Important role for NKp30 in synapse formation and activation of NK cells

Human NCR3 gene variants rs2736191 and rs11575837 alter longitudinal risk for development of pediatric malaria episodes and severe malarial anemia

BACKGROUND

Plasmodium falciparum malaria is a leading cause of pediatric morbidity and mortality in holoendemic transmission areas. Severe malarial anemia [SMA, hemoglobin (Hb) < 5.0 g/dL in children] is the most common clinical manifestation of severe malaria in such regions. Although innate immune response genes are known to influence the development of SMA, the role of natural killer (NK) cells in malaria pathogenesis remains largely undefined. As such, we examined the impact of genetic variation in the gene encoding a primary NK cell receptor, natural cytotoxicity-triggering receptor 3 (NCR3), on the occurrence of malaria and SMA episodes over time.

METHODS

Susceptibility to malaria, SMA, and all-cause mortality was determined in carriers of NCR3 genetic variants (i.e., rs2736191:C > G and rs11575837:C > T) and their haplotypes. The prospective observational study was conducted over a 36 mos. follow-up period in a cohort of children (n = 1,515, aged 1.9-40 mos.) residing in a holoendemic P. falciparum transmission region, Siaya, Kenya.

RESULTS

Poisson regression modeling, controlling for anemia-promoting covariates, revealed a significantly increased risk of malaria in carriers of the homozygous mutant allele genotype (TT) for rs11575837 after multiple test correction [Incidence rate ratio (IRR) = 1.540, 95% CI = 1.114-2.129, P = 0.009]. Increased risk of SMA was observed for rs2736191 in children who inherited the CG genotype (IRR = 1.269, 95% CI = 1.009-1.597, P = 0.041) and in the additive model (presence of 1 or 2 copies) (IRR = 1.198, 95% CI = 1.030-1.393, P = 0.019), but was not significant after multiple test correction. Modeling of the haplotypes revealed that the CC haplotype had a significant additive effect for protection against SMA (i.e., reduced risk for development of SMA) after multiple test correction (IRR = 0.823, 95% CI = 0.711-0.952, P = 0.009). Although increased susceptibility to SMA was present in carriers of the GC haplotype (IRR = 1.276, 95% CI = 1.030-1.581, P = 0.026) with an additive effect (IRR = 1.182, 95% CI = 1.018-1.372, P = 0.029), the results did not remain significant after multiple test correction. None of the NCR3 genotypes or haplotypes were associated with all-cause mortality.

CONCLUSIONS

Variation in NCR3 alters susceptibility to malaria and SMA during the acquisition of naturally-acquired malarial immunity. These results highlight the importance of NK cells in the innate immune response to malaria.

Deciphering the Role of Mucosal Immune Responses and the Cervicovaginal Microbiome in Resistance to HIV Infection in HIV-Exposed Seronegative (HESN) Women

The female genital tract (FGT) is an important site of human immunodeficiency virus (HIV) infection. Discerning the nature of HIV-specific local immune responses is crucial for identifying correlates of protection in HIV-exposed seronegative (HESN) individuals. The present study involved a comprehensive analysis of soluble immune mediators, secretory immunoglobulins (sIg), natural killer (NK) cells, CXCR5⁺ CD8⁺ T cells, T follicular helper (Tfh) cells, and T regulatory cells (Tregs) in the vaginal mucosa as well as the nature and composition of the cervicovaginal microbiome in HESN women. We found significantly elevated antiviral cytokines, soluble immunoglobulins, and increased frequencies of activated NK cells, CXCR5⁺ CD8⁺ T cells, and Tfh cells in HESN females compared to HIV-unexposed healthy (UH) women. Analysis of the genital microbiome of HESN women revealed a greater bacterial diversity and increased abundance of Gardnerella spp. in the mucosa. The findings suggest that the female genital tract of HESN females represents a microenvironment equipped with innate immune factors, antiviral mediators, and critical T cell subsets that protect against HIV infection.

IMPORTANCE The vast majority of human immunodeficiency virus (HIV) infections across the world occur via the sexual route. The genital tract mucosa is thus the primary site of HIV replication, and discerning the nature of HIV-specific immune responses in this compartment is crucial. The role of the innate immune system at the mucosal level in exposed seronegative individuals and other HIV controllers remains largely unexplored. This understanding can provide valuable insights to improve vaccine design. We investigated mucosal T follicular helper (Tfh) cells, CXCR5⁺ CD8⁺ T cells, natural killer (NK) cells subsets, soluble immune markers, and microbiome diversity in HIV-exposed seronegative (HESN) women. We found a significantly higher level of mucosal CXCR5⁺ CD8⁺ T cells, CD4⁺ Tfh cells, activated NK cell subsets, and antiviral immune cell mediators in HESN women. We also found a higher abundance of Gardnerella spp., microbiome dysbiosis, and decreased levels of inflammatory markers to be associated with reduced susceptibility to HIV infection. Our findings indicate that increased distribution of mucosal NK cells, CXCR5⁺ CD8⁺ T cells, Tfh cells, and soluble markers in HIV controllers with a highly diverse cervicovaginal microbiome could contribute effectively to protection against HIV infection. Overall, our findings imply that future vaccine design should emphasize inducing these highly functional cell types at the mucosal sites.

Human NK cells prime inflammatory DC precursors to induce Tc17 differentiation

Adaptive immune responses are acknowledged to evolve from innate immunity. However, limited information exists regarding whether encounters between innate cells direct the generation of specialized T-cell subsets. We aim to understand how natural killer (NK) cells modulate cell-mediated immunity in humans. We found that human CD14+CD16- monocytes that differentiate into inflammatory dendritic cells (DCs) are shaped at the early stages of differentiation by cell-to-cell interactions with NK cells. Although a fraction of monocytes is eliminated by NK-cell-mediated cytotoxicity, the polarization of interferon-γ (IFN-γ) at the NKp30-stabilized synapses triggers a stable IFN-γ signature in surviving monocytes that persists after their differentiation into DCs. Notably, NK-cell-instructed DCs drive the priming of type 17 CD8+ T cells (Tc17) with the capacity to produce IFN-γ and interleukin-17A. Compared with healthy donors, this cellular network is impaired in patients with classical NK-cell deficiency driven by mutations in the GATA2 gene. Our findings reveal a previously unrecognized connection by which Tc17-mediated immunity might be regulated by NK-cell-mediated tuning of antigen-presenting cells.

Escape of tumor cells from the NK cell cytotoxic activity

In recent years, NK cells, initially identified as potent cytotoxic effector cells, have revealed an unexpected complexity, both at phenotypic and functional levels. The discovery of different NK cell subsets, characterized by distinct gene expression and phenotypes, was combined with the characterization of the diverse functions NK cells can exert, not only as circulating cells, but also as cells localized or recruited in lymphoid organs and in multiple tissues. Besides the elimination of tumor and virus-infected cells, these functions include the production of cytokines and chemokines, the regulation of innate and adaptive immune cells, the influence on tissue homeostasis. In addition, NK cells display a remarkable functional plasticity, being able to adapt to the environment and to develop a kind of memory. Nevertheless, the powerful cytotoxic activity of NK cells remains one of their most relevant properties, particularly in the antitumor response. In this review, the process of tumor cell recognition and killing mediated by NK cells, starting from the generation of cytolytic granules and recognition of target cell, to the establishment of the NK cell immunological synapse, the release of cytotoxic molecules, and consequent tumor cell death is described. Next, the review focuses on the heterogeneous mechanisms, either intrinsic to tumors or induced by the tumor microenvironment, by which cancer cells can escape the NK cell-mediated attack.

Bitter Melon Enhances Natural Killer-Mediated Toxicity against Head and Neck Cancer Cells

Natural killer (NK) cells are one of the major components of innate immunity, with the ability to mediate antitumor activity. Understanding the role of NK-cell-mediated tumor killing in controlling of solid tumor growth is still in the developmental stage. We have shown recently that bitter melon extract (BME) modulates the regulatory T cell (Treg) population in head and neck squamous cell carcinoma (HNSCC). However, the role of BME in NK-cell modulation against HNSCC remains unknown. In this study, we investigated whether BME can enhance the NK-cell killing activity against HNSCC cells. Our results indicated that treatment of human NK-cell line (NK3.3) with BME enhances ability to kill HNSCC cells. BME increases granzyme B accumulation and translocation/accumulation of CD107a/LAMP1 in NK3.3 cells exposed to BME. Furthermore, an increase in cell surface expression of CD16 and NKp30 in BME-treated NK3.3 cells was observed when cocultured with HNSCC cells. Collectively, our results demonstrated for the first time that BME augments NK-cell-mediated HNSCC killing activity, implicating an immunomodulatory role of BME. Cancer Prev Res; 10(6); 337-44. ©2017 AACR.

BPTF inhibits NK cell activity and the abundance of natural cytotoxicity receptor co-ligands

Using syngeneic BALB/c mouse breast cancer models, we show that the chromatin remodeling subunit bromodomain PHD finger transcription factor (BPTF) suppresses natural killer (NK) cell antitumor activity in the tumor microenvironment (TME). In culture, BPTF suppresses direct natural cytotoxicity receptor (NCR) mediated NK cell cytolytic activity to mouse and human cancer cell lines, demonstrating conserved functions. Blocking mouse NCR1 in vivo rescues BPTF KD tumor weights, demonstrating its importance for the control of tumor growth. We discovered that BPTF occupies heparanase (Hpse) regulatory elements, activating its expression. Increased heparanase activity results in reduced cell surface abundance of the NCR co-ligands: heparan sulfate proteoglycans (HSPGs). Using gain and loss of function approaches we show that elevated heparanase levels suppress NK cell cytolytic activity to tumor cells in culture. These results suggest that BPTF activates heparanase expression, which in turn reduces cell surface HSPGs and NCR co-ligands, inhibiting NK cell activity. Furthermore, gene expression data from human breast cancer tumors shows that elevated BPTF expression correlates with reduced antitumor immune cell signatures, supporting conserved roles for BPTF in suppressing antitumor immunity. Conditional BPTF depletion in established mouse breast tumors enhances antitumor immunity, suggesting that inhibiting BPTF could provide a novel immunotherapy.

Phosphorylated Radix Cyathulae officinalis Polysaccharides Act as Adjuvant via Promoting Dendritic Cell Maturation

The aim of this study was to investigate whether phosphorylated Radix Cyathulae officinalis Kuan polysaccharides (pRCPS) used as adjuvant with foot-and-mouth disease vaccine (FMDV) can stimulate specific humoral and cellular immune responses in ICR mice. The results demonstrated that pRCPS significantly up-regulated FMDV-specific IgG, IgG1, IgG2b and IgG2a antibody levels and splenocyte proliferation. pRCPS also promoted the killing activities of cytotoxic T lymphocytes (CTL) and natural killer cells (NK). In addition, pRCPS enhanced the expression levels of IL-2, IL-4, and IFN-γ in CD4⁺ T cells and the level of IFN-γ in CD8⁺ T cells. Importantly, pRCPS enhanced the expression of MHCII, CD40⁺, CD86⁺, and CD80⁺ in dendritic cells (DCs). This study indicated that phosphorylation modification could increase immune-enhancing activities of RCPS, and pRCPS could promote humoral and cellular immune responses through facilitating DC maturation.

Natural cytotoxicity receptor splice variants orchestrate the distinct functions of human natural killer cell subtypes

The natural cytotoxicity receptors NKp46/NCR1, NKp44/NCR2 and NKp30/NCR3 are critical for natural killer (NK) cell functions. Their genes are transcribed into several splice variants whose physiological relevance is not yet fully understood. Here we report that decidua basalis NK (dNK) cells of the pregnant uterine mucosa and peripheral blood NK (pNK) cells, two functionally distinct subsets of the physiological NK cell pool, display differential expression of NKp30/NCR3 and NKp44/NCR2 splice variants. The presence of cytokines that are enriched within the decidual microenvironment is sufficient to convert the splice variant profile of pNK cells into one similar to that of dNK cells. This switch is associated with decreased cytotoxic function and major adaptations to the secretome, hallmarks of the decidual phenotype. Thus, NKp30/NCR3 and NKp44/NCR2 splice variants delineate functionally distinct NK cell subsets. To our knowledge, this is the first conclusive evidence underlining the physiological importance of NCR splice variants.

Decidual natural killer (NK) cells from the pregnant uterus play an important role in the physiology of pregnancy and differ functionally from peripheral blood NK cells. Siewiera et al. reveal that this is partly due to the differential expression of splice variants of natural cytotoxicity receptors by these two cell subsets.

Practical NK cell phenotyping and variability in healthy adults

Human natural killer (NK) cells display a wide array of surface and intracellular markers that indicate various states of differentiation and/or levels of effector function. These NK cell subsets exist simultaneously in peripheral blood and may vary among individuals. We examined variety among selected NK cell receptors expressed by NK cells from normal donors, as well as the distribution of select NK cell subsets and NK cell receptor expression over time in several individual donors. Peripheral blood mononuclear cells were evaluated using flow cytometry via fluorochrome-conjugated antibodies against a number of NK cell receptors. Results were analyzed for both mean fluorescence intensity (MFI) and the percent positive cells for each receptor. CD56(bright) and CD56(dim) NK cell subsets were also considered separately, as was variation in receptor expression in NK cell subsets over time in selected individuals. Through this effort, we provide ranges of NK cell surface receptor expression for a local adult population as well as provide insight into intra-individual variation.

Higher Expression of Activating Receptors on Cytotoxic NK Cells is Associated with Early Control on HIV-1C Multiplication

Natural killer (NK) cells may be important in modulating HIV replication in early course of HIV infection. The effector function of NK cells is finely tuned by a balance between signals delivered by activating and inhibitory receptors. However, the influence of expression of these receptors on the early course of HIV replication and subsequent disease progression is not explored in the context of HIV-1C infection. The expression pattern of activating (NKp46, NKp44, NKp30, NKG2D, and NKG2C) and inhibitory (CD158b, NKG2A, and ILT2) receptors was determined in 20 patients with recent HIV-1C infection within 3–7 months of acquiring HIV infection and was compared with the expression pattern in individuals with progressive (N = 12), non-progressive HIV-1C infection (LTNPs, N = 12) and healthy seronegative individuals (N = 20). The association of the expression of these receptors on the rate of disease progression was assessed using viral load set point of recently infected individuals as a marker of disease progression. The study showed that higher cytotoxic potency of NK cells was associated with low viral load set point in recent HIV infection (r = −0.701; p = 0.0006) and higher CD4 counts (r = 0.720; p = 0.001). The expression of activating receptors (NKp46, NKp30, and NKG2D) on cytotoxic NK cells but not on regulatory NK cells was also significantly associated with low viral set point (p < 0.01) and viral load in LTNPs and progressors (p < 0.01). The study also indicated that cytotoxic NK cells might show the ability to specifically lyse HIV infected CD4 cells. This data collectively showed that early and sustained higher expression of activating receptors on cytotoxic NK cells could be responsible for increased cytotoxicity, reduced viral burden, and thus delaying the disease progression. The study to identify the molecular mechanism of the expression of these receptors in HIV infection will be helpful in further understanding of NK cell mediated control in early HIV infection.

Abnormalities of quantities and functions of natural killer cells in severe aplastic anemia

Severe aplastic anemia (SAA) is a rare disease characterized by severe pancytopenia and bone marrow failure. Natural killer (NK) cells are large granular lymphocytes derived from hematopoietic stem cells (HSCs) or common lymphoid progenitors (CLP). They play a key role in n the innate immunity and adaptive immune. In this study, the quantitative and functional changes of natural killer (NK) cell subsets in peripheral blood of severe aplastic anemia (SAA) patients before and after immunosuppressive therapy (IST) were investigated. Results showed that the percentage of NK cells and its subsets in peripheral blood lymphocytes was decreased in SAA patients. After IST, the percentage of NK cells and their subsets increased dramatically. The median expressions of CD158a, NKG2D and NKp46 on NK cells were higher in SAA patients compared to that in normal controls, and the expressions of perforin in newly diagnosed and recovery SAA patients were higher than that in controls. Therefore, we concluded that the decrease of total NK cells, and CD56(bright), CD56(dim) NK cell subsets and the higher expressions of NKp46 and perforin on NK cells may cause the over-function of T lymphocytes and thus lead to hematopoiesis failure in SAA.