Hox-driven conditional immortalization of myeloid and lymphoid progenitors: Uses, advantages, and future potential.

Those who study macrophage biology struggle with the decision whether to utilize primary macrophages derived directly from mice or opt for the convenience and genetic tractability of immortalized macrophage-like cell lines in in vitro studies. Particularly when it comes to studying phagocytosis and phagosomal maturation-a signature cellular process of the macrophage-many commonly used cell lines are not representative of what occurs in primary macrophages. A system developed by Mark Kamps' group, that utilizes conditionally constitutive activity of Hox transcription factors (Hoxb8 and Hoxa9) to immortalize differentiation-competent myeloid cell progenitors of mice, offers an alternative to the macrophage/macrophage-like dichotomy. In this resource, we will review the use of Hoxb8 and Hoxa9 as hematopoietic regulators to conditionally immortalize murine hematopoietic progenitor cells which retain their ability to differentiate into many functional immune cell types including macrophages, neutrophils, basophils, osteoclasts, eosinophils, dendritic cells, as well as limited potential for the generation of lymphocytes. We further demonstrate that the use of macrophages derived from Hoxb8/Hoxa9 immortalized progenitors and their similarities to bone marrow-derived macrophages. To supplement the existing data, mass spectrometry-based proteomics, flow cytometry, cytology, and in vitro phagosomal assays were conducted on macrophages derived from Hoxb8 immortalized progenitors and compared to bone marrow-derived macrophages and the macrophage-like cell line J774. We additionally propose the use of a standardized nomenclature to describe cells derived from the Hoxb8/Hoxa9 system in anticipation of their expanded use in the study of leukocyte cell biology.

Blockade of Proteinase-Activated Receptor 2 (PAR2) Attenuates Neuroinflammation in Experimental Autoimmune Encephalomyelitis.

Proteinase-activated receptor-2 (PAR2), which modulates inflammatory responses, is elevated in the central nervous system in multiple sclerosis (MS) and in its murine model, experimental autoimmune encephalomyelitis (EAE). In PAR2-null mice, disease severity of EAE is markedly diminished. We therefore tested whether inhibiting PAR2 activation in vivo might be a viable strategy for the treatment of MS. Using the EAE model, we show that a PAR2 antagonist, the pepducin palmitoyl-RSSAMDENSEKKRKSAIK-amide (P2pal-18S), attenuates EAE progression by affecting immune cell function. P2pal-18S treatment markedly diminishes disease severity and reduces demyelination, as well as the infiltration of T-cells and macrophages into the central nervous system. Moreover, P2pal-18S decreases granulocyte-macrophage colony-stimulating factor (GM-CSF) production and T-cell activation in cultured splenocytes and prevents macrophage polarization in vitro. We conclude that PAR2 plays a key role in regulating neuroinflammation in EAE and that PAR2 antagonists represent promising therapeutic agents for treating MS and other neuroinflammatory diseases. SIGNIFICANCE STATEMENT: Proteinase-activated receptor-2 modulates inflammatory responses and is increased in multiple sclerosis lesions. We show that the proteinase-activated receptor-2 antagonist palmitoyl-RSSAMDENSEKKRKSAIK-amide reduces disease in the murine experimental autoimmune encephalomyelitis model of multiple sclerosis by inhibiting T-cell and macrophage activation and infiltration into the central nervous system, making it a potential treatment for multiple sclerosis.

Extracellular cathepsin Z signals through the α5 integrin and augments NLRP3 inflammasome activation.

Respiratory silicosis is a preventable occupational disease that develops secondary to the aspiration of crystalline silicon dioxide (silica) into the lungs, activation of the NLRP3 inflammasome, and IL-1ß production. Cathepsin Z has been associated with the development of inflammation and IL-1ß production; however, the mechanism of how cathepsin Z leads to IL-1ß production is unknown. Here, the requirement for cathepsin Z in silicosis was determined using WT mice and mice deficient in cathepsin Z. The activation of the NLRP3 inflammasome in macrophages was studied using WT and cathepsin Z-deficient bone marrow-derived murine dendritic cells and the human monocytic cell line THP-1. The cells were activated with silica, and IL-1ß release was determined using enzyme-linked immunosorbent assay or IL-1ß bioassays. The relative contribution of the active domain or integrin-binding domain of cathepsin Z was studied using recombinant cathepsin Z constructs and the α5 integrin neutralizing antibody. We report that the lysosomal cysteine protease cathepsin Z potentiates the development of inflammation associated with respiratory silicosis by augmenting NLRP3 inflammasome-derived IL-1ß expression in response to silica. The secreted cathepsin Z functions nonproteolytically via the internal integrin-binding domain to impact caspase-1 activation and the production of active IL-1ß through integrin α5 without affecting the transcription levels of NLRP3 inflammasome components. This work reveals a regulatory pathway for the NLRP3 inflammasome that occurs in an outside-in fashion and provides a link between extracellular cathepsin Z and inflammation. Furthermore, it reveals a level of NLRP3 inflammasome regulation that has previously only been found downstream of extracellular pathogens.

Gestational bisphenol-A exposure lowers the threshold for autoimmunity in a model of multiple sclerosis.

Environmental and hormonal factors are implicated in dysimmunity in multiple sclerosis. We investigated whether bisphenol-A, a prominent contaminant with endocrine-disrupting capabilities, altered susceptibility in an inflammatory model of multiple sclerosis. We found that gestational, but not adult, exposure to bisphenol-A increased the development of experimental autoimmune encephalomyelitis in adulthood in male, but not female, mice when a suboptimal disease-inducing immunization was used. Gestational bisphenol-A in male mice primed macrophages in adulthood and raised granulocyte-colony stimulating factor and neutrophil counts/activity postsuboptimal immunization. Neutralizing granulocyte-colony stimulating factor blocked susceptibility to disease in bisphenol-A mice. Early life exposure to bisphenol-A may represent an environmental consideration in multiple sclerosis.

The cooling compound icilin attenuates autoimmune neuroinflammation through modulation of the T-cell response.

The synthetic supercooling drug, icilin, and its primary receptor target, the cation channel transient receptor potential (TRP) melastatin-8 (TRPM8), have been described as potent negative regulators of inflammation in the colon. The aim of this study was to determine whether the anti-inflammatory action of icilin could potentially be used to treat autoimmune neuroinflammatory disorders, such as multiple sclerosis (MS). During experimental autoimmune encephalomyelitis (EAE)-a CD4+ T cell-driven murine model of MS-we found that both wild-type (WT) and TRPM8-deficient EAE mice were protected from disease progression during icilin treatment, as evidenced by delays in clinical onset and reductions in neuroinflammation. In vitro, icilin potently inhibited the proliferation of murine and human CD4+ T cells, with the peripheral expansion of autoantigen-restricted T cells similarly diminished by the administration of icilin in mice. Attenuation of both TRPM8-/- and TRP ankyrin-1-/- T-cell proliferation by icilin was consistent with the WT phenotype, which suggests a mechanism that is independent of these channels. In addition, icilin treatment altered the expressional profile of activated CD4+ T cells to one that was indicative of restricted effector function and limited neuroinflammatory potential. These findings identify a potent anti-inflammatory role for icilin in lymphocyte-mediated neuroinflammation and highlight clear pleiotropic effects of the compound beyond classic TRP channel activation.-Ewanchuk, B. W., Allan, E. R. O., Warren, A. L., Ramachandran, R., Yates, R. M. The cooling compound icilin attenuates autoimmune neuroinflammation through modulation of the T-cell response.

Ligation of FcγR Alters Phagosomal Processing of Protein via Augmentation of NADPH Oxidase Activity.

Proteolysis and the reduction of disulfides, both major components of protein degradation, are profoundly influenced by phagosomal redox conditions in macrophages. We evaluated the activation of phagocytic receptors that are known to influence activation of the phagocyte NADPH oxidase (NOX2), and its effect on phagosomal protein degradation. Population-based and single phagosome analyses of phagosomal chemistries in murine macrophages revealed that activation of NOX2 via the Fcγ receptor (FcγR) during phagocytosis decreased rates of proteolysis and disulfide reduction. Immunoglobulin G (IgG)-stimulated reactive oxygen species (ROS) production and the inhibition of phagosomal proteolysis and disulfide reduction were dependent on NOX2, FcγR and protein kinase C (PKC)/spleen tyrosine kinase (Syk) signaling. In contrast, low levels of ROS production were observed following the phagocytosis of unopsonized beads, which resulted in higher rates of phagosomal proteolysis and disulfide reduction. Phagosomes displayed autonomy with respect to FcγR-mediated differences in NOX2 activation and proteolysis, as phagosomes containing unopsonized cargo retained low NOX2 activation and high proteolysis even in the presence of phagosomes containing IgG-opsonized cargo in the same macrophage. These results show that opsonization of phagocytic cargo results in vastly different phagosomal processing of proteins through the FcγR-triggered, PKC/Syk-dependent local assembly and activation of NOX2.

A role for cathepsin Z in neuroinflammation provides mechanistic support for an epigenetic risk factor in multiple sclerosis.

BACKGROUND: Hypomethylation of the cathepsin Z locus has been proposed as an epigenetic risk factor for multiple sclerosis (MS). Cathepsin Z is a unique lysosomal cysteine cathepsin expressed primarily by antigen presenting cells. While cathepsin Z expression has been associated with neuroinflammatory disorders, a role for cathepsin Z in mediating neuroinflammation has not been previously established. METHODS: Experimental autoimmune encephalomyelitis (EAE) was induced in both wildtype mice and mice deficient in cathepsin Z. The effects of cathepsin Z-deficiency on the processing and presentation of the autoantigen myelin oligodendrocyte glycoprotein, and on the production of IL-1ß and IL-18 were determined in vitro from cells derived from wildtype and cathepsin Z-deficient mice. The effects of cathepsin Z-deficiency on CD4+ T cell activation, migration, and infiltration to the CNS were determined in vivo. Statistical analyses of parametric data were performed by one-way ANOVA followed by Tukey post-hoc tests, or by an unpaired Student's t test. EAE clinical scoring was analyzed using the Mann-Whitney U test. RESULTS: We showed that mice deficient in cathepsin Z have reduced neuroinflammation and dramatically lowered circulating levels of IL-1ß during EAE. Deficiency in cathepsin Z did not impact either the processing or the presentation of MOG, or MOG- specific CD4+ T cell activation and trafficking. Consistently, we found that cathepsin Z-deficiency reduced the efficiency of antigen presenting cells to secrete IL-1ß, which in turn reduced the ability of mice to generate Th17 responses-critical steps in the pathogenesis of EAE and MS. CONCLUSION: Together, these data support a novel role for cathepsin Z in the propagation of IL-1ß-driven neuroinflammation.

Phagosomal proteolysis in dendritic cells is modulated by NADPH oxidase in a pH-independent manner.

The level of proteolysis within phagosomes of dendritic cells (DCs) is thought to be tightly regulated, as it directly impacts the cell's efficiency to process antigen. Activity of the antimicrobial effector NADPH oxidase (NOX2) has been shown to reduce levels of proteolysis within phagosomes of both macrophages and DCs. However, the proposed mechanisms underlying these observations in these two myeloid cell lineages are dissimilar. Using real-time analysis of lumenal microenvironmental parameters within phagosomes in live bone marrow-derived DCs, we show that the levels of phagosomal proteolysis are diminished in the presence of NOX2 activity, but in contrast to previous reports, the acidification of the phagosome is largely unaffected. As found in macrophages, we show that NOX2 controls phagosomal proteolysis in DCs through redox modulation of local cysteine cathepsins. Aspartic cathepsins were unaffected by redox conditions, indicating that NOX2 skews the relative protease activities in these antigen processing compartments. The ability of DC phagosomes to reduce disulphides was also compromised by NOX2 activity, implicating this oxidase in the control of an additional antigen processing chemistry of DCs.

Infection of porcine bone marrow-derived macrophages by porcine respiratory and reproductive syndrome virus impairs phagosomal maturation.

Porcine reproductive and respiratory syndrome virus (PRRSV), a positive-sense, ssRNA virus of the genus Arterivirus, is a devastating disease of swine worldwide. Key early targets of PRRSV infection in pigs include professional phagocytes in the lung, such as alveolar and interstitial macrophages and dendritic cells, the dysfunction of which is believed to be responsible for much of the associated mortality. In order to study the effect of virus infection on phagocyte function, the development of a robust, reproducible model would be advantageous. Given the limitations of current models, we set out to develop a porcine bone marrow-derived macrophage (PBMMΦ) cell model to study phagosomal maturation and function during PRRSV infection. Derivation of PBMMΦs from marrow using cultured L929 fibroblast supernatant produced a homogeneous population of cells that exhibited macrophage-like morphology and proficiency in Fc-receptor-mediated phagocytosis and phagosomal maturation. PBMMΦs were permissive to PRRSV infection, resulting in a productive infection that peaked at 24 h. Assessment of the effect of PRRSV infection on the properties of phagosomal maturation in PBMMΦs revealed a significant decrease in phagosomal proteolysis and lowered production of reactive oxygen species, but no change in PBMMΦ viability, phagocytosis or the ability of phagosomes to acidify. In this study, we present a new model to investigate PRRSV infection of phagocytes, which demonstrates a significant effect on phagosomal maturation with the associated implications on proper macrophage function. This model can also be used to study the effect on the phagosomal microenvironment of infection by other viruses targeting porcine macrophages.

Redirecting soluble antigen for MHC class I cross-presentation during phagocytosis.

Peptides presented by MHC class I molecules are mostly derived from proteins synthesized by the antigen-presenting cell itself, while peptides presented by MHC class II molecules are predominantly from materials acquired by endocytosis. External antigens can also be presented by MHC class I molecules in a process referred to as cross-presentation. Here, we report that mouse dendritic cell (DC) engagement to a phagocytic target alters endocytic processing and inhibits the proteolytic activities. During phagocytosis, endosome maturation is delayed, shows less progression toward the lysosome, and the endocytosed soluble antigen is targeted for MHC class I cross-presentation. The antigen processing in these arrested endosomes is under the control of NAPDH oxidase associated ROS. We also show that cathepsin S is responsible for the generation of the MHC class I epitope. Taken together, our results suggest that in addition to solid structure uptake, DC phagocytosis simultaneously modifies the kinetics of endosomal trafficking and maturation. As a consequence, external soluble antigens are targeted into the MHC class I cross-presentation pathway.

NADPH oxidase modifies patterns of MHC class II-restricted epitopic repertoires through redox control of antigen processing.

The chemistries within phagosomes of APCs mediate microbial destruction as well as generate peptides for presentation on MHC class II. The antimicrobial effector NADPH oxidase (NOX2), which generates superoxide within maturing phagosomes, has also been shown to regulate activities of cysteine cathepsins through modulation of the lumenal redox potential. Using real-time analyses of lumenal microenvironmental parameters, in conjunction with hydrolysis pattern assessment of phagocytosed proteins, we demonstrated that NOX2 activity not only affects levels of phagosomal proteolysis as previously shown, but also the pattern of proteolytic digestion. Additionally, it was found that NOX2 deficiency adversely affected the ability of bone marrow-derived macrophages, but not dendritic cells, to process and present the I-A(b)-immunodominant peptide of the autoantigen myelin oligodendrocyte glycoprotein (MOG). Computational and experimental analyses indicated that the I-A(b) binding region of the immunodominant peptide of MOG is susceptible to cleavage by the NOX2-controlled cysteine cathepsins L and S in a redox-dependent manner. Consistent with these findings, I-A(b) mice that were deficient in the p47(phox) or gp91(phox) subunits of NOX2 were partially protected from MOG-induced experimental autoimmune encephalomyelitis and displayed compromised reactivation of MOG-specific CD4(+) T cells in the CNS, despite eliciting a normal primary CD4(+) T cell response to the inoculated MOG Ag. Taken together, this study demonstrates that the redox microenvironment within the phagosomes of APCs is a determinant in MHC class II repertoire production in a cell-specific and Ag-specific manner, which can ultimately impact susceptibility to CD4(+) T cell-driven autoimmune disease processes.

γ-Interferon-inducible lysosomal thiol reductase (GILT) maintains phagosomal proteolysis in alternatively activated macrophages.

Although it is known that lysosomal cysteine cathepsins require a reducing environment for optimal activity, it is not firmly established how these enzymes are maintained in their reduced-active state in the acidic and occasionally oxidative environment within phagosomes and lysosomes. γ-Interferon-inducible lysosomal thiol reductase (GILT) has been the only enzyme described in the endosomes, lysosomes, and phagosomes with the potential to catalyze the reduction of cysteine cathepsins. Our goal in the current study was to assess the effect of GILT on major phagosomal functions with an emphasis on proteolytic efficiency in murine bone marrow-derived macrophages. Assessment of phagosomal disulfide reduction upon internalization of IgG-opsonized experimental particles confirmed a major role for GILT in phagosomal disulfide reduction in both resting and interferon-γ-activated macrophages. Furthermore we observed a decrease in early phagosomal proteolytic efficiency in GILT-deficient macrophages, specifically in the absence of an NADPH oxidase-mediated respiratory burst. This deficiency was more prominent in IL-4-activated macrophages that inherently possess lower levels of NADPH oxidase activity. Finally, we provide evidence that GILT is required for optimal activity of the lysosomal cysteine protease, cathepsin S. In summary, our results suggest a role for GILT in maintaining cysteine cathepsin proteolytic efficiency in phagosomes, particularly in the absence of high NADPH oxidase activity, which is characteristic of alternatively activated macrophages.

Targeting mitochondria-derived reactive oxygen species to reduce epithelial barrier dysfunction and colitis.

Epithelial permeability is often increased in inflammatory bowel diseases. We hypothesized that perturbed mitochondrial function would cause barrier dysfunction and hence epithelial mitochondria could be targeted to treat intestinal inflammation. Mitochondrial dysfunction was induced in human colon-derived epithelial cell lines or colonic biopsy specimens using dinitrophenol, and barrier function was assessed by transepithelial flux of Escherichia coli with or without mitochondria-targeted antioxidant (MTA) cotreatment. The impact of mitochondria-targeted antioxidants on gut permeability and dextran sodium sulfate (DSS)-induced colitis in mice was tested. Mitochondrial superoxide evoked by dinitrophenol elicited significant internalization and translocation of E. coli across epithelia and control colonic biopsy specimens, which was more striking in Crohn's disease biopsy specimens; the mitochondria-targeted antioxidant, MitoTEMPO, inhibited these barrier defects. Increased gut permeability and reduced epithelial mitochondrial voltage-dependent anion channel expression were observed 3 days after DSS. These changes and the severity of DSS-colitis were reduced by MitoTEMPO treatment. In vitro DSS-stimulated IL-8 production by epithelia was reduced by MitoTEMPO. Metabolic stress evokes significant penetration of commensal bacteria across the epithelium, which is mediated by mitochondria-derived superoxide acting as a signaling, not a cytotoxic, molecule. MitoTEMPO inhibited this barrier dysfunction and suppressed colitis in DSS-colitis, likely via enhancing barrier function and inhibiting proinflammatory cytokine production. These novel findings support consideration of MTAs in the maintenance of epithelial barrier function and the management of inflammatory bowel diseases.

Giardia duodenalis cathepsin B proteases degrade intestinal epithelial interleukin-8 and attenuate interleukin-8-induced neutrophil chemotaxis.

Giardia duodenalis (syn. G. intestinalis, G. lamblia) infections are a leading cause of waterborne diarrheal disease that can also result in the development of postinfectious functional gastrointestinal disorders via mechanisms that remain unclear. Parasite numbers exceed 10(6) trophozoites per centimeter of gut at the height of an infection. Yet the intestinal mucosa of G. duodenalis-infected individuals is devoid of signs of overt inflammation. G. duodenalis infections can also occur concurrently with infections with other proinflammatory gastrointestinal pathogens. Little is known of whether and how this parasite can attenuate host inflammatory responses induced by other proinflammatory stimuli, such as a gastrointestinal pathogen. Identifying hitherto-unrecognized parasitic immunomodulatory pathways, the present studies demonstrated that G. duodenalis trophozoites attenuate secretion of the potent neutrophil chemoattractant interleukin-8 (CXCL8); these effects were observed in human small intestinal mucosal tissues and from intestinal epithelial monolayers, activated through administration of proinflammatory interleukin-1ß or Salmonella enterica serovar Typhimurium. This attenuation is caused by the secretion of G. duodenalis cathepsin B cysteine proteases that degrade CXCL8 posttranscriptionally. Furthermore, the degradation of CXCL8 via G. duodenalis cathepsin B cysteine proteases attenuates CXCL8-induced chemotaxis of human neutrophils. Taken together, these data demonstrate for the first time that G. duodenalis trophozoite cathepsins are capable of attenuating a component of their host's proinflammatory response induced by a separate proinflammatory stimulus.

Intracellular chloride channel protein CLIC1 regulates macrophage function through modulation of phagosomal acidification.

Intracellular chloride channel protein 1 (CLIC1) is a 241 amino acid protein of the glutathione S transferase fold family with redox- and pH-dependent membrane association and chloride ion channel activity. Whilst CLIC proteins are evolutionarily conserved in Metazoa, indicating an important role, little is known about their biology. CLIC1 was first cloned on the basis of increased expression in activated macrophages. We therefore examined its subcellular localisation in murine peritoneal macrophages by immunofluorescence confocal microscopy. In resting cells, CLIC1 is observed in punctate cytoplasmic structures that do not colocalise with markers for endosomes or secretory vesicles. However, when these macrophages phagocytose serum-opsonised zymosan, CLIC1 translocates onto the phagosomal membrane. Macrophages from CLIC1(-/-) mice display a defect in phagosome acidification as determined by imaging live cells phagocytosing zymosan tagged with the pH-sensitive fluorophore Oregon Green. This altered phagosomal acidification was not accompanied by a detectable impairment in phagosomal-lysosomal fusion. However, consistent with a defect in acidification, CLIC1(-/-) macrophages also displayed impaired phagosomal proteolytic capacity and reduced reactive oxygen species production. Further, CLIC1(-/-) mice were protected from development of serum transfer induced K/BxN arthritis. These data all point to an important role for CLIC1 in regulating macrophage function through its ion channel activity and suggest it is a suitable target for the development of anti-inflammatory drugs.

Alternative activation of macrophages by IL-4 enhances the proteolytic capacity of their phagosomes through synergistic mechanisms.

Alternatively activated macrophages, generated in a T-helper 2 environment, have demonstrated roles in wound repair and tissue remodeling in addition to being charged with immune tasks. Because the hydrolytic chemistries of the phagosomal lumen are central to many of these functions, we investigated their modification after alternative activation with IL-4 and IL-13. Most significantly, we found striking up-regulation of the proteolytic levels within the phagosome of IL-4-activated macrophages. Two synergistic mechanisms were determined to underlie this up-regulation. First, IL-4-activated macrophages displayed increased expression of cathepsin S and L, providing greater proteolytic machinery to the phagosome despite unchanged rates of lysosomal contribution. Secondly, decreased phagosomal NADPH oxidase (NOX2) activity, at least partially resulting from decreased expression of the NOX2 subunit gp91(phox), resulted in a more reductive lumenal microenvironment, which in turn, enhanced activities of local cysteine cathepsins. Decreased NOX2 activity additionally increased the phagosome's ability to reduce disulfides, further enhancing the efficiency of the macrophage to degrade proteins containing disulfide bonds. Together, these changes initiated by IL-4 act synergistically to rapidly and dramatically enhance the macrophage's ability to degrade phagocytosed protein, which, we reason, better equips this cell for its roles in wound repair and tissue remodeling.

NADPH oxidase activity controls phagosomal proteolysis in macrophages through modulation of the lumenal redox environment of phagosomes.

The phagosomal lumen in macrophages is the site of numerous interacting chemistries that mediate microbial killing, macromolecular degradation, and antigen processing. Using a non-hypothesis-based screen to explore the interconnectivity of phagosomal functions, we found that NADPH oxidase (NOX2) negatively regulates levels of proteolysis within the maturing phagosome of macrophages. Unlike the NOX2 mechanism of proteolytic control reported in dendritic cells, this phenomenon in macrophages is independent of changes to lumenal pH and is also independent of hydrolase delivery to the phagosome. We found that NOX2 mediates the inhibition of phagosomal proteolysis in macrophages through reversible oxidative inactivation of local cysteine cathepsins. We also show that NOX2 activity significantly compromises the phagosome's ability to reduce disulfides. These findings indicate that NOX2 oxidatively inactivates cysteine cathepsins through sustained ablation of the reductive capacity of the phagosomal lumen. This constitutes a unique mechanism of spatiotemporal control of phagosomal chemistries through the modulation of the local redox environment. In addition, this work further implicates the microbicidal effector NOX2 as a global modulator of phagosomal physiologies, particularly of those pertinent to antigen processing.

Eructophagy: macrophages use autophagic machinery to burp out parts of their meal.

The phagolysosome is an antimicrobial and degradative organelle that plays key roles in macrophage-mediated inflammatory and homeostatic functions. Whereas mature phagolysosomes are known to sequester and degrade their contents into basic nutrients, they were not previously assigned an active role in amplifying inflammation. We have described a novel macrophage process in which partially digested immunostimulatory PAMPs are released extracellularly from the mature phagolysosome via discrete events we term eructophagy. Eructophagy is induced by proinflammatory stimuli, negatively regulated by IL4 and MTOR, and is dependent on key autophagy proteins, including fusion machinery of degradative and secretory autophagy. We propose that macrophages use eructophagy to release processed PAMPs/DAMPs to amplify local inflammation.

The Derivation and Use of HoxB8-Driven Conditionally Immortalized Macrophages.

The use of Hox-driven conditionally immortalized immune cells has significantly increased in biomedical research over the past 15 years. HoxB8-driven conditionally immortalized myeloid progenitor cells maintain their ability to differentiate into functional macrophages. There are multiple benefits to this conditional immortalization strategy including the ability for unlimited propagation, genetic mutability, primary-like immune cells (macrophages, dendritic cells, and granulocytes) on demand, derivation from variety of mouse strains, and simple cryopreservation and reconstitution. In this chapter, we will discuss how to derive and use these HoxB8-conditionally immortalized myeloid progenitor cells.

Approaches to Measuring Reductive and Oxidative Events in Phagosomes.

The phagosome is a redox-active organelle. Numerous reductive and oxidative systems play both direct and indirect roles in phagosomal function. With the advent of newer methodologies to study these redox events in live cells, the details of how redox conditions change within the maturing phagosome, how they are regulated, and how they influence other phagosomal functions can be investigated. In this chapter, we detail phagosome-specific, fluorescence-based assays that measure disulfide reduction and the production of reactive oxygen species in live phagocytes such as macrophages and dendritic cells, in real time.