Natural killer cell responses during viral infections: flexibility and conditioning of innate immunity by experience

Comprehensive snapshots of natural killer cells functions, signaling, molecular mechanisms and clinical utilization

Natural killer (NK) cells, initially identified for their rapid virus-infected and leukemia cell killing and tumor destruction, are pivotal in immunity. They exhibit multifaceted roles in cancer, viral infections, autoimmunity, pregnancy, wound healing, and more. Derived from a common lymphoid progenitor, they lack CD3, B-cell, or T-cell receptors but wield high cytotoxicity via perforin and granzymes. NK cells orchestrate immune responses, secreting inflammatory IFNγ or immunosuppressive TGFβ and IL-10. CD56dim and CD56bright NK cells execute cytotoxicity, while CD56bright cells also regulate immunity. However, beyond the CD56 dichotomy, detailed phenotypic diversity reveals many functional subsets that may not be optimal for cancer immunotherapy. In this review, we provide comprehensive and detailed snapshots of NK cells' functions and states of activation and inhibitions in cancer, autoimmunity, angiogenesis, wound healing, pregnancy and fertility, aging, and senescence mediated by complex signaling and ligand-receptor interactions, including the impact of the environment. As the use of engineered NK cells for cancer immunotherapy accelerates, often in the footsteps of T-cell-derived engineering, we examine the interactions of NK cells with other immune effectors and relevant signaling and the limitations in the tumor microenvironment, intending to understand how to enhance their cytolytic activities specifically for cancer immunotherapy.

Monkeypox (Mpox) vs. Innate immune responses: Insights into evasion mechanisms and potential therapeutic strategies

Orthopoxviruses, a group of zoonotic viral infections, have emerged as a significant health emergency and global concern, particularly exemplified by the re-emergence of monkeypox (Mpox). Effectively addressing these viral infections necessitates a comprehensive understanding of the intricate interplay between the viruses and the host's immune response. In this review, we aim to elucidate the multifaceted aspects of innate immunity in the context of orthopoxviruses, with a specific focus on monkeypox virus (MPXV). We provide an in-depth analysis of the roles of key innate immune cells, including natural killer (NK) cells, dendritic cells (DCs), and granulocytes, in the host defense against MPXV. Furthermore, we explore the interferon (IFN) response, highlighting the involvement of toll-like receptors (TLRs) and cytosolic DNA/RNA sensors in detecting and responding to the viral presence. This review also examines the complement system's contribution to the immune response and provides a detailed analysis of the immune evasion strategies employed by MPXV to evade host defenses. Additionally, we discuss current prevention and treatment strategies for Mpox, including pre-exposure (PrEP) and post-exposure (PoEP) prophylaxis, supportive treatments, antivirals, and vaccinia immune globulin (VIG).

The interaction between NK cells and ILC cells and their subsets in atopic dermatitis patients with and without dupilumab therapy

BACKGROUND

Natural killer cells (NK) and innate lymphoid cells with their subsets (ILC) are part of the innate immune system.

OBJECTIVE

The aim is to evaluate how NK cells and ILC cells interact in atopic dermatitis (AD) patients (with and without dupilumab therapy) compared to control group.

MATERIALS AND METHODS

Complete dermatological examination was performed in all patients included in the study (19 AD patients with dupilumab, 17 AD patients without dupilumab). Surface molecules expressed on NK cells and ILC cells were analyzed by flow cytometry. The association between NK cells and total ILC cells, ILC-1, ILC-2, ILC-3, NCR+ILC3, NCR-ILC3 were compared in AD patients and in the control group. The non-parametric Spearman's rank correlation coefficient was used for this statistical analysis. We evaluated the association of parameters with AD severity at the time of treatment.Non-parametric Mann-Whitney, Kolmogorov-Smirnov tests were used.

RESULTS

We confirmed the higher association between NK cells and total ILC cells in AD patients without dupilumab therapy (in 30.3 %) and in healthy controls (in 27.2 %); this association is low in AD patients with dupilumab therapy (in 0.1 %). The higher association was confirmed between NK cells and ILCs subsets only in AD patients without dupilumab therapy; in these patients the highest association was confirmed between NK cells and ILC-2 cells (in 38.6 %). No statistically significant difference in the count of NK cells and ILC cells was found between mild and moderate form of AD patients treated with dupilumab.

CONCLUSION

Targeting these cell types or the cytokines they produce could represent potential therapeutic strategies for controlling inflammation and alleviating symptoms in AD patients.

Persistence of a Skewed Repertoire of NK Cells in People with HIV-1 on Long-Term Antiretroviral Therapy

HIV-1 infection greatly alters the NK cell phenotypic and functional repertoire. This is highlighted by the expansion of a rare population of FcRγ- NK cells exhibiting characteristics of traditional immunologic memory in people with HIV (PWH). Although current antiretroviral therapy (ART) effectively controls HIV-1 viremia and disease progression, its impact on HIV-1-associated NK cell abnormalities remains unclear. To address this, we performed a longitudinal analysis detailing conventional and memory-like NK cell characteristics in n = 60 PWH during the first 4 y of ART. Throughout this regimen, a skewed repertoire of cytokine unresponsive FcRγ- memory-like NK cells persisted and accompanied an overall increase in NK surface expression of CD57 and KLRG1, suggestive of progression toward immune senescence. These traits were linked to elevated serum inflammatory biomarkers and increasing Ab titers to human CMV, with human CMV viremia detected in approximately one-third of PWH at years 1-4 of ART. Interestingly, 40% of PWH displayed atypical NK cell subsets, representing intermediate stages of NK-poiesis based on single-cell multiomic trajectory analysis. Our findings indicate that NK cell irregularities persist in PWH despite long-term ART, underscoring the need to better understand the causative mechanisms that prevent full restoration of immune health in PWH.

OV Modulators of the Paediatric Brain TIME: Current Status, Combination Strategies, Limitations and Future Directions

Oncolytic viruses (OVs) are characterised by their preference for infecting and replicating in tumour cells either naturally or after genetic modification, resulting in oncolysis. Furthermore, OVs can elicit both local and systemic anticancer immune responses while specifically infecting and lysing tumour cells. These characteristics render them a promising therapeutic approach for paediatric brain tumours (PBTs). PBTs are frequently marked by a cold tumour immune microenvironment (TIME), which suppresses immunotherapies. Recent preclinical and clinical studies have demonstrated the capability of OVs to induce a proinflammatory immune response, thereby modifying the TIME. In-depth insights into the effect of OVs on different cell types in the TIME may therefore provide a compelling basis for using OVs in combination with other immunotherapy modalities. However, certain limitations persist in our understanding of oncolytic viruses' ability to regulate the TIME to enhance anti-tumour activity. These limitations primarily stem from the translational limitations of model systems, the difficulties associated with tracking reliable markers of efficacy throughout the course of treatment and the role of pre-existing viral immunity. In this review, we describe the different alterations observed in the TIME in PBTs due to OV treatment, combination therapies of OVs with different immunotherapies and the hurdles limiting the development of effective OV therapies while suggesting future directions based on existing evidence.

Balancing act: the complex role of NK cells in immune regulation

Natural killer (NK) cells, as fundamental components of innate immunity, can quickly react to abnormalities within the body. In-depth research has revealed that NK cells possess regulatory functions not only in innate immunity but also in adaptive immunity under various conditions. Multiple aspects of the adaptive immune process are regulated through NK cells. In our review, we have integrated multiple studies to illuminate the regulatory function of NK cells in regulating B cell and T cell responses during adaptive immune processes, focusing on aspects including viral infections and the tumor microenvironment (TME). These insights provide us with many new understandings on how NK cells regulate different phases of the adaptive immune response.

Identification of novel lactic acid bacteria with enhanced protective effects against influenza virus

Lactic acid bacteria (LAB) exert health-beneficial effects by regulating innate immunity in the intestinal tract. Due to growing health awareness, the demand for LAB and studies have focused on identifying beneficial LAB strains is increasing, especially those that stimulate innate immunity. In this study, the LAB strain D279 (NITE_BP-03645, Latilactobacillus sakei) was isolated from among 741 LAB strains that were analyzed for their ability to induce interleukin 12 (IL-12) production and was subsequently characterized. D279 induced the highest expression of IL-12 among the screened LABs. Furthermore, D279 significantly activated antiviral genes and preferentially induced interferon (IFN)λ expression in vitro, which plays a critical role in the epithelial tissue, thereby conferring strong anti-influenza potency without inflammation. However, it decreased the IFNα levels. The administration of pasteurized D279 to mice resulted in strong anti-influenza potency, with higher natural killer (NK) cell activity and a lower viral load in the lung than in the control. Importantly, none of the D279-administered mice were sacrificed during the viral infection tests. These results suggest that D279 administration confers beneficial effects by regulating innate immunity and that it may be relevant for commercial use in the future.

HLA-E*01:01 + HLA-E*01:01 genotype confers less susceptibility to COVID-19, while HLA-E*01:03 + HLA-E*01:03 genotype is associated with more severe disease

BACKGROUND

HLA-E interaction with inhibitory receptor, NKG2A attenuates NK-mediated cytotoxicity. NKG2A overexpression by SARS-CoV-2 exhausts NK cells function, whereas virus-induced down-regulation of MHC-Ia reduces its derived-leader sequence peptide levels required for proper binding of HLA-E to NKG2A. This leads HLA-E to become more complex with viral antigens and delivers them to CD8⁺ T cells, which facilitates cytolysis of infected cells. Now, the fact that alleles of HLA-E have different levels of expression and affinity for MHC Ia-derived peptide raises the question of whether HLA-E polymorphisms affect susceptibility to COVID-19 or its severity.

METHODS

104 COVID-19 convalescent plasma donors with/without history of hospitalization and 18 blood donors with asymptomatic COVID-19, all were positive for anti-SARS-CoV-2 IgG antibody as well as a group of healthy control including 68 blood donors with negative antibody were subjected to HLA-E genotyping. As a privilege, individuals hadn't been vaccinated against COVID-19 and therefore naturally exposed to the SARS-CoV-2.

RESULTS

The absence of HLA-E*01:03 allele significantly decreases the odds of susceptibility to SARS-CoV-2 infection [p = 0.044; OR (95 %CI) = 0.530 (0.286 - 0.983)], suggesting that HLA-E*01:01 + HLA-E*01:01 genotype favors more protection against SARS-CoV-2 infection. HLA-E*01:03 + HLA-E*01:03 genotype was also significantly associated with more severe COVID-19 [p = 0.020; 2.606 (1.163 - 5.844) CONCLUSION: Here, our observation about lower susceptibility of HLA-E*01:01 + HLA-E*01:01 genotype to COVID-19 could be clinical evidence in support of some previous studies suggesting that the lower affinity of HLA-E*01:01 to peptides derived from the leader sequence of MHC class Ia may instead shift its binding to virus-derived peptides, which then facilitates target recognition by restricted conventional CD8⁺ T cells and leads to efficient cytolysis. On the other hand, according to other studies, less reactivity of HLA-E*01:01 with NKG2A abrogates NK cells or T cells inhibition, which may also lead to a greater cytotoxicity against SARS-CoV-2 infected cells compared to HLA-E*01:03. Taken together given HLA-E polymorphisms, the data presented here may be useful in identifying more vulnerable individuals to COVID-19 for better care and management. Especially since along with other risk factors in patients, having HLA-E*01:03 + HLA-E*01:03 genotype may also be associated with the possibility of severe cases of the disease.

The Mechanisms of Zinc Action as a Potent Anti-Viral Agent: The Clinical Therapeutic Implication in COVID-19

The pandemic of COVID-19 was caused by a novel coronavirus termed as SARS-CoV2 and is still ongoing with high morbidity and mortality rates in the whole world. The pathogenesis of COVID-19 is highly linked with over-active immune and inflammatory responses, leading to activated cytokine storm, which contribute to ARDS with worsen outcome. Currently, there is no effective therapeutic drug for the treatment of COVID-19. Zinc is known to act as an immune modulator, which plays an important role in immune defense system. Recently, zinc has been widely considered as an anti-inflammatory and anti-oxidant agent. Accumulating numbers of studies have revealed that zinc plays an important role in antiviral immunity in several viral infections. Several early clinical trials clearly indicate that zinc treatment remarkably decreased the severity of the upper respiratory infection of rhinovirus in humans. Currently, zinc has been used for the therapeutic intervention of COVID-19 in many different clinical trials. Several clinical studies reveal that zinc treatment using a combination of HCQ and zinc pronouncedly reduced symptom score and the rates of hospital admission and mortality in COVID-19 patients. These data support that zinc might act as an anti-viral agent in the addition to its anti-inflammatory and anti-oxidant properties for the adjuvant therapeutic intervention of COVID-19.

How Can We Improve Vaccination Response in Old People? Part I: Targeting Immunosenescence of Innate Immunity Cells

Vaccination, being able to prevent millions of cases of infectious diseases around the world every year, is the most effective medical intervention ever introduced. However, immunosenescence makes vaccines less effective in providing protection to older people. Although most studies explain that this is mainly due to the immunosenescence of T and B cells, the immunosenescence of innate immunity can also be a significant contributing factor. Alterations in function, number, subset, and distribution of blood neutrophils, monocytes, and natural killer and dendritic cells are detected in aging, thus potentially reducing the efficacy of vaccines in older individuals. In this paper, we focus on the immunosenescence of the innate blood immune cells. We discuss possible strategies to counteract the immunosenescence of innate immunity in order to improve the response to vaccination. In particular, we focus on advances in understanding the role and the development of new adjuvants, such as TLR agonists, considered a promising strategy to increase vaccination efficiency in older individuals.

The gamble between oncolytic virus therapy and IFN

Various studies are being conducted on oncolytic virotherapy which one of the mechanisms is mediating interferon (IFN) production by it exerts antitumor effects. The antiviral effect of IFN itself has a negative impact on the inhibition of oncolytic virus or tumor eradication. Therefore, it is very critical to understand the mechanism of IFN regulation by oncolytic viruses, and to define its mechanism is of great significance for improving the antitumor effect of oncolytic viruses. This review focuses on the regulatory mechanisms of IFNs by various oncolytic viruses and their combination therapies. In addition, the exerting and the producing pathways of IFNs are briefly summarized, and some current issues are put forward.

Exercise Training Improves Mitochondrial Bioenergetics of Natural Killer Cells

INTRODUCTION

Mitochondrial bioenergetics is critical for immune function in natural killer (NK) cell. Physical exercise modulates NK cell functionality, depending on the intensity and type of exercise. This study elucidates how interval and continuous exercise regimens affect the phenotypes and mitochondrial bioenergetics of NK cells.

METHODS

Sixty healthy sedentary males were randomly assigned to engage in either high-intensity interval training (HIIT, 3-min intervals at 80% and 40% maximal O2, n = 20; age, 22.2 yr; body mass index [BMI], 24.3 kg·m-2) or moderate-intensity continuous training (MICT, sustained 60% maximal O2, n = 20; age, 22.3 yr; BMI, 23.3 kg·m-2) for 30 min·d-1, 5 d·wk-1 for 6 wk or were assigned to a control group that did not receive exercise intervention (n = 20; age, 22.6 yr; BMI, 24.0 kg·m-2). Natural killer cell phenotypes, granule proteins, and mitochondrial oxidative stress/oxidative phosphorylation after graded exercise test (GXT) were measured before and after the various interventions.

RESULTS

Before the intervention, the GXT increased the mobilization of CD57+NK cells into the blood and elevated mitochondrial matrix oxidant burden (MOB) in NK cells, Following the 6 wk of interventions, both HIIT and MICT (i) diminished mobilization of CD57+NK cells into the blood and depressed mitochondrial MOB level in NK cells immediately after GXT, (ii) increased mitochondrial membrane potential and cellular perforin and granzyme B levels in NK cells, and (iii) enhanced the maximal and reserve O2 consumption rates and heightened bioenergetic health index in NK cells. In addition, HIIT increased maximal work rate than those of MICT.

CONCLUSIONS

Either HIIT or MICT increases the expressions of cytotoxic granule proteins and depresses mitochondrial MOB elevated by GXT, along with improving mitochondrial bioenergetic functionality in NK cells. Moreover, HIIT is superior to MICT in improving aerobic capacity.

Oncolytic virus treatment differentially affects the CD56dim and CD56bright NK cell subsets in vivo and regulates a spectrum of human NK cell activity

Natural killer (NK) cells protect against intracellular infection and cancer. These properties are exploited in oncolytic virus (OV) therapy, where antiviral responses enhance anti-tumour immunity. We have analysed the mechanism by which reovirus, an oncolytic dsRNA virus, modulates human NK cell activity. Reovirus activates NK cells in a type I interferon (IFN-I) dependent manner, inducing STAT1 and STAT4 signalling in both CD56dim and CD56bright NK cell subsets. Gene expression profiling revealed the dominance of IFN-I responses and identified induction of genes associated with NK cell cytotoxicity and cell cycle progression, with distinct responses in the CD56dim and CD56bright subsets. However, reovirus treatment inhibited IL-15 induced NK cell proliferation in an IFN-I dependent manner and was associated with reduced AKT signalling. In vivo, human CD56dim and CD56bright NK cells responded with similar kinetics to reovirus treatment, but CD56bright NK cells were transiently lost from the peripheral circulation at the peak of the IFN-I response, suggestive of their redistribution to secondary lymphoid tissue. Coupled with the direct, OV-mediated killing of tumour cells, the activation of both CD56dim and CD56bright NK cells by antiviral pathways induces a spectrum of activity that includes the NK cell-mediated killing of tumour cells and modulation of adaptive responses via the trafficking of IFN-γ expressing CD56bright NK cells to lymph nodes.

Analysis of MicroRNA Expression in Tears of Patients with Herpes Epithelial Keratitis: A Preliminary Study

Purpose

Herpes epithelial keratitis (HEK) is the most common form of herpes simplex virus (HSV) eye involvement, and understanding the molecular mechanisms underlying HEK is important. We investigated the expression of microRNAs (miRNAs) in the tears of patients with HEK.

Methods

Tear samples from eight patients with HEK and seven age-matched controls were evaluated. Clinical ophthalmologic evaluation was performed, and an anterior segment photograph was obtained after fluorescence staining. Dendritic or geographic ulcer areas were measured using ImageJ software. The expression of 43 different miRNAs in tears was measured using real-time polymerase chain reaction and compared between patients with HEK and controls. Differences in miRNA expression between the dendritic and geographic ulcer groups and correlations involving miRNA expression and ulcer area were evaluated.

Results

Of the 43 miRNAs, 23 were upregulated in patients with HEK compared to normal controls. MiR-15b-5p, miR-16-5p, miR-20b-5p, miR-21-5p, miR-23b-3p, miR-25-3p, miR-29a-3p, miR-30a-3p, miR-30d-5p, miR-92a-3p, miR-124-3p, miR-127-3p, miR-132-3p, miR-142-3p, miR-145-5p, miR-146a-5p, miR-146b-5p, miR-155-5p, miR-182-5p, miR-183-5p, miR-221-3p, miR-223-3p, and miR-338-5p were significantly upregulated in patients with HEK. MiR-29a-3p exhibited significant differences between the dendritic and geographic ulcer groups. All 23 miRNAs with significant differences between patients with HEK and the control group were not significantly correlated with ulcer area.

Conclusions

Twenty-three miRNAs were significantly upregulated in the tears of patients with HEK, and the expression of miRNAs may play important roles in herpes infection in relation to host immunity.

Identifying SARS-CoV-2 'memory' NK cells from COVID-19 convalescent donors for adoptive cell therapy

COVID-19 disease is the manifestation of syndrome coronavirus 2 (SARS-CoV-2) infection, which is causing a worldwide pandemic. This disease can lead to multiple and different symptoms, being lymphopenia associated with severity one of the most persistent. Natural killer cells (NK cells) are part of the innate immune system, being fighting against virus-infected cells one of their key roles. In this study, we determined the phenotype of NK cells after COVID-19 and the main characteristic of SARS-CoV-2-specific-like NK population in the blood of convalescent donors. CD57+ NKG2C+ phenotype in SARS-CoV-2 convalescent donors indicates the presence of 'memory'/activated NK cells as it has been shown for cytomegalovirus infections. Although the existence of this population is donor dependent, its expression may be crucial for the specific response against SARS-CoV-2, so that, it gives us a tool for selecting the best donors to produce off-the-shelf living drug for cell therapy to treat COVID-19 patients under the RELEASE clinical trial (NCT04578210).

Exhausted NK cells and cytokine storms in COVID-19: Whether NK cell therapy could be a therapeutic choice

The global outbreak of coronavirus-2019 (COVID-19) still claims more lives daily around the world due to the lack of a definitive treatment and the rapid tendency of virus to mutate, which even jeopardizes vaccination efficacy. At the forefront battle against SARS-CoV-2, an effective innate response to the infection has a pivotal role in the initial control and treatment of disease. However, SARS-CoV-2 subtly interrupts the equations of immune responses, disrupting the cytolytic antiviral effects of NK cells, while seriously activating infected macrophages and other immune cells to induce an unleashed "cytokine storm", a dangerous and uncontrollable inflammatory response causing life-threatening symptoms in patients. Notably, the NK cell exhaustion with ineffective cytolytic function against the sources of exaggerated cytokine release, acts as an Achilles' heel which exacerbates the severity of COVID-19. Given this, approaches that improve NK cell cytotoxicity may benefit treatment protocols. As a suggestion, adoptive transfer of NK or CAR-NK cells with proper cytotolytic potentials and the lowest capacity of cytokine-release (for example CD56dim NK cells brightly express activating receptors), to severe COVID-19 patients may provide an effective cure especially in cases suffering from cytokine storms. More intriguingly, the ongoing evidence for persistent clonal expansion of NK memory cells characterized by an activating phenotype in response to viral infections, can benefit the future studies on vaccine development and adoptive NK cell therapy in COVID-19. Whether vaccinated volunteers or recovered patients can also be considered as suitable candidates for cell donation could be the subject of future research.

Assessing the Response of Human NK Cell Subsets to Infection by Clinically Isolated Virus Strains

Natural killer (NK) cells play a critical role in defending against virus infections.Investigating human NK cell antiviral functions is of prime importance; however, there are challenges such as the human-specific nature of many viruses and differences in NK cell surface markers between humans and rodents. Research on the antivirus response of human NK cells must therefore be carefully planned around species tropism of the viruses of interest and the specific biological questions to be answered. The initial site of many virus infections is a mucosal/epithelial surface. In this context, a clinical virus infection at the ocular surface enables direct analyses on the mechanisms and consequences of infection and immune reactions in situ over the course of disease. For example, the site of infection of a clinical infection in the conjunctiva and cornea can be directly observed in real-time, utilizing split-lamp microscopy, and specimens are readily accessed with minimally invasive techniques.In this chapter, we describe protocols for investigating NK cell responses using clinically isolated viruses in co-culture assays. We also describe procedures for ex vivo analysis of conjunctiva-derived NK cells in adenovirus infection.

Alarmins, COVID-19 and comorbidities

The coronavirus SARS-CoV-2, the aetiological agent of COVID-19 disease, is representing a worldwide threat for the medical community and the society at large so that it is being defined as "the twenty-first-century disease". Often associated with a severe cytokine storm, leading to more severe cases, it is mandatory to block such occurrence early in the disease course, to prevent the patients from having more severe, sometimes fatal, outcomes. In this framework, early detection of "danger signals", possibly represented by alarmins, can represent one of the most promising strategies to effectively tailor the disease and to better understand the underlying mechanisms eventually leading to death or severe consequences. In light of such considerations, the present article aims at evaluating the role of alarmins in patients affected by COVID-19 disease and the relationship of such compounds with the most commonly reported comorbidities. The conducted researches demonstrated yet poor literature on this specific topic, however preliminarily confirming a role for danger signals in the amplification of the inflammatory reaction associated with SARS-CoV-2 infection. As such, a number of chronic conditions, including metabolic syndrome, gastrointestinal and respiratory diseases, in turn, associated with higher levels of alarmins, both foster the infection and predispose to a worse prognosis. According to these preliminary data, prompt detection of high levels of alarmins in patients with COVID-19 and co-morbidities could suggest an immediate intense anti-inflammatory treatment.Key messageAlarmins have a role in the amplification of the inflammatory reaction associated with SARS-CoV-2 infectiona prompt detection of high levels of alarmins in patients with COVID-19 could suggest an immediate intense anti-inflammatory treatment.

β-Glucans Could Be Adjuvants for SARS-CoV-2 Virus Vaccines (COVID-19)

Waiting for an effective treatment against the SARS-CoV-2 virus (the cause of COVID-19), the current alternatives include prevention and the use of vaccines. At the moment, vaccination is the most effective strategy in the fight against pandemic. Vaccines can be administered with different natural biological products (adjuvants) with immunomodulating properties. Adjuvants can be taken orally, complementing vaccine action. Adjuvant compounds could play a key role in alleviating the symptoms of the disease, as well as in enhancing vaccine action. Adjuvants also contribute to an effective immune response and can enhance the protective effect of vaccines in immunocompromised individuals such as the elderly. Adjuvants must not produce adverse effects, toxicity, or any other symptoms that could alter immune system function. Vaccine adjuvants are substances of wide varying chemical structure that are used to boost the immune response against a simultaneously administered antigen. Glucans could work as adjuvants due to their immunomodulatory biological activity. In this respect, β-(1,3)-(1,6) glucans are considered the most effective and safe according to the list issued by the European Commission. Only glucans with a β-(1,3) bond linked to a β-(1,6) are considered modulators of certain biological responses. The aim of this review is to present the possible effects of β-glucans as adjuvants in the efficacy of vaccines against SARS-CoV-2 virus.

The Biological Role and Therapeutic Potential of NK Cells in Hematological and Solid Tumors

NK cells are an attractive target for cancer immunotherapy due to their potent antitumor activity. The main advantage of using NK cells as cytotoxic effectors over T cells is a reduced risk of graft versus host disease. At present, several variants of NK-cell-based therapies are undergoing clinical trials and show considerable effectiveness for hematological tumors. In these types of cancers, the immune cells themselves often undergo malignant transformation, which determines the features of the disease. In contrast, the current use of NK cells as therapeutic agents for the treatment of solid tumors is much less promising. Most studies are at the stage of preclinical investigation, but few progress to clinical trials. Low efficiency of NK cell migration and functional activity in the tumor environment are currently considered the major barriers to NK cell anti-tumor therapies. Various therapeutic combinations, genetic engineering methods, alternative sources for obtaining NK cells, and other techniques are aiming at the development of promising NK cell anticancer therapies, regardless of tumorigenesis. In this review, we compare the role of NK cells in the pathogenesis of hematological and solid tumors and discuss current prospects of NK-cell-based therapy for hematological and solid tumors.

Immunopathology and Immunosenescence, the Immunological Key Words of Severe COVID-19. Is There a Role for Stem Cell Transplantation?

The outcomes of Coronavirus disease-2019 (COVID-19) vary depending on the age, health status and sex of an individual, ranging from asymptomatic to lethal. From an immunologic viewpoint, the final severe lung damage observed in COVID-19 should be caused by cytokine storm, driven mainly by interleukin-6 and other pro-inflammatory cytokines. However, which immunopathogenic status precedes this "cytokine storm" and why the male older population is more severely affected, are currently unanswered questions. The aging of the immune system, i.e., immunosenescence, closely associated with a low-grade inflammatory status called "inflammageing," should play a key role. The remodeling of both innate and adaptive immune response observed with aging can partly explain the age gradient in severity and mortality of COVID-19. This review discusses how aging impacts the immune response to the virus, focusing on possible strategies to rejuvenate the immune system with stem cell-based therapies. Indeed, due to immunomodulatory and anti-inflammatory properties, multipotent mesenchymal stem cells (MSCs) are a worth-considering option against COVID-19 adverse outcomes.

Glycophosphopeptical AM3 Food Supplement: A Potential Adjuvant in the Treatment and Vaccination of SARS-CoV-2

The world is currently experiencing the coronavirus disease 2019 (COVID-19) pandemic caused by Severe Acute Respiratory Syndrome-2 (SARS-CoV-2). Its global spread has resulted in millions of confirmed infections and deaths. While the global pandemic continues to grow, the availability of drugs to treat COVID-19 infections remains limited to supportive treatments. Moreover, the current speed of vaccination campaigns in many countries has been slow. Natural substrates with biological immunomodulatory activity, such as glucans, may represent an adjuvant therapeutic agent to treat SARS-CoV-2. AM3, a natural glycophosphopeptical, has previously been shown to effectively slow, with no side effects, the progression of infectious respiratory diseases by regulating effects on innate and adaptive immunity in experimental models. No clinical studies, however, exist on the use of AM3 in SARS-CoV-2 infected patients. This review aims to summarize the beneficial effects of AM3 on respiratory diseases, the inflammatory response, modulation of immune response, and attenuation of muscle. It will also discuss its potential effects as an immune system adjuvant for the treatment of COVID-19 infections and adjuvant for SARS-CoV-2 vaccination.

KSHV infection drives poorly cytotoxic CD56-negative natural killer cell differentiation in vivo upon KSHV/EBV dual infection

Herpesvirus infections shape the human natural killer (NK) cell compartment. While Epstein-Barr virus (EBV) expands immature NKG2A⁺ NK cells, human cytomegalovirus (CMV) drives accumulation of adaptive NKG2C⁺ NK cells. Kaposi sarcoma-associated herpesvirus (KSHV) is a close relative of EBV, and both are associated with lymphomas, including primary effusion lymphoma (PEL), which nearly always harbors both viruses. In this study, KSHV dual infection of mice with reconstituted human immune system components leads to the accumulation of CD56^-CD16⁺CD38⁺CXCR6⁺ NK cells. CD56^-CD16⁺ NK cells were also more frequently found in KSHV-seropositive Kenyan children. This NK cell subset is poorly cytotoxic against otherwise-NK-cell-susceptible and antibody-opsonized targets. Accordingly, NK cell depletion does not significantly alter KSHV infection in humanized mice. These data suggest that KSHV might escape NK-cell-mediated immune control by driving CD56^-CD16⁺ NK cell differentiation.

COVID-19 - pathogenesis and immunological findings across the clinical manifestation spectrum

PURPOSE OF REVIEW

The wide spectrum of COVID-19 clinical manifestations demonstrates the determinant role played by the individual immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the course of the disease. Thanks to the large number of published data, we are beginning to understand the logic of the human response to a virus adapted to bat immunity.

RECENT FINDINGS

Impairment of types I and III interferon responses may facilitate the occurrence of severe COVID-19 with reduced antiviral activity associated to potent inflammation. The human T and B-cell germline repertoire contain the specificities able to react against SARS-CoV-2 antigens. Although inflammation disrupts the structure of germinal centers, memory T and B cells can be found in the blood of patients after mild and severe COVID 19.

SUMMARY

Further studies are indispensable to better understand the human immune response to SARS-CoV-2. The diversity of the individual reaction may contribute to explain the clinical manifestation spectrum. Immunological memory can be demonstrated in patients, convalescent from mild, moderate, or severe COVID-19, but we do not know whether asymptomatic individuals have memory of the virus. Tailored vaccination protocols may be needed for individuals with previous SAS-CoV-2 infection.

Systems Biology behind Immunoprotection of Both Sheep and Goats after Sungri/96 PPRV Vaccination

Immune response is a highly coordinated cascade involving all the subsets of peripheral blood mononuclear cells (PBMCs). In this study, RNA sequencing (RNA-Seq) analysis of PBMC subsets was done to delineate the systems biology behind immune protection of the vaccine in sheep and goats. The PBMC subsets studied were CD4⁺, CD8⁺, CD14⁺, CD21⁺, and CD335⁺ cells from day 0 and day 5 of sheep and goats vaccinated with Sungri/96 peste des petits ruminants virus. Assessment of the immune response processes enriched by the differentially expressed genes (DEGs) in all the subsets suggested a strong dysregulation toward the development of early inflammatory microenvironment, which is very much required for differentiation of monocytes to macrophages, and activation as well as the migration of dendritic cells into the draining lymph nodes. The protein-protein interaction networks among the antiviral molecules (IFIT3, ISG15, MX1, MX2, RSAD2, ISG20, IFIT5, and IFIT1) and common DEGs across PBMC subsets in both species identified ISG15 to be a ubiquitous hub that helps in orchestrating antiviral host response against peste des petits ruminants virus (PPRV). IRF7 was found to be the key master regulator activated in most of the subsets in sheep and goats. Most of the pathways were found to be inactivated in B lymphocytes of both the species, indicating that 5 days postvaccination (dpv) is too early a time point for the B lymphocytes to react. The cell-mediated immune response and humoral immune response pathways were found more enriched in goats than in sheep. Although animals from both species survived the challenge, a contrast in pathway activation was observed in CD335⁺ cells.

IMPORTANCE Peste des petits ruminants (PPR) by PPR virus (PPRV) is an World Organisation for Animal Health (OIE)-listed acute, contagious transboundary viral disease of small ruminants. The attenuated Sungri/96 PPRV vaccine used all over India against this PPR provides long-lasting robust innate and adaptive immune response. The early antiviral response was found mediated through type I interferon-independent interferon-stimulated gene (ISG) expression. However, systems biology behind this immune response is unknown. In this study, in vivo transcriptome profiling of PBMC subsets (CD4⁺, CD8⁺, CD14⁺, CD21⁺, and CD335⁺) in vaccinated goats and sheep (at 5 days postvaccination) was done to understand this systems biology. Though there are a few differences in the systems biology across cells (specially the NK cells) between sheep and goats, the coordinated response that is inclusive of all the cell subsets was found to be toward the induction of a strong innate immune response, which is needed for an appropriate adaptive immune response.

Stem Cell Therapy Potency in Personalizing Severe COVID-19 Treatment

Currently, there are no specific and efficient vaccines or drugs for COVID-19, particularly in severe cases. A wide range of variations in the clinical symptoms of different patients attributed to genomic differences. Therefore, personalized treatments seem to play a critical role in improving these symptoms and even similar conditions. Prompted by the uncertainties in the area of COVID-19 therapies, we reviewed the published papers and concepts to gather and provide useful information to clinicians and researchers interested in personalized medicine and cell-based therapy. One novel aspect of this study focuses on the potential application of personalized medicine in treating severe cases of COVID-19. However, it is theoretical, as any real-world examples of the use of genuinely personalized medicine have not existed yet. Nevertheless, we know that stem cells, especially MSCs, have immune-modulatory effects and can be stored for future personalized medicine applications. This theory has been conjugated with some evidence that we review in the present study. Besides, we discuss the importance of personalized medicine and its possible aspects in COVID-19 treatment, then review the cell-based therapy studies for COVID-19 with a particular focus on stem cell-based therapies as a primary personalized tool medicine. However, the idea of cell-based therapy has not been accepted by several scientific communities due to some concerns of lack of satisfactory clinical studies; still, the MSCs and their clinical outcomes have been revealed the safety and potency of this therapeutic approach in several diseases, especially in the immune-mediated inflammatory diseases and some incurable diseases. Promising outcomes have resulted in that clinical studies are going to continue.

The role of NK cells in fighting the virus infection and sepsis

Natural killer cells, one of the important types of innate immune cells, play a pivotal role in the antiviral process in vivo. It has been shown that increasing NK cell activity may promote the alleviation of viral infections, even severe infection-induced sepsis. Given the current state of the novel coronavirus (SARS-CoV-2) global pandemic, clarifying the anti-viral function of NK cells would be helpful for revealing the mechanism of host immune responses and decipher the progression of COVID-19 and providing important clues for combating this pandemic. In this review, we summarize the roles of NK cells in viral infection and sepsis as well as the potential possibilities of NK cell-based immunotherapy for treating COVID-19.

Different Innate and Adaptive Immune Responses to SARS-CoV-2 Infection of Asymptomatic, Mild, and Severe Cases

SARS-CoV-2 is a novel coronavirus, not encountered before by humans. The wide spectrum of clinical expression of SARS-CoV-2 illness suggests that individual immune responses to SARS-CoV-2 play a crucial role in determining the clinical course after first infection. Immunological studies have focused on patients with moderate to severe disease, demonstrating excessive inflammation in tissues and organ damage. In order to understand the basis of the protective immune response in COVID-19, we performed a longitudinal follow-up, flow-cytometric and serological analysis of innate and adaptive immunity in 64 adults with a spectrum of clinical presentations: 28 healthy SARS-CoV-2-negative contacts of COVID-19 cases; 20 asymptomatic SARS-CoV-2-infected cases; eight patients with Mild COVID-19 disease and eight cases of Severe COVID-19 disease. Our data show that high frequency of NK cells and early and transient increase of specific IgA, IgM and, to a lower extent, IgG are associated with asymptomatic SARS-CoV-2 infection. By contrast, monocyte expansion and high and persistent levels of IgA and IgG, produced relatively late in the course of the infection, characterize severe disease. Modest increase of monocytes and different kinetics of antibodies are detected in mild COVID-19. The importance of innate NK cells and the short-lived antibody response of asymptomatic individuals and patients with mild disease suggest that only severe COVID-19 may result in protective memory established by the adaptive immune response.

Innate and Adaptive Immunity in Aging and Longevity: The Foundation of Resilience

The interrelation of the processes of immunity and senescence now receives an unprecedented emphasis during the COVID-19 pandemic, which brings to the fore the critical need to combat immunosenescence and improve the immune function and resilience of older persons. Here we review the historical origins and the current state of the science of innate and adaptive immunity in aging and longevity. From the modern point of view, innate and adaptive immunity are not only affected by aging but also are important parts of its underlying mechanisms. Excessive levels or activity of antimicrobial peptides, C-reactive protein, complement system, TLR/NF-κB, cGAS/STING/IFN 1,3 and AGEs/RAGE pathways, myeloid cells and NLRP3 inflammasome, declined levels of NK cells in innate immunity, thymus involution and decreased amount of naive T-cells in adaptive immunity, are biomarkers of aging and predisposition factors for cellular senescence and aging-related pathologies. Long-living species, human centenarians, and women are characterized by less inflamm-aging and decelerated immunosenescence. Despite recent progress in understanding, the harmonious theory of immunosenescence is still developing. Geroprotectors targeting these mechanisms are just emerging and are comprehensively discussed in this article.

COVID-19: The Emerging Immunopathological Determinants for Recovery or Death

Hyperactivation of the host immune system during infection by SARS-CoV-2 is the leading cause of death in COVID-19 patients. It is also evident that patients who develop mild/moderate symptoms and successfully recover display functional and well-regulated immune response. Whereas a delayed initial interferon response is associated with severe disease outcome and can be the tipping point towards immunopathological deterioration, often preceding death in COVID-19 patients. Further, adaptive immune response during COVID-19 is heterogeneous and poorly understood. At the same time, some studies suggest activated T and B cell response in severe and critically ill patients and the presence of SARS-CoV2-specific antibodies. Thus, understanding this problem and the underlying molecular pathways implicated in host immune function/dysfunction is imperative to devise effective therapeutic interventions. In this comprehensive review, we discuss the emerging immunopathological determinants and the mechanism of virus evasion by the host cell immune system. Using the knowledge gained from previous respiratory viruses and the emerging clinical and molecular findings on SARS-CoV-2, we have tried to provide a holistic understanding of the host innate and adaptive immune response that may determine disease outcome. Considering the critical role of the adaptive immune system during the viral clearance, we have presented the molecular insights of the plausible mechanisms involved in impaired T cell function/dysfunction during various stages of COVID-19.

IL-18 Responsiveness Defines Limitations in Immune Help for Specialized FcRγ- NK Cells

Despite being prolific innate killers, NK cells are also key helper cells in antiviral defense, influencing adaptive immune responses via interactions with dendritic cells (DCs). In addition to causing NK cell dysfunction, HIV-1 infection contributes to the expansion of a rare population of NK cells deficient in FcRγ (FcRγ^-), an intracellular adaptor protein that associates with CD16. The implications of this inflated NK cell subset in treated HIV-1 infection remain unclear. In this study, we explored the helper function of human NK cells in chronic HIV-1 infection, with a particular focus on characterizing FcRγ^- NK cells. Exposure of NK cells to innate DC-derived costimulatory factors triggered their helper activity, defined by their ability to produce IFN-γ and to drive the maturation of high IL-12-producing DCs. In this setting, however, FcRγ^- NK cells were defective at producing the dominant DC-polarizing agent IFN-γ. The reduced responsiveness of FcRγ^- NK cells to IL-18 in particular, which was attributable to impaired inducible expression of IL-18Rα, extended beyond an inability to produce IFN-γ, as FcRγ^- NK cells showed limited potential to differentiate into CD16^-/CD25⁺/CD83⁺ helper cells. Notwithstanding their deficiencies in responsiveness to innate environmental cues, FcRγ^- NK cells responded robustly to adaptive Ab-mediated signaling through CD16. The presence of an expanded population of FcRγ^- NK cells with a diminished capacity to respond to IL-18 and to effectively modulate DC function may contribute to disturbances in proper immune homeostasis associated with HIV-1 infection and to defects in the initiation of optimal adaptive antiviral responses.

IFN-γ is an independent risk factor associated with mortality in patients with moderate and severe COVID-19 infection

BACKGROUND

Innate and adaptive immune responses have been evaluated in infected patients with COVID-19. The severity of the disease has been supposed to be associated with some profile not reported with other bacterial and viral pneumonia. We proposed a study in patients with moderate to severe COVID-19 infection to evaluate the interleukin patterns and its role as prognosis factors.

METHODS

A prospective cohort with moderate and severe cases of COVID-19 infection from June to July 2020. Blood samples from patients were collected regularly to evaluate IFN-γ, TNF-α, IL-4, IL-6, and IL-10. Clinical, laboratory, radiological data, and outcomes were recorded. The outcome variable was in-hospital death, survival, mechanical ventilation, and admission at the intensive care unit. Data are presented in median and interquartile range [IQR].

RESULTS

We evaluated the Th1 and Th2 responses according to evolution, distinguishing possible predictive markers. The IFN-γ median of 323 pg/mL [IQR 166-570] was found in patients who died and 208 pg/mL [IQR 155-392] in the survival group (p = 0.017). IFN-γ was also higher in the early stages of the disease (394 pg/mL [IQR 229-575] against 162 pg/mL [IQR 117-259], p < 0.001). IL-4 that was increased in late-stage (182 pg/mL [IQR 162-199] against 131 pg/mL [IQR 124-152], p < 0.001) but not associated with mortality. Also, death was also related to male gender (relative risk = 1.5 [95 % confidence interval = 1.1-2.0]).

CONCLUSION

Our results suggest that the activation of the host immune response between Th1 or Th2 in COVID-19 infection may be related to the final result between discharge or death. This implies an attempt to control cytokines, such as IFN-γ, with combined therapies for clinical treatment.

Immunopathology and immunotherapeutic strategies in severe acute respiratory syndrome coronavirus 2 infection

The outbreak of coronavirus disease 2019 (COVID-19) and pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a major concern globally. As of 14 April 2020, more than 1.9 million COVID-19 cases have been reported in 185 countries. Some patients with COVID-19 develop severe clinical manifestations, while others show mild symptoms, suggesting that dysregulation of the host immune response contributes to disease progression and severity. In this review, we have summarized and discussed recent immunological studies focusing on the response of the host immune system and the immunopathology of SARS-CoV-2 infection as well as immunotherapeutic strategies for COVID-19. Immune evasion by SARS-CoV-2, functional exhaustion of lymphocytes, and cytokine storm have been discussed as part of immunopathology mechanisms in SARS-CoV-2 infection. Some potential immunotherapeutic strategies to control the progression of COVID-19, such as passive antibody therapy and use of interferon αβ and IL-6 receptor (IL-6R) inhibitor, have also been discussed. This may help us to understand the immune status of patients with COVID-19, particularly those with severe clinical presentation, and form a basis for further immunotherapeutic investigations.

Transcriptome analyses provide insights into maternal immune changes at several critical phases of giant panda reproduction

Giant pandas (Ailuropoda melanoleuca) possess highly specialized reproductive characteristics, but the maternal immune changes during reproduction are largely unclear. Here, 20 blood transcriptomes were used to determine immune changes at four key phases of giant panda reproduction, and a total of 4640 differential expression genes were identified. During estrus, six immune-related genes (TLR4, IL1B, SYK, SPI1, CD80, and ITK) were identified as hub genes. The up-regulation of the TLR family genes (TLR4, TLR5, TLR6, and TLR8) and inflammatory response related genes (IL1B) may reflect innate immune enhancement and local tissue remodeling events, while the up-regulation of SYK and SPI1, and the down-regulation of CD80 and ITK suggested that the enhanced humoral immunity and inhibited cellular immunity of female giant pandas during estrus. During early pregnancy, antigen presentation related genes and proinflammatory cytokine (IL1B) were down-regulated. This may indicate that partial immune functions were suppressed in early pregnancy to achieve immune tolerance, including reducing inflammatory to protect embryos. By the late pregnancy, the antiviral related genes were up-regulated to strengthen defenses against external pathogen infection. KLRK1, which acts as a primary activation receptor for NK cells, was down regulated in estrus and pregnancy, suggesting that the activities of NK cells were inhibited, and KLRK1 may play a key role in the regulation the activities of pbNK cells during reproduction of giant pandas. Our results showed that there was no significant immune change in lactating females (post-natal 2 months) compared to anestrus females. This is the first time to observe the immune changes of giant panda during the breeding period and our data is expected to provide valuable resources for further studies on reproductive immunology of giant pandas.

Control of HCV Infection by Natural Killer Cells and Macrophages

Host defense against invading pathogens within the liver is dominated by innate immunity. Natural killer (NK) cells have been implicated at all stages of hepatitis C virus (HCV) infection, from providing innate protection to contributing to treatment-induced clearance. Decreased NK cell levels, altered NK cell subset distribution, activation marker expression, and functional polarization toward a cytolytic phenotype are hallmarks of chronic HCV infection. Interferon α (IFN-α) is a potent activator of NK cells; therefore, it is not surprising that NK cell activation has been identified as a key factor associated with sustained virological response (SVR) to IFN-α-based therapies. Understanding the role of NK cells, macrophages, and other innate immune cells post-SVR remains paramount for prevention of disease pathogenesis and progression. Novel strategies to treat liver disease may be aimed at targeting these cells.

Immunological approaches and therapy in burns (Review)

Burns have become an important public health problem in the last two decades, with just over a quarter of a million deaths annually. Major burns are accompanied by a strong inflammatory response, which will most often lead to systemic response inflammatory syndrome, followed by sepsis and finally induce multiple organ failure. The main mechanism involved in wound healing after burns is the inflammatory process, characterized by the recruitment of myeloid and T cells and by the involvement of numerous cytokines, chemokines, complement fractions, as well as various growth factors. Inflammasomes, protein-based cytosolic complexes, activated during metabolic stress or infection, play a role in modulating and improving the defense capacity of the innate immune system. Nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome has been studied predominantly and several hypotheses have been issued. Restoring the balance between the pro-inflammatory response and the anti-inflammatory activity is the key element to effective therapy in burns. Severe burns require nutritional support and pharmacotherapy not only for burn area but for different pathological complications of burn injury. In-depth research is required to find new ways to modulate the defense capacity, to prevent the complications of abnormal immune response and to treat burn injuries efficiently.

Effects of probiotic supplementation on natural killer cell function in healthy elderly individuals: a meta-analysis of randomized controlled trials

To evaluate evidence for the role of probiotic supplementation in enhancing natural killer (NK) cell function in healthy elderly individuals. Five electronic databases were searched, and references of included articles and eligible reviews up to December 2019, with English language and human subject restrictions, were examined. Two independent reviewers identified randomized control trials (RCTs) of probiotic supplementation influencing NK cell function in healthy elderly individuals, assessed the quality of every article, and extracted data for subsequent meta-analysis. We identified six eligible trials including 364 healthy elderly subjects. Trials were heterogeneous in study design and probiotic supplementation (including genus, strain, dose, and duration). Five trials used Lactobacillus interventions alone or in combination with Bifidobacterium. Only one trial focused on Bacillus coagulans. The duration of supplementation ranged from 3 to 12 weeks, and the doses, from 1 × 10⁹ to 4 × 10¹⁰ colony-forming units. Pooling data of eligible trials showed that probiotics significantly (P < 0.05) increased NK cell activity in healthy elderly individuals (standardized mean difference = 0.777, 95% confidence interval: 0.187‒1.366, P = 0.01, I² = 84.6%). Although we obtained a significant outcome, the data do not provide convincing evidence for associations between probiotic supplementation and enhancement of NK cell function, given the small final number and very large heterogeneity. More RCTs with sufficient sample sizes and long-term follow-up are needed to focus on optimal probiotic dose, species, and duration of supplementation for healthy elderly individuals.

Targeting Natural Killer Cells for Improved Immunity and Control of the Adaptive Immune Response

Natural killer (NK) cells are critical for targeting and killing tumor, virus-infected and stressed cells as a member of the innate immune system. Recently, NK cells have also emerged as key regulators of adaptive immunity and have become a prominent therapeutic target for cancer immunotherapy and infection control. NK cells display a diverse array of phenotypes and function. Determining how NK cells develop and are regulated is critical for understanding their role in both innate and adaptive immunity. In this review we discuss current research approaches into NK cell adaptive immunity and how these cells are being harnessed for improving cancer and vaccination outcomes.

Mechanisms of Natural Killer Cell Evasion Through Viral Adaptation

The continuous interactions between host and pathogens during their coevolution have shaped both the immune system and the countermeasures used by pathogens. Natural killer (NK) cells are innate lymphocytes that are considered central players in the antiviral response. Not only do they express a variety of inhibitory and activating receptors to discriminate and eliminate target cells but they can also produce immunoregulatory cytokines to alert the immune system. Reciprocally, several unrelated viruses including cytomegalovirus, human immunodeficiency virus, influenza virus, and dengue virus have evolved a multitude of mechanisms to evade NK cell function, such as the targeting of pathways for NK cell receptors and their ligands, apoptosis, and cytokine-mediated signaling. The studies discussed in this article provide further insights into the antiviral function of NK cells and the pathways involved, their constituent proteins, and ways in which they could be manipulated for host benefit.

CD49a+CD49b+ NK cells induced by viral infection reflect an activated state of conventional NK cells

Natural killer (NK) cells are important innate effectors that play a pivotal role in the defense against tumors and infections and participate in regulating adaptive immunity. Recent studies have revealed phenotypic and functional heterogeneity of NK cells. Here, using murine models of acute and chronic lymphocytic choriomeningitis virus infection, we observed that a CD49a⁺ CD49b⁺ NK cell subset emerged in the liver and other tissues, and underwent vigorous expansion following viral infection, before progressively decreasing in cell number. These viral infection-induced CD49a⁺CD49b⁺ NK cells displayed an activated and mature phenotype. Moreover, compared with liver-resident NK cells and conventional NK (cNK) cells, CD49a⁺CD49b⁺ NK cells showed increased functional competence, as evidenced by higher amounts of IFN-γ production and stronger cytotoxic capabilities during viral infection. Generation of these CD49a⁺CD49b⁺ NK cells was shown to be independent of the T-bet transcription factor. Adoptive transfer experiments revealed that cNK cells could convert into CD49a⁺CD49b⁺ NK cells following viral infection. Collectively, these results suggest that viral infection-induced CD49a⁺CD49b⁺ NK cells represent a transiently activated state of cNK cells.

DNA Sensors' Signaling in NK Cells During HHV-6A, HHV-6B and HHV-7 Infection

Objectives

The host DNA sensor proteins TLR9, STING, IFI16 are central signaling molecules that control the innate immune response to cytosolic nucleic acids. Here we propose to investigate how Natural killer (NK) cell infection by human herpesvirus (HHV)-6A, HHV-6B or HHV-7 is able to modify DNA sensor signaling in NK cells.

Methods

We infected the NK92 cell line and primary NK cells with cell-free inocula of HHV-6A, HHV-6B or HHV-7 and evaluated TLR9, STING, and IFI16 pathway expression by Real-Time PCR, Western Blot, immunofluorescence and flow cytometry for 1, 2, 3, and 6 days post-infection. We evaluated NK cell cytokine-producing by Real-Time PCR and enzyme immunosorbent assay.

Results

NK92 and primary NK cells were promptly infected by three viruses, as demonstrated by virus presence (DNA) and transcription (RNA) analysis. Our data show STING/STAT6 up-modulation in HHV-6A infected NK cells. NK cells infected with HHV-6B and HHV-7 up-regulated CCL3, IFN-alpha, TNF-alpha, IL-8 and IFN-gamma and slightly induced IL-4, and CCL4. HHV-6A infected NK cells up-regulated IL-4 and IL-13 and slightly induced IL-10, TNF-alpha, IFN-alpha, and IFN-gamma.

Conclusion

For the first time, we demonstrate that HHV-6A, HHV-6B, and HHV-7 infections have a differential impact on intracellular DNA sensors. HHV-6B and HHV-7 mainly lead to the active control of in vivo viral spreading by pro-inflammatory cytokine secretion via TLR9. HHV-6A infected NK cells conversely induced STING/STAT6 pathway, as a mechanism of anti-viral activation, but they were characterized by a Th2 type response and a non-cytotoxic profile, suggesting a potential novel mechanism of HHV-6A-mediated immunosuppression.

Host immune response in chronic hepatitis C infection: involvement of cytokines and inflammasomes

Chronic liver disease is a major health issue worldwide and chronic hepatitis C (CHC) is associated with an increased risk of cirrhosis and hepatocellular carcinoma (HCC). There is evidence that the hepatitis C virus (HCV) infection is correlated with immune senescence by way of immune activation and chronic inflammation, which lead to increased metabolic and cardiovascular risk, as well as progressive liver damage. Both the innate and adaptive immunity are firmly tied to the prognosis of an infection with HCV and its response to antiviral therapy. HCV is therefore associated with increased pro-inflammatory status, heightened production of cytokines, prolonged systemic inflammation, as well as increased morbidity and mortality, mainly due to the progression of hepatic fibrosis and HCC, but also secondary to cardiovascular diseases. Viral hepatic pathology is increasingly considered a disease that is no longer merely limited to the liver, but one with multiple metabolic consequences. Numerous in vitro studies, using experimental models of acute or chronic inflammation of the liver, has brought new information on immunopathological mechanisms resulting from viral infections and have highlighted the importance of involving complex structures, inflammasomes complex, in these mechanisms, in addition to the involvement of numerous proinflammatory cytokines. Beyond obtaining a sustained viral response and halting the aforementioned hepatic fibrosis, the current therapeutic "treat-to-target" strategies are presently focused on immune-mediated and metabolic disorders, to improve the quality of life and long-term prognosis of CHC patients.

Direct antiviral agents upregulate natural killer cell potential activity in chronic hepatitis C patients

Direct antiviral agents (DAAs) can eliminate hepatitis C virus rapidly and make chronic hepatitis C (CHC) curable. The changes in the innate immune system during treatment with DAAs are still in dispute. To investigate how the functions of natural killer (NK) cells change during and after treatment with DAAs in each NK cell subset. Thirteen CHC patients were treated with sofosbuvir/ledipasvir, and the expression levels of NKp46 and NKG2A were tested via flow cytometry at baseline, at 2, 4, 8 and 12 weeks during the therapy and 12 and 24 weeks after the end of treatment; expression levels were compared between CHC patients and 13 healthy controls. A redirected killing assay was used to detect the cytotoxicity of NK cells. After coculturing NK cells with JFH-Huh7 cells for 72 h, HCV RNA was tested to analyze the inhibition ability of NK cells. All patients achieved sustained virologic response. The expression of the activating receptor NKp46 was decreased first at week 8 during therapy with DAAs and then increased and normalized to levels in healthy controls after treatment with DAAs. The expression of the inhibitory receptor NKG2A was decreased during and after treatment with DAAs. Each NK cell subset has a similar changing trend during and after treatment with DAAs, although some differences can be found earlier and later. The ratio of NKp46 and NKG2A was upregulated after treatment with DAAs. CD56bright NK cells have less amplitude in the frequency ratio changes after treatment with DAAs. The coculture results showed that both the specific lysis and the inhibition of HCV replication were significantly upregulated after treatment with DAAs. DAA treatments can affect patients' NK cell function. After DAA treatments, the expression of functional markers is downregulated, but the potential activity of NK cells is upregulated. The function of NK cells is normalized to levels in healthy controls. CD56bright NK cells play an important role in this process.

Human NK cell receptor KIR2DS4 detects a conserved bacterial epitope presented by HLA-C

Natural killer (NK) cells have an important role in immune defense against viruses and cancer. Activation of human NK cell cytotoxicity toward infected or tumor cells is regulated by killer cell immunoglobulin-like receptors (KIRs) that bind to human leukocyte antigen class I (HLA-I). Combinations of KIR with HLA-I are genetically associated with susceptibility to disease. KIR2DS4, an activating member of the KIR family with poorly defined ligands, is a receptor of unknown function. Here, we show that KIR2DS4 has a strong preference for rare peptides carrying a Trp at position 8 (p8) of 9-mer peptides bound to HLA-C*05:01. The complex of a peptide bound to HLA-C*05:01 with a Trp at p8 was sufficient for activation of primary KIR2DS4+ NK cells, independent of activation by other receptors and of prior NK cell licensing. HLA-C*05:01+ cells that expressed the peptide epitope triggered KIR2DS4+ NK cell degranulation. We show an inverse correlation of the worldwide allele frequency of functional KIR2DS4 with that of HLA-C*05:01, indicative of functional interaction and balancing selection. We found a highly conserved peptide sequence motif for HLA-C*05:01-restricted activation of human KIR2DS4+ NK cells in bacterial recombinase A (RecA). KIR2DS4+ NK cells were stimulated by RecA epitopes from multiple human pathogens, including Helicobacter, Chlamydia, Brucella, and Campylobacter. We predict that over 1,000 bacterial species could activate NK cells through KIR2DS4, and propose that human NK cells also contribute to immune defense against bacteria through recognition of a conserved RecA epitope presented by HLA-C*05:01.

JAK/STAT signaling in regulation of innate lymphoid cells: The gods before the guardians

Immunity to pathogens is ensured through integration of early responses mediated by innate cells and late effector functions taking place after terminal differentiation of adaptive lymphocytes. In this context, innate lymphoid cells (ILCs) and adaptive T cells represent a clear example of how prototypical effector functions, including polarized expression of cytokines and/or cytotoxic activity, can occur with overlapping modalities but different timing. The ability of ILCs to provide early protection relies on their poised epigenetic state, which determines their propensity to quickly respond to cytokines and to activate specific patterns of signal-dependent transcription factors. Cytokines activating the Janus kinases (JAKs) and members of the signal transducer and activator of transcription (STAT) pathway are key regulators of lymphoid development and sustain the processes underlying T-cell activation and differentiation. The role of the JAK/STAT pathway has been recently extended to several aspects of ILC biology. Here, we discuss how JAK/STAT signals affect ILC development and effector functions in the context of immune responses, highlighting the molecular mechanisms involved in regulation of gene expression as well as the potential of targeting the JAK/STAT pathway in inflammatory pathologies.

Characterization of human natural killer cells for therapeutic use

As a part of the innate immune system, natural killer (NK) cells are cytotoxic lymphocytes that can exert cytotoxic activity against infected or transformed cells. Furthermore, due to their expression of a functional Fc receptor, they have also been eluded as a major effector fraction in antibody-dependent cellular cytotoxicity. These characteristics have led to multiple efforts to use them for adoptive immunotherapy against various malignancies.  There are now at least 70 clinical trials testing the safety and efficacy of NK cell products around the world in early-phase clinical trials. NK cells are also being tested in the context of tumor retargeting via chimeric antigen receptors, other genetic modification strategies, as well as tumor-specific activation strategies such as bispecific engagers with or without cytokine stimulations. One advantage of the use of NK cells for adoptive immunotherapy is their potential to overcome HLA barriers. This has led to a plethora of sources, such as cord blood hematopoietic stem cells and induced pluripotent stem cells, which can generate comparatively high cytotoxic NK cells to peripheral blood counterparts. However, the variety of the sources has led to a heterogeneity in the characterization of the final infusion product. Therefore, in this review, we will discuss a comparative assessment strategy, from characterization of NK cells at collection to final product release by various phenotypic and functional assays, in an effort to predict potency of the cellular product.

Enhancing the natural killer cell activity and anti-influenza effect of heat-treated Lactobacillus plantarum nF1-fortified yogurt in mice

Influenza A virus (IAV) infection is a global public health concern. It causes respiratory diseases ranging from mild illness to fatal disease. Natural killer (NK) cells are an innate immune component that kill infected cells and secrete cytokines to modulate the adaptive immune system; they constitute the first-line defense and play important roles in controlling IAV infection. This study evaluated the effect of daily administration of heat-treated Lactobacillus plantarum nF1-fortified yogurt on immunity and protection against IAV infection. Mice administered with heat-treated L. plantarum nF1-fortified yogurt showed elevated NK cell-related cytokine expression levels. Daily administration of the L. plantarum nF1-fortified yogurt before IAV infection also enhanced splenic NK activity, lung inflammatory cytokine responses, and survival rate. Thus, daily administration of nF1-fortified yogurt enhances host immunity and helps prevent IAV infection.

Is There Natural Killer Cell Memory and Can It Be Harnessed by Vaccination? Can Natural Killer and CD8 T Cells Switch Jobs?

Natural killer (NK) cells are components of innate immunity mediating defense at early times after viral infections. Their cytokine production and cell-mediated cytotoxicity functions overlap those of CD8 T cells elicited later during primary adaptive immune responses, but the populations are distinguished by their basal states and activating receptors as well as the kinetics of their responses. Demonstration of long-lived NK cells has led to speculation on the potential for inducing these to contribute to immunological memory. Conversely, activated CD8 T cells can acquire responses to innate cytokines and, as a result, have the potential to contribute to innate immunity. These observations beg the question: what is required to be a player in innate and adaptive immunity?