Lytic immune synapse function requires filamentous actin deconstruction by Coronin 1A

Disruption of Coronin 1 Signaling in T Cells Promotes Allograft Tolerance while Maintaining Anti-Pathogen Immunity

The ability of the immune system to discriminate self from non-self is essential for eradicating microbial pathogens but is also responsible for allograft rejection. Whether it is possible to selectively suppress alloresponses while maintaining anti-pathogen immunity remains unknown. We found that mice deficient in coronin 1, a regulator of naive T cell homeostasis, fully retained allografts while maintaining T cell-specific responses against microbial pathogens. Mechanistically, coronin 1-deficiency increased cyclic adenosine monophosphate (cAMP) concentrations to suppress allo-specific T cell responses. Costimulation induced on microbe-infected antigen presenting cells was able to overcome cAMP-mediated immunosuppression to maintain anti-pathogen immunity. In vivo pharmacological modulation of this pathway or a prior transfer of coronin 1-deficient T cells actively suppressed allograft rejection. These results define a coronin 1-dependent regulatory axis in T cells important for allograft rejection and suggest that modulation of this pathway may be a promising approach to achieve long-term acceptance of mismatched allografts.

Emerging insights into human health and NK cell biology from the study of NK cell deficiencies

Human NK cells are innate immune effectors that play a critical roles in the control of viral infection and malignancy. The importance of their homeostasis and function can be demonstrated by the study of patients with primary immunodeficiencies (PIDs), which are part of the family of diseases known as inborn defects of immunity. While NK cells are affected in many PIDs in ways that may contribute to a patient's clinical phenotype, a small number of PIDs have an NK cell abnormality as their major immunological defect. These PIDs can be collectively referred to as NK cell deficiency (NKD) disorders and include effects upon NK cell numbers, subsets, and/or functions. The clinical impact of NKD can be severe including fatal viral infection, with particular susceptibility to herpesviral infections, such as cytomegalovirus, varicella zoster virus, and Epstein-Barr virus. While NKD is rare, studies of these diseases are important for defining specific requirements for human NK cell development and homeostasis. New themes in NK cell biology are emerging through the study of both known and novel NKD, particularly those affecting cell cycle and DNA damage repair, as well as broader PIDs having substantive impact upon NK cells. In addition, the discovery of NKD that affects other innate lymphoid cell (ILC) subsets opens new doors for better understanding the relationship between conventional NK cells and other ILC subsets. Here, we describe the biology underlying human NKD, particularly in the context of new insights into innate immune cell function, including a discussion of recently described NKD with accompanying effects on ILC subsets. Given the impact of these disorders upon human immunity with a common focus upon NK cells, the unifying message of a critical role for NK cells in human host defense singularly emerges.

Actin Cytoskeleton Remodeling Drives Breast Cancer Cell Escape from Natural Killer-Mediated Cytotoxicity

Elucidation of the underlying molecular mechanisms of immune evasion in cancer is critical for the development of immunotherapies aimed to restore and stimulate effective antitumor immunity. Here, we evaluate the role of the actin cytoskeleton in breast cancer cell resistance to cytotoxic natural killer (NK) cells. A significant fraction of breast cancer cells responded to NK-cell attack via a surprisingly rapid and massive accumulation of F-actin near the immunologic synapse, a process we termed "actin response." Live-cell imaging provided direct evidence that the actin response is associated with tumor cell resistance to NK-cell-mediated cell death. High-throughput imaging flow cytometry analyses showed that breast cancer cell lines highly resistant to NK cells were significantly enriched in actin response-competent cells as compared with susceptible cell lines. The actin response was not associated with a defect in NK-cell activation but correlated with reduced intracellular levels of the cytotoxic protease granzyme B and a lower rate of apoptosis in target cells. Inhibition of the actin response by knocking down CDC42 or N-WASP led to a significant increase in granzyme B levels in target cells and was sufficient to convert resistant breast cancer cell lines into a highly susceptible phenotype. The actin response and its protective effects were fully recapitulated using donor-derived primary NK cells as effector cells. Together, these findings establish the pivotal role of actin remodeling in breast cancer cell resistance to NK-cell-mediated killing.Significance: These findings establish the pivotal role of the actin cytoskeleton in driving breast cancer cell resistance to natural killer cells, a subset of cytotoxic lymphocytes with important roles in innate antitumor immunity. Cancer Res; 78(19); 5631-43. ©2018 AACR.

Primary Immunodeficiencies Unravel the Role of IL-2/CD25/STAT5b in Human Natural Killer Cell Maturation

Natural killer (NK) cells play a pivotal role during immunity against viruses and circumstantial evidence also indicates that they can protect the host against developing tumors. Peripheral blood NK cells comprise CD56^brightCD16^lo/− cells that constitutively express CD25 (IL-2Rα) and CD56^dimCD16^hi cells that express CD25 upon activation. Using NK cells from two patients, one with a primary immunodeficiency characterized by a homozygous mutation in CD25 (born in year 2007 and studied since she was 3 years old) and one with a homozygous mutation in STAT5b (born in year 1992 and studied since she was 10 years old), we observed that the absence of IL-2 signaling through CD25 promotes the accumulation of CD56^brightCD16^high NK cells, and that CD56^brightCD16^lo, CD56^brightCD16^high, and CD56^dimCD16^high NK cells of this patient exhibited higher content of perforin and granzyme B, and proliferation capacity, compared to healthy donors. Also, CD56^bright and CD56^dim NK cells of this patient exhibited a reduced IFN-γ production in response to cytokine stimulation and increased degranulation against K562 cells. Also, the CD25-deficient patient presented a lower frequency of terminally differentiated NK cells in the CD56^dimCD16^hi NK subpopulation compared to the HD (assessed by CD57 and CD94 expression). Remarkably, CD56^dimCD16^high NK cells from both patients exhibited notoriously higher expression of CD62L compared to HD, suggesting that in the absence of IL-2 signaling through CD25 and STAT5b, NK cells fail to properly downregulate CD62L during their transition from CD56^brightCD16^lo/− to CD56^dimCD16^hi cells. Thus, we provide the first demonstration about the in vivo requirement of the integrity of the IL-2/CD25/STAT5b axis for proper human NK cell maturation.

Inherited Immunodeficiencies With High Predisposition to Epstein-Barr Virus-Driven Lymphoproliferative Diseases

Epstein–Barr Virus (EBV) is a gamma-herpes virus that infects 90% of humans without any symptoms in most cases, but has an oncogenic potential, especially in immunocompromised individuals. In the past 30 years, several primary immunodeficiencies (PIDs) associated with a high risk to develop EBV-associated lymphoproliferative disorders (LPDs), essentially consisting of virus-associated hemophagocytic syndrome, non-malignant and malignant B-cell LPDs including non-Hodgkin and Hodgkin’s types of B lymphomas have been characterized. Among them are SH2D1A (SAP), XIAP, ITK, MAGT1, CD27, CD70, CTPS1, RASGRP1, and CORO1A deficiencies. Penetrance of EBV infection ranges from 50 to 100% in those PIDs. Description of large cohorts and case reports has refined the specific phenotypes associated with these PIDs helping to the diagnosis. Specific pathways required for protective immunity to EBV have emerged from studies of these PIDs. SLAM-associated protein-dependent SLAM receptors and MAGT1-dependent NKG2D pathways are important for T and NK-cell cytotoxicity toward EBV-infected B-cells, while CD27–CD70 interactions are critical to drive the expansion of EBV-specific T-cells. CTPS1 and RASGRP1 deficiencies further strengthen that T-lymphocyte expansion is a key step in the immune response to EBV. These pathways appear to be also important for the anti-tumoral immune surveillance of abnormal B cells. Monogenic PIDs should be thus considered in case of any EBV-associated LPDs.

Sailing to and Docking at the Immune Synapse: Role of Tubulin Dynamics and Molecular Motors

The different cytoskeleton systems and their connecting molecular motors move vesicles and intracellular organelles to shape cells. Polarized cells with specialized functions display an exquisite spatio-temporal regulation of both cytoskeletal and organelle arrangements that support their specific tasks. In particular, T cells rapidly change their shape and cellular function through the establishment of cell surface and intracellular polarity in response to a variety of cues. This review focuses on the contribution of the microtubule-based dynein/dynactin motor complex, the tubulin and actin cytoskeletons, and different organelles to the formation of the antigen-driven immune synapse.

From Phagocytes to Immune Defense: Roles for Coronin Proteins in Dictyostelium and Mammalian Immunity

Microbes have interacted with eukaryotic cells for as long as they have been co-existing. While many of these interactions are beneficial for both the microbe as well as the eukaryotic cell, several microbes have evolved into pathogenic species. For some of these pathogens, host cell invasion results in irreparable damage and thus host cell destruction, whereas others use the host to avoid immune detection and elimination. One of the latter pathogens is Mycobacterium tuberculosis, arguably one of the most notorious pathogens on earth. In mammalian macrophages, M. tuberculosis manages to survive within infected macrophages by avoiding intracellular degradation in lysosomes using a number of different strategies. One of these is based on the recruitment and phagosomal retention of the host protein coronin 1, that is a member of the coronin protein family and a mammalian homolog of coronin A, a protein identified in Dictyostelium. Besides mediating mycobacterial survival in macrophages, coronin 1 is also an important regulator of naïve T cell homeostasis. How, exactly, coronin 1 mediates its activity in immune cells remains unclear. While in lower eukaryotes coronins are involved in cytoskeletal regulation, the functions of the seven coronin members in mammals are less clear. Dictyostelium coronins may have maintained multiple functions, whereas the mammalian coronins may have evolved from regulators of the cytoskeleton to modulators of signal transduction. In this minireview, we will discuss the different studies that have contributed to understand the molecular and cellular functions of coronin proteins in mammals and Dictyostelium.

Impedance-based analysis of Natural Killer cell stimulation

The use of impedance-based label free cell analysis is increasingly popular and has many different applications. Here, we report that a real-time cell analyzer (RTCA) can be used to study the stimulation of Natural Killer (NK) cells. Engagement of NK cells via plate-bound antibodies directed against different activating surface receptors could be measured in real time using the label-free detection of impedance. The change in impedance was dependent on early signal transduction events in the NK cells as it was blocked by inhibitors of Src-family kinases and by inhibiting actin polymerization. While CD16 was the only receptor that could induce a strong change in impedance in primary NK cells, several activating receptors induced changes in impedance in expanded NK cells. Using PBMCs we could detect T cell receptor-mediated T cell activation and CD16-mediated NK cell activation in the same sample. Performing a dose-response analysis for the Src-family kinases inhibitor PP1 we show that T cells are more sensitive to inhibition compared to NK cells. Our data demonstrate that the RTCA can be used to detect physiological activation events in NK cells in a label-free and real-time fashion.

Phosphoinositide-3-Kinase Signaling in Human Natural Killer Cells: New Insights from Primary Immunodeficiency

Human natural killer (NK) cells play a critical role in the control of viral infections and malignancy. Their importance in human health and disease is illustrated by severe viral infections in patients with primary immunodeficiencies that affect NK cell function and/or development. The recent identification of patients with phosphoinositide-3-kinase (PI3K)-signaling pathway mutations that can cause primary immunodeficiency provides valuable insight into the role that PI3K signaling plays in human NK cell maturation and lytic function. There is a rich literature that demonstrates a requirement for PI3K in multiple key aspects of NK cell biology, including development/maturation, homing, priming, and function. Here, I briefly review these previous studies and place them in context with recent findings from the study of primary immunodeficiency patients, particularly those with hyperactivating mutations in PI3Kδ signaling.

Nanoscale Dynamism of Actin Enables Secretory Function in Cytolytic Cells

Natural killer (NK) cells are innate immune effectors that lyse virally infected and tumorigenic cells through the formation of an immunological synapse. Actin remodeling at the lytic immunological synapse is a critical requirement for multiple facets of cytotoxic function. Activating receptor and integrin signaling leads to the regulated turnover and remodeling of actin, which is required for adhesion, sustained receptor signaling, and ultimately exocytosis. NK cells undergo lytic granule exocytosis in hypodense regions of a pervasive actin network. Although these requirements have been well demonstrated, neither the dynamic regulation of synaptic actin nor its specific function, however, has been determined at a nanoscale level. Here, live-cell super-resolution microscopy demonstrates nanoscale filamentous actin dynamism in NK cell lytic granule secretion. Following cell spreading, the overall content of the branched actin network at an immune synapse is stable over time and contains branched actin fibers and discrete actin foci. Similar actin architecture is generated in cytolytic T cells, although the timescale differs from that of NK cells. Individual filament displacement leads to stochastic clearance formation and disappearance, which are independent of lytic granule positioning. Actin dynamism is dependent upon branched network formation mediated by Arp2/3 and contractility generated by myosin IIA. Importantly, the use of small-molecule inhibitors demonstrates that actin dynamism is ultimately needed for granule secretion. Thus, we describe a requirement for nanoscale actin fiber rearrangement in generating the complex actin architecture that enables lytic granule secretion.

Actin retrograde flow controls natural killer cell response by regulating the conformation state of SHP-1

Natural killer (NK) cells are a powerful weapon against viral infections and tumor growth. Although the actin-myosin (actomyosin) cytoskeleton is crucial for a variety of cellular processes, the role of mechanotransduction, the conversion of actomyosin mechanical forces into signaling cascades, was never explored in NK cells. Here, we demonstrate that actomyosin retrograde flow (ARF) controls the immune response of primary human NK cells through a novel interaction between β-actin and the SH2-domain-containing protein tyrosine phosphatase-1 (SHP-1), converting its conformation state, and thereby regulating NK cell cytotoxicity. Our results identify ARF as a master regulator of the NK cell immune response. Since actin dynamics occur in multiple cellular processes, this mechanism might also regulate the activity of SHP-1 in additional cellular systems.

Educated natural killer cells show dynamic movement of the activating receptor NKp46 and confinement of the inhibitory receptor Ly49A

Educated natural killer (NK) cells have inhibitory receptors specific for self major histocompatibility complex (MHC) class I molecules and kill cancer cells more efficiently than do NK cells that do not have such receptors (hyporesponsive NK cells). The mechanism behind this functional empowerment through education has so far not been fully described. In addition, distinctive phenotypic markers of educated NK cells at the single-cell level are lacking. We developed a refined version of the image mean square displacement (iMSD) method (called iMSD carpet analysis) and used it in combination with single-particle tracking to characterize the dynamics of the activating receptor NKp46 and the inhibitory receptor Ly49A on resting educated versus hyporesponsive murine NK cells. Most of the NKp46 and Ly49A molecules were restricted to microdomains; however, individual NKp46 molecules resided in these domains for shorter periods and diffused faster on the surface of educated, compared to hyporesponsive, NK cells. In contrast, the movement of Ly49A was more constrained in educated NK cells compared to hyporesponsive NK cells. Either disrupting the actin cytoskeleton or adding cholesterol to the cells prohibited activating signaling, suggesting that the dynamics of receptor movements within the cell membrane are critical for the proper activation of NK cells. The faster and more dynamic movement of NKp46 in educated NK cells may facilitate a swifter response to interactions with target cells.

Beta and Gamma Human Herpesviruses: Agonistic and Antagonistic Interactions with the Host Immune System

Viruses are the most abundant and diverse biological entities in the planet. Historically, our main interest in viruses has focused on their pathogenic role, recognized by pandemics that have decimated the world population. However, viral infections have also played a major role in the evolution of cellular organisms, both through interchanging of genes with novel functions and shaping the immune system. Examples abound of infections that seriously compromise the host integrity, but evidence of plant and insect viruses mutualistic relationships have recently surfaced in which infected hosts are better suited for survival, arguing that virus-host interactions are initially parasitic but become mutualistic over years of co-evolution. A similar mutual help scenario has emerged with commensal gut bacteria. EBV is a herpesvirus that shares more than a hundred million years of co-evolution with humans, today successfully infecting close to 100% of the adult world population. Infection is usually acquired early in childhood persisting for the host lifetime mostly without apparent clinical symptoms. Disturbance of this homeostasis is rare and results in several diseases, of which the best understood are infectious mononucleosis and several EBV-associated cancers. Less understood are recently found inborn errors of the immune system that result in primary immunodeficiencies with an increased predisposition almost exclusive to EBV-associated diseases. Puzzling to these scenarios of broken homeostasis is the co-existence of immunosuppression, inflammation, autoimmunity and cancer. Homologous to EBV, HCMV, HHV-6 and HHV-7 are herpesviruses that also latently infect most individuals. Several lines of evidence support a mutualistic equilibrium between HCMV/EBV and hosts, that when altered trigger diseases in which the immune system plays a critical role. Interestingly, these beta and gamma herpesviruses persistently infect all immune lineages and early precursor cells. In this review, we will discuss the evidence of the benefits that infection of immune cells with these herpesviruses brings to the host. Also, the circumstances in which this positive relationship is broken, predisposing the host to diseases characterized by an abnormal function of the host immune system.

Live-Cell Super-resolution Reveals F-Actin and Plasma Membrane Dynamics at the T Cell Synapse

The cortical actin cytoskeleton has been shown to be critical for the reorganization and heterogeneity of plasma membrane components of many cells, including T cells. Building on previous studies at the T cell immunological synapse, we quantitatively assess the structure and dynamics of this meshwork using live-cell superresolution fluorescence microscopy and spatio-temporal image correlation spectroscopy. We show for the first time, to our knowledge, that not only does the dense actin cortex flow in a retrograde fashion toward the synapse center, but the plasma membrane itself shows similar behavior. Furthermore, using two-color, live-cell superresolution cross-correlation spectroscopy, we demonstrate that the two flows are correlated and, in addition, we show that coupling may extend to the outer leaflet of the plasma membrane by examining the flow of GPI-anchored proteins. Finally, we demonstrate that the actin flow is correlated with a third component, α-actinin, which upon CRISPR knockout led to reduced plasma membrane flow directionality despite increased actin flow velocity. We hypothesize that this apparent cytoskeletal-membrane coupling could provide a mechanism for driving the observed retrograde flow of signaling molecules such as the TCR, Lck, ZAP70, LAT, and SLP76.

Role for coronin 1 in mouse NK cell function

Coronin 1, a member of the evolutionary conserved WD repeat protein family of coronin proteins is expressed in all leukocytes, but a role for coronin 1 in natural killer (NK) cell homeostasis and function remains unclear. Here, we have analyzed the number and functionality of NK cells in the presence and absence of coronin 1. In coronin 1-deficient mice, absolute NK cell numbers and phenotype were comparable to wild type mice in blood, spleen and liver. Following in vitro stimulation of the activating NK cell receptors NK1.1, NKp46, Ly49D and NKG2D, coronin 1-deficient NK cells were functional with respect to interferon-γ production, degranulation and intracellular Ca2+ mobilization. Also, both wild type as well as coronin 1-deficient NK cells showed comparable cytotoxic activity. Furthermore, activation and functionality of NK cells following Vesicular Stomatitis Virus (VSV) infection was similar between wild type and coronin 1-deficient mice. Taken together these data suggest that coronin 1 is dispensable for mouse NK cell homeostasis and function.

PKCθ links proximal T cell and Notch signaling through localized regulation of the actin cytoskeleton

Notch is a critical regulator of T cell differentiation and is activated through proteolytic cleavage in response to ligand engagement. Using murine myelin-reactive CD4 T cells, we demonstrate that proximal T cell signaling modulates Notch activation by a spatiotemporally constrained mechanism. The protein kinase PKCθ is a critical mediator of signaling by the T cell antigen receptor and the principal costimulatory receptor CD28. PKCθ selectively inactivates the negative regulator of F-actin generation, Coronin 1A, at the center of the T cell interface with the antigen presenting cell (APC). This allows for effective generation of the large actin-based lamellum required for recruitment of the Notch-processing membrane metalloproteinase ADAM10. Such enhancement of Notch activation is critical for efficient T cell proliferation and Th17 differentiation. We reveal a novel mechanism that, through modulation of the cytoskeleton, controls Notch activation at the T cell:APC interface thereby linking T cell receptor and Notch signaling pathways.

Coronins and their role in immunological phenomena

Coronins are a large family of proteins occurring in many eukaryotes. In mammals, seven coronin genes have been identified, evidencing that coronins 1 to 6 present classic coronin structure, while coronin 7 is a tandem coronin particle, without a spiral domain, although the best characterised coronin, in terms of both structure and function, is the mammalian coronin 1. It has been proven that they are related to regulation of actin dynamics, e.g. as a result of interaction with the complex of proteins Arp2/3. These proteins also modulate the activity of immune system cells, including lymphocyte T and B cells, neutrophils and macrophages. They are involved in bacterial infections with Mycobacterium tuberculosis, M. leprae and Helicobacter pylori and participate in the response to viral infections, e.g. infections of lymphocytic choriomeningitis virus (LCMV) and vesicular stomatitis Indiana virus (VSV). Also their involvement in autoimmune diseases such as lupus erythematosus has been recorded.

Monocyte/Macrophage: NK Cell Cooperation-Old Tools for New Functions

Monocyte/macrophage and natural killer (NK) cells are partners from a phylogenetic standpoint of innate immune system development and its evolutionary progressive interaction with adaptive immunity. The equally conservative ways of development and differentiation of both invertebrate hemocytes and vertebrate macrophages are reviewed. Evolutionary conserved molecules occurring in macrophage receptors and effectors have been inherited by vertebrates after their common ancestor with invertebrates. Cytolytic functions of mammalian NK cells, which are rooted in immune cells of invertebrates, although certain NK cell receptors (NKRs) are mammalian new events, are characterized. Broad heterogeneity of macrophage and NK cell phenotypes that depends on surrounding microenvironment conditions and expression profiles of specific receptors and activation mechanisms of both cell types are discussed. The particular tissue specificity of macrophages and NK cells, as well as their plasticity and mechanisms of their polarization to different functional subtypes have been underlined. The chapter summarized studies revealing the specific molecular mechanisms and regulation of NK cells and macrophages that enable their highly specific cross-cooperation. Attention is given to the evolving role of human monocyte/macrophage and NK cell interaction in pathogenesis of hypersensitivity reaction-based disorders, including autoimmunity, as well as in cancer surveillance and progression.

Primary immunodeficiencies associated with EBV-Induced lymphoproliferative disorders

Primary immunodeficiency diseases (PIDs) are a subgroup of inherited immunological disorders that increase susceptibility to viral infections. Among the range of viral pathogens involved, EBV remains a major threat because of its high prevalence of infection among the adult population and its tendency to progress to life-threatening lymphoproliferative disorders (LPDs) and/or malignancy. The high mortality in immunodeficient patients with EBV-driven LPDs, despite institution of diverse and often intensive treatments, prompts the need to better study these PIDs to identify and understand the affected molecular pathways that increase susceptibility to EBV infection and progression. In this article, we have provided a detailed literature review of the reported cases of EBV-driven LPDs in patients with PID. We discuss the PIDs associated with development of EBV-LPDs. Then, we review the nature and the therapeutic outcome of common EBV- driven LPDs in the PID patients and review the mechanisms common to the major PIDs. Deep study of these common pathways and gaining a better insight into the disease nature and outcomes, may lead to earlier diagnosis of the disease, choosing the best treatment modalities available and development of novel therapeutic strategies to decrease morbidity and mortality brought about by EBV infection.

Severe Epstein-Barr virus infection in primary immunodeficiency and the normal host

Epstein-Barr virus (EBV) infection is ubiquitous in humans, but the majority of infections have an asymptomatic or self-limiting clinical course. Rarely, individuals may develop a pathological EBV infection with a variety of life threatening complications (including haemophagocytosis and malignancy) and others develop asymptomatic chronic EBV viraemia. Although an impaired ability to control EBV infection has long been recognised as a hallmark of severe T-cell immunodeficiency, the advent of next generation sequencing has identified a series of Primary Immunodeficiencies in which EBV-related pathology is the dominant feature. Chronic active EBV infection is defined as chronic EBV viraemia associated with systemic lymphoproliferative disease, in the absence of immunodeficiency. Descriptions of larger cohorts of patients with chronic active EBV in recent years have significantly advanced our understanding of this clinical syndrome. In this review we summarise the current understanding of the pathophysiology and natural history of these diseases and clinical syndromes, and discuss approaches to the investigation and treatment of severe or atypical EBV infection.

Proof of Principle for a T Lymphocyte Intrinsic Function of Coronin 1A

Coronins are evolutionarily conserved proteins that were originally identified as modulators of actin-dependent processes. Studies analyzing complete Coronin 1a knock-out mice have shown that this molecule is an important regulator of naive T cell homeostasis and it has been linked to immune deficiencies as well as autoimmune disorders. Nevertheless, because Coronin 1A is strongly expressed in all leukocyte subsets, it is not conclusive whether or not this phenotype is attributed to a T cell-intrinsic function of Coronin 1A. To address this research question, we have generated a T cell-specific Coronin 1a knock-out mouse (Coro1afl/fl × Cd4[Cre]). Deletion of Coronin 1A specifically in T cells led to a strong reduction in T cell number and a shift toward the effector/memory phenotype in peripheral lymphoid organs when compared with Cd4[Cre] mice expressing wild-type Coronin 1A. In contrast to peripheral lymphoid tissue, thymocyte number and subsets were not affected by the deletion of Coronin 1a Furthermore, T cell-specific Coronin 1a knock-out mice were largely resistant to the induction of autoimmunity when tested in the myelin oligoglycoprotein-induced EAE mouse model of multiple sclerosis. Thus, the phenotype of T cell-specific Coronin 1a deletion resembles the phenotype observed with conventional (whole body) Coronin 1a knock-out mice. In summary, our findings provide formal proof of the predominant T cell-intrinsic role of Coronin 1A.

The pro-oxidative drug WF-10 inhibits serial killing by primary human cytotoxic T-cells

Cytotoxic T-cells (CTLs) play an important role in many immune-mediated inflammatory diseases. Targeting cytotoxicity of CTLs would allow to interfere with immune-mediated tissue destruction. Here we demonstrate that WF-10, a pro-oxidative compound, inhibits CTL-mediated cytotoxicity. WF-10 did not influence early steps of target-cell killing, but impaired the ability of CTLs to detach from the initial target cell and to move to a second target cell. This reduced serial killing was accompanied by stronger enrichment of the adhesion molecule LFA-1 in the cytolytic immune synapse. LFA-1 clustering requires activation of the actin-bundling protein L-plastin and was accordingly diminished in L-plastin knockdown cells. Interestingly, WF-10 likely acts through regulating L-plastin: (I) It induced L-plastin activation through phosphorylation leading to enhanced LFA-1-mediated cell adhesion, and, importantly, (II) WF-10 lost its influence on target-cell killing in L-plastin knockdown cells. Finally, we demonstrate that WF-10 can improve immunosuppression by conventional drugs. Thus, while cyclosporine A alone had no significant effect on cytotoxicity of CTLs, a combination of cyclosporine A and WF-10 blocked target-cell killing synergistically. Together, our findings suggest that WF-10 – either alone or in combination with conventional immunosuppressive drugs – may be efficient to control progression of diseases, in which CTLs are crucially involved.

A major secretory defect of tumour-infiltrating T lymphocytes due to galectin impairing LFA-1-mediated synapse completion

Surface galectin has been shown to contribute to dysfunctions of human tumour-infiltrating lymphocytes (TILs). We show here that galectin-covered CD8 TILs produce normal amounts of intracellular cytokines, but fail to secrete them because of defective actin rearrangements at the synapse. The non-secreting TILs also display reduced adhesion to their targets, together with defective LFA-1 recruitment and activation at the synapse. These defects are relieved by releasing surface galectin. As mild LFA-1 blockade on normal blood T cells emulate the defects of galectin-covered TILs, we conclude that galectin prevents the formation of a functional secretory synapse by preventing optimal LFA-1 triggering. Our results highlight a major secretory defect of TILs that is not revealed by widely used intracellular cytokine immunomonitoring assays. They also provide additional insights into the T-cell response, by showing that different thresholds of LFA-1 triggering are required to promote the intracellular production of cytokines and their secretion.

Galectin-3 is a sugar-binding protein that can inhibit antitumour cytotoxic immunity. Here the authors show that Galectin-3 expressed by tumour cells inhibits LFA-1 on cytotoxic lymphocytes, impairing immunological synapse formation, IFNg secretion, and target cell killing.

WASH has a critical role in NK cell cytotoxicity through Lck-mediated phosphorylation

Natural killer (NK) cells are important effector cells of the innate immune system to kill certain virus-infected and transformed cells. Wiskott–Aldrich Syndrome protein (WASP) and SCAR homolog (WASH) has been identified as a member of WASP family proteins implicated in regulating the cytoskeletal reorganization, yet little is known about its function in lymphocytes. Here we demonstrate that WASH is crucial for NK cell cytotoxicity. WASH was found to colocalize with lytic granules upon NK cell activation. Knockdown of WASH expression substantially inhibited polarization and release of lytic granules to the immune synapse, resulting in the impairment of NK cell cytotoxicity. More importantly, our data also define a previously unappreciated mechanism for WASH function, in which Src family kinase Lck can interact with WASH and induce WASH phosphorylation. Mutation of tyrosine residue Y141, identified here as the major site of WASH phosphorylation, partially blocked WASH tyrosine phosphorylation and NK cell cytotoxicity. Taken together, these observations suggest that WASH has a pivotal role for regulation of NK cell cytotoxicity through Lck-mediated Y141 tyrosine phosphorylation.

Origins of the cytolytic synapse

Cytotoxic T lymphocytes (CTLs) kill virus-infected and tumour cells with remarkable specificity. Upon recognition, CTLs form a cytolytic immune synapse with their target cell, and marked reorganization of both the actin and the microtubule cytoskeletons brings the centrosome up to the plasma membrane to the point of T cell receptor signalling. Secretory granules move towards the centrosome and are delivered to this focal point of secretion. Such centrosomal docking at the plasma membrane also occurs during ciliogenesis; indeed, striking similarities exist between the cytolytic synapse and the primary cilium that throw light on the possible origins of immune synapses.

Concerning immune synapses: a spatiotemporal timeline

The term “immune synapse” was originally coined to highlight the similarities between the synaptic contacts between neurons in the central nervous system and the cognate, antigen-dependent interactions between T cells and antigen-presenting cells. Here, instead of offering a comprehensive molecular catalogue of molecules involved in the establishment, stabilization, function, and resolution of the immune synapse, we follow a spatiotemporal timeline that begins at the initiation of exploratory contacts between the T cell and the antigen-presenting cell and ends with the termination of the contact. We focus on specific aspects that distinguish synapses established by cytotoxic and T helper cells as well as unresolved issues and controversies regarding the formation of this intercellular structure.

Recurrent viral infections associated with a homozygous CORO1A mutation that disrupts oligomerization and cytoskeletal association

BACKGROUND

Coronin-1A (CORO1A) is a regulator of actin dynamics important for T-cell homeostasis. CORO1A deficiency causes T(-)B(+) natural killer-positive severe combined immunodeficiency or T-cell lymphopenia with severe viral infections. However, because all known human mutations in CORO1A abrogate protein expression, the role of the protein's functional domains in host immunity is unknown.

OBJECTIVE

We sought to identify the cause of the primary immunodeficiency in 2 young adult siblings with a history of disseminated varicella, cutaneous warts, and CD4(+) T-cell lymphopenia.

METHODS

We performed immunologic, genetic, and biochemical studies in the patients, family members, and healthy control subjects.

RESULTS

Both patients had CD4(+) T-cell lymphopenia and decreased lymphocyte proliferation to mitogens. IgG, IgM, IgA, and specific antibody responses were normal. Whole-genome sequencing identified a homozygous frameshift mutation in CORO1A disrupting the last 2 C-terminal domains by replacing 61 amino acids with a novel 91-amino-acid sequence. The CORO1A(S401fs) mutant was expressed in the patients' lymphocytes at a level comparable with that of wild-type CORO1A in normal lymphocytes but did not oligomerize and had impaired cytoskeletal association. CORO1A(S401fs) was associated with increased filamentous actin accumulation in T cells, severely defective thymic output, and impaired T-cell survival but normal calcium flux and cytotoxicity, demonstrating the importance of CORO1A oligomerization and subcellular localization in T-cell homeostasis.

CONCLUSIONS

We describe a truncating mutation in CORO1A that permits protein expression and survival into young adulthood. Our studies demonstrate the importance of intact CORO1A C-terminal domains in thymic egress and T-cell survival, as well as in defense against viral pathogens.

Chemokines, their receptors and human disease: the good, the bad and the itchy

Chemokines are a highly specialized group of cytokines that coordinate trafficking and homing of leucocytes between bone marrow, lymphoid organs and sites of infection or inflammation. They are also responsible for structural organization within lymphoid organs. Aberrant expression or function of these molecules, or their receptors, has been linked to protection or susceptibility to specific infectious diseases, as well as the risk of autoimmune disease and malignancy, revealing critical roles of chemokines and their receptors in human health, disease and therapeutics. In this review, we focus on human diseases that provide lessons regarding the critical role of these specialized and complex cytokines.

F-actin remodeling defects as revealed in primary immunodeficiency disorders

Primary immunodeficiencies (PIDs) are a heterogeneous group of immune-related diseases. PIDs develop due to defects in gene-products that have consequences to immune cell function. A number of PID-proteins is involved in the remodeling of filamentous actin (f-actin) to support the generation of a contact zone between the antigen-specific T cell and antigen presenting cell (APC): the immunological synapse (IS). IS formation is the first step towards T-cell activation and essential for clonal expansion and acquisition of effector function. We here evaluated PIDs in which aberrant f-actin-driven IS formation may contribute to the PID disease phenotypes as seen in patients. We review examples of such contributions to PID phenotypes from literature, and highlight cases in which PID-proteins were evaluated for a role in f-actin polymerization and IS formation. We conclude with the proposition that patient groups might benefit from stratifying them in distinct functional groups in regard to their f-actin remodeling phenotypes in lymphocytes.

High- and Super-Resolution Microscopy Imaging of the NK Cell Immunological Synapse

Recent advances in imaging technology have enabled significant advances in the study of NK cell cytotoxic effector function through quantitative analysis of the NK cell immunological synapse. This can include the use of high- and super-resolution microscopy to quantify dynamics of cytoskeletal elements and the role they play in the regulation and execution of NK cell directed secretion. Here we describe a protocol for the recapitulation of the NK cell lytic synapse on glass, the acquisition of microscopy images, and suggested approaches for the processing and analysis of microscopy data.

Insights into primary immune deficiency from quantitative microscopy

Recent advances in genomics-based technology have resulted in an increase in our understanding of the molecular basis of many primary immune deficiencies. Along with this increased knowledge comes an increased responsibility to understand the underlying mechanism of disease, and thus increasingly sophisticated technologies are being used to investigate the cell biology of human immune deficiencies. One such technology, which has itself undergone a recent explosion in innovation, is that of high-resolution microscopy and image analysis. These advances complement innovative studies that have previously shed light on critical cell biological processes that are perturbed by single-gene mutations in primary immune deficiency. Here we highlight advances made specifically in the following cell biological processes: (1) cytoskeletal-related processes; (2) cell signaling; (3) intercellular trafficking; and (4) cellular host defense.

Severe combined immunodeficiencies and related disorders

Severe combined immunodeficiencies (SCIDs) comprise a group of rare, monogenic diseases that are characterized by an early onset and a profound block in the development of T lymphocytes. Given that adaptive immunity is abrogated, patients with SCID are prone to recurrent infections caused by both non-opportunistic and opportunistic pathogens, leading to early death unless immunity can be restored. Several molecular defects causing SCIDs have been identified, along with many other defects causing profound, albeit incomplete, T cell immunodeficiencies; the latter are referred to as atypical SCIDs or combined immunodeficiencies. The pathophysiology of many of these conditions has now been characterized. Early, accurate and precise diagnosis combined with the ongoing implementation of newborn screening have enabled major advances in the care of infants with SCID, including better outcomes of allogeneic haematopoietic stem cell transplantation. Gene therapy is also becoming an effective option. Further advances and a progressive extension of the indications for gene therapy can be expected in the future. The assessment of long-term outcomes of patients with SCID is now a major challenge, with a view to evaluating the quality and sustainability of immune restoration, the risks of sequelae and the ability to relieve the non-haematopoietic syndromic manifestations that accompany some of these conditions.

UNC-45A Is a Nonmuscle Myosin IIA Chaperone Required for NK Cell Cytotoxicity via Control of Lytic Granule Secretion

NK cell's killing is a tightly regulated process under the control of specific cytoskeletal proteins. This includes Wiskott-Aldrich syndrome protein, Wiskott-Aldrich syndrome protein-interacting protein, cofilin, Munc13-4, and nonmuscle myosin IIA (NMIIA). These proteins play a key role in controlling NK-mediated cytotoxicity either via regulating the attachment of lytic granules to the actin-based cytoskeleton or via promoting the cytoskeletal reorganization that is requisite for lytic granule release. UNC-45A is a highly conserved member of the UNC-45/CRO1/She4p family of proteins that act as chaperones for both conventional and nonconventional myosin. Although we and others have shown that in lower organisms and in mammalian cells NMIIA-associated functions, such as cytokinesis, cell motility, and organelle trafficking, are dependent upon the presence of UNC-45A, its role in NK-mediated functions is largely unknown. In this article, we describe UNC-45A as a key regulator of NK-mediated cell toxicity. Specifically we show that, in human NK cells, UNC-45A localize at the NK cell immunological synapse of activated NK cells and is part of the multiprotein complex formed during NK cell activation. Furthermore, we show that UNC-45A is disposable for NK cell immunological synapse formation and lytic granules reorientation but crucial for lytic granule exocytosis. Lastly, loss of UNC-45A leads to reduced NMIIA binding to actin, suggesting that UNC-45A is a crucial component in regulating human NK cell cytoskeletal dynamics via promoting the formation of actomyosin complexes.

The disease-linked Glu-26-Lys mutant version of Coronin 1A exhibits pleiotropic and pathway-specific signaling defects

Coronin 1A is involved in cell shape dynamics and Rac1 GTPase signaling. Loss-of-function mutations in the Coro1A gene promote severe immunodeficiency. An immunodeficiency-linked Coro1A point mutant is described that becomes dysfunctional due to changes in actin-binding, actin-remodeling, and signaling activities.

Coronin 1A (Coro1A) is involved in cytoskeletal and signaling events, including the regulation of Rac1 GTPase– and myosin II–dependent pathways. Mutations that generate truncated or unstable Coro1A proteins cause immunodeficiencies in both humans and rodents. However, in the case of the peripheral T-cell–deficient (Ptcd) mouse strain, the immunodeficiency is caused by a Glu-26-Lys mutation that targets a surface-exposed residue unlikely to affect the intramolecular architecture and stability of the protein. Here we report that this mutation induces pleiotropic effects in Coro1A protein, including the exacerbation of Coro1A-dependent actin-binding and -bundling activities; the formation of large meshworks of Coro1A^E26K-decorated filaments endowed with unusual organizational, functional, and staining properties; and the elimination of Coro1A functions associated with both Rac1 and myosin II signaling. By contrast, it does not affect the ability of Coro1A to stimulate the nuclear factor of activated T-cells (NF-AT). Coro1A^E26K is not a dominant-negative mutant, indicating that its pathological effects are derived from the inability to rescue the complete loss of the wild-type counterpart in cells. These results indicate that Coro1A^E26K behaves as either a recessive gain-of-function or loss-of-function mutant protein, depending on signaling context and presence of the wild-type counterpart in cells.

Lenalidomide augments actin remodeling and lowers NK-cell activation thresholds

As multiple myeloma (MM) progresses, natural killer (NK)-cell responses decline against malignant plasma cells. The immunomodulatory drug lenalidomide is widely used for treatment of MM but its influence on NK-cell biology is unclear. Here, we report that lenalidomide lowers the threshold for NK-cell activation, causing a 66% decrease in the 50% effective concentration (EC50) for activation through CD16, and a 38% decrease in EC50 for NK group 2 member D (NKG2D)-mediated activation, allowing NK cells to respond to lower doses of ligand. In addition, lenalidomide augments NK-cell responses, causing a twofold increase in the proportion of primary NK cells producing interferon-γ (IFN-γ), and a 20-fold increase in the amount of IFN-γ produced per cell. Importantly, lenalidomide did not trigger IFN-γ production in unstimulated NK cells. Thus, lenalidomide enhances the NK-cell arm of the immune response, without activating NK cells inappropriately. Of particular clinical importance, lenalidomide also allowed NK cells to be activated by lower doses of rituximab, an anti-CD20 monoclonal antibody (mAb) widely used to treat B-cell malignancies. This supports combined use of lenalidomide and rituximab in a clinical setting. Finally, superresolution microscopy revealed that lenalidomide increased the periodicity of cortical actin at immune synapses, resulting in an increase in the area of the actin mesh predicted to be penetrable to vesicles containing IFN-γ. NK cells from MM patients also responded to lenalidomide in this way. This indicates that nanometer-scale rearrangements in cortical actin, a recently discovered step in immune synapse assembly, are a potential new target for therapeutic compounds.

Dances with Membranes: Breakthroughs from Super-resolution Imaging

Biological membrane organization mediates numerous cellular functions and has also been connected with an immense number of human diseases. However, until recently, experimental methodologies have been unable to directly visualize the nanoscale details of biological membranes, particularly in intact living cells. Numerous models explaining membrane organization have been proposed, but testing those models has required indirect methods; the desire to directly image proteins and lipids in living cell membranes is a strong motivation for the advancement of technology. The development of super-resolution microscopy has provided powerful tools for quantification of membrane organization at the level of individual proteins and lipids, and many of these tools are compatible with living cells. Previously inaccessible questions are now being addressed, and the field of membrane biology is developing rapidly. This chapter discusses how the development of super-resolution microscopy has led to fundamental advances in the field of biological membrane organization. We summarize the history and some models explaining how proteins are organized in cell membranes, and give an overview of various super-resolution techniques and methods of quantifying super-resolution data. We discuss the application of super-resolution techniques to membrane biology in general, and also with specific reference to the fields of actin and actin-binding proteins, virus infection, mitochondria, immune cell biology, and phosphoinositide signaling. Finally, we present our hopes and expectations for the future of super-resolution microscopy in the field of membrane biology.

Molecular control of B cell activation and immunological synapse formation

B cells form an essential part of the adaptive immune system by producing specific antibodies that can neutralize toxins and target infected or malignant cells for destruction. During B cell activation, a fundamental role is played by a specialized intercellular structure called the immunological synapse (IS). The IS serves as a platform for B cell recognition of foreign, often pathogenic, antigens on the surface of antigen-presenting cells (APC). This recognition is elicited by highly specific B cell receptors (BCR) that subsequently trigger carefully orchestrated intracellular signaling cascades that lead to cell activation. Furthermore, antigen internalization, essential for full B cell activation and differentiation into antibody producing effector cells or memory cells, occurs in the IS. Recent developments especially in various imaging-based methods have considerably advanced our understanding of the molecular control of B cell activation. Interestingly, the cellular cytoskeleton is emerging as a key player at several stages of B cell activation, including the initiation of receptor signaling. Here, we discuss the functions and molecular mechanisms of the IS and highlight the multifaceted role of the actin cytoskeleton in several aspects of B cell activation.

The expanding spectrum of human coronin 1A deficiency

Since the first discovery of coronin in the amoeba Dictyostelium discoideum, remarkable insights have been gained regarding the structure and function of coronins, highly conserved from yeast to humans. It has been speculated that coronins have evolved from actin-binding molecules in lower eukaryotes to regulators of various cellular processes in mammals. Indeed, coronins are not only involved in cytokinesis, cell motility, and other actin-related processes but they are also implicated in immune homeostasis and calcium-calcineurin signaling. Most strikingly, coronin 1 deficiencies give rise to immune deficiencies in mice and humans that are characterized by severe T lymphocytopenia. Whereas complete absence of coronin 1A is associated with severe combined immunodeficiency in humans, hypomorphic mutations lead to a profound defect in naïve T cells, expansion of oligoclonal memory T cells, and exquisite susceptibility to EBV-associated B cell lymphoproliferation. Recent publications show that coronin 1A also plays a role in natural killer cell cytotoxic function and in neurobehavioral processes. It can be expected that future identification of coronin 1A-deficient patients will further extend the phenotypic spectrum thereby increasing our knowledge of this fascinating molecule.

Molecular mechanisms and functional implications of polarized actin remodeling at the T cell immunological synapse

Transient,specialized cell-cell interactions play a central role in leukocyte function by enabling specific intercellular communication in the context of a highly dynamic systems level response. The dramatic structural changes required for the formation of these contacts are driven by rapid and precise cytoskeletal remodeling events. In recent years, the immunological synapse that forms between a T lymphocyte and its antigen-presenting target cell has emerged as an important model system for understanding immune cell interactions. In this review, we discuss how regulators of the cortical actin cytoskeleton control synaptic architecture and in this way specify T cell function.