NK cell activation: distinct stimulatory pathways counterbalancing inhibitory signals

Investigation of NK cell function against two target hematological cell line using radioactive chromium assay

NK (Natural killer) cells are a special population of peripheral blood lymphocytes that kill virus-infected cells as well as tumor cells. For testing NK cell function, the classic gold standard assay has been used for a long time, determining the activity from target tumor cells using radioactive chromium in cell cultures for 4h. In this study two hematological cell lines K562 and MDS where used and target and results showed different sensitivity to killing by NK cells separated from healthy volunteers. Results have been shown that MDS release significantly more radioactive chromium indicating higher degree of necrosis during cell culture. In addition, K562 cell line is better target for NK killing in all different E:T ratio in comparison to MDS cell line previously described. Based on this, it is suggested that K562 cells be continues used in the future as better target for investigation NK killing.

The role of the natural killer (NK) cell modulation in breast cancer incidence and progress

The importance of the immune system on tumor surveillance has been investigated for many years, and its impact on controlling tumor progression has been verified. An important subgroup of the innate immune system is natural killer (NK) cells, whose essential function in modulating tumor behavior and suppressing metastasis and tumor growth has been demonstrated. The first idea of NK cells' crucial biological processes was demonstrated through their potent ability to conduct direct cellular cytotoxicity, even without former sensitization. These properties of NK cells allow them to recognize transformed cells that have attenuated self-ligand and express stress-induced ligands. Furthermore, secretion of various cytokines and chemokines after their activation leads to tumor elimination via either direct cytotoxic effect on malignant cells or activation of the adaptive immune system. In addition, novel immunotherapeutic approaches tend to take advantage of NK cells' ability, leading to antibody-based approaches, the formation of engineered CAR-NK cells, and adoptive cell transfer. However, the restricted functionality of NK cells and the inability to infiltrate tumors are its blind spots in breast cancer patients. In this review, we gathered newly acquired data on the biology and functions of NK cells in breast cancer and proposed ways to employ this knowledge for novel therapeutic approaches in cancers, particularly breast cancer.

Immunotherapy and CRISPR Cas Systems: Potential Cure of COVID-19?

The COVID-19 has plunged the world into a pandemic that affected millions. The continually emerging new variants of concern raise the question as to whether the existing vaccines will continue to provide sufficient protection for individuals from SARS-CoV-2 during natural infection. This narrative review aims to briefly outline various immunotherapeutic options and discuss the potential of clustered regularly interspaced short palindromic repeat (CRISPR Cas system technology against COVID-19 treatment as specific cure. As the development of vaccine, convalescent plasma, neutralizing antibodies are based on the understanding of human immune responses against SARS-CoV-2, boosting human body immune responses in case of SARS-CoV-2 infection, immunotherapeutics seem feasible as specific cure against COVID-19 if the present challenges are overcome. In cell based therapeutics, apart from the high costs, risks and side effects, there are technical problems such as the production of sufficient potent immune cells and antibodies under limited time to treat the COVID-19 patients in mild conditions prior to progression into a more severe case. The CRISPR Cas technology could be utilized to refine the specificity and safety of CAR-T cells, CAR-NK cells and neutralizing antibodies against SARS-CoV-2 during various stages of the COVID-19 disease progression in infected individuals. Moreover, CRISPR Cas technology are proposed in hypotheses to degrade the viral RNA in order to terminate the infection caused by SARS-CoV-2. Thus personalized cocktails of immunotherapeutics and CRISPR Cas systems against COVID-19 as a strategy might prevent further disease progression and circumvent immunity escape.

Hijacking TYRO3 from Tumor Cells via Trogocytosis Enhances NK-Cell Effector Functions and Proliferation

Trogocytosis is a fast, cell-cell contact-dependent uptake of membrane patches and associated molecules by one cell from another. Here, we report our investigation of trogocytosis of TYRO3, a cell membrane protein, from tumor target cells to natural killer (NK) cells and the associated functional consequences for NK cells. We found that although NK cells did not express endogenous TYRO3 on the cell surface, activated NK cells rapidly acquired TYRO3 from tumor cells via trogocytosis in vitro and in vivo. NK cells that acquired TYRO3, which we termed TYRO3⁺ NK cells, had significantly enhanced cytotoxicity and IFNγ production as well as higher expression of some activated surface markers compared with TYRO3^- NK cells. Furthermore, the activation status of NK cells and TYRO3 expression levels on donor cells, either endogenous or ectopic, positively correlated with trogocytosis levels. When the antigen-presenting cell (APC) K562 leukemia cell line, a feeder cell line to expand NK cells, overexpressed TYRO3, TYRO3 was transferred to NK cells via trogocytosis, which improved NK-cell proliferation ex vivo. This provides a strategy to manufacture NK cells or their engineered counterparts, such as chimeric antigen receptor NK cells, for the treatment of cancer or infectious diseases.

The effects of stereotactic body radiotherapy on peripheral natural killer and CD3+CD56+ NKT-like cells in patients with hepatocellular carcinoma

BACKGROUND

Both natural killer (NK) and CD3⁺CD56⁺natural killer T (NKT)-like cells play critical roles in the antitumor response. This study aimed to explore the effects of stereotactic body radiotherapy (SBRT) on peripheral NK and NKT-like cells in patients with hepatocellular carcinoma (HCC), and to identify possible surface markers on these cells that correlate with the prognosis.

METHODS

Twenty-five HCC patients were prospectively enrolled in our study, and 10 healthy individuals were served as healthy controls. Flow cytometry was used to determine the counts and the percentages of peripheral NK and NKT-like cells, cells with certain receptors, and cells with intracellular interferon-γ and TNF-α secretion at different time points, including time points of prior to SBRT, at post-SBRT, and 3-month and 6-month after treatment. The Kaplan-Meier method with the log-rank test was applied for survival analysis.

RESULTS

The peripheral NKT-like cells was increased at post-SBRT. Meanwhile, elevated levels of inhibitory receptors and reduced levels of activating receptors of NK cells were also observed in NK cells at post-SBRT, but the levels was not significantly different at 3-month and 6-month as compared with the baseline levels. Lower percentage of NKp30⁺NK cells before SBRT and higher percentage of CD158b⁺NK cells after SBRT were associated with poor progression-free survival. In addition, higher percentage of CD3⁺CD56⁺ NKT-like cells was associated with a higher overall survival rate in HCC patients.

CONCLUSIONS

SBRT has an apparent effect on both peripheral NK and CD3⁺CD56⁺NKT-like cells. Lower percentage of NKp30⁺NK cells before SBRT and higher percentage of CD158b⁺NK cells after SBRT are correlated with poor patients' PFS. Higher percentage of CD3⁺CD56⁺ NKT-like cells is associated with higher OS in HCC patients.

Oral cancer-derived exosomal NAP1 enhances cytotoxicity of natural killer cells via the IRF-3 pathway

OBJECTIVE

To examine the effects of oral cancer-derived exosomes (OCEXs) on natural killer (NK) cells and to explore the underlying mechanism.

MATERIALS AND METHODS

OCEXs were isolated from the cell culture supernatant of oral cancer (OC) cells using ultrafiltration and affinity chromatography and were identified using electron microscopy, nanoparticle tracking analysis (NTA) and immunoblotting. The effects of OCEXs on NK cells were analyzed using laser scanning confocal microscopy and several functional assays of NK cells. To explore the mechanism of their effects, antibody array, protein mass spectrometry and RNA interference were adopted.

RESULTS

The particles isolated from the OC cells were identified as exosomes with satisfactory morphology, concentration and purity. The OCEXs were internalized by NK cells and then promoted the biological functions of NK cells, including proliferation, release of perforin and granzyme M and cytotoxicity. Furthermore, OCEXs increased the expression of interferon regulatory factor 3 (IRF-3) and its phosphorylation, which drove the expression of the type I interferon (IFN) gene and the chemokine (C-X-C motif) ligand (CXCL) genes, thereby promoting the functions of NK cells. In addition, NF-κB-activating kinase-associated protein 1 (NAP1), an upstream activator of IRF-3, was enriched in OCEXs, and treatment with OCEXs increased the expression of NAP1 in NK cells. Importantly, NAP1-depleted OCEXs obtained from OC cells had a dramatically weakened influence on NK cells.

CONCLUSION

Our findings reveal a previously unrecognized function of exosomal NAP1 derived from OC cells in enhancing the cytotoxicity of NK cells via the IRF-3 pathway.

Differential immune response to Eimeria maxima infection in fast- and slow-growing broiler genotypes

Very little has been reported comparing resistance to coccidiosis in fast or slow growing broilers, the latter of which are becoming more prevalent in the broiler industry. We examined mRNA expression in the intestines of fast and slow growing broilers following Eimeria infection. We show that by day 13 post-infection (d pi) with 2500 or 7000 oocysts of Eimeria maxima, slower-growing (Ranger Classic) broilers significantly (P < 0.01) upregulated expression of proinflammatory cyclooxygenase genes (LTB4DH, PTSG1 and PTSG2) above that detected in fast growing (Ross 308) broilers. Expression of CD8α mRNA was downregulated in Ross 308 at day 6d pi with either 2500 or 7000 oocysts of E maxima (P < 0.05), compared to uninfected controls, but was not differentially expressed in Ranger Classic. CD4 genes were not differentially expressed in either chicken line infected with either infectious oocyst dose at d6 pi, compared to uninfected controls. However, at d13 pi, CD4 expression was significantly upregulated in both chicken lines infected with either infectious oocyst dose, compared to uninfected controls (P < 0.05) but this was significantly greater in Ranger Classic broilers compared to Ross 308 (P < 0.05). At d13 pi, expression of CD3 chains (required for T lymphocyte activation) was significantly increased in Ranger Classic compared to Ross 308, infected with either oocyst dose (P < 0.05-0.01). Expression of IL-2 and IL-15 mRNA, required for T lymphocyte proliferation was also significantly upregulated, or maintained longer, in Ranger Classic broilers compared to Ross 308. These differences in immune response to E maxima corresponded with a reduction in E maxima genome detected in the intestines of Ranger Classic compared to Ross 308.

Cryopreserved Human Natural Killer Cells Exhibit Potent Antitumor Efficacy against Orthotopic Pancreatic Cancer through Efficient Tumor-Homing and Cytolytic Ability (Running Title: Cryopreserved NK Cells Exhibit Antitumor Effect)

Pancreatic cancer is known to be highly aggressive, and desmoplasia-induced accumulation of extracellular matrix (ECM), which is a hallmark of many pancreatic cancers, severely restricts the therapeutic efficacy of both immunotherapeutics and conventional chemotherapeutics due to the ECM functioning as a major physical barrier against permeation and penetration. In the case of cell-based immunotherapeutics, there are several other bottlenecks preventing translation into clinical use due to their biological nature; for example, poor availability of cell therapeutic in a readily usable form due to difficulties in production, handling, shipping, and storage. To address these challenges, we have isolated allogeneic natural killer (NK) cells from healthy donors and expanded them in vitro to generate cryopreserved stocks. These cryopreserved NK cells were thawed to evaluate their therapeutic efficacy against desmoplastic pancreatic tumors, ultimately aiming to develop a readily accessible and mass-producible off-the-shelf cell-based immunotherapeutic. The cultured NK cells post-thawing retained highly pure populations of activated NK cells that expressed various activating receptors and a chemokine receptor. Furthermore, systemic administration of NK cells induced greater in vivo tumor growth suppression when compared with gemcitabine, which is the standard chemotherapeutic used for pancreatic cancer treatment. The potent antitumor effect of NK cells was mediated by efficient tumor-homing ability and infiltration into desmoplastic tumor tissues. Moreover, the infiltration of NK cells led to strong induction of apoptosis, elevated expression of the antitumor cytokine interferon (IFN)-γ, and inhibited expression of the immunosuppressive transforming growth factor (TGF)-β in tumor tissues. Expanded and cryopreserved NK cells are strong candidates for future cell-mediated systemic immunotherapy against pancreatic cancer.

Immunomodulatory activity of a water-soluble polysaccharide obtained from highland barley on immunosuppressive mice models

A water-soluble polysaccharide (BP-1) was extracted and purified from highland barley (Hordeum vulgare L.) and its average molecular weight was about 6.7 × 104 Da. In this study, the immunomodulatory activity of BP-1 on the immunosuppressive BALB/c mice model and its molecular mechanism were elucidated. It was found that the weight indexes of spleen and thymus were significantly increased by BP-1 (80 mg kg-1 and 160 mg kg-1) treatment in the immunosuppressive mice model. The results showed that BP-1 (80 mg kg-1 and 160 mg kg-1) could significantly increase the number of bone marrow cells (BMC) and peripheral blood white blood cells (WBC) in the immunosuppressive mice model. In addition, the result further confirmed that BP-1 could increase the serum levels of IL-2, TNF-α and IFN-γ, so as to improve the immune function of immunosuppressive mice. The results showed that BP-1 (80 mg kg-1 and 160 mg kg-1) could promote the proliferation of spleen cells and the natural killer (NK) cell activity in vivo. The quantitative real-time polymerase chain reaction (qRT-PCR) and ELISA results revealed that BP-1 (80 mg kg-1 and 160 mg kg-1) could enhance the production of IL-2, TNF-α, IFN-γ, IgG and IgM in the spleen of immunosuppressive mice. The HE (hematoxylin and eosin) stained histopathological images showed that BP-1 (80 mg kg-1 and 160 mg kg-1) could repair the damage induced by CTX in the spleen cells of immunosuppressive mice. The result of macrophages showed that BP-1 (80 mg kg-1 and 160 mg kg-1) could promote the proliferation and phagocytosis activity of macrophages in immunosuppressive mice. Furthermore, BP-1 could activate macrophages by the TLR-4, TRAF6, TAK1 and nuclear factor κB (NF-κB) p65 pathways in vivo. These results suggested that BP-1 has a remarkable immunomodulatory activity on the immunosuppressive mice model.

VASP Regulates NK Cell Lytic Granule Convergence

NK cells eliminate viral-infected and malignant cells through a highly orchestrated series of cytoskeletal rearrangements, resulting in the release of cytolytic granule contents toward the target cell. Central to this process is the convergence of cytolytic granules to a common point, the microtubule-organizing center (MTOC), before delivery to the synapse. In this study, we show that vasodialator-stimulated phosphoprotein (VASP), an actin regulatory protein, localizes to the cytolytic synapse, but surprisingly, shows no impact on conjugate formation or synaptic actin accumulation despite being required for human NK cell-mediated killing. Interestingly, we also find that a pool of VASP copurifies with lytic granules and localizes with lytic granules at the MTOC. Significantly, depletion of VASP decreased lytic granule convergence without impacting MTOC polarization. Using the KHYG-1 cell line in which lytic granules are in a constitutively converged state, we find that either VASP depletion or F-actin destabilization promoted spreading of formerly converged granules. Our results demonstrate a novel requirement for VASP and actin polymerization in maintaining lytic granule convergence during NK cell-mediated killing.

The immunomodulatory activity and mechanism of docosahexenoic acid (DHA) on immunosuppressive mice models

In this study, the immunomodulatory activity of docosahexaenoic acid (DHA) on the immunosuppressive BALB/c mice model and its molecular mechanism are elucidated. It was found that the weight indexes of the spleen and thymus were significantly increased by DHA (44.0 mg kg-1 and 88.0 mg kg-1) treatment in the prevention or cure groups. The result of macrophages showed that DHA (44.0 mg kg-1 and 88.0 mg kg-1) could promote the proliferation and phagocytosis activity of macrophages in the prevention or cure groups. In addition, DHA could activate macrophages by the G-protein coupled cell membrane receptor GPR120- Mitogen-Activated Protein Kinases (MAPKs)-nuclear factor κB (NF-κB) p65 pathway in vivo. The result of the spleen showed that DHA (44.0 mg kg-1 and 88.0 mg kg-1) could promote the proliferation of spleen cells and the natural killer (NK) cells activity in vivo. In the prevention or cure groups, the quantitative real-time polymerase chain reaction (qRT-PCR) results revealed that DHA (44.0 mg kg-1 and 88.0 mg kg-1) could enhance the production of cytokines IL-1β, IL-2, TNF-α and IFN-γ in the spleen of immunosuppressive mice. The HE (hematoxylin and eosin) stained histopathological images showed that DHA could repair the damage induced by CTX in the spleen cells of the prevention or cure groups. These results suggested that DHA has a remarkable immunomodulatory activity on the immunosuppressive mice model in the prevention or cure groups.

Microglial TREM2/DAP12 Signaling: A Double-Edged Sword in Neural Diseases

Microglia are activated after neuronal injury and in neurodegenerative diseases, and trigger neuroinflammation in the central nervous system (CNS). Microglia-derived neuroinflammation has both beneficial and detrimental effects on neurons. Because the timing and magnitude of microglial activation is thought to be a critical determinant of neuronal fate, understanding the molecular mechanisms underlying microglial activation is required to enable establishment of microglia-targeted therapies for neural diseases. Plasma membrane receptors play primary roles as activators of microglia and in this review, we focus on a receptor complex involving triggering receptor expressed on myeloid cells 2 (TREM2) and DNAX-activating protein of 12 kDa (DAP12), both of which are causative genes for Nasu-Hakola disease, a dementia with bone cysts. Recent transcriptome approaches demonstrated TREM2/DAP12 signaling as the principal regulator that transforms microglia from a homeostatic to a neural disease-associated state. Furthermore, animal model studies revealed critical roles for TREM2/DAP12 in the regulation of microglial activity, including survival, phagocytosis, and cytokine production, not only in Alzheimer's disease but also in other neural diseases, such as Parkinson's disease, demyelinating disease, ischemia, and peripheral nerve injury. Intriguingly, while TREM2/DAP12-mediated microglial activation is detrimental for some diseases, including peripheral nerve injury, it is beneficial for other diseases. As the role of activated microglia differs among disease models, TREM2/DAP12 signaling may result in different outcomes in different diseases. In this review we discuss recent perspectives on the role of TREM2/DAP12 in microglia and their contribution to neural diseases.

Chimeric antigen receptor (CAR)-modified natural killer cell-based immunotherapy and immunological synapse formation in cancer and HIV

Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells contribute to the body’s immune defenses. Current chimeric antigen receptor (CAR)-modified T cell immunotherapy shows strong promise for treating various cancers and infectious diseases. Although CAR-modified NK cell immunotherapy is rapidly gaining attention, its clinical applications are mainly focused on preclinical investigations using the NK92 cell line. Despite recent advances in CAR-modified T cell immunotherapy, cost and severe toxicity have hindered its widespread use. To alleviate these disadvantages of CAR-modified T cell immunotherapy, additional cytotoxic cell-mediated immunotherapies are urgently needed. The unique biology of NK cells allows them to serve as a safe, effective, alternative immunotherapeutic strategy to CAR-modified T cells in the clinic. While the fundamental mechanisms underlying the cytotoxicity and side effects of CAR-modified T and NK cell immunotherapies remain poorly understood, the formation of the immunological synapse (IS) between CAR-modified T or NK cells and their susceptible target cells is known to be essential. The role of the IS in CAR T and NK cell immunotherapies will allow scientists to harness the power of CAR-modified T and NK cells to treat cancer and infectious diseases. In this review, we highlight the potential applications of CAR-modified NK cells to treat cancer and human immunodeficiency virus (HIV), and discuss the challenges and possible future directions of CAR-modified NK cell immunotherapy, as well as the importance of understanding the molecular mechanisms of CAR-modified T cell- or NK cell-mediated cytotoxicity and side effects, with a focus on the CAR-modified NK cell IS.

KIR Genes and Their Ligands Predict the Response to Anti-EGFR Monoclonal Antibodies in Solid Tumors

Killer-cell immunoglobulin-like receptors (KIRs) regulate the killing function of natural killer cells, which play an important role in the antibody-dependent cell-mediated cytotoxicity response exerted by therapeutic monoclonal antibodies (mAbs). However, it is unknown whether the extensive genetic variability of KIR genes and/or their human leukocyte antigen (HLA) ligands might influence the response to these treatments. This study aimed to explore whether the variability in KIR/HLA genes may be associated with the variable response observed to mAbs based anti-epidermal growth factor receptor (EGFR) therapies. Thirty-nine patients treated with anti-EGFR mAbs (trastuzumab for advanced breast cancer, or cetuximab for advanced colorectal or advanced head and neck cancer) were included in the study. All the patients had progressed to mAbs therapy and were grouped into two categories taking into account time to treatment failure (TTF ≤6 and ≥10 months). KIR genotyping (16 genetic variability) was performed in genomic DNA from peripheral blood by PCR sequence-specific primer technique, and HLA ligand typing was performed for HLA-B and -C loci by reverse polymerase chain reaction sequence-specific oligonucleotide methodology. Subjects carrying the KIR/HLA ligand combinations KIR2DS1/HLAC2C2-C1C2 and KIR3DS1/HLABw4w4-w4w6 showed longer TTF than non-carriers counterparts (14.76 vs. 3.73 months, p < 0.001 and 14.93 vs. 4.6 months, p = 0.005, respectively). No other significant differences were observed. Two activating KIR/HLA ligand combinations predict better response of patients to anti-EGFR therapy. These findings increase the overall knowledge on the role of specific gene variants related to responsiveness to anti-EGFR treatment in solid tumors and highlight the importance of assessing gene polymorphisms related to cancer medications.

TRAIL-mediated killing of acute lymphoblastic leukemia by plasmacytoid dendritic cell-activated natural killer cells

Acute lymphoblastic leukemia (ALL) still frequently recurs after hematopoietic stem cell transplantation (HSCT), underscoring the need to improve the graft-versus-leukemia (GvL) effect. Natural killer (NK) cells reconstitute in the first months following HSCT when leukemia burden is at its lowest, but ALL cells have been shown to be resistant to NK cell-mediated killing. We show here that this resistance is overcome by NK cell stimulation with TLR-9-activated plasmacytoid dendritic cells (pDCs). NK cell priming with activated pDCs resulted in TRAIL and CD69 up-regulation on NK cells and IFN-γ production. NK cell activation was dependent on IFN-α produced by pDCs, but was not reproduced by IFN-α alone. ALL killing was further enhanced by inhibition of KIR engagement. We showed that ALL lysis was mainly mediated by TRAIL engagement, while the release of cytolytic granules was involved when ALL expressed NK cell activating receptor ligands. Finally, adoptive transfers of activated-pDCs in ALL-bearing humanized mice delayed the leukemia onset and cure 30% of mice. Our data therefore demonstrate that TLR-9 activated pDCs are a powerful tool to overcome ALL resistance to NK cell-mediated killing and to reinforce the GvL effect of HSCT. These results open new therapeutic avenues to prevent relapse in children with ALL.

Biochemical and Functional Insights into the Integrated Regulation of Innate Immune Cell Responses by Teleost Leukocyte Immune-Type Receptors

Across vertebrates, innate immunity consists of a complex assortment of highly specialized cells capable of unleashing potent effector responses designed to destroy or mitigate foreign pathogens. The execution of various innate cellular behaviors such as phagocytosis, degranulation, or cell-mediated cytotoxicity are functionally indistinguishable when being performed by immune cells isolated from humans or teleost fishes; vertebrates that diverged from one another more than 450 million years ago. This suggests that vital components of the vertebrate innate defense machinery are conserved and investigating such processes in a range of model systems provides an important opportunity to identify fundamental features of vertebrate immunity. One characteristic that is highly conserved across vertebrate systems is that cellular immune responses are dependent on specialized immunoregulatory receptors that sense environmental stimuli and initiate intracellular cascades that can elicit appropriate effector responses. A wide variety of immunoregulatory receptor families have been extensively studied in mammals, and many have been identified as cell- and function-specific regulators of a range of innate responses. Although much less is known in fish, the growing database of genomic information has recently allowed for the identification of several immunoregulatory receptor gene families in teleosts. Many of these putative immunoregulatory receptors have yet to be assigned any specific role(s), and much of what is known has been based solely on structural and/or phylogenetic relationships with mammalian receptor families. As an attempt to address some of these shortcomings, this review will focus on our growing understanding of the functional roles played by specific members of the channel catfish (Ictalurus punctatus) leukocyte immune-type receptors (IpLITRs), which appear to be important regulators of several innate cellular responses via classical as well as unique biochemical signaling networks.

NK cells regulating T cell responses: mechanisms and outcome

Natural killer (NK) cells are important innate effectors in immunity. NK cells also have a role in the regulation of the adaptive immune response, and have been shown, in different contexts, to stimulate or inhibit T cell responses. Recent findings have expanded our understanding of the mechanisms underlying this regulation, revealing that regulation by NK cells can result from both direct interactions between NK cells and T cells, as well as indirectly, involving interactions with antigen presenting cells and the impact of NK cells on infected cells and pathogen load. We review these recent findings here, and outline emerging principles of how this regulation influences the overall outcome of adaptive immunity in infection and disease.

Natural killer cell in the developing life

\Natural killer (NK) cells that provide first-line innate immune reactions against virus-infected and tumor cells have different roles in different body sites and in different stages. From the beginning of life, NK cells participate in many aspects of development, especially in a successful pregnancy and a healthy neonatal stage. This article reviews recent advances regarding the role of NK cells in implantation, placentation and immune tolerance during pregnancy as well as in the neonatal immune defense. The interactions between NK cells and other immune cells in each developmental stage are discussed.

Donor NK cell licensing in control of malignancy in hematopoietic stem cell transplant recipients

Among cancers treated with allogeneic hematopoietic stem-cell transplantation (HSCT), some are sensitive to natural killer (NK) cell reactivity, described as the "missing self" recognition effect. However, this model disregarded the NK cell licensing effect, which highly increases the NK cell reactivity against tumor and is dependent on the coexpression of inhibitory killer cell immunoglobulin-like receptor (iKIR) and its corresponding HLA Class I ligand. We assessed clinical data, HLA and donor iKIR genotyping in 283 patients with myelo- and lymphoproliferative malignancies who underwent HSCT from unrelated donors. We found dramatically reduced overall survival (OS), progression free survival (PFS), and time to progression (TTP) among patients with malignant diseases with the lack of HLA ligand cognate with this iKIR involved in NK cell licensing in corresponding donor (events 83.3% vs. 39.8%, P = 0.0010; 91.6% vs. 47.7%, P = 0.00010; and 30.0% vs. 17.3%, P = 0.013, for OS, PFS, and TTP, respectively). The extremely adverse PFS have withstand the correction when patient group was restricted to HLA mismatched donor-recipient pairs. The incidence of aGvHD was comparable in two groups of patients. In malignant patients after HSCT the missing HLA ligand for iKIR involved in NK cell licensing in corresponding donor ("missing licensing proof") induced extremely adverse survival of the patients due to the progression of malignancy and not to the aGvHD. Avoiding the selection of HSCT donors with the "missing licensing proof" in the malignant patient is strongly advisable.

High CD56++CD16- natural killer (NK) cells among suboptimal immune responders after four years of suppressive antiretroviral therapy in an African adult HIV treatment cohort

Background

Up to 40% of HIV-infected individuals receiving Highly Active Antiretroviral Therapy (HAART) have poor CD4+ T-cell recovery. The role of natural killer (NK) cells in immune recovery during HAART is not well understood. We described the profiles of NK cell subsets and their expression of activating receptor, NKG2D and cytotoxicity receptor NKp46 among suboptimal immune responders to despite four years of suppressive HAART.

Methods

A case control study utilized frozen peripheral blood mononuclear cells (PBMC) from a cohort of HIV-infected adults that initiated HAART in 2004/5, at CD4 < 200 cells/μl. Cases were ‘suboptimal’ responders; patients within the lowest quartile of CD4+ T-cell reconstitution, with a median CD4 count increase of 129 (-43-199) cells/μl (difference between CD4 count at baseline and after 4 years of HAART) and controls were ‘super-optimal’ responders; patients within the highest quartile of CD4 T-cell reconstitution with a median CD4 count increase of 528 (416-878) cells/μl). Expression of NK cell lineage markers (CD56^+/-CD16^+/-) and receptors NKG2D and NKp46, was measured among PBMC from 29 cases of ‘suboptimal’ responders’ and 23 controls of ‘super-optimal responders’, and compared among ‘suboptimal’ and ‘super-optimal’ responders. NK cell populations were compared using the Holm Sidak multiple comparison test and p values < 0.05 were considered statistically significant. Data was analyzed using FLOWJO and GraphPad Prism 6.

Results

‘Suboptimal responders’ had a higher proportion of cytokine producing CD56⁺⁺CD16^+/- (CD56^bri) NK cells than the ‘super-optimal responders’ p = 0.017, and CD56^neg NK cells were lower among suboptimal than super-optimal responders (p = 0.007). The largest NK cell subset, CD56^dim, was comparable among suboptimal responders and ‘super-optimal immune responders’. Expression of NKG2D and NKp46 receptors on NK cell subsets (CD56^bri, CD56^neg and CD56^dim), was comparable among ‘suboptimal’ and ‘super-optimal’ immune responders.

Conclusions

The pro-inflammatory CD56⁺⁺CD16^-- NK cells were higher among ‘suboptimal’ responders relative to ‘super-optimal’ responders, despite four years of suppressive HAART. Alteration of NK cell populations could inhibit host immune responses to infections among suboptimal responders. We recommend further analysis of NK cell function among suboptimal immune responders in order to inform targeted interventions to optimize immune recovery among HAART-treated adults.

Synergistic cytotoxicity of ex vivo expanded natural killer cells in combination with monoclonal antibody drugs against cancer cells

The adoptive transfer of highly cytotoxic natural killer (NK) cells is an emerging tool for cancer immunotherapy. Antibody-dependent cellular cytotoxicity (ADCC) has recently been identified as one of the critical factors for the clinical efficacy of anticancer antibodies, in which NK cells are the major effectors of ADCC. NK cells were expanded from PBMC by a feeder-cell-free expansion method. NK cell expansion efficiency was evaluated within a period of 21 days. The kinetics of NK cell expansion and the expression of activating and inhibitory receptors on NK cells were monitored. NK cells producing IFN-γ and TNF-α were detected by intracellular cytokine staining. The cytotoxicity of expanded NK cells against various cancer cells was compared with that of freshly isolated NK cells. The ADCC functions of expanded NK cells in combination with rituximab against CD20+ lymphoma cell lines were evaluated. Our method efficiently expanded NK cells ex vivo, which showed a much higher activity to induce the expression of activating receptors and to produce IFN-γ and TNF-α as well as cytotoxicity against various cancer cell lines including CD133+ primary cancer cells than freshly isolated NK cells. We observed a synergistic cytotoxicity of our expanded NK cells against CD20+ B lymphoma cell lines as well as higher IFN-γ and TNF-α production when combined with rituximab. Our results suggest that the adoptive transfer of a large number of ex vivo expanded NK cells, particularly in combination with monoclonal antibody drugs, is a useful tool for cancer immunotherapy.

Channel catfish leukocyte immune-type receptor mediated inhibition of cellular cytotoxicity is facilitated by SHP-1-dependent and -independent mechanisms

Channel catfish (Ictalurus punctatus) leukocyte immune-type receptors (IpLITRs) are immunoregulatory proteins belonging to the immunoglobulin superfamily that likely play an important role in the regulation of teleost immune cell effector responses. IpLITRs are expressed by myeloid and lymphoid subsets and based on their structural features can be classified as either putative stimulatory or inhibitory forms. We have recently demonstrated at the biochemical and functional levels that stimulatory IpLITR-types induced intracellular signaling cascades resulting in immune cell activation. Alternatively, we have shown that putative inhibitory IpLITRs may abrogate immune cell responses by recruiting teleost Src homology 2 (SH2) domain-containing cytoplasmic phosphatases (SHP) to their tyrosine-containing cytoplasmic tails. In the present study, we used vaccinia virus to express recombinant chimeric proteins encoding the extracellular and transmembrane regions of human KIR2DL3 fused with the cytoplasmic tails of two putative inhibitory IpLITRs (i.e. IpLITR1.2a and IpLITR1.1b) in mouse spleen-derived cytotoxic lymphocytes. This approach allowed us to study the specific effects of IpLITR-induced signaling on lymphocyte killing of B cell targets (e.g. 721.221 cells) using a standard chromium release assay. Our results suggest that both IpLITR1.2a and IpLITR1.1b are potent inhibitors of lymphocyte-mediated cellular cytotoxicity. Furthermore, using a catalytically inactive SHP-1 mutant in combination with site-directed mutagenesis and co-immunoprecipitations, we also demonstrate that the IpLITR1.2a-mediated functional inhibitory response is SHP-1-dependent. Alternatively, IpLITR1.1b-mediated inhibition of cellular cytotoxicity is facilitated by both SHP-1-dependent and independent mechanisms, possibly involving the C-terminal Src kinase (Csk). The involvement of this inhibitory kinase requires binding to a tyrosine residue encoded in the unique membrane proximal cytoplasmic tail region of IpLITR1.1b. Overall, this represents the first functional information for inhibitory IpLITR-types and reveals that catfish LITRs engage SHP-dependent and -independent inhibitory signaling pathways to abrogate lymphocyte-mediated killing.

Activating signals dominate inhibitory signals in CD137L/IL-15 activated natural killer cells

Natural killer (NK) cells can mediate potent antitumor effects, but factors regulating the efficiency of tumor lysis remain unclear. Studies in allogeneic stem cell transplantation highlight an important role for killer cell immunoglobulin-like receptor (KIR) mismatch in overcoming human leukocyte antigen-mediated inhibitory signals. However, other activating and inhibitory signals also modulate tumor lysis by NK cells. We used rhIL15 and artificial antigen presenting cells expressing CD137L and IL15Rα to activate and expand peripheral blood NK cells (CD137L/IL15 NK) up to 1000-fold in 3 weeks. Compared with resting NK cells, CD137L/IL15 NK cells show modest increases in KIR expression and substantial increases in NKG2D, tumor necrosis factor-related apoptosis-inducing ligand, and natural cytotoxicity receptors (NCRs: NKp30, NKp44, NKp46). Compared with resting NK cells, CD137L/IL15 NK cells mediate enhanced cytotoxicity against allogeneic and autologous tumors and KIR signaling did not substantially inhibit cytotoxicity. Rather, tumor lysis by CD137L/IL15 activated NK cells was predominantly driven by NCR signaling as blockade of NCRs dramatically diminished the lysis of a wide array of tumor targets. Furthermore, tumor lysis by CD137L/IL15 NK cells was tightly linked to NCR expression levels that peaked on day 8 to 10 after NK activation, and cytotoxicity diminished on subsequent days as NCR expression declined. We conclude that KIR mismatch is not a prerequisite for tumor killing by CD137L/IL15 NK cells and that NCR expression provides a biomarker for predicting potency of CD137L/IL15 NK cells in studies of NK cell-based immunotherapy.

Natural killer cell immunotherapy for cancer: a new hope

Recently there has been a substantial gain in our understanding of the role NK-cells play in mediating innate host immune responses. Although NK cells have long been known to mediate antigen independent tumor cytotoxicity, the therapeutic potential of NK cell-based immunotherapy has yet to be realized. Manipulating the balance between inhibitory and activating NK receptor signals, sensitization of tumor target cells to NK cell-mediated apoptosis, and recent discoveries in NK-cell receptor biology have fueled translational research that has led to clinical trials investigating a number of novel methods to potentiate NK cytotoxicity against human malignancies.

Blocking NK cell inhibitory self-recognition promotes antibody-dependent cellular cytotoxicity in a model of anti-lymphoma therapy

Human NK cells lyse Ab-coated target cells through the process of Ab-dependent cellular cytotoxicity (ADCC). Improving ADCC responses is desirable because it is thought to be an important antitumor mechanism for some Abs. NK cell inhibitory receptors, such as killer cell Ig-like receptors, engage with MHC class I molecules on self-cells to block NK cell activation. Accordingly, we enhanced ADCC responses by blocking NK cell inhibitory receptors, thus perturbing induction of the self-recognition signal. In a cell line model of anti-lymphoma therapy, the combination of rituximab with an Ab that blocks inhibitory self-recognition yielded increased NK cell-mediated target cell lysis when compared with rituximab alone. To validate this proof-of-concept, we then used a more representative approach in which an individual's fresh primary NK cells encountered autologous, EBV-transformed B cells. In this system, rituximab and a combination of Abs that block NK cell inhibitory receptors yielded improved NK cell-mediated lysis over rituximab alone. The results show, for the first time, that disruption of inhibitory self-recognition can efficiently promote ADCC in a human model, applying an autologous system in which physiologic checkpoints are in place. This method provides an alternative approach to potentiate the therapeutic benefit of antitumor Abs that mediate ADCC.

Expression of ligands to NKp46 in benign and malignant melanocytes

Human melanoma cell lines were shown to express ligands for the natural cytotoxicity receptor, NKp46, expressed by natural killer (NK) cells. We aimed to examine the expression of ligands for NKp46 by various primary human melanocytic cells and melanocytic lesions. Sections from primary nevi and melanomas were tested for expression of NKp46 ligands employing chimeric NKp46-Fc for staining. The melanocytes present in the reticular dermis were negative for NKp46 ligands in common nevi; in malignant melanocytic lesions, the deeper melanocytes were focally positive. In dermoepidermal junction of all melanocytic lesions, the melanocytes showed enhanced expression of NKp46 ligands. Melanophages in all lesions were consistently positive for NKp46 ligands. These observations establish the expression of NKp46 ligands by primary-transformed melanocytes. Normal melanocytes did not express ligands to NKp46. Therefore, the results show (i) a correlation between the malignant potential of the lesion and the expression of NKp46 ligands in the reticular dermis, and (ii) enhanced expression of NKp46 ligands in the active proliferation zone (dermoepidermal junction) of nevi and melanomas. Ligands to NKp46 were expressed on the membrane and within the cells. The physiological role of NKp46 ligands in the progression of malignancy within melanocytic lesions should be explored further.

The microglial networks of the brain and their role in neuronal network plasticity after lesion

Microglia are the resident inflammatory cells of the central nervous system (CNS) extending a network of processes in the CNS parenchyma. Following axon lesion to neurons, most extensively studied in motoneurons, there is a typical retrograde response at the cell body level, including the removal or 'stripping' of synapses from the perikaryon and dendrites of affected cells. Microglia have been attributed a main and active role in this process, although also an involvement of activated astrocytes has been suggested. The signaling pathways for this 'synaptic stripping' have so far been unknown, but recently some classical immune recognition molecules, the MHC class I molecules, have been shown to have a strong influence on the strength and pattern of the synapse elimination response. Since there is an expression of MHC class I in both neurons and glia, in particular microglia, as well as MHC class I related receptors in axons and microglia, there are good reasons to believe that classical immune recognition signaling between neurons and glia underlies part of the 'stripping' response. A role for microglia in an interplay with synapses based on this type of signaling is further exemplified by the fact that, in the absence of some MHC class I related receptors normally found on microglia during development, profound effects on synaptic function and biochemistry have been demonstrated. Such effects may be linked to the development of various disorders of the CNS, such as degenerative disease.

MHC class I expression and synaptic plasticity after nerve lesion

An axon lesion to a bulbar or spinal motoneuron is followed by a typical retrograde response at the cell body level, including the removal or 'stripping' of synapses from the perikaryon and dendrites of affected cells. Both activated microglia and astrocytes have been attributed roles in this process. The signalling pathways for this 'synaptic stripping' have so far been unknown, but recently a classical set of immune recognition molecules, the MHC class I molecules, have been shown to have a strong influence on the strength and pattern of the synapse elimination response. Thus, when MHC class I signalling is severely impaired in mice lacking the MHC class I subunit beta2-microglobulin (beta2m) and transporter associated with antigen processing 1 (TAP 1) genes, both of which are necessary for surface expression of MHC class I, there is a stronger elimination of synapses from injured neurons, with the surplus elimination directed towards clusters of putatively inhibitory synapses. Moreover, the regenerative capacity of motoneurons in such mice is lower than in wild-type animals. The expression of MHC class I, as well as MHC class I-related receptors in both neurons and glia, lend support to a hypothesis that classical immune recognition signalling between neurons and glia underlie part of the 'stripping' response.

Reduced natural killer (NK) function associated with high-risk myelodysplastic syndrome (MDS) and reduced expression of activating NK receptors

Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis with potential for progression to acute myeloid leukemia (AML). We compared natural killer (NK) cytolytic function in 48 MDS patients with 37 healthy donors and found reduced activity in the patient population (K562 cytolysis, 19% +/- 21% SD versus 40% +/- 17%) (P < .001). NK cytotoxicity in MDS patients was reduced against 3 disparate tumor targets with differential activating receptor requirement, suggesting global defects in NK function. Reduced NK function in MDS was significantly associated with higher International Prognostic Score (P = .01), abnormal karyotype (P = .05), the presence of excess blasts (P = .01), and age-adjusted bone marrow hypercellularity (P = .04). MDS patients had a display of the activating receptor NKp30, and NKG2D down-regulation closely correlated with impaired NK function (P = .001). NKG2D ligands (MICA and MICB) were expressed on CD34(+) cells from bone marrow of 30% of MDS patients and a leukemic cell line derived from an MDS patient (MDS1). Collectively, these findings suggest that impairment of NK cytolytic function derives in part from reduced activating NK receptors such as NKG2D in association with disease progression. Evasion of NK immunosurveillance may have importance for MDS disease progression.

Characterization of the Recognition of Tumor Cells by the Natural Cytotoxicity Receptor, NKp44

NKp44 is a natural cytotoxicity receptor expressed by human NK cells upon activation. In this study, we demonstrate that cell surface heparan sulfate proteoglycans (HSPGs), expressed by target cells, are involved in the recognition of tumor cells by NKp44. NKp44 showed heparan sulfate-dependent binding to tumor cells; this binding was partially blocked with an antibody to heparan sulfate. In addition, direct binding of NKp44 to heparin was observed, and soluble heparin/heparan sulfate enhanced the secretion of IFNgamma by NK92 cells activated with anti-NKp44 monoclonal antibody. Basic amino acids, predicted to constitute the putative heparin/heparan sulfate binding site of NKp44, were mutated. Tumor cell recognition of the mutated NKp44 proteins was significantly reduced and correlated with their lower recognition of heparin. We previously reported that NKp44 recognizes the hemagglutinin of influenza virus (IV). Nevertheless, the ability of the mutated NKp44 proteins to bind viral hemagglutinin expressed by IV-infected cells was not affected. Thus, we suggest that heparan sulfate epitope(s) are ligands/co-ligands of NKp44 and are involved in its tumor recognition ability.

Lymphocyte activation in response to melanoma: interaction of NK-associated receptors and their ligands

In recent years, studies on the molecular and cellular mechanisms of immune responses against melanoma have contributed to a better understanding of how these tumours can be recognised by cytotoxic cells and the mechanisms they have developed to escape from innate and adaptive immunity. Lysis of melanoma cells by natural killer (NK) cells and cytolytic T cells is the result of a fine balance between signals transmitted by activating and inhibitory receptors. In addition to the T cell receptor, these were initially described as NK cell-associated receptors (NKRs) and were later also found on subsets of T lymphocytes, particularly effector-memory and terminally differentiated CD8 T cells. An increase of NKR(+)CD8(+) T cells has been found in melanoma patients, correlating with the expansion of differentiated effector CD8(+)CD28(null) CD27(null) T cells. NKRs can regulate the lysis of target cells expressing appropriate ligands. Activating receptors recognise ligands on tumours whereas inhibitory receptors are specific for MHC class I antigens and sense missing self. Altered expression of MHC class I antigens is frequently found on melanoma cells, preventing recognition by specific cytolytic T cells but favouring NK cell recognition. Changes in the expression of NKR-ligands in melanoma contribute in explaining the differences in the capacity of cytotoxic immune cells to control melanoma growth and dissemination.

Tumor-Primed Human Natural Killer Cells Lyse NK-Resistant Tumor Targets: Evidence of a Two-Stage Process in Resting NK Cell Activation

NK cells are defined as those cells that lyse tumor cells without priming. In this study, we show that the preincubation of resting human NK cells with the leukemia cell CTV-1 primes NK cells to lyse NK-resistant cell lines, primary leukemias, and solid tumors even when HLA-matched, allogeneic or autologous. The primed NK cells remained nonresponsive to HLA-C matched and mismatched normal mononuclear cells from multiple donors. CD69, a known NK trigger receptor, was shown to be the predominant trigger on the tumor-primed NK cells because lysis was blocked with the rCD69 protein. The lack of lytic activity against normal hemopoietic cells implied that the ligand for CD69 is tumor restricted, and this was confirmed by experiments using fluorochrome labeled rCD69. It has been recently shown that resting NK cells require prior stimulation with IL-2 before triggering by all known NK-triggering ligands. In this study, we show that a tumor cell can provide the NK priming signal independently of IL-2. These data provide evidence for two NK evasion strategies for tumor cells, namely the prevention of priming (type1 evasion) and failure to trigger (type 2 evasion). Most NK-resistant cell lines are type 1 and fail to prime resting NK cells but are lysed by IL-2-primed NK cells. In contrast, CTV-1 cells prime resting NK cells but fail to trigger (type 2), and coincubation with CTV-1 primes for triggering by type 1 NK-resistant tumor cells. These tumor-activated NK cells lyse a broad spectrum of tumor cells with a degree of specificity never previously reported.

Modulation of natural killer (NK) receptors on NK (CD3-/CD56+), T (CD3+/CD56-) and NKT-like (CD3+/CD56+) cells after heart transplantation

BACKGROUND

After undergoing heart transplantation and the subsequent compulsive immunosuppressive treatments, patients are at risk of rejection episodes, infectious complications or cancer development. Thus, it is probable that the various subsets of peripheral cytotoxic lymphocytes are modulated in such patients. This area of study can now be investigated by examining the numerous recently described natural killer (NK)-cell-related surface receptors.

METHODS

A prospective cohort of 60 heart transplant recipients and 60 controls was studied. The partitioning of lymphocyte subsets, especially NK (CD3-/CD56+), T (CD3+/CD56-) and NKT-like (CD3+/CD56+) cells, was compared in both groups using multi-parametric flow cytometry. Moreover, expression of a series of seven NK-related receptors was compared on the three subsets defined by CD56 expression.

RESULTS

A significant increase in NK-cell levels was observed in transplanted patients, as compared with controls, whereas T and NKT-like cells were in similar proportions in both groups. Two NK-related receptors showed significantly different levels of expression in heart transplant recipients: the cytotoxic effector, CD244, which was in a significantly increased proportion on T and NKT-like cells; and the activating receptor, CD161, which was expressed significantly less on NK and NKT-like cells, but more on T cells.

CONCLUSIONS

These findings indicate that cytotoxic NK-related cells, increased in proportion, also display increased levels of activity-associated markers in heart transplant recipients. Viral infection or the immunosuppressive regimen could be responsible for the modulation of regulatory receptors on NK and NKT-like cells in heart transplant recipients.

Ligation of CD8alpha on human natural killer cells prevents activation-induced apoptosis and enhances cytolytic activity

It has been previously shown that the subset of human natural killer (NK) cells which express CD8 in a homodimeric alpha/alpha form are more cytotoxic than their CD8- counterparts but the mechanisms behind this differential cytolytic activity remained unknown. Target cell lysis by CD8- NK cells is associated with high levels of effector cell apoptosis, which is in contrast to the significantly lower levels found in the CD8alpha+ cells after lysis of the same targets. We report that cross-linking of the CD8alpha chains on NK cells induces rapid rises in intracellular Ca2+ and increased expression of CD69 at the cell surface by initiating the influx of extracellular Ca2+ ions. We demonstrate that secretion of cytolytic enzymes initiates NK-cell apoptosis from which CD8alpha+ NK cells are protected by an influx of exogenous calcium following ligation of CD8 on the NK-cell surface. This ligation is through interaction with fellow NK cells in the cell conjugate and can occur when the target cells lack major histocompatibility complex (MHC) Class I expression. Protection from apoptosis is blocked by preincubation of the NK cells with anti-MHC Class I antibody. Thus, in contrast to the CD8- subset, CD8alpha+ NK cells are capable of sequential lysis of multiple target cells.

NK cells infiltrating a MHC class I-deficient lung adenocarcinoma display impaired cytotoxic activity toward autologous tumor cells associated with altered NK cell-triggering receptors

NK cells are able to discriminate between normal cells and cells that have lost MHC class I (MHC-I) molecule expression as a result of tumor transformation. This function is the outcome of the capacity of inhibitory NK receptors to block cytotoxicity upon interaction with their MHC-I ligands expressed on target cells. To investigate the role of human NK cells and their various receptors in the control of MHC-I-deficient tumors, we have isolated several NK cell clones from lymphocytes infiltrating an adenocarcinoma lacking beta2-microglobulin expression. Unexpectedly, although these clones expressed NKG2D and mediated a strong cytolytic activity toward K562, Daudi and allogeneic MHC-class I+ carcinoma cells, they were unable to lyse the autologous MHC-I- tumor cell line. This defect was associated with alterations in the expression of natural cytotoxicity receptor (NCR) by NK cells and the NKG2D ligands, MHC-I-related chain A, MHC-I-related chain B, and UL16 binding protein 1, and the ICAM-1 by tumor cells. In contrast, the carcinoma cell line was partially sensitive to allogeneic healthy donor NK cells expressing high levels of NCR. Indeed, this lysis was inhibited by anti-NCR and anti-NKG2D mAbs, suggesting that both receptors are required for the induced killing. The present study indicates that the MHC-I-deficient lung adenocarcinoma had developed mechanisms of escape from the innate immune response based on down-regulation of NCR and ligands required for target cell recognition.

Characterization of the Heparin/Heparan Sulfate Binding Site of the Natural Cytotoxicity Receptor NKp46†

NKp46 is a member of a group of receptors collectively termed natural cytotoxicity receptors (NCRs) that are expressed by natural killer (NK) cells. NCRs are capable of mediating direct killing of tumor and virus-infected cells by NK cells. We have recently shown that NKp46 recognizes the heparan sulfate moieties of membranal heparan sulfate proteoglycans (HSPGs), thus enabling lysis of tumor cells by NK cells. In the current study, we further examined the residues in NKp46 that may be involved in heparan sulfate binding on tumor cells. On the basis of both the electrostatic potential map and comparison to the heparin binding site on human fibronectin, we predicted a continuous region containing the basic amino acids K133, R136, H139, R142, and K146 to be involved in NKp46 binding to heparan sulfate. Mutating these amino acids on NKp46D2 to noncharged amino acids retained its virus binding capacity but reduced its binding to tumor cells with a 10-100 fold lower K(D) when tested for direct binding to heparin. The minimal length of the heparin/heparan sulfate epitope recognized by NKp46 was eight saccharides as predicted from the structure and proven by testing heparin oligomers. Testing selectively monodesulfated heparin oligomers emphasized the specific contributions of O-sulfation, N-sulfation, and N-acetylation to epitope recognition by NKp46. The characterization of heparan sulfate binding region in NKp46 offers further insight into the identity of the ligands for NKp46 and the interaction of NK and cancers.

Impaired synaptic function in the microglial KARAP/DAP12-deficient mouse

Several proteins are expressed in both immune and nervous systems. However, their putative nonimmune functions in the brain remain poorly understood. KARAP/DAP12 is a transmembrane polypeptide associated with cell-surface receptors in hematopoeitic cells. Its mutation in humans induces Nasu-Hakola disease, characterized by presenile dementia and demyelinization. However, alteration of white matter occurs months after the onset of neuropsychiatric symptoms, suggesting that other neuronal alterations occur in the early phases of the disease. We hypothesized that KARAP/DAP12 may impact synaptic function. In mice deficient for KARAP/DAP12 function, long-term potentiation was enhanced and was partly NMDA receptor (NMDAR) independent. This effect was accompanied by changes in synaptic glutamate receptor content, as detected by the increased rectification of AMPA receptor EPSCs and increased sensitivity of NMDAR EPSCs to ifenprodil. Biochemical analysis of synaptic proteins confirmed these electrophysiological data. In mutants, the AMPA receptor GluR2 subunit expression was decreased only in the postsynaptic densities but not in the whole membrane fraction, demonstrating specific impairment of synaptic receptor accumulation. Alteration of the BNDF-tyrosine kinase receptor B (TrkB) signaling in the mutant was demonstrated by the dramatic decrease of synaptic TrkB with no change in other regulatory or scaffolding proteins. Finally, KARAP/DAP12 was detected only in microglia but not in neurons, astrocytes, or oligodendrocytes. KARAP/DAP12 may thus alter microglial physiology and subsequently synaptic function and plasticity through a novel microglia-neuron interaction.

An innately interesting decade of research in immunology

"Nature has provided, in the white corpuscles as you call them-in the phagocytes as we call them-a natural means of devouring and destroying all disease germs. There is at bottom only one genuinely scientific treatment for all diseases, and that is to stimulate the phagocytes." So opined B.B. in G.B. Shaw's The Doctor's Dilemma in a dramatic restatement of a key portion of Ilya Metchnikoff's Nobel Prize address: "Whenever the organism enjoys immunity, the introduction of infectious microbes is followed by the accumulation of mobile cells, of white corpuscles of the blood in particular which absorb the microbes and destroy them. The white corpuscles and the other cells capable of doing this have been designated 'phagocytes,' (i.e., devouring cells) and the whole function that ensures immunity has been given the name of 'phagocytosis'". Based on these insights into the foundation of resistance to infectious disease, Metchnikoff was awarded the 1908 Nobel Prize in Physiology or Medicine together with Paul Ehrlich (Fig. 1). Although both were cited for discoveries in immunity, the contributions of the two men seem worlds apart. Ehrlich's studies did not deal with generic responses to infection, but rather with the highly specific nature of antibodies and their relationship to the cells producing them: "As the cell receptor is obviously preformed, and the artificially produced antitoxin only the consequence, i.e. secondary, one can hardly fail to assume that the antitoxin is nothing else but discharged components of the cell, namely receptors discharged in excess". But biological systems are just that-systems-and the parts need to work together. And so we arrive, a century later, at an appreciation for just how intimately related these two seemingly disparate aspects of host defense really are.

Difference in target cell recognition of naive and activated human natural killer cells: Role of Haymaker (p38.5) in tumoricidal activity

The human Haymaker gene, at 19q13.2 in the Leukocyte Receptor-Receptor-Related Complexes, encodes a 38.5-kDa non-MHC protein found on the plasma membrane of tumor cell lines that are highly susceptible to lysis by naive (unstimulated) natural killer (nNK) cells. We hypothesized that Haymaker might act as a ligand in the tumoricidal activity of nNK cells because this molecule was absent from the surface of malignant cell lines that were resistant to their cytolytic activity. We examined the capacity of this protein to act as a ligand in the tumoricidal activity of freshly isolated nNK cells and IL-2 activated natural killer (NK) cells (aNK cells) by performing blocking studies with recombinant Haymaker (r-Haymaker) and peptide-specific anti-Haymaker antibodies. These competition studies demonstrated that both r-Haymaker and anti-Haymaker antibodies inhibited the tumoricidal function of nNK but not aNK cells. We conclude that Haymaker likely plays an essential role as an activating ligand in nNK-cell-mediated cytotoxicity, whereas the tumoricidal activity of aNK cells is, for the most part, induced by other molecules.

Enhanced tolerance to autoimmune uveitis in CD200-deficient mice correlates with a pronounced Th2 switch in response to antigen challenge

A single exposure to inhaled Ag 10 days before immunization leads to long term, Ag-specific tolerance. Respiratory tract myeloid APCs are implicated, but how regulation is invoked, and how tolerance is sustained are unclear. This study examines the in vivo function of the myeloid regulatory molecule CD200 in the process of tolerance induction. Despite earlier onset of experimental autoimmune uveitis in sham-tolerized, CD200-deficient mice, disease incidence and subsequent severity were actually reduced compared with those in wild-type mice. Protection was more effective and long term, lasting at least 28 days. Halting disease progression and tolerance in CD200(-/-) mice correlated with a marked increase in Th2-associated cytokine production by Ag-challenged splenocytes. Reduced overall disease and enhanced tolerance in the CD200-deficient mice in this model system were unexpected and may be related to altered populations of MHC class II(low) APC in the respiratory tract compared with wild-type mice together with associated activation of STAT6 in draining lymph nodes of tolerized mice. These data indicate that in the absence of default inhibitory CD200 receptor signaling, alternative, powerful regulatory mechanisms are invoked. This may represent either permissive dominant Th2 activation or an altered hierarchy of negative signaling by other myeloid cell-expressed regulatory molecules.

NKG2D receptor-mediated NK cell function is regulated by inhibitory Ly49 receptors

Interaction of the activating ligand H60 with NKG2D receptor constitutes a major stimulatory pathway for natural killer (NK) cells. The influence of inhibitory Ly49 receptors on NKG2D-mediated activation is not clearly understood. Here we show that the magnitude of NKG2D-mediated cytotoxicity is directly proportional to both the levels of H60 and the nature of major histocompatibility complex (MHC) class I molecules expressed on the target cells. The expression levels of H60 on the target cells determined the extent to which the inhibition by Ly49C/I receptors can be overridden. In contrast, even a higher expression of H60 molecule on the target cells failed to overcome the inhibition mediated by Ly49A/G receptors. Also, the level of interferon-gamma (IFN-gamma) and granulocyte-macrophage colony-stimulating factor (GM-CSF) generated by NK cells through anti-NKG2D monoclonal antibody (mAb)-mediated activation is significantly reduced by the presence of immobilized anti-Ly49A/G mAbs. Thus, NKG2D-mediated cytotoxicity and cytokine secretion results from the fine balance between activating and inhibitory receptors, thereby defining the NK cell-mediated immune responses.

Inflammatory gene profiling in the developing mouse brain after hypoxia-ischemia

Brain ischemia triggers an inflammatory reaction that progresses for days to weeks and seems to have a role in secondary progression of injury. Inflammation induces a complex pattern of signaling molecules with partly contradictory actions, and the responses may be different in the immature and adult brain. The authors characterized the global inflammatory gene expression in the developing brain as a first step toward understanding the protective and deleterious effects of inflammation after hypoxia-ischemia. Oligonucleotide arrays were used to investigate inflammatory genes in cortex, hippocampus, thalamus, and striatum at 2, 8, 24, and 72 hours after hypoxia-ischemia, which was induced in 9-day-old mice by left carotid artery ligation followed by hypoxia. After hypoxia-ischemia, 148 inflammatory genes were differentially expressed. More than 97% of the genes were upregulated and 93% had not previously been reported after hypoxia-ischemia in the immature brain. The results indicate that microglia/macrophages, T- and B-cells, NK-cells, mast cells, dendritic cells, and polymorphonuclear leukocytes may participate in the response to hypoxia-ischemia. In addition, novel cytokines/chemokines, complement-related, interferon-regulated, components of the TIR/nuclear factor-kappaB pathway, and a number of immunomodulatory genes were induced. Several of these genes may of pathophysiologic significance after neonatal hypoxia-ischemia.

Membrane-associated heparan sulfate proteoglycans are involved in the recognition of cellular targets by NKp30 and NKp46

Lysis of virus-infected and tumor cells by NK cells is mediated via natural cytotoxicity receptors (NCRs). We have recently shown that the NKp44 and NKp46 NCRs, but not the NKp30, recognize viral hemagglutinins. In this study we explored the nature of the cellular ligands recognized by the NKp30 and NKp46 NCRs. We demonstrate that target cell surface heparan sulfate proteoglycans (HSPGs) are recognized by NKp30 and NKp46 and that 6-O-sulfation and N-acetylation state of the glucose building unit affect this recognition and lysis by NK cells. Tumor cells expressing cell surface heparanase, CHO cells lacking membranal heparan sulfate and glypican-1-suppressed pancreatic cancer cells manifest reduced recognition by NKp30 and NKp46 and are lysed to a lesser extent by NK cells. Our results are the first clue for the identity of the ligands for NKp30 and NKp46. Whether the ligands are particular HSPGs, unusual heparan sulfate epitopes, or a complex of HSPGs and either other protein or lipid moieties remains to be further explored.

A Structural basis for the association of DAP12 with mouse, but not human, NKG2D

Prior studies have revealed that alternative mRNA splicing of the mouse NKG2D gene generates receptors that associate with either the DAP10 or DAP12 transmembrane adapter signaling proteins. We report that NKG2D function is normal in human patients lacking functional DAP12, indicating that DAP10 is sufficient for human NKG2D signal transduction. Further, we show that human NKG2D is incapable of associating with DAP12 and provide evidence that structural differences in the transmembrane of mouse and human NKG2D account for the species-specific difference for this immune receptor.