Differentiation of monocytes to macrophages induced by influenza virus-infected apoptotic cells

ZIKV infection regulates inflammasomes pathway for replication in monocytes

ZIKV causes microcephaly by crossing the placental barrier, however, the mechanism of trans-placental dissemination of ZIKV remains unknown. Here, we sought to determine whether monocytes, which can cross tissue barriers, assist ZIKV dissemination to the fetus. We determined this by infecting monocytes with two strains of ZIKV: South American (PRVABC59) and Nigerian (IBH30656) and analyzing viral replication. We found that ZIKV infects and replicates in monocytes and macrophages, which results in the modulation of a large number of cellular genes. Analysis of these genes identified multiple pathways including inflammasome to be targeted by ZIKV, which was confirmed by analyzing the transcript levels of the proteins of inflammasome pathways, NLRP3, ASC, caspase 1, IL-1 and IL-18. Interestingly, IFNα and the IFN inducible gene, MxA were not enhanced, suggesting prevention of innate antiviral defense by ZIKV. Also, inhibition of inflammasome led to an increased transcriptional activity of IFNα, MxA and CXCL10. Based on these results we suggest that ZIKV transcription is regulated by inflammasomes.

The plasticity of inflammatory monocyte responses to the inflamed central nervous system

Over the last three decades it has become increasingly clear that monocytes, originally thought to have fixed, stereotypic responses to foreign stimuli, mediate exquisitely balanced protective and pathogenic roles in disease and immunity. This balance is crucial in core functional organs, such as the central nervous system (CNS), where minor changes in neuronal microenvironments and the production of immune factors can result in significant disease with fatal consequences or permanent neurological sequelae. Viral encephalitis and multiple sclerosis are examples of important human diseases in which the pathogenic contribution of monocytes recruited from the bone marrow plays a critical role in the clinical expression of disease, as they differentiate into macrophage or dendritic cells in the CNS to carry out effector functions. While antigen-specific lymphocyte populations are central to the adaptive immune response in both cases, in viral encephalitis a prominent macrophage infiltration may mediate immunopathological damage, seizure induction, and death. However, the autoimmune response to non-replicating, non-infectious, but abundant, self antigen has a different disease progression, associated with differentiation of significant numbers of infiltrating monocytes into dendritic cells in the CNS. Whilst a predominant presence of macrophages or dendritic cells in the inflamed CNS in viral encephalitis or multiple sclerosis is well described, the way in which the inflamed CNS mobilizes monocytes in the bone marrow to migrate to the CNS and the key drivers that lead to these specific differentiation pathways in vivo are not well understood. Here we review the current understanding of factors facilitating inflammatory monocyte generation, migration and entry into the brain, as well as their differentiation towards macrophages or dendritic cells in viral and autoimmune disease in relation to their respective disease outcomes.

Influenza, immune system, and pregnancy

Influenza is a major health problem worldwide. Both seasonal influenza and pandemics take a major toll on the health and economy of our country. The present review focuses on the virology and complex immunology of this RNA virus in general and in relation to pregnancy. The goal is to attempt to explain the increased morbidity and mortality seen in infection during pregnancy. We discuss elements of innate and adaptive immunity as well as placental cellular responses to infection. In addition, we delineate findings in animal models as well as human disease. Increased knowledge of maternal and fetal immunologic responses to influenza is needed. However, enhanced understanding of nonimmune, pregnancy-specific factors influencing direct interaction of the virus with host cells is also important for the development of more effective prevention and treatment options in the future.

Possible roles of proinflammatory and chemoattractive cytokines produced by human fetal membrane cells in the pathology of adverse pregnancy outcomes associated with influenza virus infection

Pregnant women are at an increased risk of influenza-associated adverse outcomes, such as premature delivery, based on data from the latest pandemic with a novel influenza A (H1N1) virus in 2009-2010. It has been suggested that the transplacental transmission of influenza viruses is rarely detected in humans. A series of our study has demonstrated that influenza virus infection induced apoptosis in primary cultured human fetal membrane chorion cells, from which a factor with monocyte differentiation-inducing (MDI) activity was secreted. Proinflammatory cytokines, such as interleukin (IL)-6, tumor necrosis factor (TNF)-α, and interferon (IFN)-β, were identified as a member of the MDI factor. Influenza virus infection induced the mRNA expression of not only the proinflammatory cytokines but also chemoattractive cytokines, such as monocyte chemoattractant protein (MCP)-1, regulated on activation, normal T-cell expressed and secreted (RANTES), macrophage inflammatory protein (MIP)-1β, IL-8, growth-regulated oncogene (GRO)-α, GRO-β, epithelial cell-derived neutrophil-activating protein (ENA)-78, and interferon inducible protein (IP)-10 in cultured chorion cells. These cytokines are postulated to associate with human parturition. This paper, therefore, reviews (1) lessons from pandemic H1N1 2009 in pregnancy, (2) production of proinflammatory and chemoattractive cytokines by human fetal membranes and their functions in gestational tissues, and (3) possible roles of cytokines produced by human fetal membranes in the pathology of adverse pregnancy outcomes associated with influenza virus infection.

Current status of monocyte differentiation-inducing (MDI) factors derived from human fetal membrane chorion cells undergoing apoptosis after influenza virus infection

Influenza virus infection induces apoptosis and the expression of a set of pro-inflammatory cytokine genes, such as interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, interferon (IFN)-beta and IFN-gamma, in cultured human fetal membrane chorion cells. Monocyte differentiation-inducing (MDI) activity in culture supernatants is simultaneously increased by the virus infection. The MDI activity is predominantly influenced by IL-6 molecule in culture supernatants, and partly by TNF-alpha and IFN-beta, but not IFN-gamma, molecules. The MDI factors are able to induce the mRNA expression of macrophage class A scavenger receptor (SR-A), which is one of adhesion and apoptotic cell-recognizing molecules, and gp91(phox), which is a catalytic subunit of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme complex, on monocytic cells. As a result, monocytes are initiated to differentiate into well-matured macrophages capable of adhering and producing superoxide through NADPH oxidase. The matured macrophages, obtained from human monocytic leukemia THP-1 cells by the treatment with MDI factors, phagocytose apoptotic chorion cell debris resulting from the virus infection. Subsequent to phagocytosis, an abrupt increase of superoxide production by macrophages may occur. In this article, we summarize recent knowledge about the MDI factors derived from human fetal membrane chorion cells undergoing apoptosis after influenza virus infection, and discuss their possible pathological roles during pregnancy.

A new simple multi-well plate-based assay for monocyte differentiation using human monocytic leukemia THP-1 cells

A new simple multi-well plate-based assay to determine monocyte differentiation-inducing activity was developed. It is based on the increase of macrophage adherence after the induction of monocyte differentiation. The assay was conducted using a human monocytic leukemia cell line, THP-1, treated with either 12-O-tetradecanoylphorbol 13-acetate or cytokines, such as tumor necrosis factor-alpha and interferon-gamma. This method is sensitive and easy to perform, especially in case of analyzing a large number of samples.

Evidence for phagocytosis of influenza virus-infected, apoptotic cells by neutrophils and macrophages in mice

Influenza virus-infected cells undergo apoptosis and become susceptible to phagocytosis by macrophages in vitro, and this leads to the propagation of the virus being inhibited. We previously showed that inhibitors of phagocytosis increased the rate of mortality among influenza virus-infected mice. However, the mode of the phagocytosis of influenza virus-infected cells in vivo has not been investigated. We, in this study, assessed this issue by histochemically analyzing bronchoalveolar lavage cells and lung tissue obtained from C57BL/6 mice infected with influenza A/WSN (H1N1) virus. Both neutrophils and macrophages accumulated in the lung soon after the viral challenge, and either type of cell was capable of phagocytosing influenza virus-infected, apoptotic cells. Changes in the level of phagocytosis and the amount of virus in lung tissue roughly correlated with each other. Furthermore, alveolar macrophages prepared from influenza virus-infected mice showed greater phagocytic activity than those from uninfected mice. The phagocytic activity of macrophages was stimulated in vitro by a heat-labile substance(s) released from influenza virus-infected cells undergoing apoptosis. These results suggested that the level of phagocytosis is augmented both quantitatively and qualitatively in the lung of influenza virus-infected animals so that infected cells are effectively eliminated. Finally, lack of TLR4 caused an increase in the rate of mortality among influenza virus-challenged mice and a decrease in the level of phagocytosis of apoptotic cells in the lung. TLR4 could thus play an important role in the host defense against influenza by positively regulating the phagocytic elimination of infected cells.

Effects of Mitogen-Activated Protein Kinase Inhibitors on Tumor Necrosis Factor-α Gene Expression and Apoptosis Induction in Cultured Human Fetal Membrane Chorion Cells Infected with Influenza Virus

OBJECTIVES

We investigated the involvement of p38 mitogen-activated protein (MAP) kinase in tumor necrosis factor (TNF)-alpha gene expression, apoptosis induction and virus replication in cultured human fetal membrane chorion cells infected with influenza virus.

METHODS

Influenza virus-infected chorion cells were incubated in the absence or presence of inhibitors of p38 MAP kinase, SB203580 and SB202190. TNF-alpha mRNA and hemagglutinin viral RNA (HA vRNA) were amplified with reverse transcriptase-polymerase chain reaction techniques. TNF-alpha protein concentrations were determined by enzyme-liked immunosorbent assay. The extent of apoptosis induction was estimated by DNA agarose gel electrophoresis. Pyrrolidine dithiocarbamate (PDTC) and ribavirin, which have been shown to inhibit apoptosis induction via the inhibition of viral gene replication, were used as positive control reagents.

RESULTS

PDTC and ribavirin inhibited the accumulation of TNF-alpha mRNA and HA vRNA in the virus-infected chorion cells, resulting in the suppression of TNF-alpha protein secretion. Both SB203580 and SB202190 suppressed TNF-alpha protein secretion, but not the accumulation of TNF-alpha mRNA as well as HA vRNA and the induction of apoptosis.

CONCLUSIONS

These results suggest that p38 MAP kinase pathway is critical in TNF-alpha gene expression at a post-transcriptional level but not in the apoptosis induction and influenza virus replication in cultured chorion cells.

Characterization of monocyte differentiation-inducing (MDI) factors derived from human fetal membrane chorion cells undergoing apoptosis after influenza virus infection

Influenza virus infection during pregnancy has been implicated as one of cause of premature delivery, abortion and stillbirth. We have reported that cultured human fetal membrane chorion cells undergoing apoptosis by influenza virus infection secrete unidentified heat-stable monocyte differentiation-inducing (MDI) factors. In this study, cellular, biological and immunochemical characteristics of MDI factors were investigated using human monocytic leukemia THP-1 cells by nitroblue tetrazolium reduction and cell adhesion assays. The treatment of THP-1 cells with culture supernatants from the influenza virus-infected chorion cells induced the nitroblue tetrazolium reduction ability, which was inhibited by the addition of superoxide dismutase and diphenyleneiodonium chloride, an inhibitor for reduced nicotinamide adenine dinucleotide phosphate oxidase. The phenomenon was also observed in human peripheral blood monocytes and histiocytic leukemia U937 cells, but not in promyelocytic leukemia HL-60 cells. The induction of nitroblue tetrazolium reduction and adhesion abilities in THP-1 cells was closely correlated with the concentrations of interleukin-6 protein in the culture supernatants. These abilities were inhibited to approximately 60% by the addition of antibodies against interleukin-6, or alpha-chain (gp80) or beta-chain (gp130) of IL-6 receptor. The induction of nitroblue tetrazolium reduction was increased by the addition of supernatants from amniochorion tissue cultures after influenza virus infection. These results indicate that chorion cell-derived interleukin-6 is partly responsible for monocyte differentiation to macrophages capable of generating superoxide anion. It is possible that these pathways represent part of the mechanism for birth complications associated with intrauterine influenza infection in pregnancy.

Secretion of bioactive interleukin-6 and tumor necrosis factor-alpha proteins from primary cultured human fetal membrane chorion cells infected with influenza virus

Influenza virus infection during pregnancy is implicated in one of the causes of premature delivery, abortion and stillbirth. Pro-inflammatory cytokines, such as interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha produced by fetal membranes, are postulated to facilitate premature delivery. We investigated the secretion of IL-6 and TNF-alpha from primary cultured human fetal membrane chorion and amnion cells infected with influenza virus at protein and bioactivity levels in order to understand the pathology of premature delivery during influenza virus infection. Concentrations of IL-6 and TNF-alpha proteins were significantly increased in culture supernatants of chorion cells by influenza virus infection. Culture supernatants of the virus-infected chorion cells stimulated the proliferation of IL-6-sensitive 7-TD-1 cells and induced the cytolysis of TNF-alpha-sensitive L929 cells, both activities of which were inhibited by the addition of respective antibody, whereas no such phenomena were observed in amnion cells. The results demonstrated that only chorion cells secreted significant amounts of bioactive IL-6 and TNF-alpha proteins responding to influenza virus infection. The present study suggests a possibility that the secretion of bioactive IL-6 and TNF-alpha proteins from fetal membrane chorion cells is implicated in the pathogenesis of premature delivery during influenza virus infection.

Influenza virus induction of apoptosis by intrinsic and extrinsic mechanisms

It is now firmly established that apoptosis is an important mechanism of influenza virus-induced cell death both in vivo and in vitro. Data are predominantly from experiments with influenza A virus and in vitro experimental systems. Multiple influenza virus factors have been identified that can activate intrinsic or extrinsic apoptotic induction pathways. Currently there is no evidence for influenza virus directly accessing the apoptosis execution factors. The best-studied influenza virus inducers of apoptosis are dsRNA, NS1, NA, and a newly described gene product PB1-F2. PB1-F2 is the only influenza virus factor to date identified to act intrinsically by localization and interaction with the mitochondrial-dependent apoptotic pathway. Both dsRNA and NA have been shown to act via an extrinsic mechanism involving proapoptotic host-defense molecules: PKR by induction of Fas-Fas ligand and NA by activation of TGF-beta. PKR is capable of controlling several important cell-signaling pathways and therefore may have multiple effects; a predominant one is increased interferon (IFN) production and activity. NS1 has been shown to be both proapoptotic and antiapoptotic. Use of influenza virus NS1 deletion mutants has provided evidence for NS1 interference with apoptosis, IFN induction, and related cell-signaling pathways. Influenza virus also has important exocrine paracrine effects, which are likely mediated via TNF family ligands and oxygen, free radicals capable of inducing apoptosis. Little is known about activation of inhibitors of apoptosis such as inhibitory apoptotic proteins. Whether all these factors always have a role in influenza virus-induced apoptosis is unknown. The kinetics of synthesis of influenza virus factors affecting apoptosis during the replication cycle may be an important aspect of apoptosis induction.