Mechanisms of suppression of poly I:C-induced activation of NK cells by ethanol

Effect of ethanol exposure on innate immune response in sepsis

Alcohol use disorder, reported by 1 in 8 critically ill patients, is a risk factor for death in sepsis patients. Sepsis, the leading cause of death, kills over 270,000 patients in the United States alone and remains without targeted therapy. Immune response in sepsis transitions from an early hyperinflammation to persistent inflammation and immunosuppression and multiple organ dysfunction during late sepsis. Innate immunity is the first line of defense against pathogen invasion. Ethanol exposure is known to impair innate and adaptive immune response and bacterial clearance in sepsis patients. Specifically, ethanol exposure is known to modulate every aspect of innate immune response with and without sepsis. Multiple molecular mechanisms are implicated in causing dysregulated immune response in ethanol exposure with sepsis, but targeted treatments have remained elusive. In this article, we outline the effects of ethanol exposure on various innate immune cell types in general and during sepsis.

Liver Fibrosis: Mechanistic Concepts and Therapeutic Perspectives

Liver fibrosis due to viral or metabolic chronic liver diseases is a major challenge of global health. Correlating with liver disease progression, fibrosis is a key factor for liver disease outcome and risk of hepatocellular carcinoma (HCC). Despite different mechanism of primary liver injury and disease-specific cell responses, the progression of fibrotic liver disease follows shared patterns across the main liver disease etiologies. Scientific discoveries within the last decade have transformed the understanding of the mechanisms of liver fibrosis. Removal or elimination of the causative agent such as control or cure of viral infection has shown that liver fibrosis is reversible. However, reversal often occurs too slowly or too infrequent to avoid life-threatening complications particularly in advanced fibrosis. Thus, there is a huge unmet medical need for anti-fibrotic therapies to prevent liver disease progression and HCC development. However, while many anti-fibrotic candidate agents have shown robust effects in experimental animal models, their anti-fibrotic effects in clinical trials have been limited or absent. Thus, no approved therapy exists for liver fibrosis. In this review we summarize cellular drivers and molecular mechanisms of fibrogenesis in chronic liver diseases and discuss their impact for the development of urgently needed anti-fibrotic therapies.

Binge alcohol consumption 18 h after induction of sepsis in a mouse model causes rapid overgrowth of bacteria, a cytokine storm, and decreased survival

Alcohol abuse increases vulnerability to infections and infection-related mortality. In previous studies, we found that acute alcohol abuse in a binge-drinking model in mice decreased resistance to bacterial sepsis when alcohol was administered near the time of bacterial challenge. In the present study, we investigated the effects of alcohol administered later in the course of sepsis (18 h after injection of Escherichia coli). Our working hypothesis was that decreased production of cytokines caused by alcohol at this time would actually improve survival, because overproduction of pro-inflammatory mediators is thought to be the proximate cause of mortality in sepsis. Unexpectedly, administration of alcohol late in the course of sepsis led to a rapid increase in the number of viable bacteria in the peritoneal cavity. Significant increases in the concentrations of several cytokines and chemokines coincided with the increased number of bacteria in alcohol-treated mice and decreased survival time. These results demonstrated our working hypothesis to be incorrect, and reiterated the complexity of sepsis. Hypothermia is a consistent feature in this model of sepsis. In control mice (E. coli only), body temperature was near normal by 18 h or 21 h after administration of E. coli, but in mice treated with alcohol 18 h after E. coli, hypothermia was significant 3 h later and ultimately mortality was significantly increased. However, counteracting the hypothermic effect of alcohol by external warming of mice led to earlier mortality, demonstrating that hypothermia was not the major cause of mortality. These results, along with previous results from studies in which alcohol was given before initiation of sepsis, suggest that decreased cytokine and chemokine production may not be the key effect of alcohol that decreases resistance to sepsis. It seems more likely that suppression of mechanisms by which macrophages and neutrophils kill bacteria is critical, and this can occur even in the presence of high levels of cytokines and chemokines.

Alcohol, aging, and innate immunity

The global population is aging: in 2010, 8% of the population was older than 65 y, and that is expected to double to 16% by 2050. With advanced age comes a heightened prevalence of chronic diseases. Moreover, elderly humans fair worse after acute diseases, namely infection, leading to higher rates of infection-mediated mortality. Advanced age alters many aspects of both the innate and adaptive immune systems, leading to impaired responses to primary infection and poor development of immunologic memory. An often overlooked, yet increasingly common, behavior in older individuals is alcohol consumption. In fact, it has been estimated that >40% of older adults consume alcohol, and evidence reveals that >10% of this group is drinking more than the recommended limit by the National Institute on Alcohol Abuse and Alcoholism. Alcohol consumption, at any level, alters host immune responses, including changes in the number, phenotype, and function of innate and adaptive immune cells. Thus, understanding the effect of alcohol ingestion on the immune system of older individuals, who are already less capable of combating infection, merits further study. However, there is currently almost nothing known about how drinking alters innate immunity in older subjects, despite innate immune cells being critical for host defense, resolution of inflammation, and maintenance of immune homeostasis. Here, we review the effects of aging and alcohol consumption on innate immune cells independently and highlight the few studies that have examined the effects of alcohol ingestion in aged individuals.

Innate immunity in alcoholic liver disease

Excessive alcohol consumption is a leading cause of chronic liver disease in the Western world. Alcohol-induced hepatotoxicity and oxidative stress are important mechanisms contributing to the pathogenesis of alcoholic liver disease. However, emerging evidence suggests that activation of innate immunity involving TLR4 and complement also plays an important role in initiating alcoholic steatohepatitis and fibrosis, but the role of adaptive immunity in the pathogenesis of alcoholic liver disease remains obscure. Activation of a TLR4-mediated MyD88-independent (TRIF/IRF-3) signaling pathway in Kupffer cells contributes to alcoholic steatohepatitis, whereas activation of TLR4 signaling in hepatic stellate cells promotes liver fibrosis. Alcohol consumption activates the complement system in the liver by yet unidentified mechanisms, leading to alcoholic steatohepatitis. In contrast to activation of TLR4 and complement, alcohol consumption can inhibit natural killer cells, another important innate immunity component, contributing to alcohol-mediated acceleration of viral infection and liver fibrosis in patients with chronic viral hepatitis. Understanding of the role of innate immunity in the pathogenesis of alcoholic liver disease may help us identify novel therapeutic targets to treat this disease.

Toll-like receptor 3 in liver diseases

Toll-like receptor 3 (TLR3) is a member of the TLR family that can recognize double-stranded RNA (dsRNA), playing an important role in antiviral immunity. Recent studies have shown that TLR3 is also expressed on parenchymal and nonparenchymal cells in the liver as well as on several types of immune cells. In this review, we summarize the role of TLR3 in liver injury, inflammation, regeneration, and liver fibrosis, and discuss the implication of TLR3 in the pathogenesis of human liver diseases including viral hepatitis and autoimmune liver disease.

Abrogation of the antifibrotic effects of natural killer cells/interferon-gamma contributes to alcohol acceleration of liver fibrosis

BACKGROUND & AIMS

Chronic alcohol drinking accelerates liver fibrosis in patients with viral hepatitis that cannot be fully explained by ethanol-enhanced liver damage. Here, we identified a novel mechanism by which alcohol accelerates liver fibrosis: inhibition of the antifibrotic effects of natural killer (NK) cells and interferon-gamma (IFN-gamma).

METHODS

Alcohol administration was achieved by feeding mice with a liquid diet containing 5% ethanol for 8 weeks. Liver fibrosis was induced by administration of carbon tetrachloride (CCl(4)) for 2 weeks. Hepatic stellate cells (HSCs) were also isolated and cultured for in vitro studies.

RESULTS

CCl(4) treatment induced greater fibrosis and less apoptosis of HSCs in ethanol-fed mice compared with pair-fed mice. Polyinosinic-polycytidylic acid (Poly I:C) or IFN-gamma treatment inhibited liver fibrosis in pair-fed but not in ethanol-fed mice. Poly I:C activation of NK cell cytotoxicity against HSCs was attenuated in ethanol-fed mice compared with pair-fed mice, which was due to reduced natural killer group 2 member D (NKG2D), tumor necrosis factor-related apoptosis-inducing ligand, and IFN-gamma expression on NK cells from ethanol-fed mice. In vitro, HSCs from ethanol-fed mice were resistant to IFN-gamma-induced cell cycle arrest and apoptosis compared with pair-fed mice. Such resistance was due to diminished IFN-gamma activation of signal transducer and activator of transcription 1 (STAT1) in HSCs from ethanol-fed mice caused by the induction of suppressors of cytokine signaling proteins and the production of oxidative stress. Finally, HSCs from ethanol-fed mice were resistant to NK cell killing, which can be reversed by transforming growth factor-beta1 (TGF-beta1) neutralizing antibody.

CONCLUSIONS

Chronic ethanol consumption attenuates the antifibrotic effects of NK/IFN-gamma/STAT1 in the liver, representing new and different therapeutic targets with which to treat alcoholic liver fibrosis.

Chronic ethanol consumption inhibits hepatic natural killer cell activity and accelerates murine cytomegalovirus-induced hepatitis

BACKGROUND

Chronic alcohol drinking accelerates the progression of liver disease in patients with hepatitis viral infection; however, the underlying mechanisms are not fully understood.

METHODS

Here, we examined the effects of chronic ethanol feeding on hepatic natural killer (NK) cells and liver injury in 2 murine models of liver injury: injection of synthetic double-stranded RNA polyinosinic-polycytidylic acid (poly I:C), which mimics viral infection, and infection with murine cytomegalovirus (MCMV). Mice were fed the Lieber-DeCarli liquid diet containing 5% (vol/vol) ethanol for 8 weeks, resulting in a significant decrease in the percentage and total number of NK cells in the liver.

RESULTS

In control, pair-fed mice, poly I:C injection induced NK cell accumulation in the liver and activated hepatic NK cell cytotoxicity, whereas such induction and activation were diminished in ethanol-fed mice. Treatment with poly I:C also induced expression of NKG2D, granzyme B, perforin, Fas L, TRAIL, and IFN-gamma on liver lymphocytes, which were delayed or reduced in ethanol-treated mice compared with pair-fed mice. In contrast, chronic ethanol feeding did not affect poly I:C-induced mild liver injury. Furthermore, MCMV infection activated hepatic NK cells and induced hepatic inflammation and injury. Chronic ethanol consumption inhibited hepatic NK cell activation during MCMV infection, but enhanced MCMV-induced liver injury, viral titer, and inflammation in the liver.

CONCLUSIONS

Taken together, these findings suggest that chronic ethanol consumption decreases hepatic NK activity, thereby accelerating MCMV-induced hepatitis and liver injury.

Poly I-C induces early embryo loss in f344 rats: a potential role for NK cells

PROBLEM

Natural killer (NK) cells were associated with first trimester embryo loss. The current study in the inbred F344 rat assessed the role of NK cells in mediating resorptions caused by poly I-C, a non-specific immunostimulator.

METHOD OF STUDY

On fifth day of gestation, rats were injected intraperitoneally with anti-NKR-P1 (1.5 mg/kg, i.p.) to deplete NK cells, and with mouse serum or saline to control for non-specific effects. Poly I-C (4 mg/kg, i.p.) or vehicle were administered 2 days later. Resorptions were assessed on day 13.5.

RESULTS

Poly I-C significantly elevated resorption rates, and anti-NKR-P1 abolished this effect. Body weight was reduced in all rats treated with poly I-C, including NK-depleted rats. This indicates the ability of NK-depleted rats to respond to poly I-C, yet to refrain from the resorption-promoting effects of poly I-C.

CONCLUSIONS

This study suggests a role for NK cells in mediating poly I-C-induced resorptions.

An explanation for the paradoxical induction and suppression of an acute phase response by ethanol

Binge ethanol (EtOH) consumption suppresses inflammatory responses and resistance to infection, but paradoxically it is associated with increased levels of acute phase proteins (which are indicators of inflammation) and an increased risk of inflammation-mediated pathologies such as cardiovascular disease and cirrhosis of the liver. The latter effect may be mediated by increased translocation of bacteria leading to activation of toll-like receptor 4 (TLR4). In this study, the dose-response and time course of the effects of EtOH alone or EtOH in conjunction with a TLR4 agonist (lipopolysaccharide [LPS]) were evaluated in mice. EtOH alone at a dosage of 6 g/kg induced an acute phase response (as indicated by enzyme-linked immunosorbent assay for serum amyloid A and serum amyloid P) that was maximal 24 h after dosing. Lower dosages of EtOH did not have this effect but did suppress the acute phase response to LPS and the production of interleukin-6 up to 3 h after dosing. EtOH at 6 g/kg did not induce an acute phase response in C3H/HeJ (TLR4 mutant) mice, indicating that this response is mediated through TLR4. These results provide a resolution for the apparently paradoxical pro- and anti-inflammatory actions of EtOH with regard to acute phase responses.

Mechanisms of alcohol-induced hepatic fibrosis: a summary of the Ron Thurman Symposium

This report is a summary of Ron Thurman Symposium on the Mechanisms of Alcohol-Induced Hepatic Fibrosis which was organized by The National Institutes of Health in Santa Barbara, California, June 25, 2005. The Symposium and this report highlight the unique aspects by which drinking alcoholic beverages may result in hepatic fibrosis. Acetaldehyde, the first metabolite of ethanol, can upregulate transcription of collagen I directly as well as indirectly by upregulating the synthesis of transforming growth factor-beta 1 (TGF-beta1). Reactive oxygen species (ROS) generated in hepatocytes by alcohol metabolism can activate collagen production in hepatic stellate cells (HSCs) in a paracrine manner. Alcohol-induced hepatocyte apoptotic bodies can be phagocytosed by HSCs and Kupffer cells and result in increased expression of TGF-beta1 and subsequent HSC activation. Kupffer cells may contribute to the activation of HSCs by releasing ROS and TGF- beta1. Innate immunity may suppress hepatic fibrosis by killing activated HSCs and blocking TGF-beta1 signaling. In patients infected with hepatitis C virus (HCV), alcohol may promote hepatic fibrosis by suppressing innate immunity. HCV core and non-structural proteins contribute to HCV-induced hepatic fibrosis. Alcohol and HCV together may promote hepatic fibrosis through increased oxidative stress and upregulation of fibrogenic cytokines. The inactive aldehyde dehydrogenase (ALDH2) and the super-active alcohol dehydrogenase (ADH2) alleles may promote hepatic fibrosis through increased accumulation of acetaldehyde in the liver. Hepatic fibrosis can be reversed by inducing selective apoptosis or necrosis of activated HSCs, or by reverse trans-differentiation of activated HSCs into the quiescent phenotype.

Alcohol suppresses IL-2-induced CC chemokine production by natural killer cells

BACKGROUND

Natural killer (NK) cells are a critical component of the host innate immune system. We investigated whether alcohol impairs NK cell function, particularly production of CC chemokines induced by interleukin (IL)-2, the natural ligands for CCR5 receptor.

METHODS

Primary NK cells and NK cell line (YTS) were cultured with or without alcohol (10 to 80 mM) for three hours. The culture supernatants were then harvested and used to treat human peripheral blood monocyte-derived macrophages and a HeLa cell line, which expresses CD4, CCR5, and CXCR4 receptors (MAGI cells). CC chemokine expression by YTS and primary NK cells treated with or without alcohol was analyzed with the real-time RT-PCR and ELISA. [Ca(2)(+)]i and Western blot assays were used to determine calcium-mediated intracellular signaling pathway and NF-kappaB p65 expression. HIV strains (Bal and UG024) were used to infect macrophages and MAGI cells. In addition, ADA (macrophage-tropic strain) and murine leukemia virus (MLV) envelope-pseudotyped HIV infection was carried out in macrophages. HIV infectivity was determined by HIV reverse transcriptase (RT) and beta-galactosidase activity assays.

RESULTS

Alcohol inhibited IL-2-induced CC chemokine (CCL3 and CCL4) expression by NK cells. Functional tests demonstrated that this reduced expression of CC chemokines was associated with diminished anti-HIV ability of NK cells. Alcohol also reduced the ability of NK cells to response to CCL3-mediated chemotaxis. Alcohol inhibited IL-2-induced NF-kappaB p65 protein expression and calcium mobilization by NK cells.

CONCLUSIONS

Alcohol, through the inhibition of IL-2-induced NF-kappaB p65 protein expression and intracellular calcium mobilization, suppressed NK cell production of CC chemokines. This suppression of CC chemokine production was associated with diminished anti-HIV activity of NK cells. Thus, by inhibiting NK cell-mediated innate immunity against HIV, alcohol consumption may have a cofactor role in the immunopathogenesis of HIV disease.

Suppression of innate immunity by acute ethanol administration: a global perspective and a new mechanism beginning with inhibition of signaling through TLR3

Excessive consumption of ethanol (EtOH) suppresses innate immunity, but the mechanisms have not been fully delineated. The present study was conducted to determine whether EtOH suppresses TLR signaling in vivo in mice and to characterize the downstream effects of such suppression. Degradation of IL-1R-associated kinase 1 induced by a TLR3 ligand in peritoneal cells ( approximately 90% macrophages) was suppressed by EtOH. Phosphorylation of p38 kinase in peritoneal macrophages (F4/80(+)) was suppressed, as was nuclear translocation of p-c-Jun and p65 in peritoneal cells. EtOH decreased IL-6 and IL-12 (p40), but did not significantly affect IL-10 in peritoneal lavage fluid or in lysates of peritoneal cells. Changes in cytokine mRNAs (by RNase protection assay) in macrophages isolated by cell sorting or using Ficoll were generally consistent with changes in protein levels in cell lysates and peritoneal lavage fluid. Thus, suppression of TLR signaling and cytokine mRNA occurred in the same cells, and this suppression generally corresponded to changes in i.p. and intracellular cytokine concentrations. DNA microarray analysis revealed the suppression of an IFN-related amplification loop in peritoneal macrophages, associated with decreased expression of numerous innate immune effector genes (including cytokines and a chemokine also suppressed at the protein level). These results indicate that EtOH suppresses innate immunity at least in part by suppressing TLR3 signaling, suppressing an IFN-related amplification loop, and suppressing the induction of a wide range of innate effector molecules in addition to proinflammatory cytokines and chemokines.

Giant basal cell carcinoma associated with human papillomaviruses infection

Different criteria have been used to define giant basal cell carcinoma (BCC). However, the majority of tumors of 10 cm or greater in diameter have a characteristic clinical and histopathologic presentation. As a group, these tumors often show metastatic spread as opposed to all other BCCs that rarely metastasize. We present an additional patient with a giant BCC greater than 100 cm2. This tumor had a characteristic location and infiltrative growth pattern. Unusual features of this tumor included a lack of expression of BCL-2 with a greater proportion of cycling tumor cells expressing proliferation markers than conventional BCC, as well as expression of anogenital human papillomaviruses (HPV) subtypes with oncogenic potential. The association of HPV with BCCs has rarely been studied and may not be identical to HPV-induced genital squamous cell carcinomas. However, the findings in this patient suggest that HPV may play a role in the development of some chronic giant BCCs.

Ethanol decreases natural killer cell activation but only minimally affects anatomical distribution after administration of polyinosinic:polycytidylic acid: role in resistance to B16F10 melanoma

BACKGROUND

Natural killer (NK) cells are critical in resistance to B16F10 lung metastases in B6C3F1 mice. Activation of NK cells by polyinosinic:polycytidylic acid (poly I:C; 0.1 mg, intraperitoneally) increases resistance to B16F10 cells. This effect is reduced after administration of ethanol (EtOH; 6 g/kg by oral gavage). The present study was conducted to determine whether decreased resistance is due to alteration of the distribution and/or the activation of NK cells.

METHODS

These parameters were measured in the spleen, lungs, and peripheral blood 4 and 12 hr after EtOH and poly I:C administration. For assessing the time after poly I:C administration during which NK cells are important in resistance to B16F10 cells, anti-NK1.1 antibody was used to deplete NK cells in vivo 48 hr before and 0, 6, 12, and 24 hr after intravenous injection of B16F10 tumor cells.

RESULTS

Depletion of NK cells at any time up to 12 hr after B16F10 administration significantly increased the number of tumor nodules in the lungs, but depletion at 24 hr had a smaller effect. Flow cytometry revealed that there was a small but significant increase in the percentage of NK cells in the lungs at 12 hr, which was not changed by EtOH. Corresponding NK cell lytic function in the lungs was increased significantly at both 4 and 12 hr by poly I:C. However, the increase was not significantly different from the naive control value at 4 hr in mice treated with poly I:C plus EtOH, indicating that EtOH decreased activation of NK cells in the lungs at 4 hr. In the spleen, no treatment significantly altered the percentage of NK cells at 4 or 12 hr. However, poly I:C significantly enhanced lytic function, and this enhancement was suppressed by EtOH (by approximately 50%). In the blood, the only significant change in NK cell percentage or lytic activity was an increase in the percentage of NK cells at 12 hr, which was equivalent in the poly I:C and the poly I:C plus EtOH groups.

CONCLUSIONS

These results demonstrate that EtOH partially abrogates the poly I:C-induced enhancement of resistance to B16F10 cells and that decreased activation of NK cells in the lungs at a critical time early in the response to poly I:C may contribute to this effect. Other parameters could also contribute, but there was little support for an important role for changes in NK cell distribution.

Reduction of perforin, granzyme B, and cytokine interferon gamma by ethanol in male Fischer 344 rats

BACKGROUND

Chronic alcohol consumption can impair the immune system and predispose individuals to an increased risk of cancer and infection. Natural killer (NK) cells are the first line of defense against viral, bacterial, and fungal infections and play an important role in cellular resistance to malignancy and tumor metastasis. We have shown previously that ethanol administration suppresses NK cell cytolytic activity in male Fischer rats. This study analyzed the effects of ethanol on perforin, granzyme B, and the cytokine interferon (IFN)-gamma, factors that modulate NK cell cytolytic activity, to understand the molecular mechanism involved in ethanol's suppression of NK cell activity.

METHODS

A group of male Fischer rats was fed an ethanol-containing diet (8.7% v/v), whereas a control group was pair-fed an isocaloric diet. At the end of 2 weeks, animals were decapitated, and spleen tissues were immediately removed and used for analysis of NK cell cytolytic activity, perforin, granzyme B, and IFN-gamma messenger RNA (mRNA) or protein levels. The mRNA levels of perforin, granzyme B, and IFN-gamma were evaluated by quantitative real-time polymerase chain reaction, and protein levels of these factors were analyzed by Western blot, enzyme-linked immunosorbent assay, or enzymatic activity assay.

RESULTS

Ethanol reduced the NK cell cytolytic activity and decreased the mRNA expression of perforin, granzyme B, and IFN-gamma in ethanol-fed animals when compared with pair-fed animals. Ethanol also significantly reduced the protein levels of perforin and IFN-gamma and the enzyme activity of granzyme B in alcohol-fed animals as compared with pair-fed animals.

CONCLUSIONS

These data suggest that chronic ethanol consumption may suppress NK cell cytolytic activity in male Fischer rats by decreasing the production, activity, or both of granzyme B, perforin, and IFN-gamma.

Acute ethanol administration profoundly alters poly I:C-induced cytokine expression in mice by a mechanism that is not dependent on corticosterone

Polyinosinic polycytidylic acid (poly I:C) is an analog of double stranded RNA, which is a common replication intermediate for many viruses. It acts through a toll-like receptor (TLR3) to induce a group of cytokines that can mediate host resistance to viruses and some cancers. The effect of ethanol (EtOH) on induction of this set of cytokines has not been determined. Mice were treated with a single dose of EtOH (by gavage) at the same time as poly I:C was administered (intraperitoneally), and cytokine mRNA expression was measured by RNAse protection assay. Concentrations of IFN-alpha, IL-10, and IL-12 in the serum were measured by ELISA. A single dose of EtOH suppressed induction of mRNA for IFN-alpha, IFN-beta, IFN-gamma, IL-6, IL-9, IL-12, and IL-15. The concentrations of IFN-alpha and IL-12 in the serum were also decreased. In contrast, IL-10 was minimally induced by poly I:C alone, but it was substantially induced by poly I:C plus EtOH. Dose response and time course studies demonstrated that significant alterations of IFN-alpha, IL-10, and IL-12 expression occurred at dosages as low as 4 g/kg (a dosage previously shown to produce blood EtOH concentrations of approximately 0.2%) and that alterations persisted at least 4-6 hr after administration of EtOH. The glucocorticoid synthesis inhibitor, aminoglutethimide, diminished corticosterone levels to normal, but did not block the effects of EtOH on cytokine expression. These results demonstrate that EtOH affects the expression of poly I:C-induced cytokines and that this action is not mediated by corticosterone. These results plus previously published findings are consistent with the idea that EtOH may be a generalized suppressor of toll-like receptor signaling.

Ethanol suppresses polyinosinic:polycytidylic acid-induced activation of natural killer cells primarily by acting on natural killer cells, not through effects on other cell types

Natural killer (NK) cells can be activated in vitro and in vivo by polyinosinic:polycytidylic acid (poly I:C) through induction of type I interferons or other cytokines. Ethanol suppresses in vivo and ex vivo poly I:C activation of NK cell activity in a mouse model for binge drinking, but it is not known whether this effect is mediated by changes in NK cells or in other cell types (e.g., those that produce NK cell-activating cytokines). Splenocytes were obtained from C57BL/6 [NK cell-competent (NKc)] and C57BL/6 perforin knockout [NK cell-incompetent (NKi)] mice 6 h after administration of ethanol (6 g/kg) or vehicle (VH; dH(2)O). Cells were incubated in vitro 18 h with poly I:C (100 micro g/ml), followed by a 4-h 51Cr release assay with the use of YAC-1 target cells. Results of cell-mixing experiments involving all relevant combinations of splenocytes obtained from NKc and NKi mice treated with VH or ethanol strongly supported the suggestion that NK cells, not other cell types, are the primary target of ethanol-induced suppression of NK cell activation. For example, mixing of splenocytes obtained from ethanol-treated NKc and VH-treated NKi mice or from ethanol-treated NKc and ethanol-treated NKi mice yielded similar cytolytic function. However, mixing of splenocytes obtained from ethanol-treated NKc and VH-treated NKi mice yielded significantly less cytolytic activity than that of splenocytes from VH-treated NKc and ethanol-treated NKi mice. In addition, mixing of splenocytes obtained from VH-treated NKc and NKi mice resulted in lower cytolytic activity than when splenocytes from the NKi mice were treated with ethanol instead of with VH, demonstrating that ethanol did not decrease the function of other cell types. A strikingly similar pattern of results was observed when B6C3F1 mice, rendered NK cell deficient by administration of anti-NK 1.1 monoclonal antibody, were used instead of perforin knockout mice. These results indicate that ethanol suppresses activation of NK cells primarily by suppressing the NK cell response to poly I:C, not by acting on another cell type.

Selective loss of viability of mouse NK cells in culture is associated with decreased NK cell lytic function

Cell culture methods can allow investigation of the mechanisms responsible for immunotoxicity. Unfortunately, natural killer (NK) cells in rodent splenic cultures rapidly lose their cytolytic function. It is not known if death of NK cells or loss of function in viable NK cells is primarily responsible for this loss. Flow cytometry and an assay of NK cell lytic function were used to address this issue and to determine if NK cell viability could be maintained by adding selected cytokines or a caspase inhibitor to the cultures. Total cells and NK cells in untreated 18 h cultures were 79 +/- 1% and 25 +/- 2% viable, respectively, and these cultured splenocytes caused only 4 +/- 1% specific release of (51)Cr from YAC-1 target cells. Cultures including polyinosinic:polycytidylic acid (poly I:C) or IL-2 had increased NK cell viability (43 +/- 2%, 47 +/- 1%) and function (58 +/- 2 and 43 +/- 1% specific release). IL-15 significantly increased NK cell viability, but not function. Previous studies demonstrated that treatment of mice with immunotoxicants such as ethanol or corticosterone diminishes NK cell activation in vitro in response to poly I:C. To determine if alterations in viability are responsible for this decreased NK cell activity, lytic function and NK activity were measured in cultures of splenocytes treated in vivo or in vitro with ethanol and/or corticosterone. Some treatments reduced IL-2 or poly I:C-enhanced lytic activity in vitro, but there was no clear relationship between these changes in function and changes in the percentage of viable NK cells. Thus, immunotoxicants that suppress NK cell activation can be investigated in vitro because commonly used activating stimuli also permit NK cell survival. However, no agents were identified that could maintain NK cell viability and function in culture (without activation) to allow investigation of the direct effects of immunotoxicants on basal NK activity in vitro.