BackgroundInvestigations on pulmonary macrophages (MΦ) mostly focus on alveolar MΦ (AM) as a well-defined cell population. Characteristics of MΦ in the interstitium, referred to as lung interstitial MΦ (IM), are rather ill-defined. In this study we therefore aimed to elucidate differences between AM and IM obtained from human lung tissue.MethodsHuman AM and IM were isolated from human non-tumor lung tissue from patients undergoing lung resection. Cell morphology was visualized using either light, electron or confocal microscopy. Phagocytic activity was analyzed by flow cytometry as well as confocal microscopy. Surface marker expression was measured by flow cytometry. Toll-like receptor (TLR) expression patterns as well as cytokine expression upon TLR4 or TLR9 stimulation were assessed by real time RT-PCR and cytokine protein production was measured using a fluorescent bead-based immunoassay.ResultsIM were found to be smaller and morphologically more heterogeneous than AM, whereas phagocytic activity was similar in both cell types. HLA-DR expression was markedly higher in IM compared to AM. Although analysis of TLR expression profiles revealed no differences between the two cell populations, AM and IM clearly varied in cell reaction upon activation. Both MΦ populations were markedly activated by LPS as well as DNA isolated from attenuated mycobacterial strains (M. bovis H37Ra and BCG). Whereas AM expressed higher amounts of inflammatory cytokines upon activation, IM were more efficient in producing immunoregulatory cytokines, such as IL10, IL1ra, and IL6.ConclusionAM appear to be more effective as a non-specific first line of defence against inhaled pathogens, whereas IM show a more pronounced regulatory function. These dissimilarities should be taken into consideration in future studies on the role of human lung MΦ in the inflammatory response.

Induction of glucocorticoid-induced leucine zipper (GILZ) by glucocorticoids plays a key role in their anti-inflammatory action. In activated macrophages, GILZ levels are downregulated via tristetraprolin-mediated GILZ mRNA destabilization. To assess the functional significance of GILZ downregulation, we generated myeloid-specific GILZ knockout (KO) mice. GILZ-deficient macrophages displayed a higher responsiveness toward LPS, as indicated by increased TNF-α and IL-1β expression. This effect was due to an activation of ERK, which was significantly amplified in GILZ KO cells. The LPS-induced activation of macrophages is attenuated upon pretreatment of macrophages with low-dose LPS, an effect termed endotoxin tolerance. In LPS-tolerant macrophages, GILZ mRNA was stabilized, whereas ERK activation was strongly decreased. In contrast, GILZ KO macrophages exhibited a strongly reduced desensitization. To explore the contribution of GILZ expression in macrophages to endotoxin tolerance in vivo, we treated GILZ KO mice with repeated i.p. injections of low-dose LPS followed by treatment with high-dose LPS. LPS pretreatment resulted in reduced proinflammatory mediator expression upon high-dose LPS treatment in serum and tissues. In contrast, cytokine induction was preserved in tolerized GILZ KO animals. In summary, our data suggest that GILZ is a key regulator of macrophage functions.

While silica nanoparticles have enabled numerous industrial and medical applications, their toxicological safety requires further evaluation. Macrophages are the major cell population responsible for nanoparticle clearance in vivo. The prevailing macrophage phenotype largely depends on the local immune status of the host. Whereas M1-polarized macrophages are considered as pro-inflammatory macrophages involved in host defense, M2 macrophages exhibit anti-inflammatory and wound-healing properties, but also promote tumor growth. We employed different models of M1 and M2 polarization: granulocyte-macrophage colony-stimulating factor/lipopolysaccharide (LPS)/interferon (IFN)-γ was used to generate primary human M1 cells and macrophage colony-stimulating factor (M-CSF)/interleukin (IL)-10 to differentiate M2 monocyte-derived macrophages (MDM). PMA-differentiated THP-1 cells were polarized towards an M1 type by LPS/IFN-γ and towards M2 by IL-10. Uptake of fluorescent silica nanoparticles (Ø26 and 41 nm) and microparticles (Ø1.75 μm) was quantified. At the concentration used (50 μg/ml), silica nanoparticles did not influence cell viability as assessed by MTT assay. Nanoparticle uptake was enhanced in M2-polarized primary human MDM compared with M1 cells, as shown by flow cytometric and microscopic approaches. In contrast, the uptake of microparticles did not differ between M1 and M2 phenotypes. M2 polarization was also associated with increased nanoparticle uptake in the macrophage-like THP-1 cell line. In accordance, in vivo polarized M2-like primary human tumor-associated macrophages obtained from lung tumors took up more nanoparticles than M1-like alveolar macrophages isolated from the surrounding lung tissue. In summary, our data indicate that the M2 polarization of macrophages promotes nanoparticle internalization. Therefore, the phenotypical differences between macrophage subsets should be taken into consideration in future investigations on nanosafety, but might also open up therapeutic perspectives allowing to specifically target M2 polarized macrophages.

Induction of the glucocorticoid-induced leucine zipper (GILZ) by glucocorticoids plays a role in their antiinflammatory action, whereas GILZ expression is reduced under inflammatory conditions. The mechanisms regulating GILZ expression during inflammation, however, have not yet been characterized. Here, we investigated GILZ expression in human alveolar macrophages (AMs) following Toll-like receptor (TLR) activation. Macrophages were shown to predominantly express GILZ transcript variant 2. Lipopolysaccharide-treated AMs, THP-1 cells, and lungs of lipopolysaccharide-exposed mice displayed decreased GILZ protein and mRNA levels. The effect was strictly dependent on the adapter molecule MyD88, as shown by using specific ligands or a knockdown strategy. Investigations on the functional significance of GILZ downregulation performed by GILZ knockdown revealed a proinflammatory response, as indicated by increased cytokine expression and NF-κB activity. We found that TLR activation reduced GILZ mRNA stability, which was mediated via the GILZ 3 -untranslated region. Finally, involvement of the mRNA-binding protein tristetraprolin (TTP) is suggested, since TTP overexpression or knockdown modulated GILZ expression and TTP was induced in a MyD88-dependent fashion. Taken together, our data show a MyD88-and TTP-dependent GILZ downregulation in human macrophages upon TLR activation. Suppression of GILZ is mediated by mRNA destabilization, which might represent a regulatory mechanism in macrophage activation.Keywords: GILZ transcript variants · Inflammation · Innate immunity · mRNA stability · Pulmonary macrophages IntroductionInflammatory processes in the lung play an important role in different diseases, such as viral and bacterial infections. Moreover, noninfectious diseases such as chronic obstructive pulmonary disCorrespondence: Prof. Alexandra K. Kiemer e-mail: pharm.bio.kiemer@mx.uni-saarland.de ease (COPD) are characterized by chronic inflammatory processes. Asthma and allergic diseases are other examples of chronic inflammatory lung diseases with major clinical relevance [1,2].Toll-like receptors (TLRs) represent an important family of innate immune receptors, which act as a first line of defense of host immunity against various pathogens. Presently, ten human TLRs are known, which recognize pathogen-associated molecular patterns including bacterial cell wall components, such as lipoproteins (TLR1/2 or TLR1/6 dimers) or lipopolysaccharide (LPS, TLR4), C 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2012. 42: 1282-1293 Innate immunity 1283 bacterial flagellin (TLR5), viral RNA (TLR3, 7 and 8), as well as bacterial DNA (TLR9) [3]. Except for TLR3, all TLRs signal via the adapter molecule MyD88. The MyD88-independent pathway used by TLR3 can also be utilized by TLR4. The different signaling pathways employ different protein kinase complexes and show distinct cytokine profiles, but all activate NF-κB [4]. In addition to their role in pathogen defense, TLRs also play a dominant role in ...

Glucocorticoids (GCs) potently inhibit pro-inflammatory responses and are widely used for the treatment of inflammatory diseases, such as allergies, autoimmune disorders, and asthma. Dual-specificity phosphatase 1 (DUSP1), also known as mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1), exerts its effects by dephosphorylation of MAPKs, i.e., extracellular-signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). Endogenous DUSP1 expression is tightly regulated at multiple levels, involving both transcriptional and post-transcriptional mechanisms. DUSP1 has emerged as a central mediator in the resolution of inflammation, and upregulation of DUSP1 by GCs has been suggested to be a key mechanism of GC actions. In this review, we discuss the impact of DUSP1 on the efficacy of GC-mediated suppression of inflammation and address the underlying mechanisms.

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Alveolar macrophages are the first line of host defence against mycobacteria, but an insufficient host response allows survival of bacteria within macrophages. We aimed to investigate the role of Toll-like receptor 9 (TLR9) activation in macrophage defence against mycobacteria. Human in vitrodifferentiated macrophages as well as human and mouse alveolar macrophages showed TLR9 mRNA and protein expression. The cells were markedly activated by DNA isolated from attenuated mycobacterial strains (H37Ra and Mycobacterium bovis BCG) as assessed by measuring cytokine expression by real-time PCR, whereas synthetic phosphorothioate-modified oligonucleotides had a much lower potency to activate human macrophages. Intracellular replication of H37Ra was higher in macrophages isolated from TLR9-deficient mice than in macrophages from wild-type mice, whereas H37Rv showed equal survival in cells from wild-type or mutant mice. Increased bacterial survival in mouse macrophages was accompanied by altered cytokine production as determined by Luminex bead assays. In vivo infection experiments also showed differential cytokine production in TLR9-deficient mice compared to wild-type animals. Both human monocyte-derived macrophages as well as human alveolar macrophages showed reduced activation upon treatment with DNA isolated from bacteria from virulent (M. bovis and H37Rv) compared to attenuated mycobacteria. We suggest attenuated TLR9 activation contributes to the insufficient host response against virulent mycobacteria.

GILZ (glucocorticoid-induced leucine zipper) is inducible by glucocorticoids and plays a key role in their mode of action. GILZ attenuates inflammation mainly by inhibition of NF-B and mitogen-activated protein kinase activation but does not seem to be involved in the severe side effects observed after glucocorticoid treatment. Therefore, GILZ might be a promising target for new therapeutic approaches. The present work focuses on the natural product curcumin, which has previously been reported to inhibit NF-B. GILZ was inducible by curcumin in macrophage cell lines, primary human monocyte-derived macrophages, and murine bone marrow-derived macrophages. The up-regulation of GILZ was neither associated with glucocorticoid receptor activation nor with transcriptional induction or mRNA or protein stabilization but was a result of enhanced translation. Because the GILZ 3-UTR contains AU-rich elements (AREs), we analyzed the role of the mRNA-binding protein HuR, which has been shown to promote the translation of ARE-containing mRNAs. Our results suggest that curcumin treatment induces HuR expression. An RNA immunoprecipitation assay confirmed that HuR can bind GILZ mRNA. In accordance, HuR overexpression led to increased GILZ protein levels but had no effect on GILZ mRNA expression. Our data employing siRNA in LPS-activated RAW264.7 macrophages show that curcumin facilitates its anti-inflammatory action by induction of GILZ in macrophages. Experiments with LPS-activated bone marrow-derived macrophages from wild-type and GILZ knock-out mice demonstrated that curcumin inhibits the activity of inflammatory regulators, such as NF-B or ERK, and subsequent TNF-␣ production via GILZ. In summary, our data indicate that HuR-dependent GILZ induction contributes to the anti-inflammatory properties of curcumin.The polyphenol curcumin (diferuloylmethane) is the principal bioactive compound of turmeric (Curcuma longa) preparations, which are commonly used as traditional remedies or spices. Recently, extensive research has shown that curcumin has a broad range of therapeutic effects, including anti-inflammatory, anti-oxidant, anti-proliferative, hypoglycemic, lipidlowering, anti-thrombotic, and anti-coagulant activity. At the same time, no dose-limiting toxicity was observed in clinical trials, indicating pharmacological safety. Thus, curcumin administration has been suggested as a potential therapeutic approach for the treatment of several pathologic conditions, especially inflammatory diseases such as cardiovascular pathologies, arthritis, asthma, ulcerative colitis, inflammatory bowel disease, and type II diabetes (1-5). Several in vivo studies suggested a profound effect of curcumin on cells of the mononuclear phagocyte system. In a mouse model of abdominal aortic aneurysms, oral administration of curcumin efficiently suppressed mononuclear inflammation in the aortic walls, i.e. proinflammatory cytokine expression and adverse connective tissue remodeling (6). In addition, curcumin decreased the number of proinflammatory M1 macro...