The role of natural killer cells in the defense against Listeria monocytogenes lessons from a rat model

Natural Killer Cells and Cytotoxic T Cells: Complementary Partners against Microorganisms and Cancer

Natural killer (NK) cells and cytotoxic T (CD8+) cells are two of the most important types of immune cells in our body, protecting it from deadly invaders. While the NK cell is part of the innate immune system, the CD8+ cell is one of the major components of adaptive immunity. Still, these two very different types of cells share the most important function of destroying pathogen-infected and tumorous cells by releasing cytotoxic granules that promote proteolytic cleavage of harmful cells, leading to apoptosis. In this review, we look not only at NK and CD8+ T cells but also pay particular attention to their different subpopulations, the immune defenders that include the CD56+CD16dim, CD56dimCD16+, CD57+, and CD57+CD16+ NK cells, the NKT, CD57+CD8+, and KIR+CD8+ T cells, and ILCs. We examine all these cells in relation to their role in the protection of the body against different microorganisms and cancer, with an emphasis on their mechanisms and their clinical importance. Overall, close collaboration between NK cells and CD8+ T cells may play an important role in immune function and disease pathogenesis. The knowledge of how these immune cells interact in defending the body against pathogens and cancers may help us find ways to optimize their defensive and healing capabilities with methods that can be clinically applied.

Recognition of Listeria monocytogenes infection by natural killer cells: Towards a complete picture by experimental studies in rats

The study of cellular immune responses in animal disease models demands detailed knowledge of development, function, and regulation of immune cells, including natural killer (NK) cells. Listeria monocytogenes (LM) bacterium has been explored in a large area of research fields, including the host pathogen interaction. Although the importance role of NK cells in controlling the first phase of LM burden has been investigated, the interaction between NK cells and infected cells in details are far from being comprehended. From in vivo and in vitro experiments, we can drive several important pieces of knowledge that hopefully contribute to illuminating the intercommunication between LM-infected cells and NK cells. Experimental studies performed in rats revealed that certain NK cell ligands are influenced in LM-infected cells. These ligands include both classical- and non-classical MHC class I molecules and C-type lectin related (Clr) molecules that are ligands for Ly49- and NKR-P1 receptors respectively. Interaction between these receptors:ligands during LM infection, demonstrated stimulation of rat NK cells. Hence, these studies provided additional knowledge to the mechanisms NK cells utilise to recognise and respond to LM infection outlined in the current review.

Effect of the Microbiome on Intestinal Innate Immune Development in Early Life and the Potential Strategy of Early Intervention

Early life is a vital period for mammals to be colonized with the microbiome, which profoundly influences the development of the intestinal immune function. For neonates to resist pathogen infection and avoid gastrointestinal illness, the intestinal innate immune system is critical. Thus, this review summarizes the development of the intestinal microbiome and the intestinal innate immune barrier, including the intestinal epithelium and immune cells from the fetal to the weaning period. Moreover, the impact of the intestinal microbiome on innate immune development and the two main way of early-life intervention including probiotics and fecal microbiota transplantation (FMT) also are discussed in this review. We hope to highlight the crosstalk between early microbial colonization and intestinal innate immunity development and offer some information for early intervention.

Listeria monocytogenes Inoculation Impedes the Development of Brain Pathology in Experimental Cerebral Malaria by Inhibition of Parasitemia

Cerebral malaria (CM) is a serious central nervous system dysfunction caused by Plasmodium falciparum infection. In this study, we investigated the effect of Listeria monocytogenes (Lm) inoculation on experimental cerebral malaria (ECM) using Plasmodium berghei ANKA (PbA)-infected C57BL/6 mice. Live Lm inoculation inhibited the parasitemia and alleviated ECM symptoms. The protective effect against ECM symptoms was connected with improved brain pathology manifested as a less-damaged blood-brain barrier, decreased parasite sequestration, and milder local inflammation. Meanwhile, Lm inoculation decreased expression of cell adhesion molecules (ICAM-1 and VCAM-1) and accumulation of pathogenic CD8⁺ T cells in the brain. In keeping with the suppression of parasitemia, there was an upregulation of IFN-γ, IL-12, MCP-1, and NO expression in the spleen by Lm inoculation upon PbA infection. Early treatment with exogenous IFN-γ exhibited a similar effect to Lm inoculation on PbA infection. Taken together, Lm inoculation impedes the development of brain pathology in ECM, and early systemic IFN-γ production may play a critical role in these protective effects.

The role of natural killer cells in Parkinson's disease

Numerous lines of evidence indicate an association between sustained inflammation and Parkinson's disease, but whether increased inflammation is a cause or consequence of Parkinson's disease remains highly contested. Extensive efforts have been made to characterize microglial function in Parkinson's disease, but the role of peripheral immune cells is less understood. Natural killer cells are innate effector lymphocytes that primarily target and kill malignant cells. Recent scientific discoveries have unveiled numerous novel functions of natural killer cells, such as resolving inflammation, forming immunological memory, and modulating antigen-presenting cell function. Furthermore, natural killer cells are capable of homing to the central nervous system in neurological disorders that exhibit exacerbated inflammation and inhibit hyperactivated microglia. Recently, a study demonstrated that natural killer cells scavenge alpha-synuclein aggregates, the primary component of Lewy bodies, and systemic depletion of natural killer cells results in exacerbated neuropathology in a mouse model of alpha-synucleinopathy, making them a highly relevant cell type in Parkinson's disease. However, the exact role of natural killer cells in Parkinson's disease remains elusive. In this review, we introduce the systemic inflammatory process seen in Parkinson's disease, with a particular focus on the direct and indirect modulatory capacity of natural killer cells in the context of Parkinson's disease.

Human Gut-Associated Natural Killer Cells in Health and Disease

It is well established that natural killer (NK) cells are involved in both innate and adaptive immunity. Indeed, they can recognize molecules induced at the cell surface by stress signals and virus infections. The functions of NK cells in the gut are much more complex. Gut NK cells are not precisely organized in lymphoid aggregates but rather scattered in the epithelium or in the stroma, where they come in contact with a multitude of antigens derived from commensal or pathogenic microorganisms in addition to components of microbiota. Furthermore, NK cells in the bowel interact with several cell types, including epithelial cells, fibroblasts, macrophages, dendritic cells, and T lymphocytes, and contribute to the maintenance of immune homeostasis and development of efficient immune responses. NK cells have a key role in the response to intestinal bacterial infections, primarily through production of IFNγ, which can stimulate recruitment of additional NK cells from peripheral blood leading to amplification of the anti-bacterial immune response. Additionally, NK cells can have a role in the pathogenesis of gut autoimmune inflammatory bowel diseases (IBDs), such as Crohn's Disease and Ulcerative Colitis. These diseases are considered relevant to the generation of gastrointestinal malignancies. Indeed, the role of gut-associated NK cells in the immune response to bowel cancers is known. Thus, in the gut immune system, NK cells play a dual role, participating in both physiological and pathogenic processes. In this review, we will analyze the known functions of NK cells in the gut mucosa both in health and disease, focusing on the cross-talk among bowel microenvironment, epithelial barrier integrity, microbiota, and NK cells.

Polymicrobial sepsis influences NK-cell-mediated immunity by diminishing NK-cell-intrinsic receptor-mediated effector responses to viral ligands or infections

The sepsis-induced cytokine storm leads to severe lymphopenia and reduced effector capacity of remaining/surviving cells. This results in a prolonged state of immunoparalysis, that contributes to enhanced morbidity/mortality of sepsis survivors upon secondary infection. The impact of sepsis on several lymphoid subsets has been characterized, yet its impact on NK-cells remains underappreciated–despite their critical role in controlling infection(s). Here, we observed numerical loss of NK-cells in multiple tissues after cecal-ligation-and-puncture (CLP)-induced sepsis. To elucidate the sepsis-induced lesions in surviving NK-cells, transcriptional profiles were evaluated and indicated changes consistent with impaired effector functionality. A corresponding deficit in NK-cell capacity to produce effector molecules following secondary infection and/or cytokine stimulation (IL-12,IL-18) further suggested a sepsis-induced NK-cell intrinsic impairment. To specifically probe NK-cell receptor-mediated function, the activating Ly49H receptor, that recognizes the murine cytomegalovirus (MCMV) m157 protein, served as a model receptor. Although relative expression of Ly49H receptor did not change, the number of Ly49H⁺ NK-cells in CLP hosts was reduced leading to impaired in vivo cytotoxicity and the capacity of NK-cells (on per-cell basis) to perform Ly49H-mediated degranulation, killing, and effector molecule production in vitro was also severely reduced. Mechanistically, Ly49H adaptor protein (DAP12) activation and clustering, assessed by TIRF microscopy, was compromised. This was further associated with diminished AKT phosphorylation and capacity to flux calcium following receptor stimulation. Importantly, DAP12 overexpression in NK-cells restored Ly49H/D receptors-mediated effector functions in CLP hosts. Finally, as a consequence of sepsis-dependent numerical and functional lesions in Ly49H⁺ NK-cells, host capacity to control MCMV infection was significantly impaired. Importantly, IL-2 complex (IL-2c) therapy after CLP improved numbers but not a function of NK-cells leading to enhanced immunity to MCMV challenge. Thus, the sepsis-induced immunoparalysis state includes numerical and NK-cell-intrinsic functional impairments, an instructive notion for future studies aimed in restoring NK-cell immunity in sepsis survivors.

Sepsis is an exaggerated host response to infection that can initially lead to significant morbidity/mortality and a long-lasting state of immunoparalysis in sepsis survivors. Sepsis-induced immunoparalysis functionally impairs numerous lymphocyte populations, including NK-cells. However, the scope and underlying mechanisms of NK-cell impairment and the consequences for NK-cell-mediated pathogen control remain underappreciated. NK-cells contribute to early host control of pathogens through a balance of activating and inhibitory receptors, and alterations in the number and capacity of NK-cells to exert receptor-mediated immunity can lead to dramatic impairment in host control of infection. The present study defines sepsis-induced numerical and cell-intrinsic functional impairments in NK-cell response to cytokine stimulation and receptor signaling that contribute to impaired host capacity to mount NK-cell-mediated effector responses and provide protection to bacterial and/or viral pathogens. Impairments in receptor signaling were due to reduced expression of adaptor protein DAP12. Importantly, the diminished ability of NK-cells from CLP hosts to provide anti-viral (MCMV) immunity is partially restored by IL-2 complex (IL-2c) therapy, which increased the number, but not function, of protective Ly49H⁺ NK-cells. Thus, these findings define sepsis-induced changes of the NK-cell compartment and provide insight into potential therapeutic interventions aimed at resolving sepsis-induced immunoparalysis in sepsis survivors.

Listeria monocytogenes infection enhances the interaction between rat non-classical MHC-Ib molecule and Ly49 receptors

Murine NK cell Ly49 receptors, functionally analogous to KIRs in humans recognize MHC class I molecules and play a key role in controlling NK cell function. We have previously shown that the paired activating Ly49s4 and inhibitory Ly49i4 receptors recognize undefined non-classical MHC-Ib ligands from the RT1-CE region in rats. Here, the RT1-CE16 gene of the RT1^d haplotype was stably transfected into the mouse RAW macrophage cell line, termed RAW-CE16^d cells. Combining RAW-CE16^d cells with Ly49 expressing reporter cells demonstrated Ly49i4 and Ly49s4 specificity for CE16^d. The Ly49s4/i4:CE16^d interaction was confirmed by specific MHC-I blocking monoclonal Abs. Further, we used our in vitro model to study the effect of Listeria monocytogenes (LM) on CE16^d after infection. LM infection and IFN-γ stimulation both led to enhanced CE16^d expression on the surface of transfected RAW-CE16^d cells. Interestingly, the reporter cells displayed increased response to LM-infected RAW-CE16^d cells compared with IFN-γ-treated RAW-CE16^d cells, suggesting a fundamental difference between these stimuli in supporting enhanced Ly49 recognition of CE16^d. Collectively, our data show that Ly49s4 and Ly49i4 recognize the non-classical RT1-CE16^d molecule, which in turn is up-regulated during LM infection and thereby may contribute to NK-mediated responses against infected cells.

Natural Killer Cells Mediate Protection against Yersinia pseudotuberculosis in the Mesenteric Lymph Nodes

Natural killer cells play a crucial role in the initial defense against bacterial pathogens. The crosstalk between host cells infected with intracellular pathogens and NK cells has been studied intensively, but not much attention has been given to characterize the role of NK cells in the response to extracellular bacterial pathogens such as yersiniae. In this study we used antibody-mediated NK cell depletion to address the importance of this immune cell type in controlling a Y. pseudotuberculosis infection. Analysis of the bacterial counts was used to follow the infection and flow cytometry was performed to characterize the composition and dynamic of immune cells. Depletion of NK cells led to higher bacterial loads within the mesenteric lymph nodes. We further show that in particular CD11b⁺ CD27⁺ NK cells which express higher levels of the activation marker CD69 increase within the mesenteric lymph nodes during a Y. pseudotuberculosis infection. Moreover, in response to the activation NK cells secrete higher levels of IFNy, which in turn triggers the production of the proinflammatory cytokine TNFα. These results suggest, that NK cells aid in the clearance of Y. pseudotuberculosis infections mainly by triggering the expression of proinflammatory cytokines manipulating the host immune response.

A deletion in FOXN1 is associated with a syndrome characterized by congenital hypotrichosis and short life expectancy in Birman cats

An autosomal recessive syndrome characterized by congenital hypotrichosis and short life expectancy has been described in the Birman cat breed (Felis silvestris catus). We hypothesized that a FOXN1 (forkhead box N1) loss-of-function allele, associated with the nude phenotype in humans, mice and rats, may account for the syndrome observed in Birman cats. To the best of our knowledge, spontaneous mutations in FOXN1 have never been described in non-human, non-rodent mammalian species. We identified a recessive c.1030_1033delCTGT deletion in FOXN1 in Birman cats. This 4-bp deletion was associated with the syndrome when present in two copies. Percentage of healthy carriers in our French panel of genotyped Birman cats was estimated to be 3.2%. The deletion led to a frameshift and a premature stop codon at position 547 in the protein. In silico, the truncated FOXN1 protein was predicted to lack the activation domain and critical parts of the forkhead DNA binding domain, both involved in the interaction between FOXN1 and its targets, a mandatory step to promote normal hair and thymic epithelial development. Our results enlarge the panel of recessive FOXN1 loss-of-function alleles described in mammals. A DNA test is available; it will help owners avoid matings at risk and should prevent the dissemination of this morbid mutation in domestic felines.

NK cells in mucosal defense against infection

Conventional natural killer cells (NK cells) provide continual surveillance for cancer and rapid responses to infection. They develop in the bone marrow, emerge as either NK precursor cells, immature, or mature cells, and disperse throughout the body. In the periphery NK cells provide critical defense against pathogens and cancer and are noted to develop features of adaptive immune responses. In the tightly regulated and dynamic mucosal tissues, they set up residency via unknown mechanisms and from sources that are yet to be defined. Once resident, they appear to have the ability to functionally mature dependent on the mucosal tissue microenvironment. Mucosal NK cells play a pivotal role in early protection through their cytolytic function and IFNγ production against bacteria, fungi, viruses, and parasitic infections. This review presents what is known about NK cell development and phenotypes of mucosal tissue resident conventional NK cells. The question of how they come to reside in their tissues and published data on their function against pathogens during mucosal infection are discussed. Dissecting major questions highlighted in this review will be important to the further understanding of NK cell homing and functional diversity and improve rational design of NK cell based therapies against mucosal infection.

Listeria septicaemia following insertion of a dynamic hip screw: A case report and literature review

INTRODUCTION

Listeria monocytogenes is a food borne bacterial pathogen which is rarely encountered in the United Kingdom. This rare and potentially life threatening infection has a high mortality rate and therefore requires early antimicrobial intervention.

PRESENTATION OF CASE

A case report of a patient who developed Listeria septicaemia following insertion of a dynamic hip screw is described. This 84 year old immunocompromised lady had a mechanical fall at home, from which she sustained a left neck of femur fracture. She had a background of rheumatoid arthritis, and for the last 10 years had been taking 5mg prednisolone daily. After early surgical intervention with a dynamic hip screw, she developed Listeria septicaemia, following which she was treated successfully with ampicillin and gentamicin.

DISCUSSION

Infection with unusual pathogens is not uncommon amongst immunocompromised patients. Regardless of the cause, this cohort of patients' requires increased post operative surveillance to ensure that such a complication does not go unnoticed.

CONCLUSION

This case report demonstrates the importance of having a low threshold for investigation in immunocompromised patients whilst also stressing the significance of early diagnosis and intervention.