The coreceptor CD2 uses plasma membrane microdomains to transduce signals in T cells

Imaging of biphasic signalosomes constructed by checkpoint receptor 2B4 in conventional and chimeric antigen receptor-T cells

A co-signaling receptor, 2B4, has dual effects in immune cells, but its actual functions in T cells remain elusive. Here, using super-resolution imaging technology with an immunological synapse model, we showed that 2B4 forms "2B4 microclusters" immediately after 2B4-CD48 binding. A lipid phosphatase, SHIP-1, subsequently combined with 2B4 to form coinhibitory signalosomes, leading to the suppression of cytokine production. An activating adapter, SLAM-associated protein (SAP), attenuated the clustering of SHIP-1 and recruited a kinase, Fyn, enhancing the Vav1 signaling pathway as costimulatory signalosomes. Furthermore, we found that a chimeric antigen receptor with a 2B4 tail (2B4-CAR) retained the original signal transduction mechanism of 2B4. With endogenous levels of SAP expression, 2B4-CAR-T cells exposed sufficient antitumor efficacy in vivo without excess cytokine production. Our results may help explain the biphasic feature of 2B4 in T cell responses from the viewpoint of the signalosome and provide a new candidate for CAR development.

Revisiting T-cell adhesion molecules as potential targets for cancer immunotherapy: CD226 and CD2

Cancer immunotherapy aims to initiate or amplify immune responses that eliminate cancer cells and create immune memory to prevent relapse. Immune checkpoint inhibitors (ICIs), which target coinhibitory receptors on immune effector cells, such as CTLA-4 and PD-(L)1, have made significant strides in cancer treatment. However, they still face challenges in achieving widespread and durable responses. The effectiveness of anticancer immunity, which is determined by the interplay of coinhibitory and costimulatory signals in tumor-infiltrating immune cells, highlights the potential of costimulatory receptors as key targets for immunotherapy. This review explores our current understanding of the functions of CD2 and CD226, placing a special emphasis on their potential as novel agonist targets for cancer immunotherapy. CD2 and CD226, which are present mainly on T and NK cells, serve important functions in cell adhesion and recognition. These molecules are now recognized for their costimulatory benefits, particularly in the context of overcoming T-cell exhaustion and boosting antitumor responses. The importance of CD226, especially in anti-TIGIT therapy, along with the CD2‒CD58 axis in overcoming resistance to ICI or chimeric antigen receptor (CAR) T-cell therapies provides valuable insights into advancing beyond the current barriers of cancer immunotherapy, underscoring their promise as targets for novel agonist therapy.

Dynamics and spatial organization of Kv1.3 at the immunological synapse of human CD4+ T cells

Formation of the immunological synapse (IS) is a key event during initiation of an adaptive immune response to a specific antigen. During this process, a T cell and an antigen presenting cell form a stable contact that allows the T cell to integrate both internal and external stimuli in order to decide whether to activate. The threshold for T cell activation depends on the strength and frequency of the calcium (Ca2+) signaling induced by antigen recognition, and it must be tightly regulated to avoid undesired harm to healthy cells. Potassium (K+) channels are recruited to the IS to maintain the negative membrane potential required to sustain Ca2+ entry. However, the precise localization of K+ channels within the IS remains unknown. Here, we visualized the dynamic subsynaptic distribution of Kv1.3, the main voltage-gated potassium channel in human T cells. Upon T cell receptor engagement, Kv1.3 polarized toward the synaptic cleft and diffused throughout the F-actin rich distal compartment of the synaptic interface-an effect enhanced by CD2-CD58 corolla formation. As the synapse matured, Kv1.3 clusters were internalized at the center of the IS and released in extracellular vesicles. We propose a model in which specific distribution of Kv1.3 within the synapse indirectly regulates the channel function and that this process is limited through Kv1.3 internalization and release in extracellular vesicles.

An "off-the-shelf" CD2 universal CAR-T therapy for T-cell malignancies

T-cell malignancies are associated with frequent relapse and high morbidity, which is partly due to the lack of effective or targeted treatment options. To broaden the use of CAR-T cells in pan T-cell malignancies, we developed an allogeneic "universal" CD2-targeting CAR-T cell (UCART2), in which the CD2 antigen is deleted to prevent fratricide, and the T-cell receptor is removed to prevent GvHD. UCART2 demonstrated efficacy against T-ALL and CTCL and prolonged the survival of tumor-engrafted NSG mice in vivo. To evaluate the impact of CD2 on CAR-T function, we generated CD19 CAR-T cells (UCART19) with or without CD2 deletion, single-cell secretome analysis revealed that CD2 deletion in UCART19 reduced frequencies of the effector cytokines (Granzyme-B and IFN-γ). We also observed that UCART19ΔCD2 had reduced anti-tumor efficacy compared to UCART19 in a CD19+NALM6 xenograft model. Of note is that the reduced efficacy resulting from CD2 deletion was reversed when combined with rhIL-7-hyFc, a long-acting recombinant human interleukin-7. Treatment with rhIL-7-hyFc prolonged UCART2 persistence and increased survival in both the tumor re-challenge model and primary patient T-ALL model in vivo. Together, these data suggest that allogeneic fratricide-resistant UCART2, in combination with rhIL-7-hyFc, could be a suitable approach for treating T-cell malignancies.

NK and NKT cells in the pathogenesis of Hidradenitis suppurativa: Novel therapeutic strategy through targeting of CD2

Hidradenitis suppurativa (HS) is a chronic debilitating inflammatory skin disease with poorly understood pathogenesis. Single-cell RNAseq analysis of HS lesional and healthy individual skins revealed that NKT and NK cell populations were greatly expanded in HS, and they expressed elevated CD2, an activation receptor. Immunohistochemistry analyses confirmed significantly expanded numbers of CD2+ cells distributed throughout HS lesional tissue, and many co-expressed the NK marker, CD56. While CD4+ T cells were expanded in HS, CD8 T cells were rare. CD20+ B cells in HS were localized within tertiary follicle like structures. Immunofluorescence microscopy showed that NK cells (CD2 + CD56 dim ) expressing perforin, granzymes A and B were enriched within the hyperplastic follicular epidermis and tunnels of HS and juxtaposed with apoptotic cells. In contrast, NKT cells (CD2 + CD3 + CD56 bright ) primarily expressed granzyme A and were associated with α-SMA expressing fibroblasts within the fibrotic regions of the hypodermis. Keratinocytes and fibroblasts expressed high levels of CD58 (CD2 ligand) and they interacted with CD2 expressing NKT and NK cells. The NKT/NK maturation and activating cytokines, IL-12, IL-15 and IL-18, were significantly elevated in HS. Inhibition of cognate CD2-CD58 interaction with blocking anti-CD2 mAb in HS skin organotypic cultures resulted in a profound reduction of the inflammatory gene signature and secretion of inflammatory cytokines and chemokines in the culture supernate. In summary, we show that a cellular network of heterogenous NKT and NK cell populations drives inflammation, tunnel formation and fibrosis in the pathogenesis of HS. Furthermore, CD2 blockade is a viable immunotherapeutic approach for the management of HS.

Antigen discrimination by T cells relies on size-constrained microvillar contact

T cells use finger-like protrusions called 'microvilli' to interrogate their targets, but why they do so is unknown. To form contacts, T cells must overcome the highly charged, barrier-like layer of large molecules forming a target cell's glycocalyx. Here, T cells are observed to use microvilli to breach a model glycocalyx barrier, forming numerous small (<0.5 μm diameter) contacts each of which is stabilized by the small adhesive protein CD2 expressed by the T cell, and excludes large proteins including CD45, allowing sensitive, antigen dependent TCR signaling. In the absence of the glycocalyx or when microvillar contact-size is increased by enhancing CD2 expression, strong signaling occurs that is no longer antigen dependent. Our observations suggest that, modulated by the opposing effects of the target cell glycocalyx and small adhesive proteins, the use of microvilli equips T cells with the ability to effect discriminatory receptor signaling.

The kinase occupancy of T cell coreceptors reconsidered

The sensitivity of the αβ T cell receptor (TCR) is enhanced by the coreceptors CD4 and CD8αβ, which are expressed primarily by cells of the helper and cytotoxic T cell lineages, respectively. The coreceptors bind to major histocompatibility complex (MHC) molecules and associate intracellularly with the Src-family kinase Lck, which catalyzes TCR phosphorylation during receptor triggering. Although coreceptor/kinase occupancy was initially believed to be high, a recent study suggested that most coreceptors exist in an Lck-free state, and that this low occupancy helps to effect TCR antigen discrimination. Here, using the same method, we found instead that the CD4/Lck interaction was stoichiometric (~100%) and that the CD8αβ/Lck interaction was substantial (~60%). We confirmed our findings in live cells using fluorescence cross-correlation spectroscopy (FCCS) to measure coreceptor/Lck codiffusion in situ. After introducing structurally guided mutations into the intracellular domain of CD4, we used FCCS to also show that stoichiometric coupling to Lck required an amphipathic α-helix present in CD4 but not CD8α. In double-positive cells expressing equal numbers of both coreceptors, but limiting amounts of kinase, CD4 outcompeted CD8αβ for Lck. In T cells, TCR signaling induced CD4/Lck oligomerization but did not affect the high levels of CD4/Lck occupancy. These findings help settle the question of kinase occupancy and suggest that the binding advantages that CD4 has over CD8 could be important when Lck levels are limiting.

Enhancing CAR T function with the engineered secretion of C. perfringens neuraminidase

Prior to adoptive transfer, CAR T cells are activated, lentivirally infected with CAR transgenes, and expanded over 9 to 11 days. An unintended consequence of this process is the progressive differentiation of CAR T cells over time in culture. Differentiated T cells engraft poorly, which limits their ability to persist and provide sustained tumor control in hematologic as well as solid tumors. Solid tumors include other barriers to CAR T cell therapies, including immune and metabolic checkpoints that suppress effector function and durability. Sialic acids are ubiquitous surface molecules with known immune checkpoint functions. The enzyme C. perfringens neuraminidase (CpNA) removes sialic acid residues from target cells, with good activity at physiologic conditions. In combination with galactose oxidase (GO), NA has been found to stimulate T cell mitogenesis and cytotoxicity in vitro. Here we determine whether CpNA alone and in combination with GO promotes CAR T cell antitumor efficacy. We show that CpNA restrains CAR T cell differentiation during ex vivo culture, giving rise to progeny with enhanced therapeutic potential. CAR T cells expressing CpNA have superior effector function and cytotoxicity in vitro. In a Nalm-6 xenograft model of leukemia, CAR T cells expressing CpNA show enhanced antitumor efficacy. Arming CAR T cells with CpNA also enhanced tumor control in xenograft models of glioblastoma as well as a syngeneic model of melanoma. Given our findings, we hypothesize that charge repulsion via surface glycans is a regulatory parameter influencing differentiation. As T cells engage target cells within tumors and undergo constitutive activation through their CARs, critical thresholds of negative charge may impede cell-cell interactions underlying synapse formation and cytolysis. Removing the dense pool of negative cell-surface charge with CpNA is an effective approach to limit CAR T cell differentiation and enhance overall persistence and efficacy.

Dephosphorylation accelerates the dissociation of ZAP70 from the T cell receptor

Protein-protein binding domains are critical in signaling networks. Src homology 2 (SH2) domains are binding domains that interact with sequences containing phosphorylated tyrosines. A subset of SH2 domain-containing proteins has tandem domains, which are thought to enhance binding affinity and specificity. However, a trade-off exists between long-lived binding and the ability to rapidly reverse signaling, which is a critical requirement of noise-filtering mechanisms such as kinetic proofreading. Here, we use modeling to show that the unbinding rate of tandem, but not single, SH2 domains can be accelerated by phosphatases. Using surface plasmon resonance, we show that the phosphatase CD45 can accelerate the unbinding rate of zeta chain-associated protein kinase 70 (ZAP70), a tandem SH2 domain-containing kinase, from biphosphorylated peptides from the T cell receptor (TCR). An important functional prediction of accelerated unbinding is that the intracellular ZAP70-TCR half-life in T cells will not be fixed but rather, dependent on the extracellular TCR-antigen half-life, and we show that this is the case in both cell lines and primary T cells. The work highlights that tandem SH2 domains can break the trade-off between signal fidelity (requiring long half-life) and signal reversibility (requiring short half-life), which is a key requirement for T cell antigen discrimination mediated by kinetic proofreading.

Prestimulation of CD2 confers resistance to HIV-1 latent infection in blood resting CD4 T cells

HIV-1 infects blood CD4 T cells through the use of CD4 and CXCR4 or CCR5 receptors, which can be targeted through blocking viral binding to CD4/CXCR4/CCR5 or virus-cell fusion. Here we describe a novel mechanism by which HIV-1 nuclear entry can also be blocked through targeting a non-entry receptor, CD2. Cluster of differentiation 2 (CD2) is an adhesion molecule highly expressed on human blood CD4, particularly, memory CD4 T cells. We found that CD2 ligation with its cell-free ligand LFA-3 or anti-CD2 antibodies rendered blood resting CD4 T cells highly resistant to HIV-1 infection. We further demonstrate that mechanistically, CD2 binding initiates competitive signaling leading to cofilin activation and localized actin polymerization around CD2, which spatially inhibits HIV-1-initiated local actin polymerization needed for viral nuclear migration. Our study identifies CD2 as a novel target to block HIV-1 infection of blood resting T cells.

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CD2 is highly expressed on human blood CD4 T cells, particularly memory T cells

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Prestimulation of CD2 rendered resting T cells highly resistant to HIV infection

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CD2 signaling activates cofilin and actin polymerization blocking HIV nuclear entry

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CD2 may serve as a novel target to inhibit HIV-1 infection of blood resting T cells

Characterization of mechanisms positioning costimulatory complexes in immune synapses

Small immunoglobulin superfamily (sIGSF) adhesion complexes form a corolla of microdomains around an integrin ring and secretory core during immunological synapse (IS) formation. The corolla recruits and retains major costimulatory/checkpoint complexes, such as CD28, making forces that govern corolla formation of particular interest. Here, we investigated the mechanisms underlying molecular reorganization of CD2, an adhesion and costimulatory molecule of the sIGSF family during IS formation. Computer simulations showed passive distal exclusion of CD2 complexes under weak interactions with the ramified F-actin transport network. Attractive forces between CD2 and CD28 complexes relocate CD28 from the IS center to the corolla. Size-based sorting interactions with large glycocalyx components, such as CD45, or short-range CD2 self-attraction successfully explain the corolla 'petals.' This establishes a general simulation framework for complex pattern formation observed in cell-bilayer and cell-cell interfaces, and the suggestion of new therapeutic targets, where boosting or impairing characteristic pattern formation can be pivotal.

Naïve Regulatory T Cell Subset Is Altered in X-Linked Agammaglobulinemia

The interplay between T- and B-cell compartments during naïve, effector and memory T cell maturation is critical for a balanced immune response. Primary B-cell immunodeficiency arising from X-linked agammaglobulinemia (XLA) offers a model to explore B cell impact on T cell subsets, starting from the thymic selection. Here we investigated characteristics of naïve and effector T cell subsets in XLA patients, revealing prominent alterations in the corresponding T-cell receptor (TCR) repertoires. We observed immunosenescence in terms of decreased diversity of naïve CD4⁺ and CD8⁺ TCR repertoires in XLA donors. The most substantial alterations were found within naïve CD4⁺ subsets, and we have investigated these in greater detail. In particular, increased clonality and convergence, along with shorter CDR3 regions, suggested narrower focused antigen-specific maturation of thymus-derived naïve T_reg (CD4⁺CD45RA⁺CD27⁺CD25⁺) in the absence of B cells - normally presenting diverse self and commensal antigens. The naïve T_reg proportion among naïve CD4 T cells was decreased in XLA patients, supporting the concept of impaired thymic naïve T_reg selection. Furthermore, the naïve T_reg subset showed prominent differences at the transcriptome level, including increased expression of genes specific for antigen-presenting and myeloid cells. Altogether, our findings suggest active B cell involvement in CD4 T cell subsets maturation, including B cell-dependent expansion of the naïve Treg TCR repertoire that enables better control of self-reactive T cells.

Increasing LFA-1 Expression Enhances Immune Synapse Architecture and T Cell Receptor Signaling in Jurkat E6.1 Cells

The Jurkat E6.1 clone has been extensively used as a powerful tool for the genetic and biochemical dissection of the TCR signaling pathway. More recently, these cells have been exploited in imaging studies to identify key players in immunological synapse (IS) assembly in superantigen-specific conjugates and to track the dynamics of signaling molecules on glass surfaces coated with activating anti-CD3 antibodies. By comparison, Jurkat cells have been used only scantily for imaging on supported lipid bilayers (SLBs) incorporating laterally mobile TCR and integrin ligands, which allow to study synaptic rearrangements of surface molecules and the fine architecture of the mature IS, likely due to limitations in the assembly of immune synapses with well-defined architecture. Here we have explored whether upregulating the low levels of endogenous LFA-1 expression on Jurkat E6.1 cells through transduction with CD11a- and CD18-encoding lentiviruses can improve IS architecture. We show that, while forced LFA-1 expression did not affect TCR recruitment to the IS, E6.1 LFA-1 high cells assembled better structured synapses, with a tighter distribution of signaling-competent TCRs at the center of the IS. LFA-1 upregulation enhanced protein phosphotyrosine signaling on SLBs but not at the IS formed in conjugates with SEE-pulsed APCs, and led to the constitutive formation of an intracellular phosphotyrosine pool co-localizing with endosomal CD3ζ. This was paralleled by an increase in the levels of p-ZAP-70 and p-Erk both under basal conditions and following activation, and in enhanced Ca2+ mobilization from intracellular stores. The enhancement in early signaling E6.1 LFA-1 high cells did not affect expression of the early activation marker CD69 but led to an increase in IL-2 expression. Our results highlight a new role for LFA-1 in the core architecture of the IS that can be exploited to study the spatiotemporal redistribution of surface receptors on SLBs, thereby extending the potential of E6.1 cells and their derivatives for fine-scale imaging studies.

CD58 Immunobiology at a Glance

The glycoprotein CD58, also known as lymphocyte-function antigen 3 (LFA-3), is a costimulatory receptor distributed on a broad range of human tissue cells. Its natural ligand CD2 is primarily expressed on the surface of T/NK cells. The CD2-CD58 interaction is an important component of the immunological synapse (IS) that induces activation and proliferation of T/NK cells and triggers a series of intracellular signaling in T/NK cells and target cells, respectively, in addition to promoting cell adhesion and recognition. Furthermore, a soluble form of CD58 (sCD58) is also present in cellular supernatant in vitro and in local tissues in vivo. The sCD58 is involved in T/NK cell-mediated immune responses as an immunosuppressive factor by affecting CD2-CD58 interaction. Altered accumulation of sCD58 may lead to immunosuppression of T/NK cells in the tumor microenvironment, allowing sCD58 as a novel immunotherapeutic target. Recently, the crucial roles of costimulatory molecule CD58 in immunomodulation seem to be reattracting the interests of investigators. In particular, the CD2-CD58 interaction is involved in the regulation of antiviral responses, inflammatory responses in autoimmune diseases, immune rejection of transplantation, and immune evasion of tumor cells. In this review, we provide a comprehensive summary of CD58 immunobiology.

Design, synthesis and immunological evaluation of self-assembled antigenic peptides from dual-antigen targets: a broad-spectrum candidate for an effective antibreast cancer therapy

Background

Considering the narrow immune response spectrum of a single epitope, and the nanoparticles (NPs) as a novel adjuvant can achieve efficient delivery of antigenic peptides safely, a nano-system (denoted as DSPE-PEG-Man@EM-NPs) based on cathepsin B-responsive antigenic peptides was designed and synthesized.

Methods

Highly affinitive antigenic peptides were delivered by self-assembled NPs, and targeted erythrocyte membranes acted as a peptide carrier to improve antigenic peptides presentation and to strengthen cytotoxic T-cells reaction. Cathepsin B coupling could release antigenic peptides rapidly in dendritic cells.

Results

Evaluations showed that DSPE-PEG-Man@EM-NPs had obvious inhibitory effects towards both MCF-7 and MDA-MB-231 human breast cancer cell lines.

Conclusion

Overall, this strategy provides a novel strategy for boosting cytotoxic T lymphocytes response, thereby expanding the adaptation range of tumor antigenic peptides and improving the therapeutic effect of tumor immunotherapy with nanomedicine.

ERM-Dependent Assembly of T Cell Receptor Signaling and Co-stimulatory Molecules on Microvilli prior to Activation

T cell surfaces are covered with microvilli, actin-rich and flexible protrusions. We use super-resolution microscopy to show that ≥90% of T cell receptor (TCR) complex molecules TCRαβ and TCRζ, as well as the co-receptor CD4 (cluster of differentiation 4) and the co-stimulatory molecule CD2, reside on microvilli of resting human T cells. Furthermore, TCR proximal signaling molecules involved in the initial stages of the immune response, including the protein tyrosine kinase Lck (lymphocyte-specific protein tyrosine kinase) and the key adaptor LAT (linker for activation of T cells), are also enriched on microvilli. Notably, phosphorylated proteins of the ERM (ezrin, radixin, and moesin) family colocalize with TCRαβ as well as with actin filaments, implying a role for one or more ERMs in linking the TCR complex to the actin cytoskeleton within microvilli. Our results establish microvilli as key signaling hubs, in which the TCR complex and its proximal signaling molecules and adaptors are preassembled prior to activation in an ERM-dependent manner, facilitating initial antigen sensing.

Regulations of T Cell Activation by Membrane and Cytoskeleton

Among various types of membrane proteins that are regulated by cytoskeleton, the T cell receptor (TCR) greatly benefits from these cellular machineries for its function. The T cell is activated by the ligation of TCR to its target agonist peptide. However, the binding affinity of the two is not very strong, while the T cell needs to discriminate agonist from many nonagonist peptides. Moreover, the strength and duration of the activation signaling need to be tuned for immunological functions. Many years of investigations revealed that dynamic acto-myosin cytoskeletons and plasma membranes in T cells facilitate such regulations by modulating the spatiotemporal distributions of proteins in plasma membranes and by applying mechanical loads on proteins. In these processes, protein dynamics in multiple scales are involved, ranging from collective molecular motions and macroscopic molecular organizations at the cell–cell interface to microscopic changes in distances between receptor and ligand molecules. In this review, details of how cytoskeletons and membranes regulate these processes are discussed, with the emphasis on how all these processes are coordinated to occur within a single cell system.

Cell-cell interfaces as specialized compartments directing cell function

Cell-cell interfaces are found throughout multicellular organisms, from transient interactions between motile immune cells to long-lived cell-cell contacts in epithelia. Studies of immune cell interactions, epithelial cell barriers, neuronal contacts and sites of cell-cell fusion have identified a core set of features shared by cell-cell interfaces that critically control their function. Data from diverse cell types also show that cells actively and passively regulate the localization, strength, duration and cytoskeletal coupling of receptor interactions governing cell-cell signalling and physical connections between cells, indicating that cell-cell interfaces have a unique membrane organization that emerges from local molecular and cellular mechanics. In this Review, we discuss recent findings that support the emerging view of cell-cell interfaces as specialized compartments that biophysically constrain the arrangement and activity of their protein, lipid and glycan components. We also review how these biophysical features of cell-cell interfaces allow cells to respond with high selectivity and sensitivity to multiple inputs, serving as the basis for wide-ranging cellular functions. Finally, we consider how the unique properties of cell-cell interfaces present opportunities for therapeutic intervention.

A dynamic CD2-rich compartment at the outer edge of the immunological synapse boosts and integrates signals

The CD2-CD58 recognition system promotes adhesion and signaling and counters exhaustion in human T cells. We found that CD2 localized to the outer edge of the mature immunological synapse, with cellular or artificial APC, in a pattern we refer to as a 'CD2 corolla'. The corolla captured engaged CD28, ICOS, CD226 and SLAM-F1 co-stimulators. The corolla amplified active phosphorylated Src-family kinases (pSFK), LAT and PLC-γ over T cell receptor (TCR) alone. CD2-CD58 interactions in the corolla boosted signaling by 77% as compared with central CD2-CD58 interactions. Engaged PD-1 invaded the CD2 corolla and buffered CD2-mediated amplification of TCR signaling. CD2 numbers and motifs in its cytoplasmic tail controlled corolla formation. CD8+ tumor-infiltrating lymphocytes displayed low expression of CD2 in the majority of people with colorectal, endometrial or ovarian cancer. CD2 downregulation may attenuate antitumor T cell responses, with implications for checkpoint immunotherapies.

Human CD8+ T Cells Exhibit a Shared Antigen Threshold for Different Effector Responses

CD8⁺ T cells produce TNF-α, IL-2, and IFN-γ with similar Ag thresholds.

Costimulation decreases Ag thresholds similarly for different cytokines.

A common rate-limiting switch downstream of the TCR can explain these findings.

T cells recognizing cognate pMHC Ags become activated to elicit a myriad of cellular responses, such as target cell killing and the secretion of different cytokines, that collectively contribute to adaptive immunity. These effector responses have been hypothesized to exhibit different Ag dose and affinity thresholds, suggesting that pathogen-specific information may be encoded within the nature of the Ag. In this study, using systematic experiments in a reductionist system, in which primary human CD8⁺ T cell blasts are stimulated by recombinant peptides presented on MHC Ag alone, we show that different inflammatory cytokines have comparable Ag dose thresholds across a 25,000-fold variation in affinity. Although costimulation by CD28, CD2, and CD27 increased cytokine production in this system, the Ag threshold remained comparable across different cytokines. When using primary human memory CD8⁺ T cells responding to autologous APCs, equivalent thresholds were also observed for different cytokines and killing. These findings imply a simple phenotypic model of TCR signaling in which multiple T cell responses share a common rate-limiting threshold and a conceptually simple model of CD8⁺ T cell Ag recognition, in which Ag dose and affinity do not provide any additional response-specific information.

CD2 Immunobiology

The glycoprotein CD2 is a costimulatory receptor expressed mainly on T and NK cells that binds to LFA3, a cell surface protein expressed on e.g., antigen-presenting cells. CD2 has an important role in the formation and organization of the immunological synapse that is formed between T cells and antigen-presenting cells upon cell-cell conjugation and associated intracellular signaling. CD2 expression is upregulated on memory T cells as well as activated T cells and plays an important role in activation of memory T cells despite the coexistence of several other costimulatory pathways. Anti-CD2 monoclonal antibodies have been shown to induce immune modulatory effects in vitro and clinical studies have proven the safety and efficacy of CD2-targeting biologics. Investigators have highlighted that the lack of attention to the CD2/LFA3 costimulatory pathway is a missed opportunity. Overall, CD2 is an attractive target for monoclonal antibodies intended for treatment of pathologies characterized by undesired T cell activation and offers an avenue to more selectively target memory T cells while favoring immune regulation.

Phosphoproteomics of CD2 signaling reveals AMPK-dependent regulation of lytic granule polarization in cytotoxic T cells

Understanding the costimulatory signaling that enhances the activity of cytotoxic T cells (CTLs) could identify potential targets for immunotherapy. Here, we report that CD2 costimulation plays a critical role in target cell killing by freshly isolated human CD8⁺ T cells, which represent a challenging but valuable model to gain insight into CTL biology. We found that CD2 stimulation critically enhanced signaling by the T cell receptor in the formation of functional immune synapses by promoting the polarization of lytic granules toward the microtubule-organizing center (MTOC). To gain insight into the underlying mechanism, we explored the CD2 signaling network by phosphoproteomics, which revealed 616 CD2-regulated phosphorylation events in 373 proteins implicated in the regulation of vesicular trafficking, cytoskeletal organization, autophagy, and metabolism. Signaling by the master metabolic regulator AMP-activated protein kinase (AMPK) was a critical node in the CD2 network, which promoted granule polarization toward the MTOC in CD8⁺ T cells. Granule trafficking was driven by active AMPK enriched on adjacent lysosomes, revealing previously uncharacterized signaling cross-talk between vesicular compartments in CD8⁺ T cells. Our results thus establish CD2 signaling as key for mediating cytotoxic killing and granule polarization in freshly isolated CD8⁺ T cells and strengthen the rationale to choose CD2 and AMPK as therapeutic targets to enhance CTL activity.

T11TS immunotherapy potentiates the repressed calcineurin-NFAT signalling pathway of T cells in Cryptococcus neoformans infected rats: a cue towards T-cell activation for antifungal immunity

AIMS

To examine the modulation of the interacting partners of the calcineurin (CaN)-NFAT pathway in T cells during Cryptococcus neoformans fungal infection and post-T11TS immunotherapy.

METHODS AND RESULTS

Wistar rats were infected with C. neoformans and followed by immunotherapy with immune-potentiator T11TS. T cells were analysed by flow cytometry, immunoblotting and nuclear translocation study. The signalling proteins LCK, FYN, LAT, PLCγ1 and CaN in T cells were regulated by C. neoformans infection resulting in reduced nuclear translocation of NFAT and IL-2 expression. Following T11TS immunotherapy, the expressions of the above-mentioned proteins were boosted and thus resulting in the clearance of C. neoformans from lung and spleen.

CONCLUSIONS

The precise mechanism of suppression of the T-cell function by C. neoformans is still unknown. Previously, we have shown that T11TS positively regulates the function of T cells to abrogate glioma and other immunosuppressive conditions. T11TS immunotherapy increased the expression of the above signalling partners of the CaN-NFAT pathway in T cells and improved nuclear retention of NFAT. As a result, an increased IL-2 expression leads to activation and proliferation of T cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results demonstrate the role of T11TS in restoring the CaN-NFAT signalling pathway in T cells. It identifies T11TS as an immunotherapeutic agent with potential clinical outcomes to counteract C. neoformans infection.

Synaptic Interactions in Germinal Centers

The germinal center (GC) is a complex, highly dynamic microanatomical niche that allows the generation of high-affinity antibody-producing plasma cells and memory B cells. These cells constitute the basis of long-lived highly protective antibody responses. For affinity maturation to occur, B cells undergo multiple rounds of proliferation and mutation of the genes that encode the immunoglobulin V region followed by selection by specialized T cells called follicular helper T (T_FH) cells. In order to achieve this result, the GC requires spatially and temporally coordinated interactions between the different cell types, including B and T lymphocytes and follicular dendritic cells. Cognate interactions between T_FH and GC B cells resemble cellular connections and synaptic communication within the nervous system, which allow signals to be transduced rapidly and effectively across the synaptic cleft. Such immunological synapses are particularly critical in the GC where the speed of T–B cell interactions is faster and their duration shorter than at other sites. In addition, the antigen-based specificity of cognate interactions in GCs is critical for affinity-based selection in which B cells compete for T cell help so that rapid modulation of the signaling threshold determines the outcome of the interaction. In the context of GCs, which contain large numbers of cells in a highly compacted structure, focused delivery of signals across the interacting cells becomes particularly important. Promiscuous or bystander delivery of positive selection signals could potentially lead to the appearance of long-lived self-reactive B cell clones. Cytokines, cytotoxic granules, and more recently neurotransmitters have been shown to be transferred from T_FH to B cells upon cognate interactions. This review describes the current knowledge on immunological synapses occurring during GC responses including the type of granules, their content, and function in T_FH-mediated help to B cells.

Differentially expressed genes related to major depressive disorder and antidepressant response: genome-wide gene expression analysis

Treatment response to antidepressants is limited and varies among patients with major depressive disorder (MDD). To discover genes and mechanisms related to the pathophysiology of MDD and antidepressant treatment response, we performed gene expression analyses using peripheral blood specimens from 38 MDD patients and 14 healthy individuals at baseline and at 6 weeks after the initiation of either selective serotonin reuptake inhibitor (SSRI) or mirtazapine treatment. The results were compared with results from public microarray data. Seven differentially expressed genes (DEGs) between MDD patients and controls were identified in our study and in the public microarray data: CD58, CXCL8, EGF, TARP, TNFSF4, ZNF583, and ZNF587. CXCL8 was among the top 10 downregulated genes in both studies. Eight genes related to SSRI responsiveness, including BTNL8, showed alterations in gene expression in MDD. The expression of the FCRL6 gene differed between SSRI responders and nonresponders and changed after SSRI treatment compared to baseline. In evaluating the response to mirtazapine, 21 DEGs were identified when comparing MDD patients and controls and responders and nonresponders. These findings suggest that the pathophysiology of MDD and treatment response to antidepressants are associated with a number of processes, including DNA damage and apoptosis, that can be induced by immune activation and inflammation.

Differences in the expression of several genes before and after different antidepressant treatments were found in patients with major depressive disorder (MDD), and may help identify patients most likely to benefit from specific drugs. Researchers in South Korea led by Doh Kwan Kim and Soo-Youn Lee at Samsung Medical Center, Seoul, examined gene expression across the 28,869 genes in 38 patients with MDD and 14 healthy individuals. They also validated their findings using existing databases of gene expression in patients with MDD and healthy controls. The research suggests that genes involved in the immune response and inflammation are significantly alternated in MDD and are predictable in which patients respond well to antidepressants. These findings may help develop new approaches to antidepressant therapies, and assist tailoring of treatment to the specific needs of different patients.

Single-Molecule Light-Sheet Imaging of Suspended T Cells

Adaptive immune responses are initiated by triggering of the T cell receptor. Single-molecule imaging based on total internal reflection fluorescence microscopy at coverslip/basal cell interfaces is commonly used to study this process. These experiments have suggested, unexpectedly, that the diffusional behavior and organization of signaling proteins and receptors may be constrained before activation. However, it is unclear to what extent the molecular behavior and cell state is affected by the imaging conditions, i.e., by the presence of a supporting surface. In this study, we implemented single-molecule light-sheet microscopy, which enables single receptors to be directly visualized at any plane in a cell to study protein dynamics and organization in live, resting T cells. The light sheet enabled the acquisition of high-quality single-molecule fluorescence images that were comparable to those of total internal reflection fluorescence microscopy. By comparing the apical and basal surfaces of surface-contacting T cells using single-molecule light-sheet microscopy, we found that most coated-glass surfaces and supported lipid bilayers profoundly affected the diffusion of membrane proteins (T cell receptor and CD45) and that all the surfaces induced calcium influx to various degrees. Our results suggest that, when studying resting T cells, surfaces are best avoided, which we achieve here by suspending cells in agarose.

Suppression of costimulation by human cytomegalovirus promotes evasion of cellular immune defenses

CD58 is an adhesion molecule that is known to play a critical role in costimulation of effector cells and is intrinsic to immune synapse structure. Herein, we describe a virally encoded gene that inhibits CD58 surface expression. Human cytomegalovirus (HCMV) UL148 was necessary and sufficient to promote intracellular retention of CD58 during HCMV infection. Blocking studies with antagonistic anti-CD58 mAb and an HCMV UL148 deletion mutant (HCMV∆UL148) with restored CD58 expression demonstrated that the CD2/CD58 axis was essential for the recognition of HCMV-infected targets by CD8⁺ HCMV-specific cytotoxic T lymphocytes (CTLs). Further, challenge of peripheral blood mononuclear cells ex vivo with HCMV∆UL148 increased both CTL and natural killer (NK) cell degranulation against HCMV-infected cells, including NK-driven antibody-dependent cellular cytotoxicity, showing that UL148 is a modulator of the function of multiple effector cell subsets. Our data stress the effect of HCMV immune evasion functions on shaping the immune response, highlighting the capacity for their potential use in modulating immunity during the development of anti-HCMV vaccines and HCMV-based vaccine vectors.

Natural killer cell cytotoxicity and its regulation by inhibitory receptors

Natural killer (NK) cells express an array of germ-line encoded receptors that are capable of triggering cytotoxicity. NK cells tend to express many members of a given family of signalling molecules. The presence of many activating receptors and many members of a given family of signalling molecules can enable NK cells to detect different kinds of target cells, and to mount different kinds of responses. This contributes also to the robustness of NK cells responses; cytotoxic functions of NK cells often remain unaffected in the absence of selected signalling molecules. NK cells express many MHC-I-specific inhibitory receptors. Signals from MHC-I-specific inhibitory receptors tightly control NK cell cytotoxicity and, paradoxically, maintain NK cells in a state of proper responsiveness. This review provides a brief overview of the events that underlie NK cell activation, and how signals from inhibitory receptors intercept NK cell activation to prevent inappropriate triggering of cytotoxicity.

Signals Controlling Lytic Granule Polarization at the Cytotoxic Immune Synapse

Cytotoxic immunity relies on specialized effector T cells, the cytotoxic T cells, which are endowed with specialized cytolytic machinery that permits them to induce death of their targets. Upon recognition of a target cell, cytotoxic T cells form a lytic immune synapse and by docking the microtubule-organizing center at the synaptic membrane get prepared to deliver a lethal hit of enzymes contained in lytic granules. New insights suggest that the directionality of lytic granule trafficking along the microtubules represents a fine means to tune the functional outcome of the encounter between a T cell and its target. Thus, mechanisms regulating the directionality of granule transport may have a major impact in settings characterized by evasion from the cytotoxic response, such as chronic infection and cancer. Here, we review our current knowledge on the signaling pathways implicated in the polarized trafficking at the immune synapse of cytotoxic T cells, complementing it with information on the regulation of this process in natural killer cells. Furthermore, we highlight some of the parameters which we consider critical in studying the polarized trafficking of lytic granules, including the use of freshly isolated cytotoxic T cells, and discuss some of the major open questions.

Proline-serine-threonine phosphatase interacting protein 1 (PSTPIP1) controls immune synapse stability in human T cells

BACKGROUND

Proline-serine-threonine phosphatase interacting protein 1 (PSTPIP1) is a cytosolic adaptor protein involved with T-cell activation, differentiation, and migration. On cognate T-cell contact, PSTPIP1 is recruited to surface-expressed CD2, where it regulates F-actin remodeling. An immune synapse (IS) is thereby rapidly formed, consisting of T-cell receptor clusters surrounded by a ring of adhesion molecules, including CD2.

OBJECTIVE

From genetic screening of patients with primary immunodeficiencies, we identified 2 mutations in PSTPIP1, R228C and T274M, which we further characterized in the primary patients' T cells.

METHODS

F-actin dynamics were assessed in primary T cells from the patients and control subjects by using fluorescence-activated cell sorting. HEK293T and Jurkat cells were transfected with R228C, T274M, and wild-type PSTPIP1 to visualize F-actin in IS formation. CD2-PSTPIP1 association was quantified through immunoprecipitation assays.

RESULTS

The patients presented with immunodeficiency without signs of autoinflammation. The patient with the R228C mutation had expansion of mostly naive phenotype T cells and few memory T cells; the patient with the T274M mutation had 75% reduction in CD4 T cells that were predominantly of the memory subset. We observed F-actin polymerization defects in T cells from both patients with PSTPIP1, most notably the patient with the T274M mutation. Capping of CD2-containing membrane microdomains was disrupted. Analysis of IS formation using Jurkat T-cell transfectants revealed a reduction in F-actin accumulation at the IS, again especially in cells from the patient with the T274M PSTPIP1 mutation. T cells from the patient with the T274M mutation migrated spontaneously at increased speed, as assessed in a 3-dimensional collagen matrix, whereas T-cell receptor cross-linking induced a significantly diminished calcium flux.

CONCLUSIONS

We propose that PSTPIP1 T-cell differentiation defects are caused by defective control of F-actin polymerization. A preactivated polymerized F-actin status, as seen in T cells from patients with the PSTPIP1 T274M mutation, appears particularly damaging. PSTPIP1 controls IS formation and cell adhesion through its function as an orchestrator of the F-actin cytoskeleton.

A cellular platform for the evaluation of immune checkpoint molecules

Blockade of the T cell coinhibitory molecules CTLA-4 and PD-1 has clinical utility to strengthen T cell responses. In addition to these immune checkpoints an ever-growing number of molecules has been implicated in generating coinhibitory signals in T cells. However, investigating coinhibitory molecules in primary human cells is complicated by the restricted expression and promiscuity of both coinhibitory receptors and their ligands. Here we have evaluated the potential of fluorescence-based transcriptional reporters based on the human Jurkat T cell line in conjunction with engineered T cell stimulator cell lines for investigating coinhibitory pathways. CTLA-4, PD-1, TIGIT, BTLA and 2B4 expressing reporter cells were generated and activated with T cell stimulator cells expressing cognate ligands of these molecules.

All accessory molecules tested were functional in our reporter system. Engagement of CTLA-4, PD-1, BTLA and TIGIT by their ligands significantly inhibited T cell activation, whereas binding of 2B4 by CD48 resulted in enhanced responses. Mutational analysis revealed intracellular motifs that are responsible for BTLA mediated T cell inhibition and demonstrates potent reporter inhibition by CTLA-4 independent of cytoplasmic signaling motifs. Moreover, considerably higher IC50 values were measured for the CTLA-4 blocker Ipilimumab compared to the PD-1 antibody Nivolumab.

Our findings show that coinhibitory pathways can be evaluated in Jurkat-based transcriptional reporters and yield novel insights on their function. Results obtained from this robust reductionist system can complement more time consuming and complex studies of such pathways in primary T cells.

Ca2+ Microdomains in T-Lymphocytes

Early Ca²⁺ signaling is characterized by occurrence of Ca²⁺ microdomains formed by opening of single or clusters of Ca²⁺ channels, thereby initiating first signaling and subsequently activating global Ca²⁺ signaling mechanisms. However, only few data are available focusing on the first seconds and minutes of Ca²⁺ microdomain formation and related signaling pathways in activated T-lymphocytes. In this review, we condense current knowledge on Ca²⁺ microdomain formation in T-lymphocytes and early Ca²⁺ signaling, function of Ca²⁺ microdomains, and microdomain organization. Interestingly, considering the first seconds of T cell activation, a triphasic Ca²⁺ signal is becoming apparent: (i) initial Ca²⁺ microdomains occurring in the first second of T cell activation, (ii) amplification of Ca²⁺ microdomains by recruitment of further channels in the next 5-10 s, and (iii) a transition to global Ca²⁺ increase. Apparently, the second messenger nicotinic acid adenine dinucleotide phosphate is the first second messenger involved in initiation of Ca²⁺ microdomains. Ryanodine receptors type 1 act as initial Ca²⁺ release channels in CD4⁺ T-lymphocytes. Regarding the temporal correlation of Ca²⁺ microdomains with other molecular events of T cell activation, T cell receptor-dependent microdomain organization of signaling molecules Grb2 and Src homology [SH2] domain-containing leukocyte protein of 65 kDa was observed within the first 20 s. In addition, fast cytoskeletal changes are initiated. Furthermore, the involvement of additional Ca²⁺ channels and organelles, such as the Ca²⁺ buffering mitochondria, is discussed. Future research developments will comprise analysis of the causal relation between these temporally coordinated signaling events. Taken together, high-resolution Ca²⁺ imaging techniques applied to T cell activation in the past years paved the way to detailed molecular understanding of initial Ca²⁺ signaling mechanisms in non-excitable cells.

Signaling and Polarized Communication Across the T Cell Immunological Synapse

T cells express a somatically recombined antigen receptor (αβTCR) that is calibrated during development to respond to changes in peptides displayed by major histocompatibility complex proteins (pMHC) on the surface of antigen-presenting cells (APC). A key characteristic of pMHC for adaptive immunity is the ability to sample internal states of cells and tissues to sensitively detect changes associated with infection, cell derangement, or tissue injury. Physical T cell-APC contact sets up an axis for polarization of TCR, adhesion molecules, kinases, cytoskeletal elements, and organelles inherent in this mode of juxtacrine signaling. The discovery of further lateral organization of the TCR and adhesion molecules into radially symmetric compartments, the immunological synapse, revealed an intersecting plane of symmetry and potential for regulated symmetry breaking to control duration of T cell-APC interactions. In addition to organizing signaling machinery, the immunological synapse directs the polarized transport and secretion of cytokines and cytolytic agents across the synaptic cleft and is a site for the generation and exocytic release of bioactive microvesicles that can functionally affect recipient APC and other cells in the environment. This machinery is coopted by retroviruses, and human immune deficiency virus-1 may even use antigen-specific synapses for infection of healthy T cells. Here, we discuss recent advances in the molecular and cell biological mechanisms of immunological synapse assembly and signaling and its role in intercellular communication across the synaptic cleft.

Critical Role of CD2 Co-stimulation in Adaptive Natural Killer Cell Responses Revealed in NKG2C-Deficient Humans

Infection by human cytomegalovirus (HCMV) leads to NKG2C-driven expansion of adaptive natural killer (NK) cells, contributing to host defense. However, approximately 4% of all humans carry a homozygous deletion of the gene that encodes NKG2C (NKG2C^−/−). Assessment of NK cell repertoires in 60 NKG2C^−/− donors revealed a broad range of NK cell populations displaying characteristic footprints of adaptive NK cells, including a terminally differentiated phenotype, functional reprogramming, and epigenetic remodeling of the interferon (IFN)-γ promoter. We found that both NKG2C⁻ and NKG2C⁺ adaptive NK cells expressed high levels of CD2, which synergistically enhanced ERK and S6RP phosphorylation following CD16 ligation. Notably, CD2 co-stimulation was critical for the ability of adaptive NK cells to respond to antibody-coated target cells. These results reveal an unexpected redundancy in the human NK cell response to HCMV and suggest that CD2 provides “signal 2” in antibody-driven adaptive NK cell responses.

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NKG2C^−/− donors have normal T cell immunity to cytomegalovirus

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NKG2C^−/− donors have normal frequencies of adaptive NK cells

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CD2 is critical for antibody-triggered responses by adaptive NK cells

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CD2 synergizes with NKG2C in classical adaptive NK cells

Action and Traction: Cytoskeletal Control of Receptor Triggering at the Immunological Synapse

It is well known that F-actin dynamics drive the micron-scale cell shape changes required for migration and immunological synapse (IS) formation. In addition, recent evidence points to a more intimate role for the actin cytoskeleton in promoting T cell activation. Mechanotransduction, the conversion of mechanical input into intracellular biochemical changes, is thought to play a critical role in several aspects of immunoreceptor triggering and downstream signal transduction. Multiple molecules associated with signaling events at the IS have been shown to respond to physical force, including the TCR, costimulatory molecules, adhesion molecules, and several downstream adapters. In at least some cases, it is clear that the relevant forces are exerted by dynamics of the T cell actomyosin cytoskeleton. Interestingly, there is evidence that the cytoskeleton of the antigen-presenting cell also plays an active role in T cell activation, by countering the molecular forces exerted by the T cell at the IS. Since actin polymerization is itself driven by TCR and costimulatory signaling pathways, a complex relationship exists between actin dynamics and receptor activation. This review will focus on recent advances in our understanding of the mechanosensitive aspects of T cell activation, paying specific attention to how F-actin-directed forces applied from both sides of the IS fit into current models of receptor triggering and activation.

Induction of intermembrane adhesion by incorporation of synthetic adhesive molecules into cell membranes

Modulation of cell adhesion by synthetic materials is useful for a wide range of biomedical applications. Here, we characterized cell adhesion mediated by a semisynthetic molecule, cholesteryl-modified gelatin (chol-gelatin). We found that this hybrid molecule facilitated cell adhesion by connecting two apposed membranes via multiple cholesterol moieties on the gelatin molecules, whereas unmodified gelatin did not bind to cell membranes. Analyses revealed that the rate of the formation of cell adhesions was increased by displaying more cholesterol moieties on the cell membrane. In contrast, the area of the cell adhesion site was unchanged by increasing the number of cholesterol molecules, suggesting that chol-gelatin may suppress cell spreading. Such restriction was not observed in cell adhesion mediated by the mutant of physiological adhesion protein CD2, which lacked its cytoplasmic domain and was unable to connect to cytoplasmic actin filaments, but had a similar affinity for its ligand compared with the chol-gelatin-cell membrane interaction. Further analysis suggested the restriction of cell spreading by chol-gelatin was largely independent of the modulation of the surface force, and thus we hypothesize that the restriction could be in part due to the modulation of cell membrane mechanics by membrane-incorporated chol-gelatin. Our study dissected the two roles of the hybrid molecule in cell adhesion, namely the formation of a molecular connection and the restriction of spreading, and may be useful for designing other novel synthetic agents to modulate various types of cell adhesions.

Regulation of T-cell receptor signaling by the actin cytoskeleton and poroelastic cytoplasm

The actin cytoskeleton plays essential roles in modulating T-cell activation. Most models of T-cell receptor (TCR) triggering signalosome assembly and immune synapse formation invoke actin-dependent mechanisms. As T cells are constitutively motile cells, TCR triggering and signaling occur against a cytoskeletal backdrop that is constantly remodeling. While the interplay between actin dynamics and TCR signaling have been the focus of research for many years, much of the work in T cells has considered actin largely for its 'scaffolding' function. We examine the roles of the actin cytoskeleton in TCR signaling and immune synapse formation with an emphasis on how poroelasticity, an ensemble feature of actin dynamics with the cytosol, relates to how T cells respond to stimulation.

CD28 sensitizes TCR Ca²⁺ signaling during Ag-independent polarization of plasma membrane rafts

T cells become polarized during initial interactions with an APC to form an Ag-independent synapse (AIS) composed of membrane rafts, TCR, and TCR-proximal signaling molecules. AISs occur temporally before TCR triggering, but their role in downstream TCR signaling is not understood. Using both human and murine model systems, we studied the signals that activate AIS formation and the effect of these signals on TCR-dependent responses. We show that CD28 produces AISs detectable by spinning disc confocal microscopy seconds following initial interactions between the T cell and APC. AIS formation by CD28 coincided with costimulatory signaling, evidenced by a cholesterol-sensitive activation of the MAPK ERK that potentiated Ca²⁺ signaling in response to CD3 cross-linking. CD45 also enriched in AISs but to modulate Src kinase activity, because localization of CD45 at the cell interface reduced the activation of proximal Lck. In summary, we show that signaling by CD28 during first encounters between the T cell and APC both sensitizes TCR Ca²⁺ signaling by an Erk-dependent mechanism and drives formation of an AIS that modulates the early signaling until TCR triggering occurs. Thus, early Ag-independent encounters are an important window for optimizing T cell responses to Ag by CD28.

The spatial structure of cell signaling systems

The spatial structure of the cell is highly organized at all levels: from small complexes and assemblies, to local nano- and microclusters, to global, micrometer scales across and between cells. We suggest that this multiscale spatial cell organization also organizes signaling and coordinates cellular behavior. We propose a new view of the spatial structure of cell signaling systems. This new view describes cell signaling in terms of dynamic allosteric interactions within and among distinct, spatially organized transient clusters. The clusters vary over time and space and are on length scales from nanometers to micrometers. When considered across these length scales, primary factors in the spatial organization are cell membrane domains and the actin cytoskeleton, both also highly dynamic. A key challenge is to understand the interplay across these multiple scales, link it to the physicochemical basis of the conformational behavior of single molecules and ultimately relate it to cellular function. Overall, our premise is that at these scales, cell signaling should be thought of not primarily as a sequence of diffusion-controlled molecular collisions, but instead transient, allostery-driven cluster re-forming interactions.

Genome-wide association study of antibody response to Newcastle disease virus in chicken

Background

Since the first outbreak in Indonesia in 1926, Newcastle disease has become one of the most common and contagious bird diseases throughout the world. To date, enhancing host antibody response by vaccination remains the most efficient strategy to control outbreaks of Newcastle disease. Antibody response plays an important role in host resistance to Newcastle disease, and selection for antibody response can effectively improve disease resistance in chickens. However, the molecular basis of the variation in antibody response to Newcastle disease virus (NDV) is not clear. The aim of this study was to detect genes modulating antibody response to NDV by a genome-wide association study (GWAS) in chickens.

Results

To identify genes or chromosomal regions associated with antibody response to NDV after immunization, a GWAS was performed using 39,833 SNP markers in a chicken F₂ resource population derived from a cross between two broiler lines that differed in their resistance. Two SNP effects reached 5% Bonferroni genome-wide significance (P<1.26×10^-6). These two SNPs, rs15354805 and rs15355555, were both on chicken (Gallus gallus) chromosome 1 and spanned approximately 600 Kb, from 100.4 Mb to 101.0 Mb. Rs15354805 is in intron 7 of the chicken Roundabout, axon guidance receptor, homolog 2 (ROBO2) gene, and rs15355555 is located about 243 Kb upstream of ROBO2. Rs15354805 explained 5% of the phenotypic variation in antibody response to NDV, post immunization, in chickens. Rs15355555 had a similar effect as rs15354805 because of its linkage disequilibrium with rs15354805 (r²=0.98).

Conclusion

The region at about 100 Mb from the proximal end of chicken chromosome 1, including the ROBO1 and ROBO2 genes, has a strong effect on the antibody response to the NDV in chickens. This study paves the way for further research on the host immune response to NDV.

Conformational states of the kinase Lck regulate clustering in early T cell signaling

Phosphorylation of the T cell antigen receptor (TCR) by the tyrosine kinase Lck is an essential step in the activation of T cells. Because Lck is constitutively active, spatial organization may regulate TCR signaling. Here we found that Lck distributions on the molecular level were controlled by the conformational states of Lck, with the open, active conformation inducing clustering and the closed, inactive conformation preventing clustering. In contrast, association with lipid domains and protein networks were not sufficient or necessary for Lck clustering. Conformation-driven Lck clustering was highly dynamic, so that TCR triggering resulted in Lck clusters that contained phosphorylated TCRs but excluded the phosphatase CD45. Our data suggest that Lck conformational states represent an intrinsic mechanism for the intermolecular organization of early T cell signaling.