Inflammation and the apopto-phagocytic system

Ocular Surface Allostasis-When Homeostasis Is Lost: Challenging Coping Potential, Stress Tolerance, and Resilience

The loss of ocular surface (OS) homeostasis characterizes the onset of dry eye disease. Resilience defines the ability to withstand this threat, reflecting the ability of the ocular surface to cope with and bounce back after challenging events. The coping capacity of the OS defines the ability to successfully manage cellular stress. Cellular stress, which is central to the outcome of the pathophysiology of dry eye disease, is characterized by intensity, continuity, and receptivity, which lead to the loss of homeostasis, resulting in a phase of autocatalytic dysregulation, an event that is not well-defined. To better define this event, here, we present a model providing a potential approach when homeostasis is challenged and the coping capacities have reached their limits, resulting in the stage of heterostasis, in which the dysregulated cellular stress mechanisms take over, leading to dry eye disease. The main feature of the proposed model is the concept that, prior to the initiation of the events leading to cellular stress, there is a period of intense activation of all available coping mechanisms preventing the imminent dysregulation of ocular surface homeostasis. When the remaining coping mechanisms and resilience potential have been maximally exploited and have, finally, been exceeded, there will be a transition to manifest disease with all the well-known signs and symptoms, with a shift to allostasis, reflecting the establishment of another state of balance. The intention of this review was to show that it is possibly the phase of heterostasis preceding the establishment of allostasis that offers a better chance for therapeutic intervention and optimized recovery. Once allostasis has been established, as a new steady-state of balance at a higher level of constant cell stress and inflammation, treatment may be far more difficult, and the potential for reversal is drastically decreased. Homeostasis, once lost, can possibly not be fully recovered. The processes established during heterostasis and allostasis require different approaches and treatments for their control, indicating that the current treatment options for homeostasis need to be adapted to a more-demanding situation. The loss of homeostasis necessarily implies the establishment of a new balance; here, we refer to such a state as allostasis.

Human Embryonic Stem Cell-Derived Retinal Pigment Epithelium-Role in Dead Cell Clearance and Inflammation

Inefficient removal of dying retinal pigment epithelial (RPE) cells by professional phagocytes can result in debris formation and development of age-related macular degeneration (AMD). Chronic oxidative stress and inflammation play an important role in AMD pathogenesis. Only a few well-established in vitro phagocytosis assay models exist. We propose human embryonic stem cell-derived-RPE cells as a new model for studying RPE cell removal by professional phagocytes. The characteristics of human embryonic stem cells-derived RPE (hESC-RPE) are similar to native RPEs based on their gene and protein expression profile, integrity, and barrier properties or regarding drug transport. However, no data exist about RPE death modalities and how efficiently dying hESC-RPEs are taken upby macrophages, and whether this process triggers an inflammatory responses. This study demonstrates hESC-RPEs can be induced to undergo anoikis or autophagy-associated cell death due to extracellular matrix detachment or serum deprivation and hydrogen-peroxide co-treatment, respectively, similar to primary human RPEs. Dying hESC-RPEs are efficiently engulfed by macrophages which results in high amounts of IL-6 and IL-8 cytokine release. These findings suggest that the clearance of anoikic and autophagy-associated dying hESC-RPEs can be used as a new model for investigating AMD pathogenesis or for testing the in vivo potential of these cells in stem cell therapy.

Clearance of autophagy-associated dying retinal pigment epithelial cells - a possible source for inflammation in age-related macular degeneration

Retinal pigment epithelial (RPE) cells can undergo different forms of cell death, including autophagy-associated cell death during age-related macular degeneration (AMD). Failure of macrophages or dendritic cells (DCs) to engulf the different dying cells in the retina may result in the accumulation of debris and progression of AMD. ARPE-19 and primary human RPE cells undergo autophagy-associated cell death upon serum depletion and oxidative stress induced by hydrogen peroxide (H₂O₂). Autophagy was revealed by elevated light-chain-3 II (LC3-II) expression and electron microscopy, while autophagic flux was confirmed by blocking the autophago-lysosomal fusion using chloroquine (CQ) in these cells. The autophagy-associated dying RPE cells were engulfed by human macrophages, DCs and living RPE cells in an increasing and time-dependent manner. Inhibition of autophagy by 3-methyladenine (3-MA) decreased the engulfment of the autophagy-associated dying cells by macrophages, whereas sorting out the GFP-LC3-positive/autophagic cell population or treatment by the glucocorticoid triamcinolone (TC) enhanced it. Increased amounts of IL-6 and IL-8 were released when autophagy-associated dying RPEs were engulfed by macrophages. Our data suggest that cells undergoing autophagy-associated cell death engage in clearance mechanisms guided by professional and non-professional phagocytes, which is accompanied by inflammation as part of an in vitro modeling of AMD pathogenesis.

Triamcinolone regulated apopto-phagocytic gene expression patterns in the clearance of dying retinal pigment epithelial cells. A key role of Mertk in the enhanced phagocytosis

BACKGROUND

The apopto-phagocytic gene expression patterns during clearance of dying cells in the retina and the effect of triamcinolone (TC) upon these processes have relevance to development of age-related macular degeneration (AMD).

METHODS

ARPE-19 cells and primary human retinal pigment epithelium (hRPE) were induced to undergo cell death by anoikis and the clearance of these cells by living hRPE/ARPE-19 or human monocyte-derived macrophages (HMDMs) in the presence or absence of TC was quantified by flow cytometry. TaqMan low-density gene expression array determining known markers of phagocytosis and loss-of-function studies on selected apopto-phagocytic genes was carried out in HMDM engulfing anoikic cells.

RESULTS

The glucocorticoid TC had a profound phagocytosis-enhancing effect on HMDM engulfing anoikic ARPE-19 or hRPE cells, causing a selective upregulation of the Mer tyrosine kinase (MERTK) receptor, while decreasing the expression of the AXL receptor tyrosine kinase and thrombospondin-1 (THSB-1). The key role of the MERTK could be demonstrated in HMDM engulfing dying cells using gene silencing as well as blocking antibodies. Similar pathways were found upregulated in living ARPE-19 engulfing anoikic ARPE-19 cells. Gas6 treatment enhanced phagocytosis in TC-treated HMDMs.

CONCLUSIONS

Specific agonists of the Mertk receptor may have a potential role as phagocytosis enhancers in the retina and serve as future targets for AMD therapy.

GENERAL SIGNIFICANCE

The use of Gas6 as enhancer of retinal phagocytosis via the MerTK receptor, alone or in combination with other specific ligands of the tyrosine kinase receptors' family may have a potential role in AMD therapy.

In vitro and in vivo clearance of Rose Bengal Acetate-PhotoDynamic Therapy-induced autophagic and apoptotic cells

This study focuses on the clearance of Rose Bengal Acetate (RBAc)-PhotoDynamic Therapy (PDT)-generated apoptotic and autophagic HeLa cells by murine and human macrophages. Indeed, phagocytosis of dead cells drives the therapeutic efficacy of PDT through both efficient removal of dead/dying cells and macrophages response evoked during engulfment and, up to now, clearance of dying photosensitized cells has been less investigated than PDT mechanisms of cell death induction. RBAc-PDT ensures a long onset of cytotoxicity and a time-related cell death of HeLa cells by signals originating from or converging on almost all intracellular organelles. On this basis, to clarify whether the efficacious cell death commitment is followed by an efficient clearance mechanism, we primarily focused on the analysis of 'eat me' signals exposure and 'find me' signals release, and then investigated the migration, recognition, engulfment and response of murine Raw 264.7 and human blood isolated macrophages. Dead cells secreted 'find me' signals, i.e. fractalkine and Heat Shock Protein 70 (HSP 70), to recruit macrophages and promote their fast phagocytosis. Macrophages phagocytosed apoptotic and autophagic PDT-treated cells more efficiently than the respective positive controls, i.e. puromycin-induced apoptotic and Earle's balanced salt solution-starved autophagic cells. Phagocytosis depends on the glycans exposed on dead cells. The macrophages internalization of photokilled cells elicits the production of Interleukin-10, Transforming Growth Factor-β and Tumour Necrosis Factor-α by macrophages. TNFα production, along with HSP70 release and plasma membrane translocation on dead cells, suggest an immunogenic impact of RBAc-PDT. In fact, macrophages, activated fibroblasts and endothelial cells colonized the inoculum site of photosensitized cells in rat calf muscles, endorsing the hypothesis of immunogenic elicitation of RBAc-PDT.

Study of cnidarian-algal symbiosis in the "omics" age

The symbiotic associations between cnidarians and dinoflagellate algae (Symbiodinium) support productive and diverse ecosystems in coral reefs. Many aspects of this association, including the mechanistic basis of host-symbiont recognition and metabolic interaction, remain poorly understood. The first completed genome sequence for a symbiotic anthozoan is now available (the coral Acropora digitifera), and extensive expressed sequence tag resources are available for a variety of other symbiotic corals and anemones. These resources make it possible to profile gene expression, protein abundance, and protein localization associated with the symbiotic state. Here we review the history of "omics" studies of cnidarian-algal symbiosis and the current availability of sequence resources for corals and anemones, identifying genes putatively involved in symbiosis across 10 anthozoan species. The public availability of candidate symbiosis-associated genes leaves the field of cnidarian-algal symbiosis poised for in-depth comparative studies of sequence diversity and gene expression and for targeted functional studies of genes associated with symbiosis. Reviewing the progress to date suggests directions for future investigations of cnidarian-algal symbiosis that include (i) sequencing of Symbiodinium, (ii) proteomic analysis of the symbiosome membrane complex, (iii) glycomic analysis of Symbiodinium cell surfaces, and (iv) expression profiling of the gastrodermal cells hosting Symbiodinium.

ATP release from dying autophagic cells and their phagocytosis are crucial for inflammasome activation in macrophages

Pathogen-activated and damage-associated molecular patterns activate the inflammasome in macrophages. We report that mouse macrophages release IL-1β while co-incubated with pro-B (Ba/F3) cells dying, as a result of IL-3 withdrawal, by apoptosis with autophagy, but not when they are co-incubated with living, apoptotic, necrotic or necrostatin-1 treated cells. NALP3-deficient macrophages display reduced IL-1β secretion, which is also inhibited in macrophages deficient in caspase-1 or pre-treated with its inhibitor. This finding demonstrates that the inflammasome is activated during phagocytosis of dying autophagic cells. We show that activation of NALP3 depends on phagocytosis of dying cells, ATP release through pannexin-1 channels of dying autophagic cells, P₂X₇ purinergic receptor activation, and on consequent potassium efflux. Dying autophagic Ba/F3 cells injected intraperitoneally in mice recruit neutrophils and thereby induce acute inflammation. These findings demonstrate that NALP3 performs key upstream functions in inflammasome activation in mouse macrophages engulfing dying autophagic cells, and that these functions lead to pro-inflammatory responses.

Molecular mechanisms of retinal pigment epithelium damage and development of age-related macular degeneration

Age-related macular degeneration (AMD) is attributed to a complex interaction of genetic and environmental factors. It is characterized by degeneration involving the retinal photoreceptors, retinal pigment epithelium (RPE) and Bruch's membrane, as well as alterations in choroidal capillaries. AMD pathogenesis is strongly associated with chronic oxidative stress and inflammation that ultimately lead to protein damage, aggregation and degeneration of RPE. Specific degenerative findings for AMD are accumulation of intracellular lysosomal lipofuscin and extracellular drusens. In this review, we discuss thoroughly RPE-derived mechanisms in AMD pathology.

Differentiation and glucocorticoid regulated apopto-phagocytic gene expression patterns in human macrophages. Role of Mertk in enhanced phagocytosis

The daily clearance of physiologically dying cells is performed safely mainly by cells in the mononuclear phagocyte system. They can recognize and engulf dying cells utilizing several cooperative mechanisms. In our study we show that the expression of a broad range of apopto-phagocytic genes is strongly up-regulated during differentiation of human monocytes to macrophages with different donor variability. The glucocorticoid dexamethasone has a profound effect on this process by selectively up-regulating six genes and down-regulating several others. The key role of the up-regulated mer tyrosine kinase (Mertk) in dexamethasone induced enhancement of phagocytosis could be demonstrated in human monocyte derived macrophages by gene silencing as well as blocking antibodies, and also in a monocyte-macrophage like cell line. However, the additional role of other glucocorticoid induced elements must be also considered since the presence of autologous serum during phagocytosis could almost completely compensate for the blocked function of Mertk.

Autophagy shapes inflammation

Autophagy is a basic cell biological process ongoing under physiologic circumstances in almost all cell types of the human organism and upregulated by various stress conditions including those leading to inflammation. Since autophagy affects the effector cells of innate and adaptive immunity mediating the inflammatory response, its activity in these cells influences the antimicrobial response, the development of an effective cognate immune defense, and the course of the normal sterile inflammatory reactions. The level of autophagic activity may determine whether tissue cells die by apoptosis, necrosis, or through autophagy, and, as a consequence, whether the clearance of these dying cells is a silent process or results in an inflammatory response. Loss or decreased autophagy may lead to necrotic death that can initiate an inflammatory reaction in phagocytes through their surface and cytosolic receptors. Engulfment of certain cells dying through autophagy can activate the inflammasome. The intertwining regulatory connections between inflammation and immunity extend to pathologic conditions including chronic inflammatory diseases, autoimmunity and cancer.

Apoptosis and necrosis in vaccinia virus-infected HeLa G and BSC-40 cells

In most cells, vaccinia virus (VACV) infection is considered to cause a lytic cell death, an equivalent of necrosis. However, upon infection of the epithelial cell lines HeLa G and BSC-40 with VACV strain Western Reserve (WR), we have previously observed an increased activation of and activity attributable to caspases, a typical sign of apoptosis. In this paper, we have further analyzed the type of cell death in VACV-infected cells HeLa G and BSC-40. In a cell-based flow cytometric assay, we showed a specific activation of caspase-2 and 4 in HeLa G and BSC-40 cells infected with VACV, strain WR, while we did not find any effects of inhibitors of calpain and cathepsin D and E. The actual activity of the two caspases, but also of caspase-3, was then confirmed in lysates of infected HeLa G, but not in BSC-40 cells. Accordingly, poly(ADP)-ribose polymerase (PARP) cleavage was found increased only in infected HeLa G cells. Consequently, we have determined morphological features of apoptosis and/or activity of the executioner caspase-3 in infected HeLa G cells in situ, while only a background apoptosis was observed in infected BSC-40 cells. Finally, vaccination strains Dryvax and Praha were found to induce apoptosis in both HeLa G and BSC-40 cells, as characterized morphologically and by PARP cleavage. These findings may be important for understanding the differences in VACV-host interactions and post-vaccination complications in different individuals.

Heat shock protein 70 is acute phase reactant: response elicited by tumor treatment with photodynamic therapy

Oxidative stress in photodynamic therapy (PDT)-treated tumor cells is known to instigate a strong upregulation of the expression of heat shock proteins. However, the treatment of mouse Lewis lung carcinoma (LLC) cells with Photofrin™ PDT resulted in the upregulation of heat shock protein 70 (Hsp70) gene not only in these cells but also in co-incubated untreated Hepa 1-6 cells. To investigate whether this phenomenon extends in vivo, LLC tumors growing in C57BL/6 mice were treated with Photofrin™ PDT. The tumors and the livers from the mice were collected at 4, 8, or 24 h after therapy for quantitative reverse transcriptase polymerase chain reaction-based analysis of Hsp70 gene expression. Increased Hsp70 gene expression was detected in both the tumor and liver tissues and was most pronounced at 4 h after PDT. This effect was inhibited by treatment of host mice with glucocorticoid synthesis inhibitor metyrapone. Hsp70 protein levels in the livers of mice bearing PDT-treated tumors gradually decreased after therapy while serum levels increased at 4 h after therapy and then continually decreased. The exposure of in vitro PDT-treated LLC cells to Hsp70 and subsequent flow cytometry analysis revealed binding of this protein to cells that was dependent on PDT dose and more pronounced with dying than viable cells. Thus, following the induction of tumor injury by PDT, Hsp70 can be produced in the liver and spleen as acute phase reactant and released into circulation, from where it can be rapidly sequestered to damaged tumor tissue to facilitate the disposal of dying cells.

Cancer vaccines generated by photodynamic therapy

The development of photodynamic therapy (PDT)-generated cancer vaccines is potentially one of the most significant achievements in the field of PDT. Employing vaccine protocols optimizes the capacity of PDT of inducing a strong immune response against treated tumor due to the establishment of highly favourable conditions for maximizing the avidity of the immune reaction while sustaining and prolonging its tumor-destroying attack. While the introduction of PDT vaccines into the clinics and testing on patients is still in a very early phase, much work can still be done on further improvement of the potency of PDT vaccines. Considerable advances can be expected by identifying the most effective adjuvants to be used with PDT vaccines, which will most likely be different with different types of cancerous lesions.

Altered sialylation on the cell-surface proteins of dexamethasone-treated human macrophages contributes to augmented uptake of apoptotic neutrophils

Macrophages eliminate apoptotic granulocytes before their secondary necrosis during resolution of inflammation. A well-known glucocorticoid, the anti-inflammatory dexamethasone augments phagocytosis capacity of macrophages with a so far not fully clarified mechanism. We have found that sialylation of cell-surface proteins on human macrophages is markedly altered by dexamethasone. Compared to non-treated cells, dexamethasone-treated macrophages can bind significantly less Sambucus nigra lectin specific for sialic acids on their surfaces as a result of undersialylation of annexin-II and an HLA-II protein. Non-treated macrophages covered by S. nigra lectin had increased uptake of apoptotic cells; however, the significantly higher phagocytosis capacity of dexamethasone-treated macrophages could not be stimulated further this way. Our results suggest that dexamethasone treatment leads to decreased number of sialic acids on the surfaces of human macrophages promoting recognition and uptake of apoptotic cells.

PPARγ modulated inflammatory response of human dendritic cell subsets to engulfed apoptotic neutrophils

The means of how phagocytes handle apoptotic cells has a great impact on the outcome of immune responses. Here, we show that phagocytosis of allogeneic, apoptotic neutrophils by human monocyte-derived DCs is slow and less efficient than that of macrophages, and CD1a(-) DCs are more active in the engulfment of apoptotic neutrophils than CD1a(+) DCs. Blocking DC-SIGN function partially interferes with the uptake of apoptotic cells, and long-term interaction of apoptotic neutrophils with DCs makes them prone to proinflammatory cytokine responses. Engulfment of apoptotic cells sensitizes CD1a(-) DCs for high IL-8, TNF-α, IL-6, and CD1a(+) cells for IL-12 and IL-10 cytokine secretion elicited by additional inflammatory stimuli, which also result in the polarization of autologous T lymphocytes to Th1 effector cells. Ligand-induced activation of PPARγ by RSG results in enhanced phagocytosis, but the proinflammatory response and the capacity to trigger Th1 cell activation of CD1a(-) DCs are not enhanced. These results demonstrate that DCs are able to respond to allogeneic, apoptotic neutrophils with inflammatory cytokines and T cell responses in a subtype-specific manner that is modulated by the anti-inflammatory effects of PPARγ.

Secondary cytotoxicity mediated by alveolar macrophages: a contribution to the total efficacy of nanoparticles in lung cancer therapy?

Local treatment of lung cancer using inhalable nanoparticles (NPs) is an emerging and promising treatment option. The aim of this study was to investigate the activation of alveolar macrophages by poly (isobutyl cyanoacrylate) (BIPCA) NPs and the consequences of this activation on H460 lung cancer cells. A methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay was used to determine the primary cytotoxicity, that is, the immediate and direct cytotoxicity of doxorubicin (DOX)-loaded NPs on both cell lines. Macrophages were then treated using EC(50) concentrations of different treatments and co-cultured in a two-compartment system with H460 lung cancer cells. These treatments included DOX solution, blank NPs, and DOX-loaded NPs. The results showed that alveolar macrophages exposed to blank or DOX-loaded NPs showed cytotoxicity against cancer cells after 8 and 24h; this behavior was not expressed by naïve macrophages or macrophages treated with DOX solution. Sample analysis indicated that macrophages have the ability to release back fragments of NPs that were previously phagocytized. Further investigations showed that NPs can induce an increase in the excretion of Th1 cytokines namely, monocytes chemoattractant protein-1 (MCP-1), macrophages inflammatory protein (MIP-1), tumor necrosis factor alpha (TNF-alpha), and interferon gamma (IFN-gamma). The Th1 cytokines released by the alveolar macrophages might explain the significant secondary cytotoxicity effect on H460 cancer cells. Secondary cytotoxicity mediated by macrophages might compliment the direct cytotoxic effect that NPs have on cancer cells.

Molecular mechanisms of late apoptotic/necrotic cell clearance

Phagocytosis serves as one of the key processes involved in development, maintenance of tissue homeostasis, as well as in eliminating pathogens from an organism. Under normal physiological conditions, dying cells (e.g., apoptotic and necrotic cells) and pathogens (e.g., bacteria and fungi) are rapidly detected and removed by professional phagocytes such as macrophages and dendritic cells (DCs). In most cases, specific receptors and opsonins are used by phagocytes to recognize and bind their target cells, which can trigger the intracellular signalling events required for phagocytosis. Depending on the type of target cell, phagocytes may also release both immunomodulatory molecules and growth factors to orchestrate a subsequent immune response and wound healing process. In recent years, evidence is growing that opsonins and receptors involved in the removal of pathogens can also aid the disposal of dying cells at all stages of cell death, in particular plasma membrane-damaged cells such as late apoptotic and necrotic cells. This review provides an overview of the molecular mechanisms and the immunological outcomes of late apoptotic/necrotic cell removal and highlights the striking similarities between late apoptotic/necrotic cell and pathogen clearance.

Mrp-8 and -14 mediate CNS injury in focal cerebral ischemia

Several reports have recently demonstrated a detrimental role of Toll-like receptors (TLR) in cerebral ischemia, while there is little information about the endogenous ligands which activate TLR-signaling. The myeloid related proteins-8 and-14 (Mrp8/S100A8; Mrp14/S100A9) have recently been characterized as endogenous TLR4-agonists, and thus may mediate TLR-activation in cerebral ischemia. Interestingly, not only TLR-mRNAs, but also Mrp8 and Mrp14 mRNA were found to be induced in mouse brain between 3 and 48 h after transient 1 h focal cerebral ischemia/reperfusion. Mrp-protein was expressed in the ischemic hemisphere, and co-labeled with CD11b-positive cells. To test the hypothesis that Mrp-signaling contributes to the postischemic brain damage, we subjected Mrp14-deficient mice, which also lack Mrp8 protein expression, to focal cerebral ischemia. Mrp14-deficient mice had significantly smaller lesion volumes when compared to wild-type littermates (130+/-16 mm(3) vs. 105+/-28 mm(3)) at 2 days after transient focal cerebral ischemia (1 h), less brain swelling, and a reduced macrophage/microglia cell count in the ischemic hemisphere. We conclude that upregulation and signaling of Mrp-8 and-14 contribute to neuroinflammation and the progression of ischemic damage.

Acute phase response induction by cancer treatment with photodynamic therapy

Inflammation and immunity development are well recognized as responses to tumor treatment by photodynamic therapy (PDT). To demonstrate that another major host response effector process, acute phase response, may be also induced by this cancer treatment modality, the expression of serum amyloid P component (SAP) acknowledged as a hallmark acute phase reactant in the mouse was investigated following PDT of murine FsaR fibrosarcomas. The results reveal almost 150-fold increase in the expression of SAP gene in the liver of mice bearing tumors treated by Photofrin-mediated PDT, while serum SAP levels increased around 50-fold at the peak interval about 24 hr post PDT. The same tumor treatment induced also the liver gene upregulation and serum levels elevation of another established acute phase reactant, mannose-binding lectin A (MBL-A). Both SAP and MBL-A were found to accumulate in PDT-treated tumors, but this includes local production because their genes in these tumor tissues were upregulated as well. Gene encoding C-reactive protein (CRP) was also upregulated almost 7-fold in the same tumor tissues, suggesting a rare example of CRP participation in host response of the mouse. Interleukin-6 and glucocorticoid hormones were identified as major mediators promoting tumor PDT-induced upregulation of liver SAP gene. Moreover, glucocorticoids were found to act as critical inducers of SAP gene upregulation in PDT-treated tumors. The study definitely proves the occurrence of a strong acute phase response following tumor PDT, and reveals that glucocorticoid hormones released during this development impact the expression of host response-relevant genes in PDT-treated tumors.

In vivo and in vitro methods for studying apoptotic cell engulfment in Drosophila

Proper development of all multicellular organisms involves programmed apoptosis. Completion of this process requires removal of the resulting cell corpses through phagocytosis by their neighbors or by macrophages. Studies in C. elegans have been fruitful in the genetic dissection of key pathways, but they lack the professional immune system of higher organisms. Mammalian studies have identified a plethora of factors that are required for engulfment, but redundancy in the pathways has made it difficult to explain the genetic hierarchy of these factors. Thus, Drosophila has proven to be a useful evolutionary intermediate in which to examine this phenomenon. Here we describe methods used for dissecting the mechanisms and pathways involved in the engulfment of apoptotic cells by Drosophila phagocytes. Included are methods to be used for in vivo studies in the early embryo that can be used to examine engulfment of dying cells at various stages of embryogenesis. We also describe in vitro techniques for the use of Drosophila cell culture, including cell engulfment assays, that can be used for general phenotypic analysis, as well as live cell studies. We provide advice on imaging, including the preparation of samples for high-resolution microscopy and quantification of potential engulfment phenotypes for both in vivo and in vitro methods.

The regulation of autoreactive B cells during innate immune responses

Systemic lupus erythematosus (SLE) highlights the dangers of dysregulated B cells and the importance of initiating and maintaining tolerance. In addition to central deletion, receptor editing, peripheral deletion, receptor revision, anergy, and indifference, we have described a new mechanism of B cell tolerance wherein dendritic cells (DCs) and macrophages (MPhis) regulate autoreactive B cells during innate immune responses. In part, DCs and MPhis repress autoreactive B cells by releasing IL-6 and soluble CD40L (sCD40L). This mechanism is selective in that IL-6 and sCD40L do not affect Ig secretion by naïve cells during innate immune responses, allowing immunity in the absence of autoimmunity. In lupus-prone mice, DCs and MPhis are defective in secretion of IL-6 and sCD40L and cannot effectively repress autoantibody secretion suggesting that defects in DC/MPhi-mediated tolerance may contribute to the autoimmune phenotype. Further, these studies suggest that reconstituting DCs and MPhis in SLE patients might restore regulation of autoreactive B cells and provide an alternative to immunosuppressive therapies.

TLR2 has a detrimental role in mouse transient focal cerebral ischemia

A significant up-regulation of Toll-like-receptor (TLR) mRNAs between 3 and 48 h reperfusion time after induction of transient focal cerebral ischemia for 1h was revealed by applying global gene expression profiling in postischemic mouse brains. Compared to TLR4 and TLR9, TLR2 proved to be the most significantly up-regulated TLR in the ipsilateral brain hemisphere. TLR2-protein was found to be expressed mainly in microglia in the postischemic brain tissue, but also in selected endothelial cells, neurons, and astrocytes. Additionally, TLR2-related genes with pro-inflammatory and pro-apoptotic capabilities were induced. Therefore we hypothesized that TLR2-signaling could exacerbate the primary brain damage after ischemia. Two days after induction of transient focal cerebral ischemia (1h), we found a significant decrease of the infarct volume in TLR2 deficient mice compared to wild type mice (75+/-5 vs. 42+/-7 mm(3)). We conclude that TLR2 up-regulation and TLR2-signaling are important events in focal cerebral ischemia and contribute to the deterioration of ischemic damage.

PPARgamma-dependent regulation of human macrophages in phagocytosis of apoptotic cells

Macrophages acquire their capacity for efficient phagocytosis of apoptotic cells during their differentiation from monocytes. The peroxisome proliferator-activated receptor gamma (PPARgamma) is highly up-regulated during this maturation program. We report that addition of PPARgamma antagonist during differentiation of human monocytes to macrophages significantly reduced the capacity of macrophages to engulf apoptotic neutrophils, but did not influence phagocytosis of opsonized bacteria. Macrophage-specific deletion of PPARgamma in mice also resulted in decreased uptake of apoptotic cells. The antagonist acted in a dose-dependent manner during the differentiation of human macrophages and could also reverse the previously observed augmentation of phagocytosis by glucocorticoids. Blocking activation of PPARgamma led to down-regulation of molecular elements (CD36, AXL, TG2 and PTX3) of the engulfment process. Inhibition of PPARgamma-dependent gene expression did not block the anti-inflammatory effect of apoptotic neutrophils or synthetic glucocorticoid, but significantly decreased production of IL-10 induced by LPS. Our results suggest that during differentiation of macrophages natural ligands of PPARgamma are formed, regulating the expression of genes responsible for effective clearance of apoptotic cells and macrophage-mediated inflammatory responses.

Induction of apoptosis by crambene protects mice against acute pancreatitis via anti-inflammatory pathways

Apoptosis is a teleologically beneficial form of cell death in acute pancreatitis. Our previous work has demonstrated that induction of pancreatic acinar cell apoptosis by crambene protects mice against acute pancreatitis. However, little is known about how the induction of apoptosis reduces the severity of acute pancreatitis. Because the clearance of apoptotic cells might suppress inflammation and critically regulate immune responses, we postulate that clearance of apoptotic cells stimulates an anti-inflammatory response, which has a protective action against acute pancreatitis. To test this hypothesis, induction of apoptosis in acute pancreatitis in vivo and co-cultures of peritoneal resident macrophages with apoptotic acinar cells in vitro were used as experimental systems, testing expression of phagocytic receptors and levels of inflammatory mediators. Moreover, neutralizing anti-interleukin (IL)-10 monoclonal antibody (2.5 mg/kg) was used before the induction of apoptosis in acute pancreatitis, testing whether the protection from apoptosis induction would be removed. Our study showed that clearance of apoptotic acinar cells, which may occur essentially through the CD36-positive macrophage, stimulates the release of anti-inflammatory mediators like IL-10. IL-10 plays an important role in crambene-induced protection in acute pancreatitis. Thus, induction of pancreatic acinar cell apoptosis by crambene protects mice against acute pancreatitis via induction of anti-inflammatory pathways.

Clearance of dying autophagic cells of different origin by professional and non-professional phagocytes

MCF-7 cells undergo autophagic death upon tamoxifen treatment. Plated on non-adhesive substratum these cells died by anoikis while inducing autophagy as revealed by monodansylcadaverine staining, elevated light-chain-3 expression and electron microscopy. Both de novo and anoikis-derived autophagic dying cells were engulfed by human macrophages and MCF-7 cells. Inhibition of autophagy by 3-methyladenine abolished engulfment of cells dying through de novo autophagy, but not those dying through anoikis. Blocking exposure of phosphatidylserine (PS) on both dying cell types inhibited phagocytosis by MCF-7 but not by macrophages. Gene expression profiling showed that though both types of phagocytes expressed full repertoire of the PS recognition and signaling pathway, macrophages could evolve during engulfment of de novo autophagic cells the potential of calreticulin-mediated processes as well. Our data suggest that cells dying through autophagy and those committing anoikis with autophagy may engage in overlapping but distinct sets of clearance mechanisms in professional and non-professional phagocytes.

Immunomodulatory effect of nonsteroidal anti-inflammatory drugs (NSAIDs) at the clinically available doses

Non-steroidal anti-inflammatory drugs (NSAIDs) with cyclooxygenase (COX) inhibitory activity are commonly used in various inflammatory diseases. In this study, to examine the immunomodulatory effects of well known NSAIDs at clinically available doses, macrophage- and T cell-mediated immune responses such as tumor necrosis factor (TNF)-alpha release and nitric oxide (NO) production, cell-cell adhesion, phagocytic uptake and lymphocyte proliferation were investigated. NSAIDs tested significantly enhanced TNF-alpha release from lipopolysaccharide (LPS)-activated RAW264.7 cells at certain concentrations (fenoprofen, indomethacin, piroxicam, aceclofenac, diclofenac and sulindac) or in a dose-dependent manner (aspirin and phenylbutazone). Of NSAIDs, phenylbutazone and aspirin most potently attenuated NO production, although sulindac was the only compound with cytoprotective activity against LPS-induced cytotoxicity. Most NSAIDs used displayed weak or no modulatory effects on phagocytic uptake and CD29- or CD43-mediated cell-cell adhesion. Interestingly, however, phenylbutazone itself triggered cell-cell clustering under normal culture conditions and enhanced the phagocytic activity. Aspirin and phenylbutazone also dose-dependently attenuated CD4+ T cell proliferation stimulated by concanavalin A (Con A) and CD8+ CTLL-2 cell proliferation induced by interleukin (IL)-2. Sulindac only blocked CTLL-2 cell proliferation. These results suggest that NSAIDs may differentially exert immunomodulatory effects on activated macrophages and lymphocytes, and some of the effects may enforce NSAID's therapeutic effect against inflammatory symptoms.