Liver NK Cells Research Articles

Comparative dissection of transcriptional landscapes of human iPSC-NK differentiation and NK cell development

Abstract Clinical and preclinical research has demonstrated that iPSC-derived NK (iNK) cells have a high therapeutic potential, yet poor understanding of the detailed process of their differentiation in vitro and their counterpart cell development in vivo has hindered therapeutic iNK cell production and engineering. Here we dissect the crucial differentiation of both fetal liver NK cells and iNK cells to enable the rational design of advanced iNK production protocols. We use a comparative analysis of single-cell RNA-seq (scRNA-seq) to pinpoint key factors lacking in the induced setting which we hypothesized would hinder iNK differentiation and/ or functionality. By analyzing key transcription factor regulatory networks, we discovered the importance of TBX21, EOMES, and STAT5A in the differentiation timeline. This analysis provides a blueprint for further engineering new iPSC lines to obtain iNK cells with enhanced functions. We validated this approach by creating a new line of STAT5A-iPSCs which can be differentiated to STAT5A-expressing macrophages with both NK cell and macrophage features such as perforin production, phagocytosis, and anti-tumor functions.

Liver NK cells' trail expression variability: potential to enhance immunotherapies

Liver NK cells' trail expression variability: potential to enhance immunotherapies

215.4: Identifying high TRAIL-expressing liver NK cells from deceased and living donors for effective immunotherapy

215.4: Identifying high TRAIL-expressing liver NK cells from deceased and living donors for effective immunotherapy

Comparative transcriptomics of porcine liver-resident CD8αdim, liver CD8αhigh and circulating blood CD8αhigh NK cells reveals an intermediate phenotype of liver CD8αhigh NK cells.

Liver-resident NK (lrNK) cells have been studied in humans as well as in mice. Unfortunately, important differences have been observed between murine and human lrNK cells, complicating the extrapolation of data obtained in mice to man. We previously described two NK cell subsets in the porcine liver: A CD8αhigh subset, with a phenotype much like conventional CD8αhigh NK cells found in the peripheral blood, and a specific liver-resident CD8αdim subset which phenotypically strongly resembles human lrNK cells. These data suggest that the pig might be an attractive model for studying lrNK cell biology. In the current study, we used RNA-seq to compare the transcriptome of three porcine NK cell populations: Conventional CD8αhigh NK cells from peripheral blood (cNK cells), CD8αhigh NK cells isolated from the liver, and the liver-specific CD8αdim NK cells. We found that highly expressed transcripts in the CD8αdim lrNK cell population mainly include genes associated with the (adaptive) immune response, whereas transcripts associated with cell migration and extravasation are much less expressed in this subset compared to cNK cells. Overall, our data indicate that CD8αdim lrNK cells show an immature and anti-inflammatory phenotype. Interestingly, we also observed that the CD8αhigh NK cell population that is present in the liver appears to represent a population with an intermediate phenotype. Indeed, while the transcriptome of these cells largely overlaps with that of cNK cells, they also express transcripts associated with liver residency, in particular CXCR6. The current, in-depth characterization of the transcriptome of porcine liver NK cell populations provides a basis to use the pig model for research into liver-resident NK cells.

FRI-219 - Identification of unique liver NK cells in HBV and a new perspective on exhaustion-related NK cell phenotypes by single-cell RNA sequencing

FRI-219 - Identification of unique liver NK cells in HBV and a new perspective on exhaustion-related NK cell phenotypes by single-cell RNA sequencing

Postpartum hepatitis and host immunity in pregnant women with chronic HBV infection.

In order to develop immune tolerant to the fetal, maternal immune system will have some modification comparing to the time before pregnancy. Immune tolerance starts and develops at the maternal placental interface. In innate immunity, decidual natural killer (dNK) cells, macrophages and dendritic cells play a key role in immue tolerance. In adaptive immunity, a moderate increase of number and immune inhibition function of regulatory T cells (Treg) are essential for immune tolerance. The trophoblast cells and immune cells expressing indoleamine 2,3-dioxygenase (IDO), the trophoblast cells expressing HLA-G, and Th1/Th2 shifting to Th2 dominant and Th17/Treg shifting to Treg domiant are in favor of maternal fetal immune tolerance. Steroids (estrogen and progesterone) and human chorionic gonadotropin (HCG) also participate in immune tolerance by inducing Treg cells or upregulating immunosuppressive cytokines. Most of the patients with chronic HBV infection are in the "HBV immune tolerance period" before pregnancy, and the liver disease is relatively stable during pregnancy. In chronic HBV infection women, after delivery, the relative immunosuppression in vivo is reversed, and Th1 is dominant in Th1/Th2 and Th17 is dominant in Th17/Treg balance. After delivery, the number of Treg decrease and NK cells increase in quantity and cytotoxicity in peripheral blood. Liver NK cells may cause liver inflammation through a non-antigen specific mechanism. After delivery, the number of CD8+ T cells will increase and HBV specific T cell response recovers from the disfunction in pregnancy. Under the background of postpartum inflammation, the rapid decrease of cortisol after delivery, and especially the enhancement of HBV specific T cell response induced by HBV DNA and cytokines, are the main reasons for postpartum hepatitis. HBeAg positive, especially HBeAg<700 S/CO, and HBV DNA>3-5Log10IU/ml are risk factors for postpartum hepatitis. Antiviral treatment in late pregnancy can reduce the incidence of mother to child transmission (MTCT) in chronic HBV infection women. Chronic HBV infection women have hepatitis both during pregnancy and more often in 12 weeks postpartum. It is generally agreed that postpartum hepatitis is mild symptoms and self-limited. Delaying drug withdrawal to 48 weeks can increase the seroconversion rate of HBeAg in delivery women with elevated alanine aminotransferase (ALT) in pregnancy.

Multiparametric Flow Cytometry-Based Immunophenotyping of Mouse Liver Immune Cells.

The liver is a complex organ that governs many types of metabolisms, including energy metabolism and other cellular processes. The liver also plays a crucial role in important functions in immunity, and the activity of liver tissue-associated immunity affects the outcome of many liver pathologies. A thorough characterization of the liver immune microenvironment may contribute to a better understanding of immune signaling, the mechanisms of specific immune responses, and even to improved predictions about therapy outcomes. In this paper, we present an optimized, simple, and rapid protocol to characterize the liver-associated immune cell milieu. We believe that the most suitable technique for obtaining a complex immune cell suspension and for removing contaminating blood cells is to perform mouse liver perfusion, using only phosphate buffer saline. Combining an enzymatic digestion and a mechanical dissociation of liver tissue, followed by cell purification, improves downstream applications. This combination is an essential prerequisite for immune cell determination and characterization. We then demonstrate a flow cytometry-based multiparametric immunophenotyping along with a gating strategy to detect and quantify liver endothelial cells, T cells (helper and cytotoxic), B cells, NK cells, NKT cells, neutrophils, monocytes (subsets included), dendritic cells (subsets included), macrophages and Kupffer cells.

Panoramic comparison between NK cells in healthy and cancerous liver through single-cell RNA sequencing.

Objective:NK cells play crucial roles in the immune defense mechanisms against viral infections and transformed cells. However, the developmental progression, transcriptomic landscape, and functional subtypes of liver NK cells are not well defined. Hepatocellular carcinoma (HCC) accounts for approximately 80% of primary liver cancer worldwide, yet the biological characteristics of NK cells in the HCC environment are unclear. Therefore, we aimed to determine these cells’ roles in tumorigenesis and prognosis.Methods:We compared the single-cell RNA sequencing profiles of NK cells purified from blood (n = 1), healthy liver tissues (n = 3), HCC tumor tissues (n = 4), and peritumor liver tissues (n = 1) to identify NK cell subsets. Furthermore, we performed bioinformatics analysis by using The Cancer Genome Atlas (TCGA) data to identify prognostic biomarkers simultaneously overexpressed in the blood and tumor tissues of patients with HCC.Results:Transcriptomic analysis revealed 5 NK cell subsets (L1-NK-CD56bright, L2-NK-CD56dim, L3-NK-HLA, L4-LrNK-FCGR3A, and L5-LrNK-XCL1) in the healthy liver tissues. However, the transitional L3 subset and the CXCR6+CD16+ L4 subset with strong anti-tumor activity were absent in the HCC and peritumor liver tissues. Furthermore, 4 common prognosis-associated genes (RHOB, TALDO1, HLA-DPA1, and TKT) were significantly overexpressed in the paired tumor tissue and blood.Conclusions:Our study revealed 5 specific subsets of NK cells in healthy human liver tissues. However, only 3 of the 5 NK cell subsets were present in HCC and peritumor tissues. The cytotoxic NK cell subsets were absent in HCC tissues. Furthermore, we identified 4 potential non-invasive prognostic biomarkers in patients with HCC.

Phenotypic and Functional Plasticity of CXCR6+ Peripheral Blood NK Cells.

Human NK cells are comprised of phenotypic subsets, whose potentially unique functions remain largely unexplored. C-X-C-motif-chemokine-receptor-6 (CXCR6) + NK cells have been identified as phenotypically immature tissue-resident NK cells in mice and humans. A small fraction of peripheral blood (PB)-NK cells also expresses CXCR6. However, prior reports about their phenotypic and functional plasticity are conflicting. In this study, we isolated, expanded, and phenotypically and functionally evaluated CXCR6+ and CXCR6– PB-NK cells, and contrasted results to bulk liver and spleen NK cells. We found that CXCR6+ and CXCR6– PB-NK cells preserved their distinct phenotypic profiles throughout 14 days of in vitro expansion (“day 14”), after which phenotypically immature CXCR6+ PB-NK cells became functionally equivalent to CXCR6– PB-NK cells. Despite a consistent reduction in CD16 expression and enhanced expression of the transcription factor Eomesodermin (Eomes), day 14 CXCR6+ PB-NK cells had superior antibody-dependent cellular cytotoxicity (ADCC) compared to CXCR6– PB-NK cells. Further, bulk liver NK cells responded to IL-15, but not IL-2 stimulation, with STAT-5 phosphorylation. In contrast, bulk splenic and PB-NK cells robustly responded to both cytokines. Our findings may allow for the selection of superior NK cell subsets for infusion products increasingly used to treat human diseases.

Peptide: MHC-based DNA vaccination strategy to activate natural killer cells by targeting killer cell immunoglobulin-like receptors

BackgroundNatural killer (NK) cells are increasingly being recognized as agents for cancer immunotherapy. The killer cell immunoglobulin-like receptors (KIRs) are expressed by NK cells and are immunogenetic determinants of the...

MTOR INHIBITORS ENHANCE ANTITUMOR ACTIVITY OF LIVER NATURAL KILLER CELLS IN MICE

Background: Liver transplantation (LT) is the best available option for patients with end stage liver disease and HCC. However, recipients are at high risk of cancer recurrence and infection, due to immunosuppressive (IS) therapy. IS used in LT commonly consist of calcineurin inhibitor (CNI) or a mechanistic target of rapamycin (mTOR), anti-metabolite and corticosteroids. Liver is an important immunological organ with a unique microenvironment. Innate and adaptive immune responses shapes the balance between immune tolerance and activation. It is well-known that IS drugs targeting the adaptive component of immunity, while innate immune cells become the only self-defense mechanism against neoplastic cells and infectious agents. However, the effect of IS drugs on liver resident immune cells are not well known. In this study, we analyzed the effect of two main IS drugs, calcineurin inhibitors and mTOR inhibitors on adaptive and innate immune components of the liver in mice Method: C57/BL6 mice were treated by intraperitoneal injection of mTORi (rapamycin and everolimus) and CNI (cyclosporine) for 7 days. Twenty-four hours after the last injection, liver mononuclear cells (LMNCs), splenocytes were collected. The proportion of T cells, NKT cells and NK cells and various functional molecules were analyzed by flow cytometry. Result: The proportion of TCR+NK1.1- T cells, TCR+NK1.1+ NKT cells in LMNC did not differ in both CNI mTORi treated groups. TCR-NK1.1+NK fraction in LMNCs was significantly increased in mTORi group (9.5 in mTORi groups versus 7.8 in control group), CNI treatment had no effect on NK cells frequency. mTORi treatment significantly upregulated the TRAIL positive NK cells (38.5%±4.0 in mTORi group vs 21.0%±8.3 in untreated, p =0.003). CNI treatment oppositely significantly decreased the TRAIL positive NK cell population (16.4%±4.2 in CNI group vs 21.0%±8.3 in untreated, p <0.05). CD 69 and Nkp46 expression on liver NK cells were not changed significantly in both mTORi and CNI treated groups in comparison to control group. Moreover, liver NK cells from mTORi treated mice showed significantly higher cytotoxicity against TRAIL-sensitive Hepa1-6 cells (30.1% ± 13.0 vs 13.5 %± 6.0, p=0.009). Cytotoxicity against TRAIL resistant YAC-1 mouse lymphoma was not significantly enhanced after mTORi treatment (53.6 % ± 4.4 vs 39.9% ± 1.2). Conclusion: mTOR inhibitors has ability to enhance liver resident NK cell activity. This result suggests that mTOR inhibitors might be useful to maintain anti-microbe and anti-tumor immunity even under immunosuppressive condition after transplantation.

Mitofission impairs the anti-tumor activity of NK cells in tumor microenvironment

Abstract The survival and functional performance of NK cells is a metabolically demanding process. However, there is largely unknown how inappropriate metabolic reprogramming underlies disease microenvironments leads to NK dysfunction. Here, through analysis of human liver cancer samples (n=102) and benign liver samples (n=22), we found tumor infiltrative NK (TINK) cells present small and fragmented mitochondria in the cytoplasm, while normal liver NK and peripheral NK cells have big and tubular mitochondria. We also observed hypoxic tumor microenvironment is the main factor to induce NK cell excessive mitochondrial fission into fragmentation and that dependent on increasing Drp1 activity. Consequently, the fragmentation causes the metabolic disturbance and losing of TINK cells and that predicts poor survival in liver cancer patients. Revising mitochondrial morphology by targeting Drp1 improves mitochondrial metabolism and anti-tumor capacity of NK cells. Thus, disease-related mitochondrial restructuring drives NK cell exhaust and that is manipulated to the benefit of temper or enhance immunity.

25(OH) D3 alleviate liver NK cytotoxicity in acute but not in chronic fibrosis model of BALB/c mice due to modulations in vitamin D receptor

BackgroundLow 25-Hydroxy-vitamin-D; “25(OH)-D3” serum and vitamin D receptor (VDR) levels were recently correlated to advanced fibrosis. However, VDR mechanism in liver fibrosis modulations is not well understood. In this study, we aimed to evaluate changes in liver NK cells cytotoxicity due to modulations in VDR in CCl4 fibrosis model following 25(OH) D3 injections.MethodsCarbon-tetrachloride (CCl4) hepatic-fibrosis was induced in BALB/c mice for 1 and 4 weeks as an acute and chronic fibrosis model, respectively. Along 1th to 4th weeks, vitamin D were i.p injected/2x week. Liver were assessed histologically and for proteins quantification for VDR and αSMA expressions. In vitro, potential killing of NK cells were evaluated following co-culture with primary-hepatic-stellate-cells (pHSCs) obtained from BALB/c WT-mice.ResultsSystemic inflammation and hepatic-fibrosis increased along 4 weeks of CCl4 as indicated by serum ALT and αSMA expressions (P < 0.02) as well as histological assessments, respectively. These results were associated with increased NK1.1 activations and hypercalcemia. While vitamin D administrations delayed fibrosis of early stages, vitamin D worsen hepatic-fibrosis of late stages of CCl4. In week 4, no further activations of NK cells were seen following vitamin D injections and were associated with down-expressions of VDR (1.7 Fold, P < 0.004) indicating the inability of vitamin D to ameliorate hepatic fibrosis. In vitro, NK cells from the chronic model of CCl4 did not affect pHSCs killing and fail to reduce fibrosis.ConclusionVitamin D alleviate liver NK cytotoxicity in acute but not in chronic fibrosis model due to modulations in vitamin D receptor and calcium. Hypercalcemia associated with late fibrosis may inhibited VDR levels, however, may not explain the profibrogenic effects of vitamin D.

The Toll-Like Receptor 3 Agonist Polyriboinosinic Polyribocytidylic Acid Increases the Numbers of NK Cells with Distinct Phenotype in the Liver of B6 Mice.

One of the activating factors of the cells of the innate immune system is the agonists of toll-like receptors (TLRs). Our earlier publications detailed how poly(I:C), a TLR3 agonist, elevates the NK cell population and the associated antigen-specific CD8+ T cell responses. This study involved a single treatment of the B6 mice with poly(I:C) intraperitoneally. To perform a detailed phenotypic analysis, mononuclear cells were prepared from each of the liver, peripheral blood, and spleen. These cells were then examined for their NK cell population by flow cytometric analysis following cell staining with indicated antibodies. The findings of the study showed that the NK cell population of the liver with an NK1.1highCD11bhighCD11chigh B220+Ly6G− phenotype was elevated following the treatment with poly(I:C). In the absence of CD11b molecule (CR3−/− mice), poly(I:C) can still increase the remained numbers of NK cells with NK1.1+CD11b− and NK1.1+Ly6G− phenotypes in the liver while their numbers in the blood decrease. After the treatment with anti-AGM1 Ab, which induced depletion of NK1.1+CD11b+ cells and partial depletion of CD3+NK1.1+ and NK1.1+CD11b− cell populations, poly(I:C) normalized the partial decreases in the numbers of NK cells concomitant with increased numbers of NK1.1−CD11b+ cell population in both liver and blood. Regarding mice with a TLR3−/− phenotype, their injection with poly(I:C) resulted in the partial elevation in the NK cell population as compared to wild-type B6 mice. To summarise, the TLR3 agonist poly(I:C) results in the elevation of a subset of liver NK cells expressing the two myeloid markers CD11c and CD11b. The effect of poly(I:C) on NK cells is partially dependent on TLR3 and independent of the presence of CD11b.

Antibody-induced NKG2D blockade in a rat model of intraportal islet transplantation leads to a deleterious reaction.

Intraportal islet transplantation is plagued by an acute destruction of transplanted islets. Amongst the first responders, NK cells and macrophages harbour an activating receptor, NKG2D, recognizing ligands expressed by stressed cells. We aimed to determine whether islet NKG2D ligand expression increases with culture time, and to analyse the impact of antibody-induced NKG2D blockade in islet transplantation. NKG2D-ligand expression was analysed in rat and human islets. Syngeneic marginal mass intraportal islet transplantations were performed in rats: control group, recipients transplanted with NKG2D-recombinant-treated islets (recombinant group), and recipients treated with a mouse anti-rat anti-NKG2D antibody and transplanted with recombinant-treated islets (antibody-recombinant group). Islets demonstrated increased gene expression of NKG2D ligands with culture time. Blockade of NKG2D on NK cells decreased in vitro cytotoxicity against islets. Recipients from the control and recombinant groups showed similar metabolic results; conversely, treatment with the antibody resulted in lower diabetes reversal. The antibody depleted circulating and liver NK cells in recipients, who displayed increased macrophage infiltration of recipient origin around the transplanted islets. In vitro blockade of NKG2D ligands had no impact on early graft function. Systemic treatment of recipients with an anti-NKG2D antibody was deleterious to the islet graft, possibly through an antibody-dependent cell-mediated cytotoxicity reaction.

Critical role of IL-1β in the pathogenesis of Agrocybe aegerita galectin-induced liver injury through recruiting T cell to liver

Acute liver failure (ALF) can be the consequence of various etiologies, which immune response plays a pivotal role in the pathogenesis. For the diversity of etiologies, more animal models are still needed in this field. Here, we developed a new acute liver injury mouse model induced by a fungal lectin AAGL (Agrocybe aegerita galectin). Intravenous injection of AAGL could induce the infiltration and activation of T, NKT and NK cells in liver and T cell played an important role in the pathogenesis. However, compared with the widely used concanavalin A model, AAGL model showed different immune mechanism. Transcriptome analysis of live tissue suggested that inflammation mediated by chemokine and cytokine signaling pathway was different between AAGL and Con A model. Fluorescent quantitative PCR verification assay showed that IL-1β was expressed much higher in AAGL-treated mice and anti-IL-1β could ameliorate AAGL-induced liver injury by inhibiting NF-κB and p38 signaling pathway. The expression of CXCL9 which was responsible for T cell infiltration in liver was also inhibited in AAGL model. We found a critical role of IL-1β in the pathogenesis of AAGL model through recruiting T cells to liver, which highlighted that IL-1β antibody might be a candidate therapy for ALF.

Everolimus enhances TRAIL-mediated anti-tumor activity of liver resident natural killer cells in mice.

In transplantation, innate immunity plays a pivotal role in immunosurveillance and host defence against microbes and neoplastic cells. Liver-resident NK cells express TNF-related apoptosis-inducing ligand (TRAIL), which distinguishes them from conventional NK cells. In this study, we investigated the impact of mTOR inhibition on liver-resident NK cells in comparison with that on splenic NK cells in a mouse model. In mice that received everolimus (EVR) for 7days (range: 0.0125-0.25mg/kg/day), the proportion of splenic NK cells was unchanged, whereas the number of liver NK cells including TRAIL+ NK subpopulation increased for all doses of EVR. Consistently, liver-resident NK cells from the EVR-treated mice displayed enhanced cytotoxicity against TRAIL-sensitive neoplastic cells. EVR treatment inhibited the transition of the immature subset of liver NK cells to a mature state. The negative regulator of NK cells FoxO1 was activated as a consequence of impaired mTORC2-dependent AKT phosphorylation. Activated FoxO1 both reduced T-bet expression and induced TRAIL expression, thereby inhibiting NK cell maturation and promoting the antitumour activity of the immature subset of liver NK cells in response to EVR treatment. These findings indicate that EVR treatment enhances the antitumour activity of immature liver-resident NK cells through TRAIL upregulation.

CCL21-expression and accumulation of CCR7+ NK cells in livers of patients with primary sclerosing cholangitis.

The pathogenesis of primary sclerosing cholangitis (PSC), an autoimmune liver disease, remains unknown. The aim of this study was to characterize peripheral blood and intrahepatic NK cells from patients with PSC. Peripheral blood samples from patients with PSC, other autoimmune liver diseases, and from healthy control individuals were used, as well as liver tissues from PSC patients undergoing liver transplantation. Multiparameter flow cytometry showed that peripheral blood NK cells from PSC patients were significantly enriched for CCR7+ and CXCR3+ cells, and CCR7+ but not CXCR3+ cells were also significantly increased within intrahepatic NK cells. PSC patients undergoing liver transplantation furthermore had significantly higher plasma levels of the CCR7-ligand CCL21, and the CXCR3-ligands CXCL10 and CXCL11, and significantly higher levels of CCL21, but not CXCL10, were detected in liver tissues. CCR7+ and CXCR3+ NK cells from PSC patients exhibited significantly higher functional capacity in peripheral blood, but not liver tissues, consistent with chronic activation of these NK cells in the inflamed liver. These data show that PSC is characterized by intrahepatic CCL21 expression and accumulation of CCR7+ NK cells in the inflamed liver tissue.

Lactate-Mediated Acidification of Tumor Microenvironment Induces Apoptosis of Liver-Resident NK Cells in Colorectal Liver Metastasis.

Colorectal cancer is the third most common malignancy worldwide, with 1.3 million new cases annually. Metastasis to the liver is a leading cause of mortality in these patients. In human liver, metastatic cancer cells must evade populations of liver-resident natural killer (NK) cells with potent cytotoxic capabilities. Here, we investigated how these tumors evade liver NK-cell surveillance. Tissue biopsies were obtained from patients undergoing resection of colorectal liver metastasis (CRLM, n = 18), from the tumor, adjacent tissue, and distal resection margin. The number and phenotype of liver-resident NK cells, at each site, were analyzed by flow cytometry. Tumor-conditioned media (TCM) was generated for cytokine and metabolite quantification and used to treat healthy liver-resident NK cells, isolated from donor liver perfusate during transplantation. Liver-resident NK cells were significantly depleted from CRLM tumors. Healthy liver-resident NK cells exposed to TCM underwent apoptosis in vitro, associated with elevated lactate. Tumor-infiltrating liver-resident NK cells showed signs of mitochondrial stress, which was recapitulated in vitro by treating liver-resident NK cells with lactic acid. Lactic acid induced apoptosis by decreasing the intracellular pH of NK cells, resulting in mitochondrial dysfunction that could be prevented by blocking mitochondrial ROS accumulation. CRLM tumors produced lactate, thus decreasing the pH of the tumor microenvironment. Liver-resident NK cells migrating toward the tumor were unable to regulate intracellular pH resulting in mitochondrial stress and apoptosis. Targeting CRLM metabolism provides a promising therapeutic approach to restoring local NK-cell activity and preventing tumor growth.

PO-129 Effect of endurance training on liver NK cells in mice

Objective NK cell (natural killer cell) is a large granular lymphocyte distinct from a group of T and B lymphocytes. At present, the research shows that NK cells can specifically identify target cells and release killing media and then play a killing effect. It is confirmed that the expression of IL-15 is closely related to the differentiation and maturation of NK cells. Furthermore, skeletal muscle is an endocrine tissue and plays a key role in regulating the whole-body metabolic health by synthesizing and releasing humoral factors called myokines, such as IL-15. Whether the IL-15 induced by exercise training can promote the maturation of NK cells remain unsolved. This study aimed to explore the effects of moderate endurance training on NK cells and relative mechanism.&#x0D; Methods Twenty male C57BL/6J mice were randomly divided into 2 groups: control group (YC) and exercise group (YE). YC animals were fed normally for 12 weeks, YE animals were trained for 12 weeks on moderate intensity treadmill (12 m/min).Then the samples were isolated and RT-PCR was used to detect IL-15 and Nkg2d genes in the liver, Western blotting was used to detect the killer factor IFN-γ released by NK cells. Flow cytometry was used to detect NK1.1 cell markers in primary liver cells .&#x0D; Results 1)Compared with the YC group, the expression level of IL-15 and Nkg2d gene in the liver tissue of YE mice increased significantly (P &lt; 0.05,P &lt; 0.01); 2) Compared with the YC group, the expression of IFN-γ protein in the liver tissue of the YE mice increased significantly (P &lt; 0.05); 3) Compared with two group. The proportion of NK cells in liver cells of group YE increased significantly (P &lt; 0.05).&#x0D; Conclusions Moderate intensity endurance training can enhance the content and killing ability of NK cells through induced IL-15 in the liver.