptive immune cells. In obese and T2D patients infected by SARS-CoV-2, where immune cells are already hampered, this response appears to be stronger. In this review, we describe the abnormalities of the immune system, and summarize clinical findings of COVID-19 patients with pre-existing conditions such as obesity and T2D as this group is at greater risk of suffering severe and fatal clinical outcomes.

Cytotoxic CD8+ T cells in cancer and cancer immunotherapy

The functions of, and interactions between, the innate and adaptive immune systems are vital for anticancer immunity. Cytotoxic T cells expressing cell-surface CD8 are the most powerful effectors in the anticancer immune response and form the backbone of current successful cancer immunotherapies. Immune-checkpoint inhibitors are designed to target immune-inhibitory receptors that function to regulate the immune response, whereas adoptive cell-transfer therapies use CD8⁺ T cells with genetically modified receptors—chimaeric antigen receptors—to specify and enhance CD8⁺ T-cell functionality. New generations of cytotoxic T cells with genetically modified or synthetic receptors are being developed and evaluated in clinical trials. Furthermore, combinatory regimens might optimise treatment effects and reduce adverse events. This review summarises advances in research on the most prominent immune effectors in cancer and cancer immunotherapy, cytotoxic T cells, and discusses possible implications for future cancer treatment.

The cytoskeletal regulator HEM1 governs B cell development and prevents autoimmunity

The WAVE regulatory complex (WRC) is crucial for assembly of the peripheral branched actin network constituting one of the main drivers of eukaryotic cell migration. Here, we uncover an essential role of the hematopoietic-specific WRC component HEM1 for immune cell development. Germline-encoded HEM1 deficiency underlies an inborn error of immunity with systemic autoimmunity, at cellular level marked by WRC destabilization, reduced filamentous actin, and failure to assemble lamellipodia. Hem1^-/- mice display systemic autoimmunity, phenocopying the human disease. In the absence of Hem1, B cells become deprived of extracellular stimuli necessary to maintain the strength of B cell receptor signaling at a level permissive for survival of non-autoreactive B cells. This shifts the balance of B cell fate choices toward autoreactive B cells and thus autoimmunity.

Cyclophilin D Regulates Antiviral CD8+ T Cell Survival in a Cell-Extrinsic Manner

CD8+ T cell-mediated immunity is critical for host defense against viruses and requires mitochondria-mediated type I IFN (IFN-I) signaling for optimal protection. Cyclophilin D (CypD) is a mitochondrial matrix protein that modulates the mitochondrial permeability transition pore, but its role in IFN-I signaling and CD8+ T cell responses to viral infection has not been previously explored. In this study, we demonstrate that CypD plays a critical extrinsic role in the survival of Ag-specific CD8+ T cell following acute viral infection with lymphocytic choriomeningitis virus in mice. CypD deficiency resulted in reduced IFN-I and increased CD8+ T cell death, resulting in a reduced antiviral CD8+ T cell response. In addition, CypD deficiency was associated with an increase in pathogen burden at an early time-point following infection. Furthermore, our data demonstrate that transfer of wild-type macrophages (expressing CypD) to CypD-deficient mice can partially restore CD8+ T cell responses. These results establish that CypD plays an extrinsic role in regulating optimal effector CD8+ T cell responses to viral infection. Furthermore, this suggests that, under certain circumstances, inhibition of CypD function may have a detrimental impact on the host's ability to respond to viral infection.

Characterization Of The Interaction Between Subviral Particles Of Hepatitis B Virus And Dendritic Cells - In Vitro Study

Background

During an infection with hepatitis B virus (HBV), infectious particles (Dane particles) can be detected in addition to aggregates of the subviral particles (SVP) which is considered an immune escaping mechanism for the virus. Dendritic cells (DCs) are a specialized type of antigen-presenting cell (APC) that can activate native T-cells to prime an immune response controlling HBV infection. The aim of this study was to characterize the interaction between HBVsvp and DCs in vitro.

Methods

HBVsvp that comprises surface and core proteins were produced in vitro by HepG2.2.15 as a culturing system; DCs derived from the bone marrow of mice were pulsed by HBVsvp. A different pattern of cytokines secreted by bone-marrow-derived dendritic cells from C56BL/6 mice pulsed with HBVsvp were analyzed. The interactions between HBVsvp and DCs were characterized using FACS analysis, protein assay, Western blot, and immunofluorescence staining.

Results

Pulsation of DCs with HBVsvp resulted in strong activation and higher secretion of DC cytokines including INF-α, INF-γ, TNF-α, IL-1α, IL-10, and IL-12; but not for IL-1β, IL-2, IL-6, and IL-15. The production of CXCL-10/IP-10 was increased during the observation period and reached the maximal secretion after 24 hrs (p < 0.001). In total protein assay, we found significantly higher protein concentration in HBVsvp stimulated DC groups compared to not activated DCs (p < 0.001). Both 24 kDa small surface antigen (HBVs) and the 21 kDa core protein (HBVc) were detected in activated DCs. For DCs immunofluorescence staining, our data showed clear differences in the morphology of DCs between negative control and those pulsed with HBVsvp.

Conclusion

Result demonstrates a significant complex interaction between HBVsvp and DCs, in vitro.

Coincident airway exposure to low-potency allergen and cytomegalovirus sensitizes for allergic airway disease by viral activation of migratory dendritic cells

Despite a broad cell-type tropism, cytomegalovirus (CMV) is an evidentially pulmonary pathogen. Predilection for the lungs is of medical relevance in immunocompromised recipients of hematopoietic cell transplantation, in whom interstitial CMV pneumonia is a frequent and, if left untreated, fatal clinical manifestation of human CMV infection. A conceivable contribution of CMV to airway diseases of other etiology is an issue that so far attracted little medical attention. As the route of primary CMV infection upon host-to-host transmission in early childhood involves airway mucosa, coincidence of CMV airway infection and exposure to airborne environmental antigens is almost unavoidable. For investigating possible consequences of such a coincidence, we established a mouse model of airway co-exposure to CMV and ovalbumin (OVA) representing a protein antigen of an inherently low allergenic potential. Accordingly, intratracheal OVA exposure alone failed to sensitize for allergic airway disease (AAD) upon OVA aerosol challenge. In contrast, airway infection at the time of OVA sensitization predisposed for AAD that was characterized by airway inflammation, IgE secretion, thickening of airway epithelia, and goblet cell hyperplasia. This AAD histopathology was associated with a T helper type 2 (Th2) transcription profile in the lungs, including IL-4, IL-5, IL-9, and IL-25, known inducers of Th2-driven AAD. These symptoms were all prevented by a pre-challenge depletion of CD4+ T cells, but not of CD8+ T cells. As to the underlying mechanism, murine CMV activated migratory CD11b+ as well as CD103+ conventional dendritic cells (cDCs), which have been associated with Th2 cytokine-driven AAD and with antigen cross-presentation, respectively. This resulted in an enhanced OVA uptake and recruitment of the OVA-laden cDCs selectively to the draining tracheal lymph nodes for antigen presentation. We thus propose that CMV, through activation of migratory cDCs in the airway mucosa, can enhance the allergenic potential of otherwise poorly allergenic environmental protein antigens.

Hydrophilic Astragalin Galactoside Induces T Helper Type 1-Mediated Immune Responses via Dendritic Cells

A flavonoid Astragalin (kaempferol-3-O-β-d-glucopyranoside, Ast) has several biological activities including anti-oxidant, anti-HIV, and anti-allergic effects. Nonetheless, its insolubility in hydrophilic solvents imposes restrictions on its therapeutic applications. In this study, we investigated the effects of water-soluble astragalin-galactoside (kaempferol-3-O-β-d-isomaltotrioside, Ast-Gal) on murine bone marrow-derived dendritic cell (DC) maturation and T helper (Th) cell-mediated immune responses. Ast-Gal significantly increased maturation and activation of DCs through the upregulation of surface markers, such as cluster of differentiation (CD)80, CD86, and Major histocompatibility complex (MHC) II in a dose-dependent manner, while Ast had little effects. Additionally, Ast-Gal-treated DCs markedly secreted immune-stimulating cytokines such as interleukin (IL)-1β, IL-6, and IL-12. Importantly, Ast-Gal strongly increased expression of IL-12, a polarizing cytokine of Th1 cells. In a co-culture system of DCs and CD4⁺ T cells, Ast-Gal-treated DCs preferentially differentiates naïve CD4⁺ T cells into Th1 cells. The addition of neutralizing IL-12 monoclonal antibody (mAb) to cultures of Ast-Gal-treated DCs and CD4⁺ T cells significantly decreased interferon (IFN)-γ production, thereby indicating that Ast-Gal-stimulated DCs enhance the Th1 response through IL-12 production by DCs. Injection with Ast-Gal-treated DCs in mice increased IFN-γ-secreting Th1 cell population. Collectively, these findings indicate that hydrophilically modified astragalin can enhance Th1-mediated immune responses via DCs and point to a possible application of water-soluble astragalin-galactoside as an immune adjuvant.

Correlates of Follicular Helper Bias in the CD4 T Cell Response to a Retroviral Antigen

CD4+ T cell differentiation is influenced by a plethora of intrinsic and extrinsic factors, providing the immune system with the ability to tailor its response according to specific stimuli. Indeed, different classes of pathogens may induce a distinct balance of CD4+ T cell differentiation programmes. Here, we report an uncommonly strong bias toward follicular helper (Tfh) differentiation of CD4+ T cells reactive with a retroviral envelope glycoprotein model antigen, presented in its natural context during retroviral infection. Conversely, the response to the same antigen, presented in different immunization regimens, elicited a response typically balanced between Tfh and T helper 1 cells. Comprehensive quantitation of variables known to influence Tfh differentiation revealed the closest correlation with the strength of T cell receptor (TCR) signaling, leading to PD-1 expression, but not with surface TCR downregulation, irrespective of TCR clonotypic avidity. In contrast, strong TCR signaling leading to TCR downregulation and induction of LAG3 expression in high TCR avidity clonotypes restrained CD4+ T cell commitment and further differentiation. Finally, stunted Th1 differentiation, correlating with limited IL-2 availability in retroviral infection, provided permissive conditions for Tfh development, suggesting that Tfh differentiation is the default program of envelope-reactive CD4+ T cells.

Immune receptors CD40 and CD86 in oral keratinocytes and implications for oral lichen planus

Lichen planus (LP) is a chronic T-cell-mediated mucocutaneous inflammatory disease that targets stratified epithelia, including those lining the oral cavity. The intraoral variant of LP (OLP) is associated with interferon (IFN)-γ production by infiltrating T lymphocytes; however, the role of epithelial cells in the etiopathogenesis OLP is not completely understood. There is however a growing body of evidence regarding the involvement of epithelial-derived cytokines, immune receptors, and costimulatory molecules in the pathobiological processes that promote and sustain OLP. In the present study, we used a reverse transcriptase-polymerase chain reaction assay to assess whether CD40-a receptor found mainly on antigen presenting cells-and the costimulatory molecule CD86 were expressed in oral keratinocytes (three strains of primary normal oral keratinocytes and the H357 cell line) in the presence or absence of IFN-γ. To further characterize the involvement of CD40 in OLP, expression and distribution of receptor and ligand (CD40/CD154) in tissues from OLP were evaluated by immunohistochemistry. The present results are the first to show that both CD40 and CD86 are constitutively expressed at low levels in oral keratinocytes and that their expression was enhanced by IFN-γ stimulation. The intensity of CD40 staining in OLP tissues was strong. Taken together, the results strongly suggest that CD40 and CD86 play a role in the pathophysiology of oral inflammatory diseases such as OLP.

Comparison of gene expression in post-smolt Atlantic salmon challenged by LF-89-like and EM-90-like Piscirickettsia salmonis isolates reveals differences in the immune response associated with pathogenicity

Piscirickettsiosis is the main bacterial disease affecting the Chilean salmon farming industry and is responsible for high economic losses. The aim of this study was to describe and comparatively quantify the immune response of post-smolt Atlantic salmon infected by cohabitation with fish bearing LF-89-like and EM-90-like Piscirickettsia salmonis. The expression of 17 genes related to the immune response was studied in head kidney from cohabitant fish by RT-qPCR. Our results at the transcriptomic level suggest that P. salmonis is able to manipulate the kinetics of cytokine production in a way that might constitute a virulence mechanism that promotes intracellular bacterial replication in cells of Atlantic salmon. This strategy involves the creation of an ideal environment for the microorganism based on induction of the inflammatory and IFN-mediated response, modulation of Th1 polarization, reduced antigen processing and presentation, modulation of the evasion of the immune response mediated by CD8⁺ T cells and promotion of the CD4⁺ T-cell response during the late stage of infection as a mechanism to escape host defences. This response was significantly exacerbated in fish infected by PS-EM-90 compared with fish infected by PS-LF-89, a finding that is probably associated with the higher pathogenicity of PS-EM-90.

Clinical and Experimental Sepsis Impairs CD8 T-Cell-Mediated Immunity

Septic patients experience chronic immunosuppression resulting in enhanced susceptibility to infections normally controlled by T cells. Clinical research on septic patients has shown increased apoptosis and reduced total numbers of CD4 and CD8 T cells, suggesting contributing mechanism driving immunosuppression. Experimental models of sepsis, including cecal ligation and puncture, reverse translated this clinical observation to facilitate hypothesis-driven research and allow the use of an array of experimental tools to probe the impact of sepsis on T-cell immunity. In addition to numerical loss, sepsis functionally impairs the antigen-driven proliferative capacity and effector functions of CD4 and CD8 T cells. Sepsis-induced impairments in both the quantity and quality of T cells results in reduced protective capacity and increased susceptibility of mice to new or previously encountered infections. Therefore, the combined efforts of clinical and experimental sepsis research have begun to elucidate the impact of sepsis on T-cell-mediated immunity and potential T-cell-intrinsic and -extrinsic mechanisms driving chronic immunosuppression. Future work will explore the impact of sepsis on the recently appreciated tissue-resident memory (TRM) T cells, which provide robust protection against localized infections, and dendritic cells, which are needed to activate T cells and promote effective T-cell responses.

Vaccine-elicited memory CD4+ T cell expansion is impaired in the lungs during tuberculosis

Immunological memory is the key biological process that makes vaccines possible. Although tuberculosis vaccines elicit protective immunity in animals, few provide durable protection. To understand why protection is transient, we evaluated the ability of memory CD4⁺ T cells to expand, differentiate, and control Mycobacterium tuberculosis. Both naïve and memory CD4⁺ T cells initially proliferated exponentially, and the accumulation of memory T cells in the lung correlated with early bacterial control. However, later during infection, memory CD4⁺ T cell proliferation was curtailed and no protection was observed. We show that memory CD4⁺ T cells are first activated in the LN and their recruitment to the lung attenuates bacterial growth. However, their interaction with Mtb-infected macrophages does not promote continued proliferation. We conclude that a lack of sustained expansion by memory-derived T cells in the lung limits the durability of their protection, linking their slower expansion with transient protection in vaccinated mice.

Vaccines elicit pathogen-specific memory T cells whose early and potent activation upon infection should provide long-lasting control of bacterial growth. Although many experimental vaccines generate memory CD4⁺ T cells and can control the growth of Mycobacterium tuberculosis (Mtb) early during infection, none reliably provide protection from pulmonary tuberculosis (TB) that is durable. Although the etiology of the clinical failure of memory T cells is not well understood, few studies monitor memory T cell fate and function throughout chronic infection. Using both clonal and polyclonal models of Mtb-specific memory CD4⁺ T cell function during TB, we show that the expansion of memory-derived T cell responses is impaired in the lungs, compared with the primary (naïve) CD4 response. Despite expressing a protective effector phenotype, and reducing bacterial growth early after Mtb challenge, we further show that memory CD4⁺ T cells do not proliferate in response to Mtb-infected macrophages. Their impaired expansion corresponded with waning protection in vaccinated mice later during infection. We propose that both the induction of memory T cell proliferation by infected macrophages, and the durability of vaccine-elicited T cell responses during TB should serve as preclinical vaccine benchmarks.

Interconnected subsets of memory follicular helper T cells have different effector functions

Follicular helper T cells regulate high-affinity antibody production. Memory follicular helper T cells can be local in draining lymphoid organs and circulate in the blood, but the underlying mechanisms of this subdivision are unresolved. Here we show that both memory follicular helper T subsets sustain B-cell responses after reactivation. Local cells promote more plasma cell differentiation, whereas circulating cells promote more secondary germinal centers. In parallel, local memory B cells are homogeneous and programmed to become plasma cells, whereas circulating memory B cells are able to rediversify. Local memory follicular helper T cells have higher affinity T-cell receptors, which correlates with expression of peptide MHC-II at the surface of local memory B cells only. Blocking T-cell receptor-peptide MHC-II interactions induces the release of local memory follicular helper T cells in the circulating compartment. Our studies show that memory follicular helper T localization is highly intertwined with memory B cells, a finding that has important implications for vaccine design.Tfh cells can differentiate into memory cells. Here the authors describe distinct functional and phenotypic profiles of these memory Tfh cells dependent on their anatomical localization to the lymphoid organs or to the circulation.

Antigen presentation for priming T cells in central system

Generation of myelin antigen-specific T cells is a major event in neuroimmune responses that causes demyelination. The antigen-priming of T cells and its location is important in chronic and acute inflammation. In autoimmune multiple sclerosis, the effector T cells are considered to generate in periphery. However, the reasons for chronic relapsing-remitting events are obscure. Considering mechanisms, a feasible aim of research is to investigate the role of antigen-primed T cells in lupus cerebritis. Last thirty years of investigations emphasize the relevance of microglia and infiltrated dendritic cells/macrophages as antigen presenting cells in the central nervous system. The recent approach towards circulating B-lymphocytes is an important area in the context. Here, we analyze the existing findings on antigen presentation in the central nervous system. The aim is to visualize signaling events of myelin antigen presentation to T cells and lead to the strategy of future goals on immunotherapy research.

Polymicrobial Sepsis Diminishes Dendritic Cell Numbers and Function Directly Contributing to Impaired Primary CD8 T Cell Responses In Vivo

Patients surviving acute stages of sepsis often display impaired adaptive-immune responses. Using the cecal ligation and puncture model, we demonstrated that sepsis leads to substantial and long-lasting changes in the naive CD8 T cell repertoire, affecting the capacity of the host to respond to new infections. However, the identity of CD8 T cell-extrinsic factor(s) and mechanism(s) that contribute to impaired CD8 T cell responses after sepsis is unknown. Priming of naive CD8 T cells is critically dependent on the ability of dendritic cells (DCs) to provide Ag, costimulation, and inflammatory signal 3 cytokines; therefore, the sepsis-induced changes in the DC compartment might represent a contributing factor leading to diminished CD8 T cell immunity in septic hosts. In a direct test of this hypothesis, we show that, in addition to numerical decline, sepsis leads to functional impairments in DCs, diminishing their capacity to produce cytokines upon TLR stimulation in vitro or postinfection in vivo. Importantly, we demonstrated a direct link between DC dysfunction and impairments in CD8 T cell immunity after sepsis by directly targeting Ag to DCs. Finally, postsepsis Flt3 ligand treatment increased the number of DCs and improved DC function, including the ability to sense inflammation and produce IL-12, leading to improved primary CD8 T cell responses to newly encountered Ags. Thus, sepsis-induced numerical and functional loss of DCs contributes to the observed defects in CD8 T cell immunity, and therapeutic approaches designed to improve the status of the DC compartment after sepsis might facilitate the recovery of CD8 T cell immunity.

What Scales the T Cell Response?

T cells are known to scale their clonal expansion and effector cytokine response according to the dose and strength of antigenic signal so as to balance their role of affecting protection with the intertwined and immunologically driven tissue damage. How T cells achieve this is now beginning to be understood. We underscore temporal integration of digital T cell receptor (TCR) signaling as the basis for achieving scaled response by means of accumulating crucial mediators over time. We also discuss the role of temporally integrated crosstalk between TCR and IL2 signaling in mediating a scaled, coherent, collective response by T cells. Finally, we highlight numerous known and putative regulatory interactions in the transcriptional program that are expected to quantitatively scale the T cell response, and also offer new mechanisms to hitherto unexplained observations.

Analysis of the complementarity determining regions β-chain genomic rearrangement using high-throughput sequencing in periphery cytotoxic T lymphocytes of patients with chronic hepatitis B

Cytotoxic T lymphocytes (CTLs) are important for the recognition of the hepatitis B virus (HBV), mediating immunoprotective mechanisms and determining the clinical outcome following HBV infection. CTLs recognize the invading virus via the T cell receptor (TCR). The aim of the current study was to investigate the variability of TCR in lymphocytes from patients with chronic hepatitis B and whether TCR genomic recombination is regulated by the current treatment strategies. Peripheral blood mononuclear cells (PBMCs) were isolated from patients with chronic hepatitis B and high-throughput sequencing was performed to analyze the gene expression diversity of β chain complementarity determining region. High-throughput sequencing produced ~380,000 reads. The sequences of V and J family mRNAs of the β chain V area were analyzed and databases were created for all 30 V family and J family genes. Using the Basic Local Alignment Search Tool, 15 genes were identified to be upregulated in the samples following treatment. Among them, the expression of T cell receptor β variable 28 (TRBV28)_T cell receptor β joining 1–5 (TRBJ1.5) and TRBV6_TRBJ2.10 were significantly different in the treated samples compared with samples taken prior to treatment. Genomic recombination patterns of TRBV and TRBJ of the β chain V area were observed to be different in the samples following treatment. The data of the current study demonstrated that the genomic rearrangement of the V and J segments of TCR β chain V area may be associated with the chronic progression of HBV and impact on treatment efficacy.

Regulation of effector and memory CD8(+) T cell function by inflammatory cytokines

Cells communicate with each other through the production and secretion of cytokines, which are integral to the host response to infection. Once recognized by specific cytokine receptors expressed on the cell surface, these exogenous signals direct the biological function of a cell in order to adapt to their microenvironment. CD8(+) T cells are critical immune cells that play an important role in the control and elimination of intracellular pathogens. Current findings have demonstrated that cytokines influence all aspects of the CD8(+) T cell response to infection or immunization. The cytokine milieu induced at the time of activation impacts the overall magnitude and function of the effector CD8(+) T cell response and the generation of functional memory CD8(+) T cells. This review will focus on the impact of inflammatory cytokines on different aspects of CD8(+) T cell biology.

Narrowing the Gap: Preserving Repertoire Diversity Despite Clonal Selection during the CD4 T Cell Response

T cell immunity relies on the generation and maintenance of a diverse repertoire of T cell antigen receptors (TCRs). The strength of signaling emanating from the TCR dictates the fate of T cells during development, as well as during the immune response. Whereas development of new T cells in the thymus increases the available TCR repertoire, clonal selection during the immune response narrows TCR diversity through the outgrowth of clonotypes with the fittest TCR. To ensure maintenance of TCR diversity in the antigen-selected repertoire, specific mechanisms can be envisaged that facilitate the participation of T cell clonotypes with less than best fit TCRs. Here, we summarize the evidence for the existence of such mechanisms that can prevent the loss of diversity. A number of T cell-autonomous or extrinsic factors can reverse clonotypic hierarchies set by TCR affinity for given antigen. Although not yet complete, understanding of these factors and their mechanism of action will be critical in interventional attempts to mold the antigen-selected TCR repertoire.

Signalling mechanisms regulating phenotypic changes in breast cancer cells

In MCF-7 breast cancer cells epidermal growth factor (EGF) induces cell proliferation, whereas heregulin (HRG)/neuregulin (NRG) induces irreversible phenotypic changes accompanied by lipid accumulation. Although these changes in breast cancer cells resemble processes that take place in the tissue, there is no understanding of signalling mechanisms regulating it. To identify molecular mechanisms mediating this cell-fate decision process, we applied different perturbations to pathways activated by these growth factors. The results demonstrate that phosphoinositide 3 (PI3) kinase (PI3K) and mammalian target of rapamycin (mTOR) complex (mTORC)1 activation is necessary for lipid accumulation that can also be induced by insulin, whereas stimulation of the extracellular-signal-regulated kinase (ERK) pathway is surprisingly dispensable. Interestingly, insulin exposure, as short as 4 h, was sufficient for triggering the lipid accumulation, whereas much longer treatment with HRG was required for achieving similar cellular response. Further, activation patterns of ATP citrate lyase (ACLY), an enzyme playing a central role in linking glycolytic and lipogenic pathways, suggest that lipids accumulated within cells are produced de novo rather than absorbed from the environment. In the present study, we demonstrate that PI3K pathway regulates phenotypic changes in breast cancer cells, whereas signal intensity and duration is crucial for cell fate decisions and commitment. Our findings reveal that MCF-7 cell fate decisions are controlled by a network of positive and negative regulators of both signalling and metabolic pathways.

Excessive production and accumulation of lipids is often observed in breast cancer tissue. In the current study, we investigate signalling mechanisms regulating this process using a model cell line.

Immunotherapy for lung cancer: for whom the bell tolls?

Lung cancer is the leading cause of cancer-related death and accounts for approximately 30% of all cancer deaths. Despite the recent developments in personalized therapy, the prognosis in lung cancer is still very poor. Immunotherapy is now emerging as a new hope for patients with lung cancer. It is well known that standard chemotherapeutic regimens have devastating effects for the patient's immune system. Therefore, the aim of immunotherapy is to specifically enhance the immune response against the tumour. Recently, many trials addressed the role of such therapies for metastatic non-small cell lung cancer (NSCLC) treatment: ipilimumab, tremelimumab, nivolumab and pembrolizumab are immunotherapeutic agents of high relevance in this field. Anti-tumour vaccines, as well as dendritic cell-based therapies, have emerged as potent inducers of immune response against the tumour. Herein, we will review some of the most promising cancer immunotherapies, highlighting their advantages and try to understand, in an immunological perspective, the missteps associated with the current treatments for cancer.

The role of heat shock protein 70 (Hsp70) in radiation-induced immunomodulation

Despite enormous progress in radiation technologies (high precision image-guided irradiation, proton irradiation, heavy ion irradiation) and radiotherapeutic concepts (hypofractionated irradiation schemes), the clinical outcome of radiotherapy in locally advanced and metastasized tumors and in hypoxic tumors which are radiation-resistant remains unsatisfactory. Given their key influence on a number of biological and immunological parameters, this article considers the influence of irradiation-induced stress proteins on radiation-induced immunomodulation. Depending on its location, the major stress-inducible Heat shock protein 70 (Hsp70) has been found to fulfill multiple roles. On the one hand, increased intracellular Hsp70 levels have been found to play a key role in the recovery from stress such as radio(chemo)therapy, and on the other hand extracellular Hsp70 proteins are potent stimulators of the innate immune system and mediators of anti-tumor immunity. Furthermore, if loaded with tumor-derived peptides, members of the Heat Shock Protein 70 (HSP70) and 90 (HSP90) families can stimulate the adaptive immune system via antigen cross-presentation. An irradiation-induced enhancement of the selective expression of a membrane form of Hsp70 on the surface of tumor cells which can act as a recognition structure for activated NK cells might have significant clinical relevance, in that the outcome of irradiation therapy for advanced tumors could be improved by combining it with cell-based and other immunotherapies that target this membrane form of Hsp70.

Deficiency of the B cell-activating factor receptor results in limited CD169+ macrophage function during viral infection

The B cell-activating factor (BAFF) is critical for B cell development and humoral immunity in mice and humans. While the role of BAFF in B cells has been widely described, its role in innate immunity remains unknown. Using BAFF receptor (BAFFR)-deficient mice, we characterized BAFFR-related innate and adaptive immune functions following infection with vesicular stomatitis virus (VSV) and lymphocytic choriomeningitis virus (LCMV). We identified a critical role for BAFFR signaling in the generation and maintenance of the CD169(+) macrophage compartment. Consequently, Baffr(-) (/) (-) mice exhibited limited induction of innate type I interferon production after viral infection. Lack of BAFFR signaling reduced virus amplification and presentation following viral infection, resulting in highly reduced antiviral adaptive immune responses. As a consequence, BAFFR-deficient mice showed exacerbated and fatal disease after viral infection. Mechanistically, transient lack of B cells in Baffr(-) (/) (-) animals resulted in limited lymphotoxin expression, which is critical for maintenance of CD169(+) cells. In conclusion, BAFFR signaling affects both innate and adaptive immune activation during viral infections.

IMPORTANCE

Viruses cause acute and chronic infections in humans resulting in millions of deaths every year. Innate immunity is critical for the outcome of a viral infection. Innate type I interferon production can limit viral replication, while adaptive immune priming by innate immune cells induces pathogen-specific immunity with long-term protection. Here, we show that BAFFR deficiency not only perturbed B cells, but also resulted in limited CD169(+) macrophages. These macrophages are critical in amplifying viral particles to trigger type I interferon production and initiate adaptive immune priming. Consequently, BAFFR deficiency resulted in reduced enforced viral replication, limited type I interferon production, and reduced adaptive immunity compared to BAFFR-competent controls. As a result, BAFFR-deficient mice were predisposed to fatal viral infections. Thus, BAFFR expression is critical for innate immune activation and antiviral immunity.

Prolonged antigen presentation by immune complex-binding dendritic cells programs the proliferative capacity of memory CD8 T cells

Antibodies can regulate the quality and functionality of a subset of antiviral CD8⁺ T cell memory responses to influenza by promoting sustained DC antigen presentation during the contraction phase of primary responses.

The commitment of naive CD8 T cells to effector or memory cell fates can occur after a single day of antigenic stimulation even though virus-derived antigens (Ags) are still presented by DCs long after acute infection is resolved. However, the effects of extended Ag presentation on CD8 T cells are undefined and the mechanisms that regulate prolonged Ag presentation are unknown. We showed that the sustained presentation of two different epitopes from influenza virus by DCs prevented the premature contraction of the primary virus-specific CD8 T cell response. Although prolonged Ag presentation did not alter the number of memory CD8 T cells that developed, it was essential for programming the capacity of these cells to proliferate, produce cytokines, and protect the host after secondary challenge. Importantly, prolonged Ag presentation by DCs was dependent on virus-specific, isotype-switched antibodies (Abs) that facilitated the capture and cross-presentation of viral Ags by FcγR-expressing DCs. Collectively, our results demonstrate that B cells and Abs can regulate the quality and functionality of a subset of antiviral CD8 T cell memory responses and do so by promoting sustained Ag presentation by DCs during the contraction phase of the primary T cell response.

T cells translate individual, quantal activation into collective, analog cytokine responses via time-integrated feedbacks

Variability within isogenic T cell populations yields heterogeneous ‘local’ signaling responses to shared antigenic stimuli, but responding clones may communicate ‘global’ antigen load through paracrine messengers, such as cytokines. Such coordination of individual cell responses within multicellular populations is critical for accurate collective reactions to shared environmental cues. However, cytokine production may saturate as a function of antigen input, or be dominated by the precursor frequency of antigen-specific T cells. Surprisingly, we found that T cells scale their collective output of IL-2 to total antigen input over a large dynamic range, independently of population size. Through experimental quantitation and computational modeling, we demonstrate that this scaling is enforced by an inhibitory cross-talk between antigen and IL-2 signaling, and a nonlinear acceleration of IL-2 secretion per cell. Our study reveals how time-integration of these regulatory loops within individual cell signaling generates scaled collective responses and can be leveraged for immune monitoring.

DOI:http://dx.doi.org/10.7554/eLife.01944.001

The cells of the immune system face the challenge of removing viruses and other pathogens without endangering healthy tissues. Cells called T cells plays a variety of roles in the immune response: some T cells directly destroy infected cells, some recruit other cells called phagocytes to the site of infection, and some release small proteins called cytokines. These cytokines help cells to communicate with other cells and, therefore, to tailor the overall immune responses to deal with a particular pathogen.

It is known that mammals are capable of adjusting the T cell response to match the overall severity of an infection. However, it is not clear how individual T cells coordinate their seemingly binary response—they are either activated when they recognize a pathogen, or they are not activated—into a response at the collective cell level that can be varied continuously over a wide range of values.

Here, Tkach et al. show that T cell populations match their production of the cytokine interleukin 2 (IL-2) to the abundance of antigens—molecules released by the pathogen—over an unexpectedly large range of concentrations. Through a combination of experimental and computational analyses, Tkach et al. identified two novel IL-2 feedback loops that help to generate the correct quantity of cytokine, irrespective of the total number of T cells. Furthermore, this model can be used to estimate antigen quantities within diseased tissues. The work of Tkach et al. illustrates the potential of feedback integration in cell signalling and gene regulation as a mechanism to allow cellular populations to respond to environmental stimuli in a graded, collective fashion.

DOI:http://dx.doi.org/10.7554/eLife.01944.002

Modulation of tumor immunity by soluble and membrane-bound molecules at the immunological synapse

To circumvent pathology caused by infectious microbes and tumor growth, the host immune system must constantly clear harmful microorganisms and potentially malignant transformed cells. This task is accomplished in part by T-cells, which can directly kill infected or tumorigenic cells. A crucial event determining the recognition and elimination of detrimental cells is antigen recognition by the T cell receptor (TCR) expressed on the surface of T cells. Upon binding of the TCR to cognate peptide-MHC complexes presented on the surface of antigen presenting cells (APCs), a specialized supramolecular structure known as the immunological synapse (IS) assembles at the T cell-APC interface. Such a structure involves massive redistribution of membrane proteins, including TCR/pMHC complexes, modulatory receptor pairs, and adhesion molecules. Furthermore, assembly of the immunological synapse leads to intracellular events that modulate and define the magnitude and characteristics of the T cell response. Here, we discuss recent literature on the regulation and assembly of IS and the mechanisms evolved by tumors to modulate its function to escape T cell cytotoxicity, as well as novel strategies targeting the IS for therapy.

Presence of memory T cells and naturally acquired antibodies in Plasmodium vivax malaria-exposed individuals against a group of tryptophan-rich antigens with conserved sequences

BACKGROUND

Tryptophan-rich antigens of malarial parasites have been proposed to be the potential vaccine candidate antigens. Plasmodium vivax contains the largest number of such antigens, which need to be evaluated for their immune responses.

METHODS

Recombinant proteins of 15 P. vivax tryptophan-rich antigens (PvTRAgs) were expressed, purified, and used for the human humoral and cellular immune responses. Genetic polymorphism of these 15 genes was also determined among clinical P. vivax isolates.

RESULTS

The T lymphocytes of P. vivax exposed individuals expressed higher level of CD69 against all 15 PvTRAgs. These antigens also activated the large population of CD4(+) T cells and produced higher level of intracellular IL-2, INF-γ and IL-4. Although there was a mixed Th1 and Th2 response against these antigens, this response was biased toward Th2. The majority of P. vivax patients (75.7%-100%, n = 33) produced IgG antibodies against these antigens. Most of these antigens showed conserved T- and B-cell epitopes in the parasite population.

CONCLUSIONS

These results suggest the presence of memory T cells in humans against these antigens to generate faster and more specific immune responses to minimize the P. vivax infection. Further characterization of these PvTRAgs may lead to the identification of a potential therapeutic target.

Relaxation estimation of RMSD in molecular dynamics immunosimulations

Molecular dynamics simulations have to be sufficiently long to draw reliable conclusions. However, no method exists to prove that a simulation has converged. We suggest the method of "lagged RMSD-analysis" as a tool to judge if an MD simulation has not yet run long enough. The analysis is based on RMSD values between pairs of configurations separated by variable time intervals Δt. Unless RMSD(Δt) has reached a stationary shape, the simulation has not yet converged.

Morphologic evidence of anti-tumor specificity of T cells activated by denritic cells derived from peripheral blood mononuclear cells of thyroid cancer patients

Recent studies suggest that immunization with autologous dendritic cells (DCs) results in protective immunity and rejection of established tumors in various human malignancies. The purpose of this study is to determine whether DCs are generated from peripheral blood mononuclear cells (PBMNs) by using cytokines such as F1t-3 ligand (FL), granulocyte macrophage-colony stimulating factor (GM-CSF), IL-4, and TNF-α, and whether cytotoxic T cells activated against the thyroid cancer tissues by the DCs. Peripheral blood was obtained from 2 patients with thyroid cancer. DCs were established from PBMNs by culturing in the presence of FL, GM-CSF, IL-4, and TNF-α for 14 days. At day 14, the differentiated DCs was analyzed morphologically. The immunophenotypic features of DCs such as CDla, CD83, and CD86 were analyzed by immunofluorelescence microscopy. At day 18, DCs and T cells were incubated with thyroid cancer tissues or normal thyroid tissues for additional 4 days, respectively. DCs generated from the PBMNs showed the typical morphology of DCs. Activated cytotoxic T lymphocytes (CTLs) were observed also. DCs and the CTLs were attached to the cancer tissues on scanning electron microscope. The DCs activated the CTLs, which able to specifically attack the thyroid cancer. This study provides morphologic evidence that the coculture of T cells/cancer tissues activated the T cells and differentiated CTLs. The CTLs tightly adhered to cancer tissues and lysed cancer tissues vigorously. Therefore DCs could be used as potential vaccines in the immunotherapy.

Altered expression of TNFSF4 and TRAF2 mRNAs in peripheral blood mononuclear cells in patients with systemic lupus erythematosus: association with atherosclerotic symptoms and lupus nephritis

OBJECTIVES

This study compares the expression levels of tumor necrosis factor ligand superfamily member 4 (TNFSF4) and TNF-R-associated factor 2 (TRAF2) mRNAs in peripheral blood mononuclear cells (PBMCs) of patients with systemic lupus erythematosus (SLE) against healthy controls. The association of SLE disease activity index (SLEDAI) and clinical features of SLE with altered expression levels of TNFSF4 and TRAF2 mRNAs were also evaluated.

DESIGN

We used real-time reverse transcription polymerase chain reaction to measure TNFSF4 and TRAF2 mRNAs expression levels in peripheral blood mononuclear cells of 57 SLE patients and 57 healthy controls.

RESULTS

The expression level of TNFSF4 mRNA was significantly higher in SLE patients than in the control group. Overexpression of TNFSF4 was correlated with arthritis, atherosclerosis and lupus nephritis. TRAF2 mRNA was underexpressed in PBMCs of SLE patients, and its lower expression was associated with atherosclerosis and lupus nephritis. The altered expression levels of TNFSF4 and TRAF2 mRNAs was significantly correlated with SLEDAI.

CONCLUSION

Our results suggest that changes in the expression levels of TNFSF4 and TRAF2 mRNAs may significantly correlate with the pathogenesis of SLE, the disease activity and different clinical features of lupus, particularly lupus nephritis, atherosclerosis and arthritis.

Innate immunity and resistance to tolerogenesis in allotransplantation

The development of immunosuppressive drugs to control adaptive immune responses has led to the success of transplantation as a therapy for end-stage organ failure. However, these agents are largely ineffective in suppressing components of the innate immune system. This distinction has gained in clinical significance as mounting evidence now indicates that innate immune responses play important roles in the acute and chronic rejection of whole organ allografts. For instance, whereas clinical interest in natural killer (NK) cells was once largely confined to the field of bone marrow transplantation, recent findings suggest that these cells can also participate in the acute rejection of cardiac allografts and prevent tolerance induction. Stimulation of Toll-like receptors (TLRs), another important component of innate immunity, by endogenous ligands released in response to ischemia/reperfusion is now known to cause an inflammatory milieu favorable to graft rejection and abrogation of tolerance. Emerging data suggest that activation of complement is linked to acute rejection and interferes with tolerance. In summary, the conventional wisdom that the innate immune system is of little importance in whole organ transplantation is no longer tenable. The addition of strategies that target TLRs, NK cells, complement, and other components of the innate immune system will be necessary to eventually achieve long-term tolerance to human allograft recipients.

Adaptive immune response to model antigens is impaired in murine leukocyte-adhesion deficiency-1 revealing elevated activation thresholds in vivo

Absence of β₂ integrins (CD11/CD18) leads to leukocyte-adhesion deficiency-1 (LAD1), a rare primary immunodeficiency syndrome. Although extensive in vitro work has established an essential function of β₂ integrins in adhesive and signaling properties for cells of the innate and adaptive immune system, their respective participation in an altered adaptive immunity in LAD1 patients are complex and only partly understood in vivo. Therefore, we investigated adaptive immune responses towards different T-dependent antigens in a murine LAD1 model of β₂ integrin-deficiency (CD18^−/−). CD18^−/− mice generated only weak IgG responses after immunization with tetanus toxoid (TT). In contrast, robust hapten- and protein-specific immune responses were observed after immunization with highly haptenated antigens such as (4-hydroxy-3-nitrophenyl)₂₁ acetyl chicken γ globulin (NP₂₁-CG), even though regularly structured germinal centers with specificity for the defined antigens/haptens in CD18^−/− mice remained absent. However, a decrease in the hapten/protein ratio lowered the efficacy of immune responses in CD18^−/− mice, whereas a mere reduction of the antigen dose was less crucial. Importantly, haptenation of TT with NP (NP-TT) efficiently restored a robust IgG response also to TT. Our findings may stimulate further studies on a modification of vaccination strategies using highly haptenated antigens in individuals suffering from LAD1.

Enforced viral replication activates adaptive immunity and is essential for the control of a cytopathic virus

The innate immune system limits viral replication via type I interferon and also induces the presentation of viral antigens to cells of the adaptive immune response. Using infection of mice with vesicular stomatitis virus, we analyzed how the innate immune system inhibits viral propagation but still allows the presentation of antigen to cells of the adaptive immune response. We found that expression of the gene encoding the inhibitory protein Usp18 in metallophilic macrophages led to lower type I interferon responsiveness, thereby allowing locally restricted replication of virus. This was essential for the induction of adaptive antiviral immune responses and, therefore, for preventing the fatal outcome of infection. In conclusion, we found that enforced viral replication in marginal zone macrophages was an immunological mechanism that ensured the production of sufficient antigen for effective activation of the adaptive immune response.

Retinal self-antigen induces a predominantly Th1 effector response in Axl and Mertk double-knockout mice

The TAM family of receptors (Tyro3, Axl, and Mertk) plays an important role in the negative regulation of response of dendritic cells (DCs) and macrophages to pathogenic stimuli, and mice lacking this receptor family develop spontaneous lupus-like systemic autoimmunity against a variety of tissues, including retina. To study the molecular mechanism underlying the TAM regulation of APC functions and subsequent effects on the induction of an autoimmune response against the eye, we examined CD4 T cell differentiation following retinal self-antigen immunization. CD4 T cells prepared from naive or interphotoreceptor retinoid-binding protein (IRBP)1-20-immunized Axl and Mertk double-knockout (dko) mice reacted to activation using anti-CD3 and anti-CD28 Abs or to bolster by self-antigen in vitro with a predominantly Th1 effector response, as characterized by increased IFN-γ production and higher frequency of IFN-γ-positive CD4 T cells. The Th17 effector response to IRBP immunization was similar in dko mice to that in wild-type controls, as shown by ELISA measurement of IL-17A in the culture medium and flow cytometric analysis of IL-17A-secreting CD4 T cells. Interestingly, APCs or DCs isolated from IRBP-immunized dko mice exhibited a greater ability to drive the Th1 response. The production of two driving cytokines for Th1 differentiation, IL-12 and IL-18, was dramatically increased in dko DCs and macrophages, and LPS stimulation bolstered their production. The preferential development into the Th1 subset in dko mice suggests that the cytokine milieu produced by the mutant mice in vivo or by mutant APCs in vitro selectively creates a differentiation environment favoring the Th1 effector response.

Tetraspanins in cellular immunity

Tetraspanins are a superfamily of integral membrane proteins involved in the organization of microdomains that consist of both cell membrane proteins and cytoplasmic signalling molecules. These microdomains are important in regulating molecular recognition at the cell surface and subsequent signal transduction processes central to the generation of an efficient immune response. Tetraspanins, both immune-cell-specific, such as CD37, and ubiquitously expressed, such as CD81, have been shown to be imp-ortant in both innate and adaptive cellular immunity. This is via their molecular interaction with important immune cell-surface molecules such as antigen-presenting MHC proteins, T-cell co-receptors CD4 and CD8, as well as cytoplasmic molecules such as Lck and PKC (protein kinase C). Moreover, the generation of tetraspanin-deficient mice has enabled the study of these proteins in immunity. A variety of tetraspanins have a role in the regulation of pattern recognition, antigen presentation and T-cell proliferation. Recent studies have also begun to elucidate roles for tetraspanins in macrophages, NK cells (natural killer cells) and granulocytes.

Visualization of Cell-Cell Interaction Contacts: Synapses and Kinapses

T-cell activation requires interactions of T-cell antigen receptors (TCR) and peptides presented by major histocompatibility complex molecules (MHCp) in an adhesive junction between the T-cell and antigen-presenting cell (APC). Stable junctions with bull's eye supramolecular activation clusters (SMACs) have been defined as immunological synapses. The term synapse works in this case because it joins roots for "same" and "fasten," which could be translated as "fasten in the same place." These structures maintain T-cell-APC interaction and allow directed secretion. We have proposed that SMACs are not really clusters, but are analogous to higher order membrane-cytoskeleton zones involved in amoeboid locomotion including a substrate testing lamellipodium, an adhesive lamella and anti-adhesive uropod. Since T-cells can also integrate signaling during locomotion over antigen presenting cells, it is important to consider adhesive junctions maintained as cells move past each other. This combination of movement (kine-) and fastening (-apse) can be described as a kinapse or moving junction. Synapses and kinapses operate in different stages of T-cell priming. Optimal effector functions may also depend upon cyclical use of synapses and kinapses. Visualization of these structures in vitro and in vivo presents many distinct challenges that will be discussed in this paper.

The memory phase of the CD4 T-cell response to influenza virus infection maintains its diverse antigen specificity

A major gap in our understanding of the immune response to pathogens and vaccines is how closely the antigen specificity in the memory phase mimics repertoire that is rapidly expanded upon priming. Understanding the diversity of the CD4 T-cell memory compartment after a primary response to pathogens is hampered by the technical challenges of epitope discovery and suitable models to study primary immune responses. Recently, we have used overlapping synthetic peptides to empirically map most of the specificities present in the primary response to live influenza infection. We found that the CD4 T-cell response can be exceptionally diverse, depending on the allele(s) of MHC class II molecules expressed. In the current study, using a mouse model of primary influenza infection and peptide-specific cytokine EliSpots, we have asked how this broad CD4 T-cell immunodominance hierarchy changes as the immune response contracts and memory is established. Our studies revealed that, for the most part, diversity is maintained, and most specificities, including those for relatively minor epitopes, are preserved in the memory CD4 T-cell compartment. A modest, but reproducible shift in specificity toward haemagglutinin-derived epitopes was observed, raising the possibility that protein or peptide persistence might play a role in the evolution of the memory phase of the CD4 T-cell response.

Adeno-associated virus vectors serotype 2 induce prolonged proliferation of capsid-specific CD8+ T cells in mice

Using adoptive transfer models we determined that an adeno-associated viral vector of serotype 2 (AAV2) induces in mice proliferation of CD8(+) T cells that recognize an epitope within the viral capsid. Proliferation to an endogenous epitope within viral protein (VP)3 could be observed for at least 3 weeks while a foreign epitope placed at multiple copies within VP2 elicited CD8(+) T cell expansion for at least 10 weeks. These data show that capsid antigens of AAV2 degrade slowly over a period of weeks and during this period provide targets to CD8(+) T cells.

Dendritic cells can effectively be pulsed by HBVsvp and induce specific immune reactions in mice

Eradication of chronic Hepatitis B virus (HBV) infection, marked by HBs seroconversion, is very rarely achieved by treatment with nucleoside and nucleotide analogs. Therapeutic cell based approaches, like interferon therapy, have a higher chance of seroconversion. Dendritic cells (DC) are key players in the cellular immune response and have been shown to play an important role in controlling HBV infection. In this study, the potential of ex vivo activated DC to induce specific immune responses against HBV was examined. DC derived from bone-marrow of BALB/c or C56BL/6 mice were pulsed with HBV subviral particles (HBVsvp), derived from the HepG2.2.15 cell line. HepG2.2.15 produces subviral particles consisting of the HBc and HBs proteins. Thus, the entire "viral surface" is presented to DC to induce an immune reaction. In vitro pulsation with HBVsvp successfully activated bone-marrow derived DC, demonstrated by FACS analysis showing increased MHCII, CD 86 and CCR-7. Immunization of mice, via subcutaneous injection of the activated DC, induced HBV specific immune reactions which were measured by ELISA, ELISPOT and T-cell proliferation analysis. Vaccination with ex vivo activated DC may be a promising tool for therapeutic or prophylactic approaches against the Hepatitis B virus.

Generation of effector CD8+ T cells and their conversion to memory T cells

Immunological memory is a cardinal feature of adaptive immunity. We are now beginning to elucidate the mechanisms that govern the formation of memory T cells and their ability to acquire longevity, survive the effector-to-memory transition, and mature into multipotent, functional memory T cells that self-renew. Here, we discuss the recent findings in this area and highlight extrinsic and intrinsic factors that regulate the cellular fate of activated CD8+ T cells.

Gene expression patterns and susceptibility to allergic responses

Allergic diseases are due to hypersensitive immune responses against otherwise innocuous allergens, and involve the dysregulated expression of numerous genes in cells from both the innate and adaptive immune systems. Allergic diseases are characterized by the enhanced production of type 2 T helper (Th2) cytokines, including interleukin-4, -5 and -13. These cytokines induce many of the pathophysiologic hallmarks of allergy, and their expression is tightly regulated at the level of gene transcription by both positively and negatively-acting transcription factors. In this review, the authors summarize data indicating that some of these factors represent checkpoints in the development of allergic diseases. Th2 gene expression is also controlled at the level of chromatin remodeling, and the implications of chromatin-based Th2 gene regulation in allergic disorders is also discussed. The differentiation of Th2 cells from naive precursors is critically dependent upon instruction received from dendritic cells, although the precise signals involved in this process are not well understood. Current thinking regarding some of the environmental cues interpreted by dendritic cells during allergen encounter, and how they promote Th2 responses will be reviewed. Understanding the cross-talk between dendritic cells and T cells holds great promise for deciphering the dysregulated immune response in allergy.

OX40 induces CCL20 expression in the context of antigen stimulation: an expanding role of co-stimulatory molecules in chemotaxis

OX40 is an inducible co-stimulatory molecule expressed by activated T cells. It plays an important role in the activation and proliferation of T lymphocytes. Recently, some co-stimulatory molecules have been shown to direct leukocyte trafficking. Chemotaxis is essential for achieving an effective immune response. CCL20 is an important chemoattractant produced by activated T cells. In this study, using DO11.10 mice whose transgenic T cell receptor specifically recognizes ovalbumin, we demonstrate that ovalbumin induces OX40 expression in CD4+ lymphocytes. Further stimulation of OX40 by OX40 activating antibody up-regulates CCL20 production. Both NF-kappaB dependent and independent signaling pathways are implicated in the induction of CCL20 by OX40. Finally, we primed the DO11.10 splenocytes with or without OX40 activating antibody in the presence of ovalbumin. Intranasal administration of the cell lysates derived from the cells with OX40 stimulation results in more severe leukocyte infiltration in the lung of DO11.10 mice, which is substantially attenuated by CCL20 blocking antibody. Taken together, this study has shown that activation of OX40 induces CCL20 expression in the presence of antigen stimulation. Thus, our results broaden the role of OX40 in chemotaxis, and reveal a novel effect of co-stimulatory molecules in orchestrating both T cell up-regulation and migration.