Andrew D. Cook

Granulocyte-Macrophage Colony-Stimulating Factor (CSF) and Macrophage CSF-Dependent Macrophage Phenotypes Display Differences in Cytokine Profiles and Transcription Factor Activities: Implications for CSF Blockade in Inflammation

GM-CSF and M-CSF (CSF-1) can enhance macrophage lineage numbers as well as modulate their differentiation and function. Of recent potential significance for the therapy of inflammatory/autoimmune diseases, their blockade in relevant animal models leads to a reduction in disease activity. What the critical actions are of these CSFs on macrophages during inflammatory reactions are unknown. To address this issue, adherent macrophages (GM-BMM and BMM) were first derived from murine bone marrow precursors by GM-CSF and M-CSF, respectively, and stimulated in vitro with LPS to measure secreted cytokine production, as well as NF-κB and AP-1 activities. GM-BMM preferentially produced TNF-α, IL-6, IL-12p70, and IL-23 whereas, conversely, BMM generated more IL-10 and CCL2; strikingly the latter population could not produce detectable IL-12p70 and IL-23. Following LPS stimulation, GM-BMM displayed rapid IκBα degradation, RelA nuclear translocation, and NF-κB DNA binding relative to BMM, as well as a faster and enhanced AP-1 activation. Each macrophage population was also pretreated with the other CSF before LPS stimulation and found to adopt the phenotype of the other population to some extent as judged by cytokine production and NF-κB activity. Thus, GM-CSF and M-CSF demonstrate, at the level of macrophage cytokine production, different and even competing responses with implications for their respective roles in inflammation, including a possible dampening or suppressive role for M-CSF in certain circumstances.

Defining GM-CSF– and Macrophage-CSF–Dependent Macrophage Responses by In Vitro Models

GM-CSF and M-CSF (CSF-1) induce different phenotypic changes in macrophage lineage populations. The nature, extent, and generality of these differences were assessed by comparing the responses to these CSFs, either alone or in combination, in various human and murine macrophage lineage populations. The differences between the respective global gene expression profiles of macrophages, derived from human monocytes by GM-CSF or M-CSF, were compared with the differences between the respective profiles for macrophages, derived from murine bone marrow cells by each CSF. Only 17% of genes regulated differently by these CSFs were common across the species. Whether a particular change in relative gene expression is by direct action of a CSF can be confounded by endogenous mediators, such as type I IFN, IL-10, and activin A. Time-dependent differences in cytokine gene expression were noted in human monocytes treated with the CSFs; in this system, GM-CSF induced a more dramatic expression of IFN-regulated factor 4 (IRF4) than of IRF5, whereas M-CSF induced IRF5 but not IRF4. In the presence of both CSFs, some evidence of “competition” at the level of gene expression was observed. Care needs to be exercised when drawing definitive conclusions from a particular in vitro system about the roles of GM-CSF and M-CSF in macrophage lineage biology.

GM-CSF- and M-CSF-dependent macrophage phenotypes display differential dependence on Type I interferon signaling

M‐CSF and GM‐CSF are mediators involved in regulating the numbers and function of macrophage lineage populations and have been shown to contribute to macrophage heterogeneity. Type I IFN is an important mediator produced by macrophages and can have profound regulatory effects on their properties. In this study, we compared bone marrow‐derived macrophages (BMM) and GM‐CSF‐induced BMM (GM‐BMM) from wild‐type and IFNAR1−/− mice to assess the contribution of endogenous type I IFN to the phenotypic differences between BMM and GM‐BMM. BMM were capable of higher constitutive IFN‐β production, which contributed significantly to their basal transcriptome. Microarray analysis found that of the endogenous type I IFN‐regulated genes specific to either BMM or GM‐BMM, 488 of these gene alterations were unique to BMM, while only 50 were unique to GM‐BMM. Moreover, BMM displayed enhanced basal mRNA levels, relative to GM‐BMM, of a number of genes identified as being dependent on type I IFN signaling, including Stat1, Stat2, Irf7, Ccl5, Ccl12, and Cxcl10. As a result of prior type I IFN “priming,” upon LPS stimulation BMM displayed increased activation of the MyD88‐independent IRF‐3/STAT1 pathways compared with GM‐BMM, which correlated with the distinct cytokine/chemokine profiles of the two macrophage subsets. Furthermore, the autocrine type I IFN signaling loop regulated the production of the M1 and M2 signature cytokines, IL‐12p70 and IL‐10. Collectively, these findings demonstrate that constitutive and LPS‐induced type I IFN play significant roles in regulating the differences in phenotype and function between BMM and GM‐BMM.

Mouse neutrophilic granulocytes express mRNA encoding the macrophage colony-stimulating factor receptor (CSF-1R) as well as many other macrophage-specific transcripts and can transdifferentiate into macrophages in vitro in response to CSF-1

The differentiation of macrophages from their progenitors is controlled by macrophage colony‐stimulating factor (CSF‐1), which binds to a receptor (CSF‐1R) encoded by the c‐fms proto‐oncogene. We have previously used the promoter region of the CSF‐1R gene to direct expression of an enhanced green fluorescent protein (EGFP) reporter gene to resident macrophage populations in transgenic mice. In this paper, we show that the EGFP reporter is also expressed in all granulocytes detected with the Gr‐1 antibody, which binds to Ly‐6C and Ly‐6G or with a Ly‐6G‐specific antibody. Transgene expression reflects the presence of CSF‐1R mRNA but not CSF‐1R protein. The same pattern is observed with the macrophage‐specific F4/80 marker. Based on these findings, we performed a comparative array profiling of highly purified granulocytes and macrophages. The patterns of mRNA expression differed predominantly through granulocyte‐specific expression of a small subset of transcription factors (Egr1, HoxB7, STAT3), known abundant granulocyte proteins (e.g., S100A8, S100A9, neutrophil elastase), and specific receptors (fMLP, G‐CSF). These findings suggested that appropriate stimuli might mediate rapid interconversion of the major myeloid cell types, for example, in inflammation. In keeping with this hypothesis, we showed that purified Ly‐6G‐positive granulocytes express CSF‐1R after overnight culture and can subsequently differentiate to form F4/80‐positive macrophages in response to CSF‐1.

The TGF-β superfamily cytokine, MIC-1/GDF15: A pleotrophic cytokine with roles in inflammation, cancer and metabolism

Macrophage inhibitory cytokine-1 (MIC-1/GDF15) is associated with cardiovascular disease, inflammation, body weight regulation and cancer. Its serum levels facilitate the diagnosis and prognosis of cancer and vascular disease. Furthermore, its serum levels are a powerful predictor of all-cause mortality, suggesting a fundamental role in biological processes associated with ageing. In cancer, the data available suggest that MIC-1/GDF15 is antitumorigenic, but this may not always be the case as disease progresses. Cancer promoting effects of MIC-1/GDF15 may be due, in part, to effects on antitumour immunity. This is suggested by the anti-inflammatory and immunosuppressive properties of MIC-1/GDF15 in animal models of atherosclerosis and rheumatoid arthritis. Furthermore, in late-stage cancer, large amounts of MIC-1/GDF15 in the circulation suppress appetite and mediate cancer anorexia/cachexia, which can be reversed by monoclonal antibodies in animals. Available data suggest MIC-1/GDF15 may be an important molecule mediating the interplay between cancer, obesity and chronic inflammation.

Genetic control of collagen‐induced arthritis in a cross with NOD and C57BL/10 mice is dependent on gene regions encoding complement factor 5 and FcγRIIb and is not associated with loci controlling diabetes

The nonobese diabetic (NOD) mouse spontaneously develops autoimmune‐mediated diseases such as diabetes and Sjögren′s syndrome. To investigate whether NOD genes also promote autoimmune‐mediatedarthritis we established a NOD strain with an MHC class II fragment containing the Aq class II gene predisposing for collagen induced arthritis (NOD.Q). However, this mouse was resistant to arthritis in contrast to other Aq expressing strains such as B10.Q and DBA/1. To determine the major resistance factor/s, a genetic analysis was performed. (NOD.Q×B10.Q)F1 mice were resistant, whereas 27% of the (NOD.Q×B10.Q)F2 mice developed severe arthritis. Genetic mapping of 353 F2 mice revealed two loci associated with arthritis. One locus was found on chromosome 2 (LOD score 9.8), at the location of the complement factor 5 (C5) gene. The susceptibility allele was from B10.Q, which contains a productive C5 encoding gene in contrast to NOD.Q. The other significant locus was found on chromosome 1 (LOD score 5.6) close to the Fc‐gamma receptor IIb gene, where NOD carried the susceptible allele. An interaction between the two loci was observed, indicating that they operate on the same or on interacting pathways. The genetic control of arthritis is unique in comparison to diabetes, since none of these loci have been identified in analysis of diabetes susceptibility.

Genetic linkage analysis of collagen-induced arthritis in the mouse.

The genetic susceptibility to collagen‐induced arthritis (CIA) in mice, the most commonly used model for rheumatoid arthritis, has been analyzed. The highly susceptible B10.RIII strain was crossed with the resistant RIIIS/J strain and the F2 intercross mice were subjected to genomic screening using microsatellite markers. These strains share the MHC region on chromosome 17, known to be of importance in CIA (this locus is named Mcia1). The same cross has earlier been used to map the major genes outside the MHC controlling chronic relapsing experimental allergic encephalomyelitis (EAE). It was found that the major locus controlling CIA (Mcia2; lod 4.12) was located on chromosome 3 in the same region as one of the major loci controlling EAE (Eae3). The linkage was reproduced in a mouse strain in which the locus was isolated on the B10.RIII background at the N4I2 generation. A second putative locus was identified on chromosome 13 (lod 3.13). The present finding identifies new loci outside the MHC controlling CIA and provides evidence that mouse CIA is controlled by polymorphic genes.

The phenotype of inflammatory macrophages is stimulus dependent: Implications for the nature of the inflammatory response

Many diseases are characterized by inflammatory reactions involving both the innate and adaptive arms of the immune system. Thioglycolate medium (TM) injection into the peritoneal cavity has long been used as a stimulus for eliciting inflammatory macrophages for study and for determining the importance of a particular mediator in inflammation. However, the response to this irritant may not be relevant to many inflammatory diseases. Therefore, we have developed an Ag-specific peritonitis model using methylated BSA (mBSA) as the stimulus. Priming mice intradermally with mBSA in adjuvant and boosting 14 days later, followed by an i.p. challenge with mBSA after an additional 7 days, led to an inflammatory reaction equivalent in magnitude to that induced with TM as judged by the number of exudate cells. The inflammatory macrophages elicited by the mBSA protocol differed, being smaller and less vacuolated than TM-elicited macrophages. Also, macrophages from 4-day mBSA-induced exudates expressed more MHC class II than TM-induced exudates, were able to stimulate allogeneic T lymphocytes, and upon in vitro stimulation with LPS secreted greater levels of IL-6 and IL-1β. Macrophages from 4-day TM-induced exudates, on the other hand, expressed Ly6C and ER-MP58, immature myeloid markers. The inflammatory response elicited using the Ag mBSA may be more relevant for studying the inflammatory responses in many diseases, such as those of autoimmune origin and those involving an acquired immune response.

Macrophage Activation and Differentiation Signals Regulate Schlafen-4 Gene Expression: Evidence for Schlafen-4 as a Modulator of Myelopoiesis

Background The ten mouse and six human members of the Schlafen (Slfn) gene family all contain an AAA domain. Little is known of their function, but previous studies suggest roles in immune cell development. In this report, we assessed Slfn regulation and function in macrophages, which are key cellular regulators of innate immunity. Methodology/Principal Findings Multiple members of the Slfn family were up-regulated in mouse bone marrow-derived macrophages (BMM) by the Toll-like Receptor (TLR)4 agonist lipopolysaccharide (LPS), the TLR3 agonist Poly(I∶C), and in disease-affected joints in the collagen-induced model of rheumatoid arthritis. Of these, the most inducible was Slfn4. TLR agonists that signal exclusively through the MyD88 adaptor protein had more modest effects on Slfn4 mRNA levels, thus implicating MyD88-independent signalling and autocrine interferon (IFN)-β in inducible expression. This was supported by the substantial reduction in basal and LPS-induced Slfn4 mRNA expression in IFNAR-1−/− BMM. LPS causes growth arrest in macrophages, and other Slfn family genes have been implicated in growth control. Slfn4 mRNA levels were repressed during macrophage colony-stimulating factor (CSF-1)-mediated differentiation of bone marrow progenitors into BMM. To determine the role of Slfn4 in vivo, we over-expressed the gene specifically in macrophages in mice using a csf1r promoter-driven binary expression system. Transgenic over-expression of Slfn4 in myeloid cells did not alter macrophage colony formation or proliferation in vitro. Monocyte numbers, as well as inflammatory macrophages recruited to the peritoneal cavity, were reduced in transgenic mice that specifically over-expressed Slfn4, while macrophage numbers and hematopoietic activity were increased in the livers and spleens. Conclusions Slfn4 mRNA levels were up-regulated during macrophage activation but down-regulated during differentiation. Constitutive Slfn4 expression in the myeloid lineage in vivo perturbs myelopoiesis. We hypothesise that the down-regulation of Slfn4 gene expression during macrophage differentiation is a necessary step in development of this lineage.

Control of macrophage lineage populations by CSF-1 receptor and GM-CSF in homeostasis and inflammation

There is recent interest in the role of monocyte/macrophage subpopulations in pathology. How the hemopoietic growth factors, macrophage‐colony stimulating factor (M‐CSF or CSF‐1) and granulocyte macrophage (GM)‐CSF, regulate their in vivo development and function is unclear. A comparison is made here on the effect of CSF‐1 receptor (CSF‐1R) and GM‐CSF blockade/depletion on such subpopulations, both in the steady state and during inflammation. In the steady state, administration of neutralizing anti‐CSF‐1R monoclonal antibody (mAb) rapidly (within 3–4 days) lowered, specifically, the number of the more mature Ly6Clo peripheral blood murine monocyte population and resident peritoneal macrophages; it also reduced the accumulation of murine exudate (Ly6Clo) macrophages in two peritonitis models and alveolar macrophages in lung inflammation, consistent with a non‐redundant role for CSF‐1 (or interleukin‐34) in certain inflammatory reactions. A neutralizing mAb to GM‐CSF also reduced inflammatory macrophage numbers during antigen‐induced peritonitis and lung inflammation. In GM‐CSF gene‐deficient mice, a detailed kinetic analysis of monocyte/macrophage and neutrophil dynamics in antigen‐induced peritonitis suggested that GM‐CSF was acting, in part, systemically to maintain the inflammatory reaction. A model is proposed in which CSF‐1R signaling controls the development of the macrophage lineage at a relatively late stage under steady state conditions and during certain inflammatory reactions, whereas in inflammation, GM‐CSF can be required to maintain the response by contributing to the prolonged extravasation of immature monocytes and neutrophils. A correlation has been observed between macrophage numbers and the severity of certain inflammatory conditions, and it could be that CSF‐1 and GM‐CSF contribute to the control of these numbers in the ways proposed.