Specific dysregulation of IFNγ production by natural killer cells confers susceptibility to viral infection

Suppression of adaptive NK cell expansion by macrophage-mediated phagocytosis inhibited by 2B4-CD48

Infection of mice by mouse cytomegalovirus (MCMV) triggers activation and expansion of Ly49H+ natural killer (NK) cells, which are virus specific and considered to be "adaptive" or "memory" NK cells. Here, we find that signaling lymphocytic activation molecule family receptors (SFRs), a group of hematopoietic cell-restricted receptors, are essential for the expansion of Ly49H+ NK cells after MCMV infection. This activity is largely mediated by CD48, an SFR broadly expressed on NK cells and displaying augmented expression after MCMV infection. It is also dependent on the CD48 counter-receptor, 2B4, expressed on host macrophages. The 2B4-CD48 axis promotes expansion of Ly49H+ NK cells by repressing their phagocytosis by virus-activated macrophages through inhibition of the pro-phagocytic integrin lymphocyte function-associated antigen-1 (LFA-1) on macrophages. These data identify key roles of macrophages and the 2B4-CD48 pathway in controlling the expansion of adaptive NK cells following MCMV infection. Stimulation of the 2B4-CD48 axis may be helpful in enhancing adaptive NK cell responses for therapeutic purposes.

Co-expression of activating and inhibitory receptors on peritoneal fluid NK cells in women with endometriosis

The detailed mechanism underlying endometriosis development remains unclear; few reports have suggested the involvement of immune and genetic factors. This study aims to investigate the role of NK cells in endometriosis by analyzing the co-expression of activating (NKp46, NKG2C, and NKG2D) and inhibitory receptors (NKG2A and CD158a) on NK cells and their subsequent cytokine production in the peritoneal fluid (PF). Sixty-two patients were enrolled for this study from Hyogo Medical University between February 2018 and April 2022. Results showed that the proportions of CD56⁺/NKp46⁺, CD56^dim/NKp46^＋, NKG2C^＋/NKp46^＋, and NKG2D^＋/NKp46^＋ NK cells were significantly lower in the endometriosis group than those in the control group. Meanwhile, within the peritoneal endometriosis (n = 21) and deep infiltrating endometriosis (n = 11) groups, the co-expression of NKG2D^＋/NKp46^＋ and CD16^＋/NKp46^＋. Additionally, the abundance of IFN-γ-producing NK cells was significantly increased in the endometriosis group compared to controls, and a significant negative correlation was noted between NKp46 expression on NK cells and type 1 cytokine (IFN-γ and TNF-α) production. Taken together, the findings of this study indicate that NK cell cytotoxicity in endometriosis is reduced due to changes in NKp46 expression, as well as activating receptors co-expressed with NKp46. Consequently, NK cells do not eliminate endometrial cells in the abdominal cavity, resulting in the production of TNF-α and IFN-γ.

MyD88 is an essential regulator of NK cell-mediated clearance of MCMV infection

The signaling adapter MyD88 is critical for immune cell activation in response to viral or bacterial pathogens via several TLRs, IL-1βR and IL-18R. However, the essential role of MyD88 during activations mediated by germline-encoded NK cell receptors (NKRs), such as Ly49H or NKG2D, has yet to be investigated. To define the NK cell-intrinsic function of MyD88, we generated a novel NK cell conditional knockout mouse for MyD88 (Myd88^fl/flNcr1^Cre/+). Phenotypic characterization of these mice demonstrated that MyD88 is dispensable for NK cell development and maturation. However, the MyD88-deficient NK cells exhibited significantly reduced cytotoxic potentials in vivo. In addition, the lack of MyD88 significantly reduced the NKG2D-mediated inflammatory cytokine production in vitro. Consistent with this, mice lacking MyD88 were unable to respond and clear MCMV infection. Transcriptomic analyses of splenic NK cells following MCMV infection revealed that inflammatory gene signatures were upregulated in Ly49H⁺. In contrast, Ly49H^- NK cells have significant enrichment in G2M checkpoint genes, revealing distinct transcriptomic profiles of these subsets. Our results identify a central role for MyD88 in Ly49H-dependent gene signatures, including alterations in genes regulating proliferation in Ly49H⁺ NK cells. In summary, our study reveals a previously unknown function of MyD88 in Ly49H-dependent signaling and in vivo functions of NK cells.

A point mutation in the linker domain of mouse STAT5A is associated with impaired NK-cell regulation

The transcription factor STAT5 is critical for peripheral NK-cell survival, proliferation, and cytotoxic function. STAT5 refers to two highly related proteins, STAT5A and STAT5B. In this study, we verified the importance of STAT5A isoform for NK cells. We characterized an incidental chemically induced W484G mutation in the Stat5a gene and found that this mutation was associated with a reduction of STAT5A protein expression. Closer examination of NK-cell subsets from Stat5a mutant mice showed marked reductions in NK-cell number and maturation. IL-15 treatment of Stat5a mutant NK cells exhibited defective induction of both STAT5 and mTOR signaling pathways and reduced expression of granzyme B and IFN-γ. Finally, we observed that Stat5a mutant mice revealed more tumor growth upon injection of RMA-S tumor cell line. Overall, our results demonstrate that the W484G mutation in the linker domain of STAT5A is sufficient to compromise STAT5A function in NK-cell homeostasis, responsiveness, and tumoricidal function.

Activation Receptor-Dependent IFN-γ Production by NK Cells Is Controlled by Transcription, Translation, and the Proteasome

NK cells can recognize target cells such as virus-infected and tumor cells through integration of activation and inhibitory receptors. Recognition by NK cells can lead to direct lysis of the target cell and production of the signature cytokine IFN-γ. However, it is unclear whether stimulation through activation receptors alone is sufficient for IFN-γ production. In this study, we show that NK activation receptor engagement requires additional signals for optimal IFN-γ production, which could be provided by IFN-β or IL-12. Stimulation of murine NK cells with soluble Abs directed against NK1.1, Ly49H, Ly49D, or NKp46 required additional stimulation with cytokines, indicating that a range of activation receptors with distinct adaptor molecules require additional stimulation for IFN-γ production. The requirement for multiple signals extends to stimulation with primary m157-transgenic target cells, which triggers the activation receptor Ly49H, suggesting that NK cells do require multiple signals for IFN-γ production in the context of target cell recognition. Using quantitative PCR and RNA flow cytometry, we found that cytokines, not activating ligands, act on NK cells to express Ifng transcripts. Ly49H engagement is required for IFN-γ translational initiation. Results using inhibitors suggest that the proteasome-ubiquitin-IKK-TPL2-MNK1 axis was required during activation receptor engagement. Thus, this study indicates that activation receptor-dependent IFN-γ production is regulated on the transcriptional and translational levels.

Murine cytomegalovirus infection in mice results in an acute inflammatory reaction in peripheral nerves

Human cytomegalovirus (CMV) infection is asymptomatic in immunocompetent individuals. However, it can lead to disease in immunodeficient population. Little is known of the mechanisms underlying the pathogenicity of the virus. We investigated the impact of CMV infection on mouse nervous system. Peripheral nerves but not spinal cord was permissive to MCMV during acute infection. Activated CD8⁺ T cells, monocytes/macrophages and cytokine expression were increased in the blood and sciatic nerves of infected mice, which exhibited transient sensory dysfunction. This study indicates that systemic MCMV infection leads to a dissemination of MCMV into peripheral nerves, which is associated with a local inflammation but not nerve tissue damage in the acute phase.

NK Cells Require Cell-Extrinsic and -Intrinsic TYK2 for Full Functionality in Tumor Surveillance and Antibacterial Immunity

Tyrosine kinase 2 (TYK2) is a widely expressed receptor-associated kinase that is involved in signaling by a variety of cytokines with important immune regulatory activities. Absence of TYK2 in mice results in impaired NK cell maturation and antitumor activity, although underlying mechanisms are largely unknown. Using conditional ablation of TYK2 in NK cells we show that TYK2 is required for IFN-γ production by NK cells in response to IL-12 and for an efficient immune defense against Listeria monocytogenes Deletion of TYK2 in NK cells did not impact NK cell maturation and IFN-γ production upon NK cell activating receptor (actR) stimulation. Similarly, NK cell-mediated tumor surveillance was unimpaired upon deletion of TYK2 in NK cells only. In line with the previously reported maturation-associated Ifng promoter demethylation, the less mature phenotype of Tyk2^-/- NK cells correlated with an increased CpG methylation at the Ifng locus. Treatment with the DNA hypomethylating agent 5-aza-2-deoxycytidine restored the ability of Tyk2^-/- NK cells to produce IFN-γ upon actR but not upon IL-12 stimulation. NK cell maturation was dependent on the presence of TYK2 in dendritic cells and could be rescued in Tyk2-deficient mice by treatment with exogenous IL-15/IL-15Rα complexes. IL-15 treatment also rescued the in vitro cytotoxicity defect and the impaired actR-induced IFN-γ production of Tyk2^-/- NK cells. Collectively, our findings provide the first evidence, to our knowledge, for a key role of TYK2 in the host environment in promoting NK cell maturation and antitumor activity.

The Effects of IL10 and NK Cells on the Susceptibility to Mouse Cytomegalovirus in BALB/c Mice despite the Compensation of IFNγ

OBJECTIVE

The aim of this study was to determine which factors lead to the susceptibility to mouse cytomegalovirus (MCMV) in the spleens of BALB/c mice.

METHODS

BALB/c and C57BL/6 mice were randomly divided into a control group and an infection group and sacrificed on day 0, 1, 3, 7, 14, and 28 postinfection. The cytotoxicity of NK cells was determined by evaluating lactate dehydrogenase contents. Flow cytometry was used to analyze activated NK cells, IFNγ+ NK cells, and total NK cells in the spleen. The pathological changes of spleens in each group were analyzed by HE staining. The expression of IL10, IL18, IFNγ, Thpok, and IFNβ of spleens was determined by quantitative reverse transcriptase PCR. The viral loads of MCMV in spleens and salivary glands were also detected.

RESULTS

We found that spleen NK cells and IL10 in C57BL/6 mice possessed more powerful immunity to MCMV than BALB/c mice. In BALB/c mice, combined effects of the cytotoxicity of NK cells and IFNγ in spleens still ended up with deficient control of infection.

CONCLUSION

The functional shortage of NK cells and inappropriate expression of IL10 result in the susceptibility to MCMV in BALB/c mice.

STAT2-Dependent Immune Responses Ensure Host Survival despite the Presence of a Potent Viral Antagonist

A pathogen encounter induces interferons, which signal via Janus kinases and STAT transcription factors to establish an antiviral state. However, the host and pathogens are situated in a continuous arms race which shapes host evolution toward optimized immune responses and the pathogens toward enhanced immune-evasive properties. Mouse cytomegalovirus (MCMV) counteracts interferon responses by pM27-mediated degradation of STAT2, which directly affects the signaling of type I as well as type III interferons. Using MCMV mutants lacking M27 and mice lacking STAT2, we studied the opposing relationship between antiviral activities and viral antagonism in a natural host-pathogen pair in vitro and in vivo In contrast to wild-type (wt) MCMV, ΔM27 mutant MCMV was efficiently cleared from all organs within a few days in BALB/c, C57BL/6, and 129 mice, highlighting the general importance of STAT2 antagonism for MCMV replication. Despite this effective and relevant STAT2 antagonism, wt and STAT2-deficient mice exhibited fundamentally different susceptibilities to MCMV infections. MCMV replication was increased in all assessed organs (e.g., liver, spleen, lungs, and salivary glands) of STAT2-deficient mice, resulting in mortality during the first week after infection. Taken together, the results of our study reveal the importance of cytomegaloviral interferon antagonism for viral replication as well as a pivotal role of the remaining STAT2 activity for host survival. This mutual influence establishes a stable evolutionary standoff situation with fatal consequences when the equilibrium is disturbed.IMPORTANCE The host limits viral replication by the use of interferons (IFNs), which signal via STAT proteins. Several viruses evolved antagonists targeting STATs to antagonize IFNs (e.g., cytomegaloviruses, Zika virus, dengue virus, and several paramyxoviruses). We analyzed infections caused by MCMV expressing or lacking the STAT2 antagonist pM27 in STAT2-deficient and control mice to evaluate its importance for the host and the virus in vitro and in vivo The inability to counteract STAT2 directly translates into exaggerated IFN susceptibility in vitro and pronounced attenuation in vivo Thus, the antiviral activity mediated by IFNs via STAT2-dependent signaling drove the development of a potent MCMV-encoded STAT2 antagonist which became indispensable for efficient virus replication and spread to organs required for dissemination. Despite this clear impact of viral STAT2 antagonism, the host critically required the remaining STAT2 activity to prevent overt disease and mortality upon MCMV infection. Our findings highlight a remarkably delicate balance between host and virus.

Glycolytic requirement for NK cell cytotoxicity and cytomegalovirus control

NK cell activation has been shown to be metabolically regulated in vitro; however, the role of metabolism during in vivo NK cell responses to infection is unknown. We examined the role of glycolysis in NK cell function during murine cytomegalovirus (MCMV) infection and the ability of IL-15 to prime NK cells during CMV infection. The glucose metabolism inhibitor 2-deoxy-ᴅ-glucose (2DG) impaired both mouse and human NK cell cytotoxicity following priming in vitro. Similarly, MCMV-infected mice treated with 2DG had impaired clearance of NK-specific targets in vivo, which was associated with higher viral burden and susceptibility to infection on the C57BL/6 background. IL-15 priming is known to alter NK cell metabolism and metabolic requirements for activation. Treatment with the IL-15 superagonist ALT-803 rescued mice from otherwise lethal infection in an NK-dependent manner. Consistent with this, treatment of a patient with ALT-803 for recurrent CMV reactivation after hematopoietic cell transplant was associated with clearance of viremia. These studies demonstrate that NK cell-mediated control of viral infection requires glucose metabolism and that IL-15 treatment in vivo can reduce this requirement and may be effective as an antiviral therapy.

Elevated lead levels and adverse effects on natural killer cells in children from an electronic waste recycling area

Lead (Pb) has been proved to exert immunotoxicity to influence immune homeostasis in humans. To monitor the internal Pb level and evaluate its effect on natural killer (NK) cells and cytokine/chemokine concentrations, we recruited 285 preschool children from Guiyu, one of the largest electronic waste (e-waste) destinations and recycling areas in the world, and known to have high concentrations of Pb in the air, soil, water, sediment and plants. A total of 126 preschool children were selected from Haojiang as a reference group. Results showed that children in Guiyu, the exposed area, had higher blood Pb levels and lower percentages of NK cells than children from the reference area. A significantly negative association was found between the percentage of NK cells and increasing Pb levels. Moreover, children in Guiyu area had higher platelet counts and IL-1β concentrations, and lower levels of IL-2, IL-27, MIP-1α and MIP-1β were observed in the exposed children. These changes might not be conducive to the development and differentiation of NK cells. Taken together, the elevated Pb levels result in the lower percentages of NK cells, but also alter the levels of platelets, IL-1β and IL-27, which might be unconducive to the activity and function of NK cells.

Genomic Modifiers of Natural Killer Cells, Immune Responsiveness and Lymphoid Tissue Remodeling Together Increase Host Resistance to Viral Infection

The MHC class I D^k molecule supplies vital host resistance during murine cytomegalovirus (MCMV) infection. Natural killer (NK) cells expressing the Ly49G2 inhibitory receptor, which specifically binds D^k, are required to control viral spread. The extent of D^k-dependent host resistance, however, differs significantly amongst related strains of mice, C57L and MA/My. As a result, we predicted that relatively small-effect modifier genetic loci might together shape immune cell features, NK cell reactivity, and the host immune response to MCMV. A robust D^k-dependent genetic effect, however, has so far hindered attempts to identify additional host resistance factors. Thus, we applied genomic mapping strategies and multicolor flow cytometric analysis of immune cells in naive and virus-infected hosts to identify genetic modifiers of the host immune response to MCMV. We discovered and validated many quantitative trait loci (QTL); these were mapped to at least 19 positions on 16 chromosomes. Intriguingly, one newly discovered non-MHC locus (Cmv5) controlled splenic NK cell accrual, secondary lymphoid organ structure, and lymphoid follicle development during MCMV infection. We infer that Cmv5 aids host resistance to MCMV infection by expanding NK cells needed to preserve and protect essential tissue structural elements, to enhance lymphoid remodeling and to increase viral clearance in spleen.

Uncovering the genetic basis of resistance to viral infection and disease is critical to learning about how immune defenses might be adjusted, how to design better vaccines, and how to elicit effectual immune protection in human populations. Prior studies have shown that both MHC and non-MHC genes support host defenses, or endow specialized immune cells with efficient sensing or responsiveness to infection. Many additional resistance genes remain to be identified, including difficult to detect smaller-effect alleles, which might add to or interact with other genetic factors. Our grasp of the complex interaction involving these genetic elements is thus inadequate. We combined genomic and multiparameter phenotypic analyses to map and identify host genes that control immune cells or sensitivity to viral infection. We reasoned that some might also affect viral clearance. Thus we enumerated a range of immune cell traits in mice before and after infection, which permitted genomic analysis of viral immunity, and mapping of genetic modifiers for each trait. Our study demonstrates that distinct loci collectively regulate both NK cells and host resistance, which provides a framework to understand the genetic interactions, and a variety of potential novel targets to adjust NK cell functionality and host resistance to infection.

Dual Requirement of Cytokine and Activation Receptor Triggering for Cytotoxic Control of Murine Cytomegalovirus by NK Cells

Natural killer (NK) cells play a critical role in controlling murine cytomegalovirus (MCMV) and can mediate both cytokine production and direct cytotoxicity. The NK cell activation receptor, Ly49H, is responsible for genetic resistance to MCMV in C57BL/6 mice. Recognition of the viral m157 protein by Ly49H is sufficient for effective control of MCMV infection. Additionally, during the host response to infection, distinct immune and non-immune cells elaborate a variety of pleiotropic cytokines which have the potential to impact viral pathogenesis, NK cells, and other immune functions, both directly and indirectly. While the effects of various immune deficiencies have been examined for general antiviral phenotypes, their direct effects on Ly49H-dependent MCMV control are poorly understood. To specifically interrogate Ly49H-dependent functions, herein we employed an in vivo viral competition approach to show Ly49H-dependent MCMV control is specifically mediated through cytotoxicity but not IFNγ production. Whereas m157 induced Ly49H-dependent degranulation, efficient cytotoxicity also required either IL-12 or type I interferon (IFN-I) which acted directly on NK cells to produce granzyme B. These studies demonstrate that both of these distinct NK cell-intrinsic mechanisms are integrated for optimal viral control by NK cells.

Natural killer (NK) cells play a crucial role in the protection of the host against viruses and in particular herpesvirus infections. Through their activation receptors which recognize surface ligands on target cells, NK cells can mediate direct killing (cytotoxicity) of virus-infected cells and produce their signature cytokine IFNγ, but it is unclear to what extent these effector arms contribute to clearance of murine cytomegalovirus (MCMV) infections. Additionally, NK cells are activated through their cytokine receptors but the interplay between the activation and cytokine receptor pathways has not been elucidated. Herein we devised a viral competition assay that allowed direct evaluation of the requirements for NK cell mediated MCMV control. We found that cytotoxicity is the main effector mechanism by which NK cells control virus infection through activation receptors. Complemented by in vitro assays, we delineated the requirements for NK cell cytotoxicity and identified a 2-step mechanism for NK-mediated cytotoxicity. Firstly, NK cells require cytokine signals for the accumulation of cytotolytic proteins. Secondly, direct target cell recognition results in release of the cytolytic cargo and lysis of virus-infected cells. Our study demonstrates the integration of NK activation and cytokine receptor signals are required for effective viral control.