Role of granulocyte/macrophage colony-stimulating factor in zymocel-induced hepatic granuloma formation

Aberrant Lipid Metabolism in Macrophages Is Associated with Granuloma Formation in Sarcoidosis

Rationale: Chronic sarcoidosis is a complex granulomatous disease with limited treatment options that can progress over time. Understanding the molecular pathways contributing to disease would aid in new therapeutic development. Objectives: To understand whether macrophages from patients with nonresolving chronic sarcoidosis are predisposed to macrophage aggregation and granuloma formation and whether modulation of the underlying molecular pathways influence sarcoidosis granuloma formation. Methods: Macrophages were cultivated in vitro from isolated peripheral blood CD14+ monocytes and evaluated for spontaneous aggregation. Transcriptomics analyses and phenotypic and drug inhibitory experiments were performed on these monocyte-derived macrophages. Human skin biopsies from patients with sarcoidosis and a myeloid Tsc2-specific sarcoidosis mouse model were analyzed for validatory experiments. Measurements and Main Results: Monocyte-derived macrophages from patients with chronic sarcoidosis spontaneously formed extensive granulomas in vitro compared with healthy control participants. Transcriptomic analyses separated healthy and sarcoidosis macrophages and identified an enrichment in lipid metabolic processes. In vitro patient granulomas, sarcoidosis mouse model granulomas, and those directly analyzed from lesional patient skin expressed an aberrant lipid metabolism profile and contained increased neutral lipids. Conversely, a combination of statins and cholesterol-reducing agents reduced granuloma formation both in vitro and in vivo in a sarcoidosis mouse model. Conclusions: Together, our findings show that altered lipid metabolism in sarcoidosis macrophages is associated with its predisposition to granuloma formation and suggest cholesterol-reducing therapies as a treatment option in patients.

Differential immunological effects of silica nanoparticles on peripheral blood mononuclear cells of silicosis patients and controls

Silicosis is a fibrotic disease caused by the inhalation of respirable silica particles, which are typically engulfed by alveolar macrophages and subsequently induce the release of inflammatory cytokines. Various animal experimental and human studies have focused on modeling silicosis, to assess the interactions of macrophages and other cell types with silica particles. There is still, however, limited knowledge on the differential response upon silica-exposure between silicosis patients and controls. We focused on studying the responsiveness of peripheral blood mononuclear cells (PBMCs) to silica nanoparticles (SiNPs) - Ludox and NM-200 - of silicosis patients and controls. The proliferative capacity of T- CD3⁺ and B- CD19⁺ cells, were evaluated via Carboxyfluorescein succinimidyl ester (CFSE) assay. The activation status of lymphocyte subsets and response to silica were also evaluated by comparing the extent of micro-granuloma or aggregate formation with the cytokine secretion profiles between both groups of individuals. The proliferative capacity of CD19⁺ cells was elevated in silicotic patients as opposed to controls. Subsets of regulatory T cells (CD4⁺ CD25⁺ and CD8⁺ CD25⁺) and immunoglobulins IgM and IgG were also significantly increased in patients. The number and the size of aggregates formed were higher with SiNPs stimulation in patients compared to controls. Multivariable analysis also elucidated the role of key cytokines like interleukin-1β (IL-1β), IL-6 and interferon-gamma (IFN-γ), which were upregulated in SiNP-stimulated PBMCs of patients compared to controls. Our ex vivo model thus has potential to provide insights into the immunological effects of silica particles in lymphocytes of silicosis patients and controls.

Human Macrophages Exhibit GM-CSF Dependent Restriction of Mycobacterium tuberculosis Infection via Regulating Their Self-Survival, Differentiation and Metabolism

GM-CSF is an important cytokine that regulates the proliferation of monocytes/macrophages and its various functions during health and disease. Although growing evidences support the notion that GM-CSF could play a major role in immunity against tuberculosis (TB) infection, the mechanism of GM-CSF mediated protective effect against TB remains largely unknown. Here in this study we examined the secreted levels of GM-CSF by human macrophages from different donors along with the GM-CSF dependent cellular processes that are critical for control of M. tuberculosis infection. While macrophage of different donors varied in their ability to produce GM-CSF, a significant correlation was observed between secreted levels of GM-CSF, survial of macrophages and intra-macrophage control of Mycobacterium tuberculosis bacilli. GM-CSF levels secreted by macrophages negatively correlated with the intra-macrophage M. tuberculosis burden, survival of infected host macrophages positively correlated with their GM-CSF levels. GM-CSF-dependent prolonged survival of human macrophages also correlated with significantly decreased bacterial burden and increased expression of self-renewal/cell-survival associated genes such as BCL-2 and HSP27. Antibody-mediated depletion of GM-CSF in macrophages resulted in induction of significantly elevated levels of apoptotic/necrotic cell death and a simultaneous decrease in autophagic flux. Additionally, protective macrophages against M. tuberculosis that produced more GM-CSF, induced a stronger granulomatous response and produced significantly increased levels of IL-1β, IL-12 and IL-10 and decreased levels of TNF-α and IL-6. In parallel, macrophages isolated from the peripheral blood of active TB patients exhibited reduced capacity to control the intracellular growth of M. tuberculosis and produced significantly lower levels of GM-CSF. Remarkably, as compared to healthy controls, macrophages of active TB patients exhibited significantly altered metabolic state correlating with their GM-CSF secretion levels. Altogether, these results suggest that relative levels of GM-CSF produced by human macrophages plays a critical role in preventing cell death and maintaining a protective differentiation and metabolic state of the host cell against M. tuberculosis infection.

Kupffer cell restoration after partial hepatectomy is mainly driven by local cell proliferation in IL-6-dependent autocrine and paracrine manners

Kupffer cells (KCs), which are liver-resident macrophages, originate from the fetal yolk sac and represent one of the largest macrophage populations in the body. However, the current data on the origin of the cells that restore macrophages during liver injury and regeneration remain controversial. Here, we address the question of whether liver macrophage restoration results from circulating monocyte infiltration or local KC proliferation in regenerating livers after partial hepatectomy (PHx) and uncover the underlying mechanisms. By using several strains of genetically modified mice and performing immunohistochemical analyses, we demonstrated that local KC proliferation mainly contributed to the restoration of liver macrophages after PHx. Peak KC proliferation was impaired in Il6-knockout (KO) mice and restored after the administration of IL-6 protein, whereas KC proliferation was not affected in Il4-KO or Csf2-KO mice. The source of IL-6 was identified using hepatocyte- and myeloid-specific Il6-KO mice and the results revealed that both hepatocytes and myeloid cells contribute to IL-6 production after PHx. Moreover, peak KC proliferation was also impaired in myeloid-specific Il6 receptor-KO mice after PHx, suggesting that IL-6 signaling directly promotes KC proliferation. Studies using several inhibitors to block the IL-6 signaling pathway revealed that sirtuin 1 (SIRT1) contributed to IL-6-mediated KC proliferation in vitro. Genetic deletion of the Sirt1 gene in myeloid cells, including KCs, impaired KC proliferation after PHx. In conclusion, our data suggest that KC repopulation after PHx is mainly driven by local KC proliferation, which is dependent on IL-6 and SIRT1 activation in KCs.

Large-scale discovery of previously undetected microRNAs specific to human liver

MicroRNAs (miRNAs) are crucial regulators of gene expression in normal development and cellular homeostasis. While miRNA repositories contain thousands of unique sequences, they primarily contain molecules that are conserved across several tissues, largely excluding lineage and tissue-specific miRNAs. By analyzing small non-coding RNA sequencing data for abundance and secondary RNA structure, we discovered 103 miRNA candidates previously undescribed in liver tissue. While expression of some of these unannotated sequences is restricted to non-malignant tissue, downregulation of most of the sequences was detected in liver tumors, indicating their importance in the maintenance of liver homeostasis. Furthermore, target prediction revealed the involvement of the unannotated miRNA candidates in fatty-acid metabolism and tissue regeneration, which are key pathways in liver biology. Here, we provide a comprehensive analysis of the undiscovered liver miRNA transcriptome, providing new resources for a deeper exploration of organ-specific biology and disease.

Chronic granulomatous dermatitis induced by talimogene laherparepvec therapy of melanoma metastases

Talimogene laherparepvec (TVEC) is the first oncolytic viral immunotherapy approved by the FDA, for advanced melanoma consisting of genetically modified herpes simplex type 1 virus which selectively replicates causing tumor lysis, expressing granulocyte macrophage-colony stimulating factor (GM-CSF) and activating dendritic cells. Intratumoral injection of TVEC produces objective response in 41% of stage IIB-IV M1a melanoma. However, clinical response assessment can be problematic due to immune-related inflammation at established tumor sites. Herein, we report 5 cases of granulomatous dermatitis developing at sites of TVEC injection associated with pathologic complete response in 4 of 5 patients. Over 5 months, TVEC injections were administrated in a median of 20 tumors per patient for 9 median doses prior to biopsy of persistent, indurated nodules. Granulomatous dermatitis with melanophages and melanin pigment incontinence was observed in all samples without evidence of melanoma cells in 4 patients. The fifth patient was rendered melanoma-free by resection of the 1 nodule out of 4 with persistent tumor. Repetitive administration of TVEC or other oncolytic viral immunotherapies mimicking unresolved infection can produce granulomatous inflammation confounding assessment of the degree of tumor response and need for additional TVEC therapy. Tumor biopsies are encouraged after 4 to 6 months of TVEC administration to differentiate melanoma from granulomatous inflammation. Patients with confirmed granulomatous dermatitis replace continued with remained in remission after treatment discontinuation. Inflammatory nodules typically regress spontaneously.

GM-CSF: An immune modulatory cytokine that can suppress autoimmunity

GM-CSF was originally identified as a colony stimulating factor (CSF) because of its ability to induce granulocyte and macrophage populations from precursor cells. Multiple studies have demonstrated that GM-CSF is also an immune-modulatory cytokine, capable of affecting not only the phenotype of myeloid lineage cells, but also T-cell activation through various myeloid intermediaries. This property has been implicated in the sustenance of several autoimmune diseases like arthritis and multiple sclerosis. In contrast, several studies using animal models have shown that GM-CSF is also capable of suppressing many autoimmune diseases such as Crohn's disease, Type-1 diabetes, Myasthenia gravis and experimental autoimmune thyroiditis. Knockout mouse studies have suggested that the role of GM-CSF in maintaining granulocyte and macrophage populations in the physiological steady state is largely redundant. Instead, its immune-modulatory role plays a significant role in the development or resolution of autoimmune diseases. This is mediated either through the differentiation of precursor cells into specialized non-steady state granulocytes, macrophages and dendritic cells, or through the modulation of the phenotype of mature myeloid cells. Thus, outside of myelopoiesis, GM-CSF has a profound role in regulating the immune response and maintaining immunological tolerance.

Granulomatous inflammation in the lungs of mice with systemic candidiasis receiving a composition of amphotericin B and dialdehyde dextran

A composition of amphotericin B and dialdehyde dextran was used for the therapy of male C57Bl/6 mice with systemic candidiasis. The composition was more effective than free amphotericin B. A decrease in the number and size of candidal granulomas in the lungs was more significant after therapy with the study composition (compared to free amphotericin B).

Granulocyte-macrophage colony stimulating factor-mediated innate responses in tuberculosis

The mechanisms by which GM-CSF mediates bacterial clearance and inflammation during mycobacterial infection are poorly understood. The objective of this work was to determine how GM-CSF alters pulmonary mycobacterial infection in vivo. Differences in GM-CSF levels in the lungs of normal mice (GM(+/+)), transgenic GM-CSF-deficient (GM-CSF(-/-)), and transgenic mice with high GM-CSF expression only in lung epithelial cells (SP-C-GM-CSF(+/+)/GM(-/-)) did not affect pulmonary infection rates caused by either the attenuated Mycobacterium bovis BCG or the virulent Mycobacterium tuberculosis H37Rv. However, in contrast to findings with BCG, all GM-CSF(-/-) and SP-C-GM-CSF(+/+)/GM(-/-) mice succumbed prematurely to virulent H37Rv. Granuloma formation was impaired in both GM-CSF(-/-) and SP-C-GM-CSF(+/+)/GM(-/-) mice regardless of mycobacterial virulence. However, H37Rv-infected GM-CSF(-/-) mice suffered broncho-alveolar destruction, edema, and necrosis while only short-lived granulomas were observed in SP-C-GM-CSF(+/+)/GM(-/-) mice. Bone marrow-derived macrophages, but not dendritic cells of SP-C-GM-CSF(+/+)/GM(-/-) mice, were hypo-responsive to mycobacterial infection. Surfactant protein levels were differentially influenced by BCG and H37Rv. We conclude that GM-CSF has an essential protective role first in preserving alveolar structure and second in regulating macrophages and dendritic cells to facilitate containment of virulent mycobacteria in pulmonary granulomas. However, precise regulation of lung GM-CSF is vital to effective control of M. tuberculosis.

Extra-pulmonary aspects of acquired pulmonary alveolar proteinosis as predicted by granulocyte-macrophage colony-stimulating factor-deficient mice

Granulocyte-macrophage colony-stimulating factor (GM-CSF)-/- mice are an invaluable model for exploring the effects of systemic GM-CSF deficiency. Their lung phenotype exactly reproduces the abnormalities seen in human pulmonary alveolar proteinosis (PAP). However, GM-CSF-/- mice also have significant systemic functional abnormalities. These include immune defects which result in a reduced susceptibility to a range of experimentally induced autoimmune disorders. These immunological defects are also functionally manifest as an impaired ability to resolve a range of infections under certain conditions, usually implicating cellular effectors, including Listeria, Group B streptococcus, adenovirus, Pneumocystis carinii, and malaria. These observations are consistent with the known propensity for patients with PAP to develop a range of opportunistic infections. Conversely, the diminished immunological response to inflammatory stimuli may be beneficial in some settings by limiting inflammatory cell recruitment and pro-inflammatory mediator-release. GM-CSF-/- mice also have distinct fertility defects, manifest as reduced litter size and an increased rate of early fetal loss. These observations may be clinically relevant for women affected by PAP and further support the evaluation of the role of GM-CSF in human reproduction. These observations reinforce the importance of clinicians viewing PAP as a state of systemic functional GM-CSF deficiency, albeit with prominent pulmonary manifestations, rather than purely a 'lung disease'. These systemic manifestations of GM-CSF deficiency should also be considered when deciding on the choice between pulmonary or systemic delivery of GM-CSF as therapy for PAP, as only systemic drug delivery has the potential capacity to correct the systemic manifestations of GM-CSF deficiency in these patients.

Murine macrophages cultured with IL-4 acquire a phenotype similar to that of epithelioid cells from granulomatous inflammation

Epithelioid cells (ECs) found in granulomas are thought to derive from mononuclear phagocytes. Although GM-CSF and/or IL-4 are known to promote cell differentiation their role in the development of ECs has never been demonstrated. Here we showed that mouse macrophages treated exclusively with recombinant IL-4 (rIL-4) differentiate into epithelioid-like cells. Macrophages cultivated with rIL-4 presented a fried-egg shape, and ultrastructural studies revealed membrane interdigitations, cytoplasmic vesicles, prominent Golgi complex, and rough endoplasmic reticulum. Compared with controls, rIL-4 treated cells displayed increased expression of MHC class II molecules and of Migration Inhibitory Factor-Related Protein-14. Whereas mannose receptor-mediated phagocytosis was increased, Fcgamma-receptor mediated phagocytosis and the production of nitric oxide were decreased in treated cultures. All these features overlap those reported for ECs from granulomatous lesions. In conclusion, treatment of mouse peritoneal macrophages with rIL-4 drives their in vitro differentiation to an epithelioid phenotype and provides a tool to investigate the biology of ECs.

Granulomatous liver disease and cholestasis

Development of hepatic granulomas, especially those located within portal tracts, is associated with injury to septal and interlobular bile ducts. Dysfunction of the bile ducts in turn leads to cholestasis,and ongoing damage by the granulomatous inflammation eventually results in ductopenia. A multitude of causes of hepatic granulomas have been described over the last few decades. Diligent and prioritized search for cause of hepatic granulomas should proceed within the environmental and epidemiologic context of a given patient. The therapeutic approaches, including amelioration of the cholestatic syndrome, are often determined by successful identification of specific etiologic factors causing the granulomas in the liver.

Modulation of hepatic granulomatous responses by transgene expression of DAP12 or TREM-1-Ig molecules

DAP12 (also known as KARAP) is a novel ITAM-bearing transmembrane adapter molecule that is expressed on the cell surface of natural killer cells, monocytes, dendritic cells, and macrophages. Several myeloid cell-specific DAP12-associating receptors, such as TREM receptor family, SIRP-beta1, and MDL-1 have been identified. The in vivo function of DAP12 and its associating molecules in inflammation has remained primarily unknown. To investigate DAP12 signaling during chronic inflammation, we constructed two adenoviral gene transfer vectors to express FLAG/DAP12 (Ad-FDAP12) and the extracellular domain of mouse TREM-1 and the Fc portion of human IgG1 (Ad-TREM-1 Ig), respectively, and observed their modulatory activities in a mouse model of hepatic granulomatous inflammation elicited by zymosan A. Mice were injected with zymosan A intravenously and 24 hours after zymosan A, they were injected with Ad-FDAP12 or Ad-TREM-1 Ig. Zymosan A-induced hepatic granuloma formation peaked at day 7 and markedly declined by day 10. Although adenoviral-mediated DAP12 gene transfer did not enhance granuloma formation by day 7, it sustained and enhanced granuloma formation beyond day 7. However, an anti-FLAG monoclonal antibody used to potentiate the signaling of adenoviral-derived DAP12, enhanced granuloma formation at day 7. In sharp contrast to the effect by Ad-FDAP12, transgene expression in the liver of soluble form of extracellular domain of TREM-1 as an antagonist of DAP12 signaling, remarkably inhibited zymosan A-induced granuloma formation at all time points examined. Our findings thus suggest that both DAP12 and TREM-1 are involved in the development of granulomatous responses in the liver.

GM-CSF in inflammation and autoimmunity

Granulocyte macrophage-colony stimulating factor (GM-CSF) is now best viewed as a major regulator governing the functions of granulocyte and macrophage lineage populations at all stages of maturation. There is recent evidence for a key role for GM-CSF in inflammatory and autoimmune diseases, therefore making it worthy of consideration for targetting. Such evidence includes disease exacerbation following its administration and amelioration of disease in animal models by GM-CSF gene targetting or by anti-GM-CSF antibody blockade. The interdependence of GM-CSF formation and that of the important proinflammatory cytokines, interleukin-1 and tumour necrosis factor-alpha (TNF-alpha), is discussed, as is the greater disease suppression found in arthritis models following GM-CSF depletion compared with that observed in the absence of TNF-alpha.

Abnormal pulmonary granuloma formation in osteopontin-deficient mice

Osteopontin is a novel cytokine that is expressed in pulmonary granulomatous disease such as sarcoidosis and tuberculosis. It can regulate macrophage and T cell migration, activation, and cytokine expression, yet its role in granuloma formation and evolution is unknown. We induced hypersensitivity pulmonary granulomas by embolizing Schistosoma mansoni eggs to the lungs of osteopontin-deficient (null mutant) mice and osteopontin-sufficient (wild-type control) mice. Granulomas from osteopontin-null animals were smaller at early time points and contained remarkably few macrophages and macrophage-derived epithelioid cells and giant cells. T cell accumulation was unaffected by osteopontin deficiency. These results demonstrate that osteopontin regulates macrophage accumulation during pulmonary granuloma formation, and may explain the impaired ability of osteopontin-deficient hosts to control mycobacterial disease.