Obesity corrupts myelopoiesis

Ongoing monocyte infiltration and subsequent macrophage seeding of adipose tissue is thought to be a key feature of obesity pathophysiology. Nagareddy et al. (2014) show that adipose cells locally activate IL-1β in macrophages in part through the alarmin S100A8/A9, which stimulates bone marrow myelopoiesis to perpetuate nonresolving inflammation.

Tyrosine kinase 2 promotes sepsis-associated lethality by facilitating production of interleukin-27

The aim of this study was to test the hypothesis that gene expression and release of IL-27 may be modulated by Tyk2. Macrophages derived from the peritoneum or bone marrow of C57BL/10SnJ (WT) mice produced abundant amounts of IL-27(p28) following TLR4 activation by LPS. In contrast, production of IL-27(p28), but not EBI3, was reduced by ∼50% in TLR4-activated macrophages derived from mice with genetic deficiency of Tyk2 compared with WT macrophages. Frequencies of IL-27(p28)+F4/80+CD11b+ cells were lower in TLR4-activated macrophages derived from Tyk2-/- mice. Mechanistically, Tyk2-/- resulted in disruption of a type I IFN-dependent mechanism for production of IL-27(p28), which was induced by type I IFNs, and release of IL-27 was defective in macrophages from IFN-β-/- and IFNAR1-/- mice. In contrast, Tyk2 was not required to mediate the effects of IL-27 on target gene expression in CD4(+) T cells. In vivo, we observed that Tyk2-/- mice have improved survival following endotoxic shock or polymicrobial sepsis induced by CLP. Plasma levels of IL-27(p28) during endotoxic shock or polymicrobial sepsis were markedly reduced in Tyk2-/- mice compared with WT mice. Disruption of IL-27 signaling using IL-27RA-/- mice was protective against sepsis-associated mortality. These data suggest that Tyk2 may mediate adverse outcomes of SIRS by promoting the production of IL-27. In conclusion, this report identifies Tyk2 as a prerequisite factor in the molecular networks that are involved in generation of IL-27.

NFIL3-deficient mice develop microbiota-dependent, IL-12/23-driven spontaneous colitis

NFIL3 is a transcription factor that regulates multiple immunologic functions. In myeloid cells, NFIL3 is IL-10 inducible and has a key role as a repressor of IL-12p40 transcription. NFIL3 is a susceptibility gene for the human inflammatory bowel diseases. In this article, we describe spontaneous colitis in Nfil3(-/-) mice. Mice lacking both Nfil3 and Il10 had severe early-onset colitis, suggesting that NFIL3 and IL-10 independently regulate mucosal homeostasis. Lymphocytes were necessary for colitis, because Nfil3/Rag1 double-knockout mice were protected from disease. However, Nfil3/Rag1 double-knockout mice adoptively transferred with wild-type CD4(+) T cells developed severe colitis compared with Rag1(-/-) recipients, suggesting that colitis was linked to defects in innate immune cells. Colitis was abrogated in Nfil3/Il12b double-deficient mice, identifying Il12b dysregulation as a central pathogenic event. Finally, germ-free Nfil3(-/-) mice do not develop colonic inflammation. Thus, NFIL3 is a microbiota-dependent, IL-10-independent regulator of mucosal homeostasis via IL-12p40.

Local arginase 1 activity is required for cutaneous wound healing

Chronic nonhealing wounds in the elderly population are associated with a prolonged and excessive inflammatory response, which is widely hypothesized to impede healing. Previous studies have linked alterations in local L-arginine metabolism, principally mediated by the enzymes arginase (Arg) and inducible nitric oxide synthase (iNOS), to pathological wound healing. Over subsequent years, interest in Arg/iNOS has focused on the classical versus alternatively activated (M1/M2) macrophage paradigm. Although the role of iNOS during healing has been studied, Arg contribution to healing remains unclear. Here, we report that Arg is dynamically regulated during acute wound healing. Pharmacological inhibition of local Arg activity directly perturbed healing, as did Tie2-cre-mediated deletion of Arg1, revealing the importance of Arg1 during healing. Inhibition or depletion of Arg did not alter alternatively activated macrophage numbers but instead was associated with increased inflammation, including increased influx of iNOS(+) cells and defects in matrix deposition. Finally, we reveal that in preclinical murine models reduced Arg expression directly correlates with delayed healing, and as such may represent an important future therapeutic target.

Sustained generation of nitric oxide and control of mycobacterial infection requires argininosuccinate synthase 1

Nitric oxide (NO) defends against intracellular pathogens, but its synthesis must be regulated due to cell and tissue toxicity. During infection, macrophages import extracellular arginine to synthesize NO, generating the byproduct citrulline. Accumulated intracellular citrulline is thought to fuel arginine synthesis catalyzed by argininosuccinate synthase (Ass1) and argininosuccinate lyase (Asl), which would lead to abundant NO production. Instead, we find that citrulline is exported from macrophages during early stages of NO production with <2% retained for recycling via the Ass1-Asl pathway. Later, extracellular arginine is depleted, and Ass1 expression allows macrophages to synthesize arginine from imported citrulline to sustain NO output. Ass1-deficient macrophages fail to salvage citrulline in arginine-scarce conditions, leading to their inability to control mycobacteria infection. Thus, extracellular arginine fuels rapid NO production in activated macrophages, and citrulline recycling via Ass1 and Asl is a fail-safe system that sustains optimum NO production.

Generation of tissue-specific H-2Kd transgenic mice for the study of K(d)-restricted malaria epitope-specific CD8+ T-cell responses in vivo

CD8(+) T cells are critical for the control of various intracellular infections and cancers. To date, however, effective T cell-based vaccines remain elusive, due, in part, to the lack of in vivo models that facilitate the dissection of antigen-specific CD8(+) T-cell responses primed by different antigen-presenting cells (APCs). In this study, we generated four lines of H-2K(d) transgenic (K(d) Tg) mice that differed in their expression of H-2K(d): dendritic cells (DCs) only (CD11c-K(d)), macrophages only (huCD68-K(d)), hepatocytes only (Alb-K(d)), or all nucleated cells (major histocompatibility complex-I-K(d)). Immunization of each of these K(d) Tg mouse strains with a synthetic peptide or a recombinant adenovirus expressing a well-known immunodominant, H-2K(d)-restricted CD8(+) T-cell epitope, SYVPSAEQI, which was derived from the circumsporozoite protein of Plasmodium yoelii, promoted distinct SYVPSAEQI-specific CD8(+) T-cell responses. The route of immunization also greatly influenced the magnitude of the epitope-specific CD8(+) T-cell response. These tissue-specific K(d) Tg mice may be valuable tools for determining the mode of induction of CD8(+) T-cell responses by different APCs in vivo and for characterizing the CD8(+) T-cell responses promoted in response to various microbial infections and/or different types of vaccines.

Restraint of inflammatory signaling by interdependent strata of negative regulatory pathways

Activation of Toll-like receptor (TLR) signaling and related pathways by microbial products drives inflammatory responses, host-defense pathways and adaptive immunity. The cost of excessive inflammation is cell and tissue damage, an underlying cause of many acute and chronic diseases. Coincident with activation of TLR signaling, a plethora of anti-inflammatory pathways and mechanisms begin to modulate inflammation until tissue repair is complete. Whereas most studies have focused on the signaling components immediately downstream of the TLRs, this Review summarizes the different levels of anti-inflammatory pathways that have evolved to abate TLR signaling and how they are integrated to prevent cell and tissue destruction.

Non-canonical alternatives: what a macrophage is 4

Macrophages play pleiotropic, niche-specific roles in all tissues and organs. As immune sentinels, tissue macrophages regulate immune activation and inflammation; in turn, their function is modulated by inflammatory mediators deriving from such activation. Recent papers have established unanticipated roles for interleukin 4 and the alternative activation of tissue macrophages in the organismal response to diverse environmental stressors.

Control of NOD2 and Rip2-dependent innate immune activation by GEF-H1

BACKGROUND

Genetic variants of nucleotide-binding oligomerization domain 2 (NOD2) lead to aberrant microbial recognition and can cause chronic inflammatory diseases in patients with Crohn's disease (CD).

METHODS

We utilized gene-specific siRNA mediated knockdown and expression of guanine nucleotide exchange factor H1 (GEF-H1) in wildtype, Rip2-, and Nod2-deficient macrophages, HCT-116 and HEK 293 cells to determine the role of GEF-H1 in NOD2 and Rip2-mediated NF-κB-dependent induction of proinflammatory cytokine expression. Confocal microscopy was used to determine subcellular distribution of GEF-H1, Rip2, and NOD2.

RESULTS

We identified GEF-H1 as an unexpected component of innate immune regulation during microbial pattern recognition by NOD2. Surprisingly, GEF-H1-mediated the activation of Rip2 during signaling by NOD2, but not in the presence of the 3020 insC variant of NOD2 associated with CD. GEF-H1 functioned downstream of NOD2 as part of Rip2-containing signaling complexes and was responsible for phosphorylation of Rip2 by Src tyrosine kinase. Rip2 variants lacking the tyrosine target of GEF-H1-mediated phosphorylation were unable to mediate NF-κB activation in Rip2-deficient macrophages and failed to transduce NOD2 signaling. GEF-H1 is required downstream of NOD2 as part of Rip2-containing signaling complexes for the activation of innate immune responses.

CONCLUSIONS

GEF-H1 connects tyrosine kinase function to NOD-like receptor signaling and is fundamental to the regulation of microbial recognition by ubiquitous innate immune mechanisms mediated by Rip2 kinase.

Agammaglobulinemia and absent B lineage cells in a patient lacking the p85α subunit of PI3K

Whole exome sequencing was used to determine the causative gene in patients with B cell defects of unknown etiology. A homozygous premature stop codon in exon 6 of PIK3R1 was identified in a young woman with colitis and absent B cells. The mutation results in the absence of p85α but normal expression of the p50α and p55α regulatory subunits of PI3K. Bone marrow aspirates from the patient showed <0.1% CD19(+) B cells with normal percentages of TdT(+)VpreB(+)CD19(-) B cell precursors. This developmental block is earlier than that seen in patients with defects in the B cell receptor signaling pathway or in a strain of engineered mice with a similar defect in p85α. The number and function of the patient's T cells were normal. However, Western blot showed markedly decreased p110δ, as well as absent p85α, in patient T cells, neutrophils, and dendritic cells. The patient had normal growth and development and normal fasting glucose and insulin. Mice with p85α deficiency have insulin hypersensitivity, defective platelet function, and abnormal mast cell development. In contrast, the absence of p85α in the patient results in an early and severe defect in B cell development but minimal findings in other organ systems.

The composition and signaling of the IL-35 receptor are unconventional

Interleukin 35 (IL-35) belongs to the IL-12 family of heterodimeric cytokines but has a distinct functional profile. IL-35 suppresses T cell proliferation and converts naive T cells into IL-35-producing induced regulatory T cells (iTr35 cells). Here we found that IL-35 signaled through a unique heterodimer of receptor chains IL-12Rβ2 and gp130 or homodimers of each chain. Conventional T cells were sensitive to IL-35-mediated suppression in the absence of one receptor chain but not both receptor chains, whereas signaling through both chains was required for IL-35 expression and conversion into iTr35 cells. Signaling through the IL-35 receptor required the transcription factors STAT1 and STAT4, which formed a unique heterodimer that bound to distinct sites in the promoters of the genes encoding the IL-12 subunits p35 and Ebi3. This unconventional mode of signaling, distinct from that of other members of the IL-12 family, may broaden the spectrum and specificity of IL-35-mediated suppression.

A critical role for SOCS3 in innate resistance to Toxoplasma gondii

The innate and adaptive immune responses that confer resistance to the intracellular pathogen Toxoplasma gondii critically depend on IL-12 production, which drives interferon-γ (IFN-γ) expression. Certain cytokines can activate STAT3 and limit IL-12 production to prevent infection-associated immune pathology, but T. gondii also directly activates STAT3 to evade host immunity. We show that suppressor of cytokine signaling molecule 3 (SOCS3), a target of STAT3 that limits signaling by the pleiotropic cytokine IL-6, is upregulated in response to infection but is dispensable for the immune-inhibitory effects of T. gondii. Unexpectedly, mice with targeted deletion of SOCS3 in macrophages and neutrophils have reduced IL-12 responses and succumb to toxoplasmosis. Anti-IL-6 administration or IL-12 treatment blocked disease susceptibility, suggesting that in the absence of SOCS3, macrophages are hypersensitive to the anti-inflammatory properties of IL-6. Thus, SOCS3 has a critical role in suppressing IL-6 signals and promoting immune responses to control T. gondii infection.

A review of the nutrition of Australian peramelid marsupials

European settlement has had a dramatic impact on the distribution and abundance of peramelid (bandicoot and bilby) marsupials. Predation and competition from introduced species and altered habitat have been implicated in their decline or extinction. Bandicoots and bilbies inhabit a broad range of habitats in Australia. Research on the distribution, morphology, gastrointestinal histology, lactation, metabolism and nutritional physiology of extant peramelid species has increased in the last few decades. This paper provides a review that encompasses recent nutritional-based research. Peramelid research is mostly limited to only three species – Isoodon macrourus, Perameles nasuta and Macrotis lagotis – which prevents effective comparisons between species. Peramelids are broadly classified as omnivores and possess relatively uncomplicated gastrointestinal tracts. The caecum is the region of greatest diversity among species. The relatively large caecum of Chaeropus ecaudatus supports the theory that this species may have been the only herbivorous peramelid. The caecum of M. lagotis is less pronounced than other species and is continuous with the proximal colon. M. lagotis also has a longer total colon length, which aids water conservation to ensure survival in an arid environment. Temperate-zone species such as I. macrourus, I. obesulus and P. nasuta are more similar to each other with respect to gastrointestinal morphology than either C. ecaudatus or M. lagotis. Additional research on the morphometrics of the gastrointestinal tracts of P. gunnii, P. bougainville, P. eremiana, M. leucura and I. auratus would enable further comparisons to determine whether differences are a result of geographic distribution, habitat preference or variation between genera and/or individual species. Currently, histological information of the gastrointestinal tract is limited to the small intestine of P. nasuta and I. macrourus. The histology of the small intestine of the weaned juvenile I. macrourus more closely resembles that of P. nasuta pouch young than P. nasuta adults. The younger bandicoots possessed villi whereas in the adult P. nasuta and I. macrourus villi were arranged in a zig-zag formation. The reason for the zig-zag formation of the villi and the function it may serve remains unclear. Detailed nutritional research on captive M. lagotis, I. macrourus and P. nasuta indicate that the two temperate-zone species – I. macrourus and P. nasuta – are more similar to each other than to the arid-dwelling M. lagotis. Detailed nutritional studies are required on all species, both free-living and captive. Experimental diets do not always accurately reflect a natural diet, which means that results from captive studies may not reflect the situation for free-living animals. The hindgut of peramelids is the main region for retention of digesta, and presumably where microbial digestion occurs. However, no studies have been undertaken to examine the microflora of the gastrointestinal tract of bandicoots or the bilby. As captive husbandry is an important tool in conservation management, it should also improve their successful maintenance in captivity by the provision of diets that better meet their nutritional requirements.

Adenosine promotes alternative macrophage activation via A2A and A2B receptors

Adenosine has been implicated in suppressing the proinflammatory responses of classically activated macrophages induced by Th1 cytokines. Alternative macrophage activation is induced by the Th2 cytokines interleukin (IL)-4 and IL-13; however, the role of adenosine in governing alternative macrophage activation is unknown. We show here that adenosine treatment of IL-4- or IL-13-activated macrophages augments the expression of alternative macrophage markers arginase-1, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), and macrophage galactose-type C-type lectin-1. The stimulatory effect of adenosine required primarily A(2B) receptors because the nonselective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) increased both arginase activity (EC(50)=261.8 nM) and TIMP-1 production (EC(50)=80.67 nM), and both pharmacologic and genetic blockade of A(2B) receptors prevented the effect of NECA. A(2A) receptors also contributed to the adenosine augmentation of IL-4-induced TIMP-1 release, as both adenosine and NECA were less efficacious in augmenting TIMP-1 release by A(2A) receptor-deficient than control macrophages. Of the transcription factors known to drive alternative macrophage activation, CCAAT-enhancer-binding protein β was required, while cAMP response element-binding protein and signal transducer and activator of transcription 6 were dispensable in mediating the effect of adenosine. We propose that adenosine receptor activation suppresses inflammation and promotes tissue restitution, in part, by promoting alternative macrophage activation.

Protective and pathogenic functions of macrophage subsets

Macrophages are strategically located throughout the body tissues, where they ingest and process foreign materials, dead cells and debris and recruit additional macrophages in response to inflammatory signals. They are highly heterogeneous cells that can rapidly change their function in response to local microenvironmental signals. In this Review, we discuss the four stages of orderly inflammation mediated by macrophages: recruitment to tissues; differentiation and activation in situ; conversion to suppressive cells; and restoration of tissue homeostasis. We also discuss the protective and pathogenic functions of the various macrophage subsets in antimicrobial defence, antitumour immune responses, metabolism and obesity, allergy and asthma, tumorigenesis, autoimmunity, atherosclerosis, fibrosis and wound healing. Finally, we briefly discuss the characterization of macrophage heterogeneity in humans.

Protective and pathogenic functions of macrophage subsets

Macrophages are strategically located throughout the body tissues, where they ingest and process foreign materials, dead cells and debris and recruit additional macrophages in response to inflammatory signals. They are highly heterogeneous cells that can rapidly change their function in response to local microenvironmental signals. In this Review, we discuss the four stages of orderly inflammation mediated by macrophages: recruitment to tissues; differentiation and activation in situ; conversion to suppressive cells; and restoration of tissue homeostasis. We also discuss the protective and pathogenic functions of the various macrophage subsets in antimicrobial defence, antitumour immune responses, metabolism and obesity, allergy and asthma, tumorigenesis, autoimmunity, atherosclerosis, fibrosis and wound healing. Finally, we briefly discuss the characterization of macrophage heterogeneity in humans.

Arginase-1-expressing macrophages are dispensable for resistance to infection with the gastrointestinal helminth Trichuris muris

Alternatively activated macrophages (AAMs) have key roles in the immune response to a variety of gastrointestinal helminths such as Heligmosomoides bakeri and Nippostrongylus brasiliensis. In addition, AAMs have been implicated in the resolution of infection-induced pathology in Schistosoma mansoni infection. AAMs exert their activity in part via the enzyme arginase-1 (Arg1), which hydrolyses l-arginine into urea and ornithine, and can supply precursor substrate for proline and polyamine production. Trichuris muris is a worm that resides in the large intestine with resistance being characterized by a Th2 T-cell response, which drives alternatively activated macrophage production in the local environment of the infection. To investigate the role of AAMs in T. muris infection, we used independent genetic and pharmacologic models of arginase deficiency. In acute infection and Th2-dominated immunity, arginase-deficient models expelled worms normally. Macrophage-Arg1-deficient mice showed cytokine and antibody levels comparable to wild-type animals in acute and chronic infection. We also found no role for AAMs and Arg1 in infection-induced pathology in the response to T. muris in either chronic (Th1 dominated) or acute (Th2 dominated) infections. Our data demonstrate that, unlike other gastrointestinal helminths, Arg1 expression in AAMs is not essential for resistance to T. muris in effective resolution of helminth-induced inflammation.

Macrophages as a battleground for toxoplasma pathogenesis

In this issue of Cell Host & Microbe, Jensen et al. (2011) show that clonal lineages of Toxoplasma gondii have evolved distinct ways of subverting their favored host cell, the macrophage. The results suggest that T. gondii and the ROP kinases can be used to probe immune signaling pathways.

Gut Nod2 calls the bone marrow for monocyte reinforcements

Nod2 is an intracellular sensor linked to Crohn's disease, an inflammatory malady of the intestinal tract. In this issue of Immunity, Kim et al. (2011) demonstrate that Nod2 is responsible for regulating monocyte-attracting chemokines to the inflamed gut.

Tracking the flow of bacterially derived 13C and 15N through soil faunal feeding channels

The soil food web has been referred to as a 'black box', a 'poor man's tropical rainforest' and an 'enigma', due to its opacity, diversity and the limited insight into feeding specificity. Here we investigate the flow of C and N through the soil food web as a way to gain understanding of the feeding interactions occurring. A bacterium, Pseudomonas lurida, was introduced to soil cores from two different habitats, a grassland and a woodland with the same soil type, enriched to 99 atom% in (13)C and (15)N, to trace the flow of bacterial C and N through the soil food web. Throughout the experiment the soil remained enriched in (13)C and (15)N. Almost all the invertebrates tested gained C and N enrichment indicative of the labelled bacteria, implying that bacterial feeding is a common mechanism within the soil. Only three groups were significantly enriched in both (13)C and (15)N in both habitats. These were Collembola (Entomobryomorpha), Acari (Oribatida), and Nematoda, indicating that these organisms are consuming the most bacteria within both systems. When the invertebrates were grouped into hypothesised trophic levels, those considered secondary decomposers were gaining the most enrichment across all invertebrates tested. This enrichment was also high in the micro-predators within the soil, implying that their main food source was the secondary decomposers, particularly the Collembola. Using an enriched bacterium to track the trophic transfer between organisms within the soil food web is a novel way of empirically showing that interactions are occurring, which normally cannot be seen.

Differential growth of the fungus Absidia cylindrospora on 13C/15N-labelled media

Many studies utilise enrichment of stable isotopes as tracers to follow the interactions occurring within soil food webs and methods have been developed to enrich bacteria, soil fauna and plant litter, Here for the first time we attempt to enrich a soil fungus to 99 atom% with (13)C and (15)N stable isotopes. In this study our objectives were to (a) assess whether the saprotrophic zygomycete fungus Absidia cylindrospora could grow on a medium enriched to 99 atom% with (13)C-glucose and (15)N-ammonium chloride, (b) to determine the level of enrichment obtained, and (c) to examine the change in growth rate of this fungus while it was growing on the dually enriched medium. To achieve this, the fungus was grown on agar enriched with (13)C and (15)N to 99 atom% and its growth rate monitored. The results showed that A. cylindrospora would grow on the highly labelled growth medium, but that its rate of growth was affected compared with the rate on either natural abundance media or media highly enriched with a single isotope ((13)C or (15)N). The implications of these results is that although the fungus is able to utilise these heavier isotopes, the biochemical processes involved in growth are affected, and consideration should be given to these differences when using stable isotope tracers in, for example, soil food web studies.

A distal enhancer in Il12b is the target of transcriptional repression by the STAT3 pathway and requires the basic leucine zipper (B-ZIP) protein NFIL3

Deregulated IL-12 and IL-23 production from activated myeloid lineage cells is a key driver of numerous T cell-dependent autoimmune and inflammatory diseases. IL-12 and IL-23 share a common p40 subunit encoded by Il12b, which is negatively regulated at the transcriptional level by the STAT3 (signal transducer and activator of transcription 3)-activating anti-inflammatory cytokine IL-10. We found that IL-10 targets an enhancer 10 kb upstream of the Il12b transcriptional start site. Within the enhancer, a single 10-bp site is required for the inhibitory effects of IL-10 and is bound by NFIL3 (nuclear factor, interleukin 3-regulated), a B-ZIP transcription factor. Myeloid cells lacking NFIL3 produce excessive IL-12p40 and increased IL-12p70. Thus, the STAT3-dependent expression of NFIL3 is a key component of a negative feedback pathway in myeloid cells that suppresses proinflammatory responses.