Role of inositol phospholipid signaling in natural killer cell biology

Inositol phosphatase INPP4B sustains ILC1s and intratumoral NK cells through an AKT-driven pathway

Innate lymphoid cells (ILCs) are a heterogeneous population of lymphocytes that coordinate early immune responses and maintain tissue homeostasis. Type 1 innate immune responses are mediated by natural killer (NK) cells and group 1 ILCs (ILC1s). Despite their shared features, NK cells and ILC1s display profound differences among various tissue microenvironments. Here, we identify the inositol polyphosphatase INPP4B as a hallmark feature of tissue-resident ILC1s and intratumoral NK cells using an scRNA-seq atlas of tissue-associated and circulating NK/ILC1s. Conditional deletion of Inpp4b in ILC1s and NK cells reveals that it is necessary for the homeostasis of tissue-resident ILC1s but not circulating NK cells at steady-state. Inpp4b-deficient cells display increased rates of apoptosis and reduced activation of the prosurvival molecule AKT. Furthermore, expression of Inpp4b by NK/ILC1s is necessary for their presence in the intratumoral environment, and lack of Inpp4b impairs antitumor immunity. These findings highlight INPP4B as a novel regulator of tissue residency and antitumor function in ILC1s and NK cells.

SHIP1 and its role for innate immune regulation-Novel targets for immunotherapy

Phosphoinositide-3-kinase/AKT (PI3K/AKT) signaling plays key roles in the regulation of cellular activity in both health and disease. In immune cells, this PI3K/AKT pathway is critically regulated by the phosphoinositide phosphatase SHIP1, which has been reported to modulate the function of most immune subsets. In this review, we summarize our current knowledge of SHIP1 with a focus on innate immune cells, where we reflect on the most pertinent aspects described in the current literature. We also present several small-molecule agonists and antagonists of SHIP1 developed over the last two decades, which have led to improved outcomes in several preclinical models of disease. We outline these promising findings and put them in relation to human diseases with unmet medical needs, where we discuss the most attractive targets for immune therapies based on SHIP1 modulation.

Disinfectant dodecyl dimethyl benzyl ammonium chloride (DDBAC) disrupts gut microbiota, phospholipids, and calcium signaling in honeybees (Apis mellifera) at an environmentally relevant level

One of the impacts of the Coronavirus disease 2019 (COVID-19) pandemic has been a profound increase in the application amounts of disinfectants. Dodecyl dimethyl benzyl ammonium chloride (DDBAC) is a widely used disinfectant, yet its hazards to non-target species remain largely unknown. We are unaware of any studies assessing DDBAC's impacts on honeybee, a pollinator species that is a useful indicator of environmental pollution essential for many forms of agricultural production. Here, we assessed the potentially negative effects of DDBAC on honeybees. After conducting a formal toxicity evaluation of DDBAC on honeybee mortality, we detected an accumulation of DDBAC in the honeybee midgut. We subsequently studied the midgut tissues of honeybees exposed to sub-lethal concentrations of DDBAC: histopathological examination revealed damage to midgut tissue upon DDBAC exposure, microbiome analysis showed a decreased abundance of beneficial midgut microbiota, lipidomics analysis revealed a significant reduction in cell membrane phospholipids with known functions in signal transduction, and a transcriptome analysis detected altered expression of genes involved in calcium signaling pathways (that variously function in calcium absorption, muscle contraction, and neurotransmission). Thus, our study establishes that DDBAC impacts honeybee midgut functions at multiple levels. Our study represents an early warning about the hazards of DDBAC and appeals for the proper stewardship of DDBAC to ensure the protection of our ecological environment.

Fyn Signaling in Ischemia-Reperfusion Injury: Potential and Therapeutic Implications

Ischemic stroke caused by arterial occlusion is the most common type of stroke and is one of the leading causes of disability and death, with the incidence increasing each year. Fyn is a nonreceptor tyrosine kinase belonging to the Src family of kinases (SFKs), which is related to many normal and pathological processes of the nervous system, including neurodevelopment and disease progression. In recent years, more and more evidence suggests that Fyn may be closely related to cerebral ischemia-reperfusion, including energy metabolism disorders, excitatory neurotoxicity, intracellular calcium homeostasis, free radical production, and the activation of apoptotic genes. This paper reviews the role of Fyn in the pathological process of cerebral ischemia-reperfusion, including neuroexcitotoxicity and neuroinflammation, to explore how Fyn affects specific signal cascades and leads to cerebral ischemia-reperfusion injury. In addition, Fyn also promotes the production of superoxide and endogenous NO, so as to quickly react to produce peroxynitrite, which may also mediate cerebral ischemia-reperfusion injury, which is discussed in this paper. Finally, we revealed the treatment methods related to Fyn inhibitors and discussed its potential as a clinical treatment for ischemic stroke.

4-1BB antibody enhances cytotoxic activity of natural killer cells against prostate cancer cells via NKG2D agonist combined with IL-27

Aims: To enhance the cytotoxicity of natural killer (NK) cells against prostate cancer cells via NKG2D agonist, with 4-1BB antibody and IL-27 combination. Materials & methods: FACS was used to detect degranulation and cell surface receptors in NK cells isolated from healthy donors. Cytokine concentrations were measured using ELISA. NK-cell cytotoxicity was analyzed using Cell Counting Kit-8. Results: NKG2D agonist, 4-1BB antibody and IL-27 combination treatment improved the activating receptor expression and IFN-γ and TNF-α secretion but decreased the suppressive receptor CD158a expression and IL-10 secretion in NK cells. The combined treatment enhanced NK-cell cytotoxicity against both PC3 and DU145 cells with concurrent enhanced STAT3 activation. Conclusion: 4-1BB antibody and IL-27 improved NKG2D agonist function in NK cells against prostate cancer cells.

Metabotropic Glutamate Receptor 5 in Natural Killer Cells Attenuates Liver Fibrosis by Exerting Cytotoxicity to Activated Stellate Cells

BACKGROUND AND AIMS

The important roles of glutamate and metabotropic glutamate receptor 5 (mGluR5) in HSCs have recently been reported in various liver diseases; however, the mechanism linking the glutamine/glutamate metabolism and mGluR5 in liver fibrosis remains unclear. Here, we report that mGluR5 activation in natural killer (NK) cells attenuates liver fibrosis through increased cytotoxicity and interferon-γ (IFN-γ) production in both mice and humans.

APPROACH AND RESULTS

Following 2-week injection of carbon tetrachloride (CCl₄ ) or 5-week methionine-deficient and choline-deficient diet, liver fibrosis was more aggravated in mGluR5 knockout mice with significantly decreased frequency of NK cells compared with wild-type mice. Consistently, NK cell-specific mGluR5 knockout mice had aggravated CCl₄ -induced liver fibrosis with decreased production of IFN-γ. Conversely, in vitro activation of mGluR5 in NK cells significantly increased the expression of anti-fibrosis-related genes including Ifng, Prf1 (perforin), and Klrk1 (killer cell lectin like receptor K1) and the production of IFN-γ through the mitogen-activated extracellular signal-regulated kinase/extracellular signal-related kinase pathway, contributing to the increased cytotoxicity against activated HSCs. However, we found that the uptake of glutamate was increased in activated HSCs, resulting in shortage of extracellular glutamate and reduced stimulation of mGluR5 in NK cells. Consequently, this could enable HSCs to evade NK cell cytotoxicity in advanced liver fibrosis. In vivo, pharmacologic activation of mGluR5 accelerated CCl₄ -induced liver fibrosis regression by restoring NK cell cytotoxicity. In humans, mGluR5 activation enhanced the cytotoxicity of NK cells isolated from healthy donors, but not from patients with cirrhosis with significantly reduced mGluR5 expression in NK cells.

CONCLUSIONS

mGluR5 plays important roles in attenuating liver fibrosis by augmenting NK cell cytotoxicity, which could be used as a potential therapeutic target for liver fibrosis.

Trastuzumab Mechanism of Action; 20 Years of Research to Unravel a Dilemma

Trastuzumab as a first HER2-targeted therapy for the treatment of HER2-positive breast cancer patients was introduced in 1998. Although trastuzumab has opened a new avenue to treat patients with HER2-positive breast cancer and other types of cancer, some patients are not responsive or become resistant to this treatment. So far, several mechanisms have been suggested for the mode of action of trastuzumab; however, the findings regarding these mechanisms are controversial. In this review, we aimed to provide a detailed insight into the various mechanisms of action of trastuzumab.

If small molecules immunotherapy comes, can the prime be far behind?

Anti-cancer immunotherapy, which includes cellular immunotherapy, immune checkpoint inhibitors and cancer vaccines, has transformed the treatment strategies of several malignancies in the past decades. Immune checkpoints blockade (ICB) is the most commonly tested therapy and has the potential to induce a durable immune response in different types of cancers. However, all approved immune checkpoint inhibitors (ICIs) are monoclonal antibodies (mAbs), which are fraught with disadvantages including lack of oral bioavailability, prolonged tissue retention and poor membrane permeability. Therefore, the research focus has shifted to developing small molecule inhibitors to obviate the limitations of mAbs. Given the complexity of the tumor micro-environment (TME), the combination of ICIs with various small molecule agonists/inhibitors are currently being tested in clinical trials to improve treatment outcomes and prevent tumor recurrence. In this review, we have summarized the mechanisms and therapeutic potential of several molecular targets, along with the current status of small molecule inhibitors.

Metabolism in tumor microenvironment: Implications for cancer immunotherapy

Tumor microenvironment is a special environment for tumor survival, which is characterized by hypoxia, acidity, nutrient deficiency, and immunosuppression. The environment consists of the vasculature, immune cells, extracellular matrix, and proteins or metabolic molecules. A large number of recent studies have shown that not only tumor cells but also the immune cells in the tumor microenvironment have undergone metabolic reprogramming, which is closely related to tumor drug resistance and malignant progression. Tumor immunotherapy based on T cells gives patients new hope, but faces the dilemma of low response rate. New strategies sensitizing cancer immunotherapy are urgently needed. Metabolic reprogramming can directly affect the biological activity of tumor cells and also regulate the differentiation and activation of immune cells. The authors aim to review the characteristics of tumor microenvironment, the metabolic changes of tumor‐associated immune cells, and the regulatory role of metabolic reprogramming in cancer immunotherapy.

Systematic Multiomic Analysis of Ly75 Gene Expression and Its Prognostic Value Through the Infiltration of Natural Killer (NK) Cells in Skin Cutaneous Melanoma

Ly75 (also known as DEC-205 or CD205) is expressed in immune cells and cancers and involved in tumor immunity. However, clinical relevance of Ly75 expression in skin cutaneous melanoma (SKCM) have not been comprehensively studied. This study analyzed the correlation between Ly75 mRNA expression and patient survival using systematic multiomic analysis tools. Ly75 mRNA expression level was significantly lower in SKCM tissues than in normal tissues. Survival analysis showed that Ly75 expression significantly correlated with good patient survival. To determine possible mechanisms, the association between Ly75 expression and immune cell infiltration was analyzed. Ly75 expression was positively correlated with various infiltrated immune cells, particularly with natural killer (NK) cell infiltration and activation in SKCM. Moreover, analysis of Ly75-co-altered gene expression revealed that Ptprc (CD45) was most significantly correlated with Ly75. Gene ontology analysis of Ly75-co-altered genes indicated the relation to lymphocyte activation, including NK cell activation. Overall, our study provides the first clinical evidence that Ly75 expression is significantly associated with melanoma patient survival and NK cell infiltration, suggesting that Ly75 could be a useful prognostic factor.

Molecular regulation of the plasma membrane-proximal cellular steps involved in NK cell cytolytic function

Natural killer (NK) cells, cytolytic lymphocytes of the innate immune system, play a crucial role in the immune response against infection and cancer. NK cells kill target cells through exocytosis of lytic granules that contain cytotoxic proteins, such as perforin and granzymes. Formation of a functional immune synapse, i.e. the interface between the NK cell and its target cell enhances lysis through accumulation of polymerized F-actin at the NK cell synapse, leading to convergence of lytic granules to the microtubule organizing center (MTOC) and its subsequent polarization along microtubules to deliver the lytic granules to the synapse. In this review, we focus on the molecular mechanisms regulating the cellular processes that occur after the lytic granules are delivered to the cytotoxic synapse. We outline how - once near the synapse - the granules traverse the clearings created by F-actin remodeling to dock, tether and fuse with the plasma membrane in order to secrete their lytic content into the synaptic cleft through exocytosis. Further emphasis is given to the role of Ca²⁺ mobilization during degranulation and, whenever applicable, we compare these mechanisms in NK cells and cytotoxic T lymphocytes (CTLs) as adaptive immune system effectors.

Myo-inositol in autoimmune thyroiditis, and hypothyroidism

Myo-inositol (Myo-Ins) plays an important role in thyroid function and autoimmunity. Myo-Ins is the precursor for the synthesis of phosphoinositides, which takes part in the phosphatidylinositol (PtdIns) signal transduction pathway, and plays a decisive role in several cellular processes. In the thyroid cells, PtdIns is involved in the intracellular thyroid-stimulating hormone (TSH) signaling, via Phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) (PIP-3). Moreover, the phosphatidyl inositol 3 kinases (PI3K) family of lipid kinases regulates diverse aspects of T, B, and Tregs lymphocyte behaviour. Different mouse models deficient for the molecules involved in the PIP3 pathway suggest that impairment of PIP3 signaling leads to dysregulation of immune responses and, sometimes, autoimmunity. Studies have shown that cytokines modulate Myo-Ins in thyroid cells. Moreover, clinical studies have shown that after treatment with Myo-inositol plus seleniomethionine (Myo-Ins + Se), TSH levels significantly declined in patients with subclinical hypothyroidism due to autoimmune thyroiditis. The treatment was accompanied by a decline of antithyroid autoantibodies. After treatment serum CXCL10 levels declined, confirming the immune-modulatory effect of Myo-Ins. Additional research is necessary in larger population to evaluate the effect on the quality of life, and to study the mechanism of the effect on chemokines.

Natural killer cell metabolism

Natural killer (NK) cells are a critical component in the innate immune response against disease. NK cell function is tightly regulated by specific cytokine and activation/inhibitory receptor signalling, leading to diverse effector responses. Like all living cells, energy metabolism is a fundamental requirement for NK cell activation and survival. There is growing evidence that distinct functional profiles of NK cells are determined by alterations to cellular metabolic pathways. In this review, we summarise current literature that has explored NK cell metabolism to provide insight into how metabolic regulation controls NK cell function. We focus on metabolism pathways induced by different NK cell stimuli, metabolic regulatory proteins, and nutrient and hormonal levels in health and disease which impact on NK cell metabolic and functional activity.

Dual enhancement of T and NK cell function by pulsatile inhibition of SHIP1 improves antitumor immunity and survival

The success of immunotherapy in some cancer patients has revealed the profound capacity for cytotoxic lymphocytes to eradicate malignancies. Various immunotherapies work by blocking key checkpoint proteins that suppress immune cell activity. The phosphatase SHIP1 (SH2-containing inositol polyphosphate 5-phosphatase) limits signaling from receptors that activate natural killer (NK) cells and T cells. However, unexpectedly, genetic ablation studies have shown that the effector functions of SHIP1-deficient NK and T cells are compromised in vivo. Because chronic activation of immune cells renders them less responsive to activating signals (a host mechanism to avoid autoimmunity), we hypothesized that the failure of SHIP1 inhibition to induce antitumor immunity in those studies was caused by the permanence of genetic ablation. Accordingly, we found that reversible and pulsatile inhibition of SHIP1 with 3-α-aminocholestane (3AC; "SHIPi") increased the antitumor response of NK and CD8⁺ T cells in vitro and in vivo. Transient SHIP1 inhibition in mouse models of lymphoma and colon cancer improved the median and long-term tumor-free survival rates. Adoptive transfer assays showed evidence of immunological memory to the tumor in hematolymphoid cells from SHIPi-treated, long-term surviving mice. The findings suggest that a pulsatile regimen of SHIP1 inhibition might be an effective immunotherapy in some cancer patients.

Inositol(s) in thyroid function, growth and autoimmunity

Myo-inositol and phosphatidylinositol(s) play a pivotal function in many metabolic pathways that, if impaired, impact unfavorably on human health. This review analyzes several experimental and clinical investigations regarding the involvement of this class of molecules in physiological and pathological situations, with a major focus on thyroid. Central issues are the relationship between phosphatidylinositol and thyrotropin (TSH) signaling on one hand, and phosphatydylinositol and autoimmunity on the other hand. Other issues are the consequences of malfunction of some receptors, such as those ones for TSH (TSHR), insulin (IR) and insulin-like growth factor-1 (IGF-1R), or the connection between serum TSH concentrations and insulin resistance. Also covered are insulin resistance, metabolic syndrome and their allied disorders (diabetes, polycystic ovary syndrome [PCOS]), autoimmunity and certain malignancies, with their reciprocal links. Myoinositol has promising therapeutic potential. Appreciation of the inositol pathways involved in certain disorders, as mentioned in this review, may stimulate researchers to envisage additional therapeutic applications.

Engineering NK Cells Modified With an EGFRvIII-specific Chimeric Antigen Receptor to Overexpress CXCR4 Improves Immunotherapy of CXCL12/SDF-1α-secreting Glioblastoma

Natural killer (NK) cells are promising effector cells for adjuvant immunotherapy of cancer. So far, several preclinical studies have shown the feasibility of gene-engineered NK cells, which upon expression of chimeric antigen receptors (CARs) are redirected to otherwise NK cell-resistant tumors. Yet, we reasoned that the efficiency of an immunotherapy using CAR-modified NK cells critically relies on efficient migration to the tumor site and might be improved by the engraftment of a receptor specific for a chemokine released by the tumor. On the basis of the DNAX-activation protein 12 (DAP12), a signaling adapter molecule involved in signal transduction of activating NK cell receptors, we constructed an epidermal growth factor variant III (EGFRvIII)-CAR, designated MR1.1-DAP12 which confers specific cytotoxicity of NK cell towards EGFRvIII glioblastoma cells in vitro and to established subcutaneous U87-MG tumor xenografts. So far, infusion of NK cells with expression of MR1.1-DAP12 caused a moderate but significantly delayed tumor growth and increased median survival time when compared with NK cells transduced with an ITAM-defective CAR. Notably, the further genetic engineering of these EGFRvIII-specific NK cells with the chemokine receptor CXCR4 conferred a specific chemotaxis to CXCL12/SDF-1α secreting U87-MG glioblastoma cells. Moreover, the administration of such NK cells resulted in complete tumor remission in a number of mice and a significantly increased survival when compared with the treatment of xenografts with NK cells expressing only the EGFRvIII-specific CAR or mock control. We conclude that chemokine receptor-engineered NK cells with concomitant expression of a tumor-specific CAR are a promising tool to improve adoptive tumor immunotherapy.

Human Cytomegalovirus Induces an Atypical Activation of Akt To Stimulate the Survival of Short-Lived Monocytes

Human cytomegalovirus (HCMV) is a pervasive herpesvirus responsible for significant morbidity and mortality among immunodeficient/naive hosts. Following a primary HCMV infection, circulating blood monocytes mediate the systemic spread of the virus. Extending the short 48-h life span of monocytes is critical to the viral dissemination process, as these blood-borne cells are nonpermissive for virus replication until they are fully differentiated into macrophages. Here, we show that HCMV glycoprotein gB binding to cellular epidermal growth factor receptor (EGFR) during HCMV entry initiated a rapid (within 15 min) activation of the apoptosis suppressor Akt, which was maintained through 72 h. The virus-induced activation of Akt was more robust than that with the normal myeloid growth factor macrophage colony-stimulating factor (M-CSF) and was essential for infected monocytes to bypass the 48-h viability checkpoint. Activation of phosphoinositide 3-kinase (PI3K) following EGFR engagement by HCMV mediated the phosphorylation of Akt. Moreover, HCMV entry drove a switch away from the PI3K p110δ isoform, which was required for the viability of uninfected monocytes, to the p110β isoform in order to facilitate the Akt-dependent prosurvival state within infected cells. Simultaneously, in contrast to M-CSF, HCMV promoted a rapid increase in SH2 domain-containing inositol 5-phosphatase 1 (SHIP1) expression, leading to signaling through a noncanonical Akt activation pathway. To ensure maximum Akt activity, HCMV also induced an early phosphorylation-dependent inactivation of the negative regulator phosphatase and tensin homolog. Overall, our data indicate that HCMV hijacks the upstream Akt signaling network to induce a nontraditional activation of Akt and subsequently a prosurvival decision at the 48-h cell fate checkpoint, a vital step for HCMV's dissemination and persistence strategy.

IMPORTANCE

HCMV is found throughout the world with a prevalence of 55 to 100% within the human population. HCMV infection is generally asymptomatic in immunocompetent or naive individuals but is a significant cause of morbidity and mortality among the immunocompromised. Widespread organ inflammation is associated with symptomatic infections, which is a direct consequence of the viral dissemination strategy. Inflammatory peripheral blood monocytes facilitate the spread of HCMV. However, HCMV must subvert the naturally short life span of monocytes. In this work, we demonstrate that HCMV induces the activation of Akt, an antiapoptotic protein, in a manner distinct from that of normal myeloid growth factors. Moreover, we decipher how HCMV dysregulates the upstream Akt signaling network during viral entry to promote an Akt-dependent prosurvival state following infection. Delineation of the virus-specific mechanisms that regulate cellular prosurvival pathways in order to drive the survival of HCMV-infected monocytes is important to identifying new anti-HCMV therapeutic targets.

Phosphoinositide 3-kinase family in channel catfish and their regulated expression after bacterial infection

The phosphoinositide-3-kinase (PI3Ks) family of lipid kinases is widely conserved from yeast to mammals. In this work, we identified a total of 14 members of the PI3Ks from the channel catfish genome and transcriptome and conducted phylogenetic and syntenic analyses of these genes. The expression profiles after infection with Edwardsiella ictaluri and Flavobacterium columnare were examined to determine the involvement of PI3Ks in immune responses after bacterial infection in catfish. The results indicated that PI3Ks genes including all of the catalytic subunit and several regulatory subunits genes were widely regulated after bacterial infection. The expression patterns were quite different when challenged with different bacteria. The PI3Ks were up-regulated rapidly at the early stage after ESC infection, but their induced expression was much slower, at the middle stage after columnaris infection. RNA-Seq datasets indicated that PI3K genes may be expressed at different levels in different catfish differing in their resistance levels against columnaris. Future studies are required to confirm and validate these observations. Taken together, this study indicated that PI3K genes may be involved as a part of the defense responses of catfish after infections, and they could be one of the determinants for disease resistance.

Phosphatidylinositol 3-Kinase: A Link Between Inflammation and Pancreatic Cancer

Even though a strong association between inflammation and cancer has been widely accepted, the underlying precise molecular mechanisms are still largely unknown. A complex signaling network between tumor and stromal cells is responsible for the infiltration of inflammatory cells into the cancer microenvironment. Tumor stromal cells such as pancreatic stellate cells (PSCs) and immune cells create a microenvironment that protects cancer cells through a complex interaction, ultimately facilitating their local proliferation and their migration to different sites. Furthermore, PSCs have multiple functions related to local immunity, angiogenesis, inflammation, and fibrosis. Recently, many studies have shown that members of the phosphoinositol-3-phosphate kinase (PI3K) family are activated in tumor cells, PSCs, and tumor-infiltrating inflammatory cells to promote cancer growth. Proinflammatory cytokines and chemokines secreted by immune cells and fibroblasts within the tumor environment can activate the PI3K pathway both in cancer and inflammatory cells. In this review, we focus on the central role of the PI3K pathway in regulating the cross talk between immune/stromal cells and cancer cells. Understanding the role of the PI3K pathway in the development of chronic pancreatitis and cancer is crucial for the discovery of novel and efficacious treatment options.

The Fyn-ADAP Axis: Cytotoxicity Versus Cytokine Production in Killer Cells

Lymphocyte signaling cascades responsible for anti-tumor cytotoxicity and inflammatory cytokine production must be tightly regulated in order to control an immune response. Disruption of these cascades can cause immune suppression as seen in a tumor microenvironment, and loss of signaling integrity can lead to autoimmunity and other forms of host-tissue damage. Therefore, understanding the distinct signaling events that exclusively control specific effector functions of “killer” lymphocytes (T and NK cells) is critical for understanding disease progression and formulating successful immunotherapy. Elucidation of divergent signaling pathways involved in receptor-mediated activation has provided insights into the independent regulation of cytotoxicity and cytokine production in lymphocytes. Specifically, the Fyn signaling axis represents a branch point for killer cell effector functions and provides a model for how cytotoxicity and cytokine production are differentially regulated. While the Fyn–PI(3)K pathway controls multiple functions, including cytotoxicity, cell development, and cytokine production, the Fyn–ADAP pathway preferentially regulates cytokine production in NK and T cells. In this review, we discuss how the structure of Fyn controls its function in lymphocytes and the role this plays in mediating two facets of lymphocyte effector function, cytotoxicity and production of inflammatory cytokines. This offers a model for using mechanistic and structural approaches to understand clinically relevant lymphocyte signaling.

SHIP1 intrinsically regulates NK cell signaling and education, resulting in tolerance of an MHC class I-mismatched bone marrow graft in mice

NK cells are an important component of host immune defense against malignancy and infection. NK cells are educated by MHC class I ligands to ensure self-tolerance while also promoting lytic competency against altered self and damaged self targets. However, the intracellular molecular events that culminate in tolerance and functional competency of educated NK cells remain undefined. Mice with germline deficiency in SHIP1 were shown to have a defective NK cell compartment. However, SHIP1 is expressed in all hematopoietic lineages, and consequently several hematolymphoid phenotypes have already been identified in certain cell types that are the result of SHIP1 deficiency in cells in separate and distinct lineages, that is, cell-extrinsic phenotypes. Thus, it was previously impossible to determine the NK cell-intrinsic role of SHIP1. In the present study, through the creation of an NK cell-specific deletion mouse model of SHIP1, we show that SHIP1 plays a profound NK lineage-intrinsic role in NK cell homeostasis, development, education, and cytokine production. Moreover, we show SHIP1 expression by NK cells is required for in vivo-mismatched bone marrow allograft rejection as well as for NK memory responses to hapten.

Effector Vγ9Vδ2 T cells dominate the human fetal γδ T-cell repertoire

γδ T cells are unconventional T cells recognizing antigens via their γδ T-cell receptor (TCR) in a way that is fundamentally different from conventional αβ T cells. γδ T cells usually are divided into subsets according the type of Vγ and/or Vδ chain they express in their TCR. T cells expressing the TCR containing the γ-chain variable region 9 and the δ-chain variable region 2 (Vγ9Vδ2 T cells) are the predominant γδ T-cell subset in human adult peripheral blood. The current thought is that this predominance is the result of the postnatal expansion of cells expressing particular complementary-determining region 3 (CDR3) in response to encounters with microbes, especially those generating phosphoantigens derived from the 2-C-methyl-d-erythritol 4-phosphate pathway of isoprenoid synthesis. However, here we show that, rather than requiring postnatal microbial exposure, Vγ9Vδ2 T cells are the predominant blood subset in the second-trimester fetus, whereas Vδ1(+) and Vδ3(+) γδ T cells are present only at low frequencies at this gestational time. Fetal blood Vγ9Vδ2 T cells are phosphoantigen responsive and display very limited diversity in the CDR3 of the Vγ9 chain gene, where a germline-encoded sequence accounts for >50% of all sequences, in association with a prototypic CDR3δ2. Furthermore, these fetal blood Vγ9Vδ2 T cells are functionally preprogrammed (e.g., IFN-γ and granzymes-A/K), with properties of rapidly activatable innatelike T cells. Thus, enrichment for phosphoantigen-responsive effector T cells has occurred within the fetus before postnatal microbial exposure. These various characteristics have been linked in the mouse to the action of selecting elements and would establish a much stronger parallel between human and murine γδ T cells than is usually articulated.

PTEN is a negative regulator of NK cell cytolytic function

Human NK cells are characterized by their ability to initiate an immediate and direct cytolytic response to virally infected or malignantly transformed cells. Within human peripheral blood, the more mature CD56(dim) NK cell efficiently kills malignant targets at rest, whereas the less mature CD56(bright) NK cells cannot. In this study, we show that resting CD56(bright) NK cells express significantly more phosphatase and tensin homolog deleted on chromosome 10 (PTEN) protein when compared with CD56(dim) NK cells. Consistent with this, forced overexpression of PTEN in NK cells resulted in decreased cytolytic activity, and loss of PTEN in CD56(bright) NK cells resulted in elevated cytolytic activity. Comparable studies in mice showed PTEN overexpression did not alter NK cell development or NK cell-activating and inhibitory receptor expression yet, as in humans, did decrease expression of downstream NK activation targets MAPK and AKT during early cytolysis of tumor target cells. Confocal microscopy revealed that PTEN overexpression disrupts the NK cell's ability to organize immunological synapse components including decreases in actin accumulation, polarization of the microtubule organizing center, and the convergence of cytolytic granules. In summary, our data suggest that PTEN normally works to limit the NK cell's PI3K/AKT and MAPK pathway activation and the consequent mobilization of cytolytic mediators toward the target cell and suggest that PTEN is among the active regulatory components prior to human NK cells transitioning from the noncytolytic CD56(bright) NK cell to the cytolytic CD56(dim) NK cells.

Natural killer cells induce eosinophil activation and apoptosis

Eosinophils are potent inflammatory cells with numerous immune functions, including antigen presentation and exacerbation of inflammatory responses through their capacity to release a range of largely preformed cytokines and lipid mediators. Thus, timely regulation of eosinophil activation and apoptosis is crucial to develop beneficial immune response and to avoid tissue damage and induce resolution of inflammation. Natural Killer (NK) cells have been reported to influence innate and adaptive immune responses by multiple mechanisms including cytotoxicity against other immune cells. In this study, we analyzed the effect of the interaction between NK cells and eosinophils. Co-culture experiments revealed that human NK cells could trigger autologous eosinophil activation, as shown by up-regulation of CD69 and down-regulation of CD62L, as well as degranulation, evidenced by increased CD63 surface expression, secretion of eosinophil cationic protein (ECP) and eosinophil derived neurotoxin (EDN). Moreover, NK cells significantly and dose dependently increased eosinophil apoptosis as shown by annexin V and propidium iodide (PI) staining. Direct contact was necessary for eosinophil degranulation and apoptosis. Increased expression of phosphorylated extracellular signal-regulated kinase (ERK) in cocultured eosinophils and inhibition of eosinophil CD63 expression by pharmacologic inhibitors suggest that MAPK and PI3K pathways are involved in NK cell-induced eosinophil degranulation. Finally, we showed that NK cells increased reactive oxygen species (ROS) expression by eosinophils in co-culture and that mitochondrial inhibitors (rotenone and antimycin) partially diminished NK cell-induced eosinophil apoptosis, suggesting the implication of mitochondrial ROS in NK cell-induced eosinophil apoptosis. Pan-caspase inhibitor (ZVAD-FMK) only slightly decreased eosinophil apoptosis in coculture. Altogether, our results suggest that NK cells regulate eosinophil functions by inducing their activation and their apoptosis.

Molecular dynamic simulation to explore the molecular basis of Btk-PH domain interaction with Ins(1,3,4,5)P4

Bruton's tyrosine kinase contains a pleckstrin homology domain, and it specifically binds inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4), which is involved in the maturation of B cells. In this paper, we studied 12 systems including the wild type and 11 mutants, K12R, S14F, K19E, R28C/H, E41K, L11P, F25S, Y40N, and K12R-R28C/H, to investigate any change in the ligand binding site of each mutant. Molecular dynamics simulations combined with the method of molecular mechanics/Poisson-Boltzmann solvent-accessible surface area have been applied to the twelve systems, and reasonable mutant structures and their binding free energies have been obtained as criteria in the final classification. As a result, five structures, K12R, K19E, R28C/H, and E41K mutants, were classified as “functional mutations,” whereas L11P, S14F, F25S, and Y40N were grouped into “folding mutations.” This rigorous study of the binding affinity of each of the mutants and their classification provides some new insights into the biological function of the Btk-PH domain and related mutation-causing diseases.