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In this issue of Blood, Grants et al have identified connections between reduced expression of microRNA-146a (miR-146a), increased inflammation, impaired hematopoietic stem cell (HSC) quiescence, and a poor prognosis for acute myeloid leukemia (AML). miR-146a was originally identified as an anti-inflammatory microRNA that targets signaling proteins, which mediate inflammatory responses., Deletion of miR-146a in mice phenocopies many aspects of age-dependent inflammation,, termed “inflammaging.”

We showed that Emicro-MiR-155 transgenic mice develop acute lymphoblastic leukemia/high-grade lymphoma. Most of these leukemias start at approximately 9 months irrespective of the mouse strain. They are preceded by a polyclonal pre-B-cell proliferation, have variable clinical presentation, are transplantable, and develop oligo/monoclonal expansion. In this study, we show that in these transgenic mice the B-cell precursors have the highest MiR-155 transgene expression and are at the origin of the leukemias. We determine that Src homology 2 domain-containing inositol-5-phosphatase (SHIP) and CCAAT enhancer-binding protein beta (C/EBPbeta), 2 important regulators of the interleukin-6 signaling pathway, are direct targets of MiR-155 and become gradually more down-regulated in the leukemic than in the preleukemic mice. We hypothesize that miR-155, by down-modulating Ship and C/EBPbeta, initiates a chain of events that leads to the accumulation of large pre-B cells and acute lymphoblastic leukemia/high-grade lymphoma.

We showed that Emicro-MiR-155 transgenic mice develop acute lymphoblastic leukemia/high-grade lymphoma. Most of these leukemias start at approximately 9 months irrespective of the mouse strain. They are preceded by a polyclonal pre-B-cell proliferation, have variable clinical presentation, are transplantable, and develop oligo/monoclonal expansion. In this study, we show that in these transgenic mice the B-cell precursors have the highest MiR-155 transgene expression and are at the origin of the leukemias. We determine that Src homology 2 domain-containing inositol-5-phosphatase (SHIP) and CCAAT enhancer-binding protein beta (C/EBPbeta), 2 important regulators of the interleukin-6 signaling pathway, are direct targets of MiR-155 and become gradually more down-regulated in the leukemic than in the preleukemic mice. We hypothesize that miR-155, by down-modulating Ship and C/EBPbeta, initiates a chain of events that leads to the accumulation of large pre-B cells and acute lymphoblastic leukemia/high-grade lymphoma.

Castleman disease (CD) describes a group of heterogeneous hematologic disorders with characteristic histopathological features. CD can present with unicentric or multicentric (MCD) regions of lymph node enlargement. Some cases of MCD are caused by human herpesvirus-8 (HHV-8), whereas others are HHV-8-negative/idiopathic (iMCD). Treatment of iMCD is challenging, and outcomes can be poor because no uniform treatment guidelines exist, few systematic studies have been conducted, and no agreed upon response criteria have been described. The purpose of this paper is to establish consensus, evidence-based treatment guidelines based on the severity of iMCD to improve outcomes. An international Working Group of 42 experts from 10 countries was convened by the Castleman Disease Collaborative Network to establish consensus guidelines for the management of iMCD based on published literature, review of treatment effectiveness for 344 cases, and expert opinion. The anti-interleukin-6 monoclonal antibody siltuximab (or tocilizumab, if siltuximab is not available) with or without corticosteroids is the preferred first-line therapy for iMCD. In the most severe cases, adjuvant combination chemotherapy is recommended. Additional agents are recommended, tailored by disease severity, as secondand third-line therapies for treatment failures. Response criteria were formulated to facilitate the evaluation of treatment failure or success. These guidelines should help treating physicians to stratify patients based on disease severity in order to select the best available therapeutic option. An international registry for patients with CD (ACCELERATE, #NCT02817997) was established in October 2016 to collect patient outcomes to increase the evidence base for selection of therapies in the future. [ABSTRACT FROM AUTHOR]

Systemic iron balance is controlled by hepcidin, a liver hormone that limits iron efflux to the bloodstream by promoting degradation of the iron exporter ferroportin in target cells. Iron-dependent hepcidin induction requires hemojuvelin (HJV), a bone morphogenetic protein (BMP) coreceptor that is disrupted in juvenile hemochromatosis, causing dramatic hepcidin deficiency and tissue iron overload. Hjv-/- mice recapitulate phenotypic hallmarks of hemochromatosis but exhibit blunted hepcidin induction following lipopolysaccharide (LPS) administration. We show that Hjv-/- mice fail to mount an appropriate hypoferremic response to acute inflammation caused by LPS, the lipopeptide FSL1, or Escherichia coli infection because residual hepcidin does not suffice to drastically decrease macrophage ferroportin levels. Hfe-/- mice, a model of milder hemochromatosis, exhibit almost wild-type inflammatory hepcidin expression and associated effects, whereas double Hjv-/-Hfe-/- mice phenocopy single Hjv-/- counterparts. In primary murine hepatocytes, Hjv deficiency does not affect interleukin-6 (IL-6)/Stat, and only slightly inhibits BMP2/Smad signaling to hepcidin; however, it severely impairs BMP6/Smad signaling and thereby abolishes synergism with the IL-6/Stat pathway. Inflammatory induction of hepcidin is suppressed in iron-deficient wild-type mice and recovers after the animals are provided overnight access to an iron-rich diet. We conclude that Hjv is required for inflammatory induction of hepcidin and controls the acute hypoferremic response by maintaining a threshold of Bmp6/Smad signaling. Our data highlight Hjv as a potential pharmacological target against anemia of inflammation. [ABSTRACT FROM AUTHOR]

Lack of either bone morphogenetic protein 6 (BMP6) or the BMP coreceptor hemojuvelin (HJV) inmice leads to a similar phenotype with hepcidin insufficiency, hepatic iron loading, and extrahepatic iron accumulation in males. This is consistent with the current views that HJV is a coreceptor for BMP6in hepatocytes. To determine whether BMP6 and HJV may also signal to hepcidin independently of each other, we intercrossed Hjv-/- and Bmp6-/- mice and compared the phenotype of animals of the F2 progeny. Loss of Bmp6 further repressed Smad signaling and hepcidin expression in the liver of Hjv-/- mice of both sexes, and led to iron accumulation in the pancreas and the heart of females. These data suggest that, in Hjv-/- females,Bmp6 can provide a signal adequate to maintain hepcidin to a level sufficient to avoid extrahepatic iron loading. We also examined the impact of Bmp6 and/or Hjv deletion on the regulation of hepcidin by inflammation. Our data show that lack of 1 or both molecules does not prevent induction of hepcidin by lipopolysaccharide (LPS). However, BMP/Smad signaling in unchallenged animals is determinant for the level of hepcidin reached after stimulation, which is consistent with a synergy between interleukin 6/STAT3 andBMP/SMAD signaling in regulating hepcidin during inflammation. [ABSTRACT FROM AUTHOR]

Humanized mice are a powerful tool for the study of human hematopoiesis and immune function in vivo. However, the existing models cannot support robust adaptive immune responses, especially the generation of class-switched, antigen-specific antibody responses. Here we describe a new mouse strain, in which human interleukin 6 (IL-6) gene encoding the cytokine that is important for B- and T-cell differentiation was knocked into its respective mouse locus. The provision of human IL-6 not only enhanced thymopoiesis and periphery T-cell engraftment, but also significantly increased class switched memory B cells and serum immunoglobulin G (IgG). In addition, immunization with ovalbumin (OVA) induced OVA-specific B cells only in human IL-6 knock-in mice. These OVA-specific antibodies displayed the highest frequency of somatic mutation, further suggesting that human IL-6 is important for efficient B-cell activation and selection. We conclude that human IL-6 knock-in mice represent a novel and improved model for human adaptive immunity without relying on complex surgery to transplant humanfetal thymusand liver. These mice can therefore be used to exploit or evaluate immunization regimes that would be unethical or untenable in humans. [ABSTRACT FROM AUTHOR]

Immune cell inflammation is implicated in the pathophysiology of acute trauma-induced coagulopathy (TIC). We hypothesized that leukocyte inflammation contributes to TIC through the oxidation and proteolysis of fibrinogen. To test this hypothesis, antioxidants and a novel anti-inflammatory melanocortin fusion protein (AQB-565) were used to study the effects of interleukin-6 (IL-6)-stimulated human leukocytes on fibrinogen using single-cell imaging flow cytometry and multiplex fluorescent western blotting. We also studied the effects of AQB-565 on fibrinogen using an in vivo rat trauma model of native TIC. IL-6 induced cellular inflammation and mitochondrial superoxide production in human monocytes, causing fibrinogen oxidation and degradation in vitro. Antioxidants suppressing mitochondrial superoxide reduced oxidative stress and inflammation and protected fibrinogen. AQB-565 decreased inflammation, inhibited mitochondrial superoxide, and protected fibrinogen in vitro. Trauma with hemorrhagic shock increased IL-6 and other proinflammatory cytokines and chemokines, selectively oxidized and degraded fibrinogen, and induced TIC in rats in vivo. AQB-565, given at the onset of hemorrhage, blocked inflammation, protected fibrinogen from oxidation and degradation, and prevented TIC. Leukocyte activation contributes to TIC through the oxidation and degradation of fibrinogen, which involves mitochondrial superoxide and cellular inflammation. Suppression of inflammation by activation of melanocortin pathways may be a novel approach for the prevention and treatment of TIC., (© 2023 by The American Society of Hematology.)

Peripheral T-cell lymphomas (PTCLs), especially angioimmunoblastic and follicular TCLs, have a dismal prognosis because of the lack of efficient therapies, and patients' symptoms are often dominated by an inflammatory phenotype, including fever, night sweats, weight loss, and skin rash. In this study, we investigated the role of inflammatory granulocytes and activated cytokine signaling on T-cell follicular helper-type PTCL (TFH-PTCL) disease progression and symptoms. We showed that ITK-SYK-driven murine PTCLs and primary human TFH-PTCL xenografts both induced inflammation in mice, including murine neutrophil expansion and massive cytokine release. Granulocyte/lymphoma interactions were mediated by positive autoregulatory cytokine loops involving interferon gamma (CD4+ malignant T cells) and interleukin 6 (IL-6; activated granulocytes), ultimately inducing broad JAK activation (JAK1/2/3 and TYK2) in both cell types. Inflammatory granulocyte depletion via antibodies (Ly6G), genetic granulocyte depletion (LyzM-Cre/MCL1flox/flox), or IL-6 deletion within microenvironmental cells blocked inflammatory symptoms, reduced lymphoma infiltration, and enhanced mouse survival. Furthermore, unselective JAK inhibitors (ruxolitinib) inhibited both TCL progression and granulocyte activation in various PTCL mouse models. Our results support the important role of granulocyte-driven inflammation, cytokine-induced granulocyte/CD4+ TCL interactions, and an intact JAK/STAT signaling pathway for TFH-PTCL development and also support broad JAK inhibition as an effective treatment strategy in early disease stages., (© 2023 by The American Society of Hematology.)

Activating mutations in MYD88 are present in ∼95% of patients with Waldenström macroglobulinemia (WM), as well as other B-cell malignancies including activated B-cell (ABC) diffuse large B-cell lymphoma (DLBCL). In WM, mutated MYD88 triggers activation of Bruton tyrosine kinase (BTK). Ibrutinib, a pleiotropic kinase inhibitor that targets BTK, is highly active in patients with mutated MYD88. We observed that mutated MYD88 WM and ABC DLBCL cell lines, as well as primary WM cells show enhanced hematopoietic cell kinase (HCK) transcription and activation, and that HCK is activated by interleukin 6 (IL-6). Over-expression of mutated MYD88 triggers HCK and IL-6 transcription, whereas knockdown of HCK reduced survival and attenuated BTK, phosphoinositide 3-kinase/AKT, and mitogen-activated protein kinase/extracellular signal-regulated kinase signaling in mutated MYD88 WM and/or ABC DLBCL cells. Ibrutinib and the more potent HCK inhibitor A419259, blocked HCK activation and induced apoptosis in mutated MYD88 WM and ABC DLBCL cells. Docking and pull-down studies confirmed that HCK was a target of ibrutinib. Ibrutinib and A419259 also blocked adenosine triphosphate binding to HCK, whereas transduction of mutated MYD88 expressing WM cells with a mutated HCK gatekeeper greatly increased the half maximal effective concentration for ibrutinib and A419259. The findings support that HCK expression and activation is triggered by mutated MYD88, supports the growth and survival of mutated MYD88 WM and ABC DLBCL cells, and is a direct target of ibrutinib. HCK represents a novel target for therapeutic development in MYD88-mutated WM and ABC DLBCL, and possibly other diseases driven by mutated MYD88. [ABSTRACT FROM AUTHOR]

In this issue of Blood, Xu et al unequivocally show by using a series of elegant experiments that platelet GPIba mediates hepatic thrombopoietin (TPO) production.¹ [ABSTRACT FROM AUTHOR]

Joint bleeding after (sports) trauma, after major joint surgery, or as seen in hemophilia in general leads to arthropathy. Joint degeneration is considered to result from the direct effects of blood components on cartilage and indirectly from synovial inflammation. Blood-provided proinflammatory cytokines trigger chondrocytes and induce the production of cartilage-degrading proteases. In the presence of erythrocyte-derived iron, cytokines stimulate radical formation in the vicinity of chondrocytes inducing apoptosis. To unravel the role of interleukin (IL) 1β and tumor necrosis factor (TNF) α in the pathogenesis of this blood-induced cartilage damage, the effect of antagonizing these cytokines was examined in human in vitro cultures. Addition of recombinant human IL-1β monoclonal antibody or IL-1 receptor antagonist resulted in a dose- and time-dependent protection of cartilage from blood-induced damage. In higher concentrations, almost complete normalization of cartilage matrix proteoglycan turnover was achieved. This was accompanied by a reduction in IL-1β and IL-6 production in whole blood cultures, whereas TNFα production remained unaffected. Interestingly, addition of a TNFα monoclonal antibody, although demonstrated to inhibit the direct (transient) effects of TNFα on cartilage, exhibited no effect on blood-induced (prolonged) cartilage damage. It is demonstrated that IL-1β is crucial in the development of blood-induced joint damage, whereas TNFα is not. This hierarchical position of IL-1β in blood-induced joint damage warrants studies on targeting IL-1β to potentially prevent joint degeneration after a joint bleed. [ABSTRACT FROM AUTHOR]

The regulation of toll-like receptor (TLR) signaling in a tumor microenvironment is poorly understood despite its importance in cancer biology. To address this problem, TLR7-responses of chronic lymphocytic leukemia (CLL) cells were studied in the presence and absence of a human stromal cell-line derived from a leukemic spleen. CLL cells alone produced high levels of tumor necrosis factor (TNF)-α and proliferated in response to TLR7-agonists. A signal transducer and activator of transcription 3 -activating stromal factor, identified as interleukin (IL)-6, was found to upregulate microRNA (miR)-17 and miR-19a, target TLR7 and TNFA messenger RNA, and induce a state of tolerance to TLR7-agonists in CLL cells. Overexpression of the miR-17-92 cluster tolerized CLL cells directly and miR-17 and miR-19a antagomiRs restored TLR7-signaling. Inhibition of IL-6 signaling with antibodies or small-molecule Janus kinase inhibitors reversed tolerization and increased TLR7-stimulated CLL cell numbers in vitro and in NOD-SCIDγcnull mice. These results suggest IL-6 can act as tumor suppressor in CLL by inhibiting TLR-signaling. [ABSTRACT FROM AUTHOR]

Galectin-3-binding protein (gal3bp) and its receptor/ligand, galectin-3 (gal3), are secreted proteins that initiate signaling cascades in several diseases, and recent human proteomic data suggest they may play a role in venous thrombosis (VT). We hypothesized that gal3bp and gal3 may promote VT. Using a mouse stasis model of VT, we found that gal3bp and gal3 were localized on vein wall, red blood cells, platelets, and microparticles, whereas leukocytes expressed gal3 only. Gal3 was dramatically increased during early VT and gal3bp:gal3 colocalized in the leukocyte/endothelial cell interface, where leukocytes were partially attached to the vein wall. Thrombus size correlated with elevated gal3 and interleukin-6 (IL-6) vein wall levels. Recombinant gal3 promoted VT and increased vein wall IL-6 mRNA. Although recombinant gal3 restored the VT size in gal3-/- mice, it had no effect on IL6-/- mice, suggesting that gal3:gal3bp promotes VT through IL-6. Moreover, significantly fewer activated neutrophils were present in the gal3-/- vein walls. In a group of human patients, elevated circulating gal3bp correlated with acute VT. In conclusion, gal3bp:gal3 play a critical role in VT, likely via IL-6 and PMN-mediated thrombotic mechanisms, and may be a potential biomarker in human VT. [ABSTRACT FROM AUTHOR]

The function and survival of normal and malignant plasma cells depends on the elaborately regulated ubiquitin proteasome system. Proteasome inhibitors such as bortezomib have proved to be highly effective in the treatment of multiple myeloma (MM), and their effects are related to normal protein homeostasis which is critical for plasma cell survival. Many ubiquitin ligases are regulated by conjugation with NEDD8. Therefore, neddylation may also impact survival and proliferation of malignant plasma cells. Here, we show that MLN4924, a potent NEDD8 activating enzyme (NAE) inhibitor, induced cytotoxicity in MM cell lines, and its antitumor effect is associated with suppression of the AKT and mammalian target of rapamycin (mTOR) signaling pathways through increased expression of REDDl. Combining MLN4924 with the proteasome inhibitor bortezomib induces synergistic apoptosis in MM cell lines which can overcome the prosurvival effects of growth factors such as interleukin-6 and insulin-like growth factor-1. Altogether, our findings demonstrate an important function for REDD1 in MLN4924-induced cytotoxicity in MM and also provide a promising therapeutic combination strategy for myeloma. [ABSTRACT FROM AUTHOR]

Multicentric Castleman's disease (MCD) describes a heterogeneous group of disorders involving proliferation of morphologically benign lymphocytes due to excessive proinflammatory hypercytokinemia, most notably of interleukin-6. Patients demonstrate intense episodes of systemic inflammatory symptoms, polyclonal lymphocyte and plasma cell proliferation, autoimmune manifestations, and organ system impairment. Human herpes virus-8 (HHV-8) drives the hypercytokinemia in all HIV-positive patients and some HIV-negative patients. There is also a group of HIV-negative and HHV-8-negative patients with unknown etiology and pathophysiology, which we propose referring to as idiopathic MCD (iMCD). Here, we synthesize what is known about iMCD pathogenesis, present a new subclassification system, and propose a model of iMCD pathogenesis. MCD should be subdivided into HHV-8-associated MCD and HHV-8-negative MCD or iMCD. The lymphocyte proliferation, histopathology, and systemic features in iMCD are secondary to hypercytokinemia, which can occur with several other diseases. We propose that 1 or more of the following 3 candidate processes may drive iMCD hypercytokinemia: systemic inflammatory disease mechanisms via autoantibodies or inflammatory gene mutations, paraneoplastic syndrome mechanisms via ectopic cytokine secretion, and/or a non-HHV-8 virus. Urgent priorities include elucidating the process driving iMCD hypercytokinemia, identifying the hypercytokine-secreting cell, developing consensus criteria for diagnosis, and building a patient registry to track cases. [ABSTRACT FROM AUTHOR]

Increased IL-6 production induces, via STAT3 phosphorylation, hepatic transcription of the gene encoding the iron-regulatory hormone, hepcidin, leading to development of anemia of chronic disease (ACD). Inhibition of bone morphogenetic protein (BMP) signaling prevents the induction of hepcidin gene expression by IL-6 and ameliorates ACD. Using mice with hepatocyte-specific deficiency of Alk2 or Alk3, we sought to identify the BMP type I receptor that participates in IL-6-mediated induction of hepcidin gene expression. Mice were injected with adenovirus specifying IL-6 (Ad.IL-6) or control adenovirus. Seventy-two hours later, serum iron concentrations and hepatic levels of STAT3 phosphorylation and hepcidin messenger RNA were measured. Additional mice were injected with recombinant murine IL-6 (mIL-6) or vehicle, and hepatic hepcidin gene expression was measured 4 hours later. Deficiency of Alk2 or Alk3 did not alter the ability of Ad.IL-6 injection to induce hepatic STAT3 phosphorylation. Ad.IL-6 increased hepatic hepcidin messenger RNA levels and decreased serum iron concentrations in Alk2- but not Alk3-deficient mice. Similarly, administration of mIL-6 induced hepatic hepcidin gene expression in Alk2- but not Alk3-deficient mice. These results demonstrate that the ability of IL-6 to induce hepatic hepcidin gene expression and reduce serum iron concentrations is dependent on the BMP type I receptor Alk3. [ABSTRACT FROM AUTHOR]

Anemia of inflammation (AI) is commonly observed in chronic inflammatory states and may hinder patient recovery and survival. Induction of hepcidin, mediated by interleukin 6, leads to iron-restricted erythropoiesis and anemia. Several translational studies have been directed at neutralizing hepcidin overexpression as a therapeutic strategy against AI. However, additional hepcidin-independent mechanisms contribute to AI, which are likely mediated by a direct effect of inflammatory cytokines on erythropoiesis. In this study, we used wild-type, hepcidin knockout (Hamp-KO) and interleukin 6 knockout (IL-6-KO) mice as models of AI. AI was induced with heat-killed Brucella abortus (BA). The distinct roles of iron metabolism and inflammation triggered by interleukin 6 and hepcidin were investigated. BA-treated wild-type mice showed increased expression of hepcidin and inflammatory cytokines, as well as transitory suppression of erythropoiesis and shortened red blood cell lifespan, all of which contributed to the severe anemia of these mice. In contrast, BA-treated Hamp-KO or IL-6-KO mice showed milder anemia and faster recovery compared with normal mice. Moreover, they exhibited different patterns in the development and resolution of anemia, supporting the notion that interleukin 6 and hepcidin play distinct roles in modulating erythropoiesis in AI. [ABSTRACT FROM AUTHOR]

Increasing evidence supports the importance of cell extrinsic regulation in stem cell fate control. Hematopoietic stem cells (HSC) are responsive to local signals from their niche and to systemic feedback from progenitors and mature cells. The Notch ligand Delta-1 (DL1), a key component of the stem cell niche, regulates human hematopoietic lineage development in a dose-dependent manner and has been used clinically for primitive progenitor expansion. How DL1 acts to regulate HSC fate and whether these actions are related to its lineage skewing effects are poorly understood. Here we demonstrate that, although DL1 activates signal transducer and activator of transcription 3 signaling similarly to the gp130-activating cytokine interleukin-6 (IL-6), it has opposite effects on myeloid cell production. Mechanistically, these different outcomes are attributable to a DL1 -mediated reduction in membrane (m)-bound IL-6 receptor (R) expression, converting progenitor cells from being directly IL-6 responsive to requiring both IL-6 and soluble (s) IL-6R for activation. Concomitant reduction of both mlL-6R (by DL1 supplementation) and slL-6R (using dynamically fed cultures) reduced myeloid cell production and led to enhanced outputs of human HSCs. This work describes a new mode of cytokine action in which DL1 changes cytokine receptor distributions on hematopoietic cells, altering feedback networks and their impact on stem cell fate. [ABSTRACT FROM AUTHOR]

Kaposi sarcoma herpesvirus (KSHV)-associated multicentric Castleman disease (MCD) is a polyclonal B-cell lymphoproliferative disorder. Human (h) IL-6 and a KSHV-encoded homolog, viral IL-6, have been hypothesized to contribute to its pathogenesis, but their relative contributions to disease activity is not well understood. We prospectively characterized KSHV viral load (VL), viral (v) and hlL-6, and other cytokines during KSHV-MCD flare and remission in 21 patients with 34 flares and 20 remissions. KSHV-VL, vlL-6, hlL-6, IL-10, and to a lesser extent TNF-α, and IL-1β were each elevated during initial flares compared with remission. Flares fell into 3 distinct IL-6 profiles: those associated with elevations of vlL6-only (2 flares, 6%), hlL-6 elevations only (17 flares, 50%), and elevations in both hlL-6 and vlL-6 (13 flares, 38%). Compared with hlL-6-only flares, flares with elevated hlL-6 plus vlL-6 exhibited higher C-reactive protein (CRP) (P = .0009); worse hyponatremia (P = .02); higher KSHV VL (P = .016), and higher IL-10 (P = .012). This analysis shows vlL-6 and hlL-6 can independently or together lead to KSHV-MCD flares, and suggests that vlL-6 and hlL-6 may jointly contribute to disease severity. These findings have implications for the development of novel KSHV-MCD therapies targeting IL-6 and its downstream signaling. This trial was registered at clinicaltrials.gov as #NCT099073. [ABSTRACT FROM AUTHOR]

Neutrophils emigrate from venules to sites of infection or injury in response to chemotactic gradients. How these gradients form is not well understood. Some IL-6 family cytokines stimulate endothelial cells to express adhesion molecules and chemokines that recruit leukocytes. Receptors for these cytokines share the signaling subunit gp130. We studied knockout mice lacking gp130 in endothelial cells. Unexpectedly, gp130-deficient endothe- hal cells constitutively expressed more CXCL1 in vivo and in vitro, and even more upon stimulation with tumor necrosis factor-of. Mobilization of this increased CXCL1 from intracellular stores to the venular surface triggered β2 integrin-dependent arrest of neutrophils rolling on selectins but impaired intraluminal crawling and transendothelial migration. Superfusing CXCL1 over venules promoted neutrophil migration only after intravenously injecting mAb to CXCL1 to diminish its intravascular function or heparinase to release CXCL1 from endothehial proteoglycans. Remarkably, mice lacking gp130 in endothelial cells had impaired histamine-induced venular permeability, which was restored by injecting anti-P-selectin mAb to prevent neutrophil rolling and arrest. Thus, excessive CXCL1 expression in gp130-deficient endothelial cells augments neutrophil adhesion but hinders migration, most likely by disrupting chemotactic gradients. Our data define a role for endothelial cell gp130 in regulating integrindependent adhesion and de-adhesion of neutrophils during inflammation. [ABSTRACT FROM AUTHOR]

Plasma cells (PCs) are terminally differentiated cells of the B-cell lineage that secrete antibodies at a high rate and are thought to lack the expression of the B-cell receptor (BCR). Here, we report that human IgA and IgM, unlike IgG, PCs express a membrane functional BCR associated with the Igα/lgβ heterodimer. BCR cross-linking on IgA and IgM PCs led to Ca2+ mobilization and extracellular signal-regulated kinase 1/2 and AKT phosphorylation and impacted survival of IgA PCs. These findings demonstrate a significant difference between human IgG, IgM, and IgA PCs and suggest that the IgA PC repertoire may be modulated by specific antigens with implications for the regulation of the mucosal immune system. [ABSTRACT FROM AUTHOR]

The JAK/STAT pathway is altered in T-cell large granular lymphocytic leukemia. In all patients, leukemic LGLs display upregulation of phosphorylated STAT3 (P-STAT3) that activates expression of many antiapoptotic genes. To investigate the mechanisms maintaining STAT3 aberrantly phosphorylated using transcriptional protein and functional assays, we analyzed interleukin (IL)-6 and suppressor of cytokine signaling-3 (SOCS3), 2 key factors of the JAK/STAT pathway that induce and inhibit STAT3 activation, respectively. We showed that IL-6 was highly expressed and released by the patients' peripheral blood LGL-depleted population, accounting for a trans-signaling process. By neutralizing IL-6 or its specific receptor with specific antibodies, a significant reduction of P-STAT3 levels and, consequently, LGL survival was demonstrated. In addition, we found that SOCS3 was down-modulated in LGL and unresponsive to IL-6 stimulation. By treating neoplastic LGLs with a demethylating agent, IL-6-mediated SOCS3 expression was restored with consequent P-STAT3 and myeloid cell leukemia-1 down-modulation. Methylation in the SOCS3 promoter was not detectable, suggesting that an epigenetic inhibition mechanism occurs at a different site. Our data indicate that loss of the inhibitor SOCS3 cooperates with IL-6 to maintain JAK/STAT pathway activation, thus contributing to leukemic LGL survival, and suggest a role of demethylating agents in the treatment of this disorder. [ABSTRACT FROM AUTHOR]

The mechanisms by which CC chemokine receptor (CCR)7 ligands are selectively presented on lymphatic endothelium in the presence of inflammatory chemokines are poorly understood. The chemokine-scavenging receptor D6 is expressed on lymphatic endothelial cells (LEC) and contributes to selective presentation of CCR7 ligands by suppressing inflammatory chemokine binding to LEC surfaces. As well as preventing inappropriate inflammatory cell attachment to LECs, D6 is specifically involved in regulating the ability of LEC to discriminate between mature and immature dendritic cells (OCs). D6 overexpression reduces immature DC (iDC) adhesion to LECs, whereas D6 knockdown increases adhesion of iDCs that displace mature DCs. LEC 06 expression is regulated by growth factors, cytokines, and tumor microenvironments. In particular, interleukin-6 and interferon-γ are potent inducers, indicating a preferential role for 06 in inflamed contexts. Expression of the viral interleukin-6 homolog from Kaposi sarcoma-associated herpes-virus is also sufficient to induce significant D6 upregulation both in vitro and in vivo, and Kaposi sarcoma and primary effusion lymphoma cells demonstrate high levels of D6 expression. We therefore propose that D6, which is upregulated in both inflammatory and tumor contexts, is an essential regulator of inflammatory leukocyte interactions with LECs and is required for immature/mature DC discrimination by LECs. [ABSTRACT FROM AUTHOR]

Anemia of chronic inflammation is the most prevalent form of anemia in hospitalized patients. A hallmark of this disease is the intracellular sequestration of iron. This is a consequence of hepcidin-induced internalization and subsequent degradation of ferroportin, the hepcidin receptor and only known iron-export protein. This study describes the characterization of novel anti-hepcidin compound NOX-H94, a structured L-oligoribonucleotide that binds human hepcidin with high affinity (Kd =0 0.65 ± 0.06 nmol/L). In J774A.1 macrophages, NOX-H94 blocked hepcidin-induced ferroportin degradation and ferritin expression (half maximal inhibitory concentration = 19.8 ± 4.6 nmol/L). In an acute cynomolgus monkey model of interleukin 6 (IL-6)-induced hypoferremia, NOX-H94 inhibited serum iron reduction completely. In a subchronic model of lL-6-induced anemia, NOX-H94 inhibited the decrease in hemoglobin concentration. We conclude that NOX-H94 protects ferroportin from hepcidin-induced degradation. Therefore, this pharmacologic approach may represent an interesting treatment option for patients suffering from anemia of chronic inflammation. (Blood. 201 3;1 21 (12):231 1-2315) [ABSTRACT FROM AUTHOR]

Myeloid-derived suppressor cells (MDSC5) play an important role in the regulation of the immune response. MDSC expansion occurs in many circumstances, including cancer, inflammation, stresses, and transplant tolerance. Liver transplants in mice are spontaneously accepted, but hepatocyte transplants are acutely rejected, suggesting the immunoregulatory activities of liver nonparenchymal cells. We have reported that hepatic stellate cells (HpSCs), the stromal cells in the liver, are immensely immunosuppressive and can effectively protect islet transplants via induction of MDSCs. The present study shows that the addition of HpSCs into dendritic cell (DC) culture promoted development of MDSC5, instead of DCs, which was highly dependent on complement component 3 (C3) from HpSC5. The C3~ HpSCs lost their ability to induce MDSCs and, consequently, failed to protect the cotransplanted islet allografts. HpSC5 produced complement activation factor B and factor D which then enhanced C3 cleavage to activation products iC3b and C3d. Addition of exogenous iC3b, but not C3d, into the DC culture led to the differentiation of MDSCs with potent immune-inhibitory function. These findings provide novel mechanistic insights into the differentiation of myeloid cells mediated by local tissue cells, and may assist in the development of MDSC-based therapy in clinical settings. (Blood. 2013;121(10):1760-1768) [ABSTRACT FROM AUTHOR]

Tumors frequently induce immature myeloid cells (iMC), which suppress specific and unrelated cytotoxic T lymphocyte (CTL) responses and are termed myeloid-derived suppressor cells (MDSC). Mainly analyzed by in vitro assays in tumor transplantation `models, little is known about their function in autochthonous tumor models in vivo. We analyzed MC in 3 SV40 large T (Tag)-driven conditional autochthonous cancer models with different immune status: (1) Early Tag-specific CTL competence and rare stochastic Tag activation leading to sporadic cancer, which induces an aberrant immune response and CTL tolerance; (2) Cre/LoxP recombinase-mediated hepato-cellular carcinoma (HCC) development in neonatal Tag-tolerant mice; and (3) Tag-activation through Cre recombinase-encoding viruses in the liver and HCC development with systemic anti-Tag CTL immunity. In the first but not two latter models, tumors induced CTL hyporespônsiveness to tumor-unrelated antigens. Regardless of the model, tumors produced interleukin-6 and vascular endothelial growth factor but not granulocyte macrophage-colony-stimulating factor (GM-CSF) and induced iMC (CD11b+Gr-1 int) that suppressed CTL responses in vitro. None of the iMC from the different tumor models suppressed CTL responses in adoptive cell transfer experiments unless GM-CSF was provided in vivo. Together, iMC expand independent of the type of antitumor response and are not immunosuppressive in a cell-autonomous fashion. (Blood. 2013;1 21(10):1740-1 748) [ABSTRACT FROM AUTHOR]

Insulin-like growth factor-1 (IGF-1), insulin, and IL-6 are dysregulated in multiple myeloma pathogenesis and may also contribute to multiple myeloma etiology. To examine their etiologic role, we prospectively analyzed concentrations of serologic markers in 493 multiple myeloma cases and 978 controls from 8 cohorts in the Multiple Myeloma Cohort Consortium. We computed odds ratios (ORs) and 95% confidence intervals (CIs) for multiple myeloma per 1-SD increase in bio-marker concentration using conditional logistic regression. We examined heterogeneity by time since blood collection (⩽ 3, 4- s 6, and > 6 years) in stratified models. Fasting IGF binding protein-1 concentration was associated with multiple myeloma risk within 3 years (OR, 95% CI per 1-SD increase: 2.3, 1.4-3.8, P = .001) and soluble IL-6 receptor level was associated within 6 years after blood draw (OR=3years. 95% CI, 1.4, 1.1-1.9, P = .01; OR4-s6yearS, 95% CI, 1.4, 1.1 -1.7, P = .002). No biomarker was associated with longer-term multiple myeloma risk (ie, > 6 years). Interactions with time were statistically significant (IGF binding protein-1, P-heterogeneity = .0016; slL6R, P-heterogeneity = .016). The time-restricted associations probably reflect the bioactivity of tumor and microenviron-ment cells in transformation from monoclonal gammopathy of undetermined significance or smoldering multiple myeloma to clinically manifest multiple myeloma. [ABSTRACT FROM AUTHOR]

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma frequently involved in the lymph nodes, bone marrow, spleen, and gastrointestinal tract. We examined the role of IL-6 in MCL. Human MCL cells expressed the membrane gp130 and soluble gp80, and some of them also secreted IL-6. Neutralizing autocrine IL-6 and/or blocking IL-6 receptors in IL-6+/gp80+ MCL cells inhibited cell growth, enhanced the rate of spontaneous apoptosis, and increased sensitivity to chemotherapy drugs. For IL-6or gp80low MCL cells, paracrine or exogenous IL-6 or gp80 protected the cells from stress-induced death. Knockdown of gp80 in gp80high MCL cells rendered the cells more sensitive to chemotherapy drugs, even in the presence of exogenous IL-6. In contrast, overexpression of gp80 in gp80low/IL-6+ MCL cells protected the cells from chemotherapy drug-induced apoptosis in vitro and compromised the therapeutic effect of chemotherapy in vivo. IL-6 activated the Jak2/ STAT3 and PI3K/Akt pathways in MCL, and the inhibition of these pathways completely or partially abrogated IL-6-mediated protection of MCL cells. Hence, our study identifies IL-6 as a key cytokine for MCL growth and survival and suggests that targeting the IL-6 pathway may be a novel way to improve the efficacy of chemotherapy in MCL patients. [ABSTRACT FROM AUTHOR]

Human herpes virus 8 (HHV-8) or Kaposi sarcoma-associated herpes virus is the etiologic agent of Kaposi sarcoma, primary effusion lymphoma, and plasma cell-type multicentric Castleman disease (MCD). HHV-8 encodes a viral homolog of human IL-6, called viral IL-6 (vlL-6), which does not require the cellular IL-6 receptor for binding to the ubiquitously expressed gp130 receptor subunit and subsequent JAK-STAT signaling. Thus, in contrast to IL-6, vlL-6 can stimulate virtually all cells in the body. To elucidate the mechanism by which vlL-6 drives human diseases, we generated transgenic mice that consti-tutively express vlL-6 under control of the MHC class I promoter. The mice were found to exhibit vlL-6 serum levels comparable with those observed in HHV-8-infected patients, to contain elevated amounts of phosphorylated STAT3 in spleen and lymph nodes, where vlL-6 was produced, and to spontaneously develop key features of human plasma cell-type MCD, including splenomegaly, multifocal lymphadenopathy, hypergammaglobulinemia, and plasmacytosis. Transfer of the vlL-6 transgene onto an /L-6-def icient genetic background abrogated MCD-like phe-noty pes, indicating that endogenous mouse IL-6 is a crucial cofactor in the natural history of the disease. Our results in mice suggest that human IL-6 plays an important role in the pathogenesis of HHV-8-associated MCD. [ABSTRACT FROM AUTHOR]

Extracellular ATP and adenosine have immunoregulatory roles during inflammation. Elevated extracellular ATP is known to exacerbate GVHD, and the pharmacologic activation of the adenosine A2A receptor is protective. However, the role of endogenous adenosine is unknown. We used gene-targeted mice and a pharmacologic inhibitor to test the role of adenosine generated by CD73/ecto-5'-nucleotidase in GVHD. In allogeneic transplants, both donor and recipient CD73 were protective, with recipient CD73 playing the dominant role. CD73 deficiency led to enhanced T-cell expansion and IFN-&ggr; and IL-6 production, and the migratory capacity of Cd73-/_h T cells in vitro was increased. However, the number of regulatory T cells and expression of costimulatory molecules on antigen-presenting cells were unchanged. A2A receptor deficiency led to increased numbers of allogeneic T cells, suggesting that signaling through the A2A receptor via CD73-generated adenosine is a significant part of the mechanism by which CD73 limits the severity of GVHD. Pharmacologic blockade of CD73 also enhanced graft-versus-tumor activity. These data have clinical implications, as both the severity of GVHD and the strength of an alloimmune antitumor response could be manipulated by enhancing or blocking CD73 activity or adenosine receptor signaling depending on the clinical indication. [ABSTRACT FROM AUTHOR]

The circulating peptide hormone hepcidin maintains systemic iron homeostasis. Hepcidin production increases during inflammation and as a result of endoplasmic reticulum (ER) stress. Elevated hepcidin levels decrease dietary iron absorption and promote iron sequestration in reticuloendothelial macrophages. Furthermore, increased plasma hepcidin levels cause hypoferremia and the anemia associated with chronic diseases. The signal transduction pathways that regulate hepcidin during inflammation and ER stress include the IL-6-- dependent STAT-3 pathway and the unfolded protein response-associated cyclic AMP response element-binding protein-H (CREBH) pathway, respectively. We show that carbon monoxide (CO) suppresses hepcidin expression elicited by IL-6- and ER-stress agents by inhibiting STAT-3 phosphorylation and CREBH maturation, respectively. The inhibitory effect of CO on IL-6-inducible hepcidin expression is dependent on the suppressor of cytokine signaling-3 (SOCS-3) protein. Induction of ER stress in mice resulted in increased hepatic and serum hepcidin. CO administration inhibited ER-stress-induced hepcidin expression in vivo. Furthermore, ER stress caused iron accumulation in splenic macrophages, which could be prevented by CO. Our findings suggest novel anti-inflammatory therapeutic applications for CO, as well as therapeutic targets for the amelioration of anemia in the hypoferremic condition associated with chronic inflammatory and metabolic diseases. [ABSTRACT FROM AUTHOR]

Interleukin-6 (IL-6) signaling can be enhanced through trans-signaling by the soluble interleukin-6 receptor (sIL-6r), allowing for the pleiotropic cytokine to affect cells it would not ordinarily have an effect on. Serum levels of soluble interleukin-6 receptor (sIL-6r) can be used as an independent prognostic indicator and further stratify the GEP 70-gene low-risk group to identify an intermediate-risk group in multiple myeloma (MM). By analyzing over 600 MM patients with ELISA, genotyping, and gene expression profiling tools, we show how the combination of two independent molecular genetic events is related to synergistic increases in sIL-6r levels. We also show that the rs2228145 minor allele is related to increased expression levels of an IL-6r splice variant, which purportedly codes exclusively for a sIL-6r isoform. Together the SNP rs2228145 minor allele C and amplification of chromosome 1q21 are significantly correlated to an increase in sIL-6r levels, which are associated with lower overall survival in 70-gene low-risk disease, and aid in identification of the intermediate-risk MM group. [ABSTRACT FROM AUTHOR]

Significant comorbidites and lethality complicate GVHD and its treatment. Targeting the cytokine milieu may improve GVHD control; and IL6 is an attractive candidate, given its role in dendritic cell activation and T-cell differentiation. Tocilizumab is a humanized mAb to IL6-receptor-α (IL6R-α), which is Food and Drug Administration-approved for treatment of rheumatoid arthritis. Mouse transplant models have demonstrated that IL6 blockade also improves GVHD scores and survival. Definitive immunologic effects of IL6 inhibition have not emerged given inconsistent alterations in regulatory T cells (Tregs) and suppression of T-cell proliferation. Despite on-target suppression of IL6R-α signaling in human monocyte-derived dendritic cells (moDCs) and T cells, our data show no effect on moDC maturation/activation, alloreactive T-cell proliferation, Treg expansion, or allogeneic Th1/Th17 responses in vitro. These findings merit attention in any clinical trials of tocilizumab for GVHD prevention or treatment and provide a rationale for evaluating more specific inhibitors of downstream JAK2/STAT3 signaling as well. [ABSTRACT FROM AUTHOR]

We recently demonstrated that human BM cells can be treated in vitro with defined growth factors to induce the rapid generation of myeloid-derived suppressor cells (MDSCs), hereafter defined as BM-MDSCs. Indeed, combination of G-CSF + GM-CSF led to the development of a heterogeneous mixture of immature myeloid cells ranging from myeloblasts to band cells that were able to suppress alloantigen- and mitogen-stimulated T lymphocytes. Here, we further investigate the mechanism of suppression and define the cell subset that is fully responsible for BM-MDSC-mediated immune suppression. This population, which displays the structure and markers of promyelocytes, is however distinct from physiologic promyelocytes that, instead, are devoid of immuosuppressive function. In addition, we demonstrate that promyelocyte-like cells proliferate in the presence of activated lymphocytes and that, when these cells exert suppressive activity, they do not differentiate but rather maintain their immature phenotype. Finally, we show that promyelocyte-like BM-MDSCs are equivalent to MDSCs present in the blood of patients with breast cancer and patients with colorectal cancer and that increased circulating levels of these immunosuppressive myeloid cells correlate with worse prognosis and radiographic progression. [ABSTRACT FROM AUTHOR]

GABP is an ets transcription factor that regulates genes that are required for myeloid differentiation. The tetrameric GABP complex includes GABPa, which binds DNA via its ets domain, and GABPβ, which contains the transcription activation domain. To examine the role of GABP in myeloid differentiation, we generated mice in which Gabpa can be conditionally deleted in hematopoietic tissues. Gabpa knockout mice rapidly lost myeloid cells, and residual myeloid cells were dysplastic and immunophenotypically abnormal. Bone marrow transplantation demonstrated that Gabpa null cells could not contribute to the myeloid compartment because of cell intrinsic defects. Disruption of Gabpa was associated with a marked reduction in myeloid progenitor cells, and Gabpa null myeloid cells express reduced levels of the transcriptional repressor, Gfi-1. Gabp bound and activated the Gfi1 promoter, and transduction of Gabpa knockout bone marrow with Gfi1 partially rescued defects in myeloid colony formation and myeloid differentiation. We conclude that Gabp is required for myeloid differentiation due, in part, to its regulation of the tran-scriptional repressor Gfi-1. [ABSTRACT FROM AUTHOR]

Myeloproliferative neoplasms (MPNs) are associated with recurrent activating mutations of signaling proteins such as Janus kinase 2 (JAK2). However, the actual downstream signaling events and how these alter myeloid homeostasis are poorly understood. We developed an assay to measure basal levels of phosphorylated signaling intermediates by flow cytometry during myeloid differentiation in MPN patients. Our study provides the first systematic demonstration of specific signaling events and their comparison with disease phenotype and JAK2 mutation status. We demonstrate increased basal signaling in MPN patients, which occurs in both early and later stages of myeloid differentiation. In addition, the pattern of signaling is not correlated with JAK2 mutation status and signaling intensity is poorly correlated with mutant JAK2 allele burden. In contrast, signaling differences are detected between different MPN disease phenotypes. Finally, we demonstrate that signaling can be inhibited by a JAK2-selective small molecule, but that this inhibition is not JAK2 V617F specific, because MPN patients with mutant JAK2, wild-type JAK2, and control patients were inhibited to a similar degree. Our data suggest that, in addition to JAK2 mutations, other factors contribute significantly to the MPN phenotype, results that are relevant to both the pathogenesis and therapy of MPN. [ABSTRACT FROM AUTHOR]

The author discusses the study conducted by A. Varelias and colleagues concerning the role of interleukin (IL)-6 in the development of idiopathic pneumonia syndrome (IPS) following allogeneic stem cell transplantation (SCT) in both humans and mice. Topics discussed include the absence of interferon (IFN)-γ signaling which promotes IPS development, interaction between T helper (Th) 1 and Th17, and treatment for IPS.