Alveolar macrophage inhibition of lung-associated NK activity: involvement of prostaglandins and transforming growth factor-beta 1

Modulation of natural killer cell exhaustion in the lungs: the key components from lung microenvironment and lung tumor microenvironment

Lung cancer is the leading cause of tumor-induced death worldwide and remains a primary global health concern. In homeostasis, due to its unique structure and physiological function, the lung microenvironment is in a state of immune tolerance and suppression, which is beneficial to tumor development and metastasis. The lung tumor microenvironment is a more complex system that further enhances the immunosuppressive features in the lungs. NK cells are abundantly located in the lungs and play crucial roles in lung tumor surveillance and antitumor immunity. However, the immunosuppressive microenvironment promotes significant challenges to NK cell features, leading to their hypofunction, exhaustion, and compromised antitumor activity. Thus, understanding the complex interactions among the lung microenvironment, lung tumor microenvironment, and NK cell exhaustion is critical for the development of effective cancer immunotherapeutic strategies. The present review will discuss NK cell hypofunction and exhaustion within the lung microenvironment and lung tumor microenvironment, focusing on lung tissue-specific factors, including key cytokines and unique environmental components, that modulate NK cell activation and function. Understanding the functional mechanisms of key factors would help to design strategies to reverse NK cell exhaustion and restore their antitumor function within the lung tumor microenvironment.

Natural killer cells in the lung: potential role in asthma and virus-induced exacerbation?

Asthma is a chronic inflammatory airway disorder whose pathophysiological and immunological mechanisms are not completely understood. Asthma exacerbations are mostly driven by respiratory viral infections and characterised by worsening of symptoms. Despite current therapies, asthma exacerbations can still be life-threatening. Natural killer (NK) cells are innate lymphoid cells well known for their antiviral activity and are present in the lung as circulating and resident cells. However, their functions in asthma and its exacerbations are still unclear. In this review, we will address NK cell activation and functions, which are particularly relevant for asthma and virus-induced asthma exacerbations. Then, the role of NK cells in the lungs at homeostasis in healthy individuals will be described, as well as their functions during pulmonary viral infections, with an emphasis on those associated with asthma exacerbations. Finally, we will discuss the involvement of NK cells in asthma and virus-induced exacerbations and examine the effect of asthma treatments on NK cells.

Bortezomib Augments Natural Killer Cell Targeting of Stem-Like Tumor Cells

Tumor cells harboring stem-like/cancer stem cell (CSC) properties have been identified and isolated from numerous hematological and solid malignancies. These stem-like tumor cells can persist following conventional cytoreductive therapies, such as chemotherapy and radiotherapy, thereby repopulating the tumor and seeding relapse and/or metastasis. We have previously shown that natural killer (NK) cells preferentially target stem-like tumor cells via non- major histocompatibility complex (MHC) restricted mechanisms. Here, we demonstrated that the proteasome inhibitor, bortezomib, augments NK cell targeting of stem cell-like tumor cells against multiple solid human tumor-derived cancer lines and primary tissue samples. Mechanistically, this was mediated by the upregulation of cell surface NK ligands MHC class I chain-related protein A and B (MICA and MICB) on aldehyde dehydrogenases (ALDH)-positive CSCs. The increased expression of MICA and MICB on CSC targets thereby enhanced NK cell mediated killing in vitro and ex vivo from both human primary tumor and patient-derived xenograft samples. In vivo, the combination of bortezomib and allogeneic NK cell adoptive transfer in immunodeficient mice led to increased elimination of CSCs as well as tumor growth delay of orthotopic glioblastoma tumors. Taken together, our data support the combination bortezomib and NK transfer as a strategy for both CSC targeting and potentially improved outcomes in clinical cancer patients.

The yin-yang of the interaction between myelomonocytic cells and NK cells

NK cells are innate lymphoid cells, which play a key role in the immune response to cancer and pathogens and participate in the shaping of adaptive immunity. NK cells engage in a complex bidirectional interaction with myelomonocytic cells. In particular, macrophages, dendritic cells and neutrophils promote differentiation and effector function of NK cells and, on the other hand, myelomonocytic cells express triggers of checkpoint blockade (eg PD-L1) and other immunosuppressive molecules, which negatively regulate NK cell function. In addition, NK cells express high levels of IL-1R8, which acts as a checkpoint for IL-18 driven differentiation and activation of NK cells. Evidence suggests that targeting the myeloid cell-NK cell crosstalk unleashes effective anti-tumour and anti-viral resistance.

Local Microenvironment Controls the Compartmentalization of NK Cell Responses during Systemic Inflammation in Mice

Systemic inflammatory response syndrome is a whole-body reaction to a triggering insult that often results in life-threatening illness. Contributing to the development of this inflammatory cascade are numerous cellular partners, among which NK cells were shown to play a key role. Accumulating evidence points to organ-specific properties of systemic inflammation and NK cells. However, little is known about compartment-specific activation of NK cells during systemic inflammatory response syndrome or the relative contribution of NK cell-intrinsic properties and microenvironmental cues. In this study, we undertook a sequential characterization of NK responses in the spleen, lungs, bone marrow, peritoneum, and blood using a mouse model of endotoxemia. We report that, despite similar systemic dynamics of NK cell responses, expression of activation markers (CD69 and CD25) and effector molecules (IFN-γ, granzyme B, and IL-10) display organ-specific thresholds of maximum activation. Using adoptive transfers of spleen and lung NK cells, we found that these cells have the capacity to quickly adapt to a new environment and adjust their response levels to that of resident NK cells. This functional adaptation occurs without significant alterations in phenotype and independently of subpopulation-specific trafficking. Thus, using a dynamic in vivo-transfer system, to our knowledge our study is the first to report the compartmentalization of NK cells responses during systemic inflammation and to show that NK cell-intrinsic properties and microenvironmental cues are involved in this process, in a sequential manner.

Conditional ablation of NKp46+ cells using a novel Ncr1(greenCre) mouse strain: NK cells are essential for protection against pulmonary B16 metastases

To study gene functions specifically in NKp46+ cells we developed novel Cre mice allowing for conditional gene targeting in cells expressing Ncr1 (encoding NKp46). We generated transgenic Ncr1(greenCre) mice carrying an EGFPcre fusion under the control of a proximal Ncr1 promoter that faithfully directed EGFPcre expression to NKp46+ cells from lymphoid and nonlymphoid tissues. This approach allowed for direct detection of Cre-expressing NKp46+ cells via their GFP signature by flow cytometry and histology. Cre was functional as evidenced by the NKp46+ cell-specific expression of RFP in Ncr1(greenCre) Rosa-dtRFP reporter mice. We generated Ncr1(greenCre) Il2rg(fl/fl) mice that lack NKp46+ cells in an otherwise intact hematopoietic environment. Il2rg encodes the common gamma chain (γc ), which is an essential receptor subunit for cytokines (IL-2, -4, -7, -9, -15, and -21) that stimulate lymphocyte development and function. In Ncr1(greenCre) Il2rg(fl/fl) mice, NK cells are severely reduced and the few remaining NKp46+ cells escaping γc deletion failed to express GFP. Using this new NK-cell-deficient model, we demonstrate that the homeostasis of NKp46+ cells from all tissues (including the recently described intraepithelial ILC1 subset) requires Il2rg. Finally, Ncr1(greenCre) Il2rg(fl/fl) mice are unable to reject B16 lung metastases demonstrating the essential role of NKp46+ cells in antimelanoma immune responses.

Tissue-specific effector functions of innate lymphoid cells

Innate lymphoid cells (ILCs) is the collective term for a group of related innate lymphocytes, including natural killer (NK) cells and the more recently discovered non-NK ILCs, which all lack rearranged antigen receptors such as those expressed by T and B cells. Similar to NK cells, the newly discovered ILCs depend on the transcription factor Id2 and the common γ-chain of the interleukin-2 receptor for development. However, in contrast to NK cells, non-NK ILCs also require interleukin-7. In addition to the cytotoxic functions of NK cells, assuring protection against tumour development and viruses, new data indicate that ILCs contribute to a wide range of homeostatic and pathophysiological conditions in various organs via specialized cytokine production capabilities. Here we summarize current knowledge on ILCs with a particular emphasis on their tissue-specific effector functions, in the gut, liver, lungs and uterus. When possible, we try to highlight the role that these cells play in humans.

NK cells in immunotolerant organs

Organs such as the liver, uterus and lung possess hallmark immunotolerant features, making these organs important for sustaining self-homeostasis. These organs contain a relatively large amount of negative regulatory immune cells, which are believed to take part in the regulation of immune responses. Because natural killer cells constitute a large proportion of all lymphocytes in these organs, increasing attention has been given to the roles that these cells play in maintaining immunotolerance. Here, we review the distribution, differentiation, phenotypic features and functional features of natural killer cells in these immunotolerant organs, in addition to the influence of local microenvironments on these cells and how these factors contribute to organ-specific diseases.

Consequences of the crosstalk between monocytes/macrophages and natural killer cells

The interaction between natural killer (NK) cells and different other immune cells like T cells and dendritic cells is well-described, but the crosstalk with monocytes or macrophages and the nature of ligands/receptors implicated are just emerging. The macrophage-NK interaction is a major first-line defense against pathogens (bacteria, viruses, fungi, and parasites). The recruitment and the activation of NK cells to perform cytotoxicity or produce cytokines at the sites of inflammation are important to fight infections. The two main mechanisms by which macrophages can prime NK cells are (1) activation through soluble mediators such as IL-12, IL-18, and (2) stimulation through direct cell-to-cell contact. We will discuss the progress in matters of modulation of NK cell functions by monocytes and macrophages, in the steady state and during diseases.

Role of transforming growth factor-beta(1) in down-regulating TNF production by alveolar macrophages during asbestos-induced pulmonary fibrosis

Activation of alveolar macrophages (AM) for tumour necrosis factor production is suppressed initially during the inflammatory response to fibrogenic dusts. We investigated the mechanisms involved in TNF suppression, notably the role of other AM-derived mediators including prostaglandin E₂ (PGE₂), transforming growth factor-β₁ (TGF-β₁), and interleukin 6 (IL-6). The action of PGE₂ and TGF-β₁, on AM was different. At physiologically relevant doses (25–300 pg/ml), PGE₂ did not cause significant inhibition of Hpopolysaccharide (Lps)-induced TNF release by AM in vitro but stimulated IL-6 (up to six fold), an inhibitor of AM-derived TNT. In contrast, TGF-β₁ (0.5–50 ng/ml) inhibited both LPS-induced TNT and IL-6 release by 50% but had no effect on PGE₂ production by AM. To determine the respective contribution of these different inhibitors in TNF suppression, AM from rats exposed to fibrogenic asbestos for weeks were treated with neutralizing antibody against TGF-β₁ or indomethacin, an inhibitor of PGE₂ synthesis. Treatment of rat AM with anti-TGF-β₁ but not indomethacin, abrogated the observed TNT suppression. These results suggest that an autocrine, TGF-β₁-dependent mechanism is involved in the down-regulation of TNF production by rat AM from animals with lung fibrosis.

Natural killer (NK) cells in antibacterial innate immunity: angels or devils?

Natural killer (NK) cells were first described as immune leukocytes that could kill tumor cells and soon after were reported to kill virus-infected cells. In the mid-1980s, 10 years after their discovery, NK cells were also demonstrated to contribute to the fight against bacterial infection, particularly because of crosstalk with other leukocytes. A wide variety of immune cells are now recognized to interact with NK cells through the production of cytokines such as interleukin (IL)-2, IL-12, IL-15 and IL-18, which boost NK cell activities. The recent demonstration that NK cells express pattern recognition receptors, namely Toll-like and nucleotide oligomerization domain (NOD)-like receptors, led to the understanding that these cells are not only under the control of accessory cells, but can be directly involved in the antibacterial response thanks to their capacity to recognize pathogen-associated molecular patterns. Interferon (IFN)-γ is the predominant cytokine produced by activated NK cells. IFN-γ is a key contributor to antibacterial immune defense. However, in synergy with other inflammatory cytokines, IFN-γ can also lead to deleterious effects similar to those observed during sepsis. Accordingly, as the main source of IFN-γ in the early phase of infection, NK cells display both beneficial and deleterious effects, depending on the circumstances.

Natural killer cells in infection and inflammation of the lung

The lungs are a major site of entry of pathogens into the body and thus require rapid and effective innate responses to prevent pathogens establishing infection and to limit their spread. Additionally, the immune response in the lung must be tightly regulated such that pathogens are cleared, but immunopathology and chronic inflammation are prevented. In this review, I consider the role of natural killer (NK) cells in pulmonary infection and inflammation, specifically their contributions to influenza, tuberculosis, asthma and chronic obstructive pulmonary disease (COPD), which are major causes of morbidity and mortality world-wide. Despite evidence of the importance of NK cells in these diseases, there are still major gaps in our understanding of how their function is regulated in this unique tissue environment. Understanding how different beneficial and detrimental effector functions of NK cells are triggered will be crucial if NK cells are to be exploited therapeutically in respiratory disease.

Active suppression of the pulmonary immune response by Francisella tularensis Schu4

Francisella tularensis is an obligate, intracellular bacterium that causes acute, lethal disease following inhalation. As an intracellular pathogen F. tularensis must invade cells, replicate, and disseminate while evading host immune responses. The mechanisms by which virulent type A strains of Francisella tularensis accomplish this evasion are not understood. Francisella tularensis has been shown to target multiple cell types in the lung following aerosol infection, including dendritic cells (DC) and macrophages. We demonstrate here that one mechanism used by a virulent type A strain of F. tularensis (Schu4) to evade early detection is by the induction of overwhelming immunosuppression at the site of infection, the lung. Following infection and replication in multiple pulmonary cell types, Schu4 failed to induce the production of proinflammatory cytokines or increase the expression of MHCII or CD86 on the surface of resident DC within the first few days of disease. However, Schu4 did induce early and transient production of TGF-beta, a potent immunosuppressive cytokine. The absence of DC activation following infection could not be attributed to the apoptosis of pulmonary cells, because there were minimal differences in either annexin or cleaved caspase-3 staining in infected mice compared with that in uninfected controls. Rather, we demonstrate that Schu4 actively suppressed in vivo responses to secondary stimuli (LPS), e.g., failure to recruit granulocytes/monocytes and stimulate resident DC. Thus, unlike attenuated strains of F. tularensis, Schu4 induced broad immunosuppression within the first few days after aerosol infection. This difference may explain the increased virulence of type A strains compared with their more attenuated counterparts.

Prostaglandin e(2) suppresses NK activity in vivo and promotes postoperative tumor metastasis in rats

BACKGROUND

Prostaglandins (PGs) were shown in vitro to suppress several functions of cellular immunity. It is unclear, however, whether physiological levels of PGs can suppress cellular immunity in vivo and whether such suppression would compromise postoperative host resistance to metastasis.

METHODS

Fischer 344 rats were administered PGE(2) in doses (18 to 300 micro g/kg subcutaneously) that increased the serum levels approximately 2- to 4-fold. We then assessed the number and activity of circulating natural killer (NK) cells, as well as rats' resistance to experimental metastasis of a syngeneic NK-sensitive tumor (MADB106). To study whether endogenously released PGs after surgery compromise these indices, we tested whether laparotomy adversely affects them and whether a cyclooxygenase-synthesis inhibitor, indomethacin (4 mg/kg), attenuates these effects.

RESULTS

PGE(2) dose-dependently suppressed NK activity per NK cell and dose-dependently increased 4- and 24-hour MADB106 lung tumor retention (LTR); 240 micro g/kg of PGE(2) quadrupled the number of lung metastases counted 3 weeks later. Selective depletion of NK cells abrogated the promotion of LTR by PGE(2). Surgery significantly suppressed NK activity and increased MADB106 LTR, and indomethacin halved these effects without affecting nonoperated rats.

CONCLUSIONS

PGE(2) is a potent in vivo suppressor of NK activity, and its postoperative release may promote tumor recurrence.

Natural killer cell activity in patients with Graves' disease and Hashimoto's thyroiditis

Natural killer (NK) cell activity of peripheral blood lymphocytes (PBL) against k562 human tumor cell targets was studied in patients with Graves' disease and Hashimoto's thyroiditis. NK activity was measured in a standard 4-hour 51chromium (Cr) release assay. Cytotoxicity was expressed as lytic units (LU)/10(6) PBL. Significantly decreased NK cell activity was demonstrated in both groups of patients, with mean (+/- SE) lytic units of 10.3 (+/- 9.1) and 13.3 (+/- 10.3) for patients with Graves' disease and Hashimoto's thyroiditis, respectively, compared with 36.0 (+/- 26.3) for age- and sex-matched normal subjects. When patients with Graves' disease were analyzed according to their thyroid status; NK activity was significantly depressed in (1) hyperthyroid patients before treatment; (2) hyperthyroid patients receiving antithyroid therapy; and (3) euthyroid patients receiving antithyroid therapy, compared with normal subjects. Graves' disease patients who were hypothyroid after radioactive iodine therapy or thyroidectomy had normal NK activity. No significant differences between hyperthyroid and euthyroid patients or between hypothyroid patients and normal subjects were demonstrated. NK activity in patients with Graves' disease did not correlate with serum levels of thyroxine, the presence or severity of ophthalmopathy, or titers of serum thyroid antibodies. In patients with Hashimoto's thyroiditis there was no correlation between NK activity and goiter size, titers of antithyroid antibodies, or thyroid status. These findings suggest that depression of NK activity in both disorders is secondary to abnormalities of thyroid hormone secretion, although an effect of the underlying autoimmune reactions has not been excluded.

Generation of an Inhibitory Circuit Involving CD8+ T Cells, IL-2, and NK Cell-Derived TGF-β: Contrasting Effects of Anti-CD2 and Anti-CD3

Although the phenomenon of immunosuppression is well established, the mechanisms involved in the generation of lymphocytes with down-regulatory activity are poorly understood. Unlike anti-CD3 antibodies, mitogenic combinations of anti-CD2 antibodies do not stimulate human PBL to produce IgM or IgG. In determining the reason for this difference, we have found that anti-CD2 triggers an inhibitory circuit facilitated by TGF-β provided by NK cells. Stimulation of PBL with anti-CD2, but not anti-CD3, generated substantial amounts of active TGF-β. NK cells were found to be a significant source of TGF-β and were the only lymphocyte population that constitutively produced this cytokine. Anti-CD2 enhanced the production of active TGF-β by purified NK cells. TGF-β. After the removal of NK cells or the addition of anti-TGF-β, anti-CD2 could stimulate Ig production. Anti-TGF-β had to be added within the first 24 h for a maximal effect. Moreover, a short, overnight exposure of CD8+ T cells to TGF-β could prime them for suppressor activity provided that IL-2 was also present. Thus, the presence of active TGF-β coincident with CD8+ T cell activation can condition these cells to mediate down-regulatory activity, and NK cells can serve as the source of this cytokine.

The immunoregulatory effects of NK cells: the role of TGF-beta and implications for autoimmunity

The cytotoxic activities of natural killer (NK) cells--important in innate immunity--have received considerable attention, but NK cells also regulate T- and B-cell functions as well as hematopoiesis. Here, David Horwitz and colleagues focus on the capacity of NK cells to regulate antibody production positively and negatively, and in particular on the role of NK-cell transforming growth factor beta (TGF-beta) in downregulation of B-cell activity.

Low serum M-CSF levels are associated with unexplained recurrent abortion

PROBLEM

The purpose of this study was to determine whether the serum macrophage-colony stimulating factor (M-CSF) level is associated with early pregnancy loss in unexplained recurrent spontaneous abortion (RSA) patients.

METHOD

We therefore compared preconceptional serum M-CSF levels between unexplained RSA patients and controls. The former comprised 44 bed-rest therapy patients and 43 intradermal immunization (IDI) patients receiving paternal lymphocyte therapy, who had experienced two and three or more consecutive first-trimester pregnancy losses, respectively. The controls were 46 healthy non-pregnant women. We also prospectively studied the association between M-CSF levels during pregnancy and adverse pregnancy outcomes. Sera from a total of 31 pregnant women, including 16 of the bed-rest therapy group and 15 of the IDI therapy group, were collected at the 4th, 6th, and 8th gestational weeks and were measured for M-CSF levels, using the enzyme-linked immunoadsorbent assay (ELISA) method established by Hanamura et al.

RESULTS

Serum M-CSF levels were significantly lower in the non-pregnant RSA patients (460.0 +/- 185.6 U/ml; mean +/- SD) than in the control group (726.5 +/- 134.0 U/ml) and also were lower at the 8th, but not the 4th or 6th gestational week in those patients of both the bed-rest and IDI therapy groups whose outcome was pregnancy failure.

CONCLUSION

Thus a low level of serum M-CSF was found to be associated with unexplained recurrent pregnancy loss in both the preconceptional and conceptional phases. These results raise the possibility that M-CSF may play an important role in the maintenance of pregnancy and that it can be used as a parameter for determining individuals at risk.