GM-CSF expands dendritic cells and their progenitors in mouse liver

In vivo transfection of cytokine genes into tumor cells using a synthetic vehicle promotes antitumor immune responses in a visceral tumor model

The tumor microenvironment (TME) strongly affects the clinical outcomes of immunotherapy. This study aimed to activate the antitumor immune response by manipulating the TME by transfecting genes encoding relevant cytokines into tumor cells using a synthetic vehicle, which is designed to target tumor cells and promote the expression of transfected genes. Lung tumors were formed by injecting CT26.WT intravenously into BALB/c mice. Upon intravenous injection of the green fluorescent protein-coding plasmid encapsulated in the vehicle, 14.2% tumor-specific expression was observed. Transfection of the granulocyte-macrophage colony-stimulating factor (GM-CSF) and CD40 ligand (L)-plasmid combination and interferon gamma (IFNγ) and CD40L-plasmid combination showed 45.5% and 54.5% complete remission (CR), respectively, on day 60; alternate treatments with both the plasmid combinations elicited 66.7% CR, while the control animals died within 48 days. Immune status analysis revealed that the density of dendritic cells significantly increased in tumors, particularly after GM-CSF- and CD40L-gene transfection, while that of regulatory T cells significantly decreased. The proportion of activated killer cells and antitumoral macrophages significantly increased, specifically after IFNγ and CD40L transfection. Furthermore, the level of the immune escape molecule programmed death ligand-1 decreased in tumors after transfecting these cytokine genes. As a result, tumor cell-specific transfection of these cytokine genes by the synthetic vehicle significantly promotes antitumor immune responses in the TME, a key aim for visceral tumor therapy.

Activated Natural Killer Cell Promotes Nonalcoholic Steatohepatitis Through Mediating JAK/STAT Pathway

BACKGROUND & AIMS

Hepatic immune microenvironment plays a pivotal role in the development of nonalcoholic steatohepatitis (NASH). However, the role of natural killer (NK) cells, accounting for 10%-20% of liver lymphocytes, in NASH is still unclear. In this study, we aim to investigate the functional significance of NK cells in NASH evolution.

METHODS

NASH was induced in mice fed methionine- and choline-deficient diet (MCD), choline-deficient high-fat diet (CD-HFD), or high-fat diet with streptozotocin injection (STAM model). NK cell deficient mice (Nfil3-/-) and neutralization antibody (PK136) were used in this study.

RESULTS

Activated liver NK cells were identified with increased expression of NKG2D, CD107a, and interferon-γ but decreased inhibitory NKG2A. With NK cell deficiency Nfil3-/- mice, the absence of NK cells ameliorated both MCD- and CDHF- induced NASH development with significantly decreased hepatic triglycerides, peroxides, alanine aminotransferase, and aspartate aminotransferase compared with Nfil3+/+ mice. Further molecular analysis unveiled suppressed pro-inflammatory cytokines and associated signaling. Mechanistically, NK cells isolated from NASH liver secreted higher levels of pro-inflammatory cytokines (interferon-γ, interleukin 1β, interleukin 12, CCL4, CCL5, and granulocyte-macrophage colony-stimulating factor), which could activate hepatic JAK-STAT1/3 and nuclear factor kappa B signaling and induce hepatocyte damage evidenced by elevated reactive oxygen species and apoptosis rate. Moreover, neutralization antibody PK136-dependent NK cell depletion can significantly alleviate MCD-induced steatohepatitis with suppressed cytokine levels and JAK-STAT1/3 activity.

CONCLUSIONS

NK cells in NASH liver are activated with a more pro-inflammatory cytokine milieu and promote NASH development via cytokine-JAK-STAT1/3 axis. Modulation of NK cells provides a potential therapeutic strategy for NASH.

Molecular Genetic and Immune Functional Responses Distinguish Bone Marrow Mesenchymal Stromal Cells from Hepatic Stellate Cells

Defining the immune physiology of culture-adapted mesenchymal stromal cells (MSCs) derived from distinct tissue compartments informs their potential utility as pharmaceuticals. Here, we have investigated the comparative immune plasticity of MSCs and hepatic stellate cells (HeSCs) isolated from human and murine bone marrow (BM) and liver, respectively. Although both BM-MSCs and HeSCs share mesenchymal phenotype and overall molecular genetic responses to inflammatory cues, HeSCs differ from BM-MSCs in a meaningful manner. We show that culture-adapted HeSCs express substantially higher levels of hepatocyte growth factor (HGF), matrix metalloproteinase-1, and chemokine (CC motif) ligand 2 (CCL2) than BM-MSCs. Both human BM-MSCs and HeSCs inhibit T-cell proliferation by a shared indoleamine 2,3-dioxygenase (IDO)-dependent mechanism. However, HeSCs are distinct from BM-MSCs by their significant differential expression of HGF, CCL2, IL-8, CCL11, and GMCSF when cocultured with and/or without activated peripheral blood mononuclear cells. We have investigated MSCs and HeSCs derived from murine systems to describe interspecies comparability. Murine BM-MSCs inhibit T-cell proliferation through inducible nitric oxide synthase (iNOS) but not IDO. However, murine HeSCs inhibit T-cell proliferation through a mechanism distinct from either IDO or iNOS. Altogether, these results suggest that although culture-adapted BM-MSCs and HeSCs display a similar phenotype, their secretome and immune plasticity are in part distinct likely mirroring their tissular origins. In addition, the discordance in immune biology between mouse and human sourced HeSC and BM-MSCs speaks to the importance of comparative biology when interrogating rodent systems for human translational insights. Stem Cells 2019;37:1075-1082.

Gut symbiotic microbes imprint intestinal immune cells with the innate receptor SLAMF4 which contributes to gut immune protection against enteric pathogens

BACKGROUND

Interactions between host immune cells and gut microbiota are crucial for the integrity and function of the intestine. How these interactions regulate immune cell responses in the intestine remains a major gap in the field.

AIM

We have identified the signalling lymphocyte activation molecule family member 4 (SLAMF4) as an immunomodulator of the intestinal immunity. The aim is to determine how SLAMF4 is acquired in the gut and what its contribution to intestinal immunity is.

METHODS

Expression of SLAMF4 was assessed in mice and humans. The mechanism of induction was studied using GFP^tg bone marrow chimaera mice, lymphotoxin α and TNLG8A-deficient mice, as well as gnotobiotic mice. Role in immune protection was revealed using oral infection with Listeria monocytogenes and Cytobacter rodentium.

RESULTS

SLAMF4 is a selective marker of intestinal immune cells of mice and humans. SLAMF4 induction occurs directly in the intestinal mucosa without the involvement of the gut-associated lymphoid tissue. Gut bacterial products, particularly those of gut anaerobes, and gut-resident antigen-presenting cell (APC) ^TNLG8A are key contributors of SLAMF4 induction in the intestine. Importantly, lack of SLAMF4 expression leads the increased susceptibility of mice to infection by oral pathogens culminating in their premature death.

CONCLUSIONS

SLAMF4 is a marker of intestinal immune cells which contributes to the protection against enteric pathogens and whose expression is dependent on the presence of the gut microbiota. This discovery provides a possible mechanism for answering the long-standing question of how the intertwining of the host and gut microbial biology regulates immune cell responses in the gut.

A central role for hepatic conventional dendritic cells in supporting Th2 responses during helminth infection

Dendritic cells (DCs) are the key initiators of T-helper (Th) 2 immune responses against the parasitic helminth Schistosoma mansoni. Although the liver is one of the main sites of antigen deposition during infection with this parasite, it is not yet clear how distinct DC subtypes in this tissue respond to S. mansoni antigens in vivo, or how the liver microenvironment might influence DC function during establishment of the Th2 response. In this study, we show that hepatic DC subsets undergo distinct activation processes in vivo following murine infection with S. mansoni. Conventional DCs (cDCs) from schistosome-infected mice upregulated expression of the costimulatory molecule CD40 and were capable of priming naive CD4(+) T cells, whereas plasmacytoid DCs (pDCs) upregulated expression of MHC class II, CD86 and CD40 but were unable to support the expansion of either naive or effector/memory CD4(+) T cells. Importantly, in vivo depletion of pDCs revealed that this subset was dispensable for either maintenance or regulation of the hepatic Th2 effector response during acute S. mansoni infection. Our data provides strong evidence that S. mansoni infection favors the establishment of an immunogenic, rather than tolerogenic, liver microenvironment that conditions cDCs to initiate and maintain Th2 immunity in the context of ongoing antigen exposure.

Systemic IL-12 administration alters hepatic dendritic cell stimulation capabilities

The liver is an immunologically unique organ containing tolerogenic dendritic cells (DC) that maintain an immunosuppressive microenvironment. Although systemic IL-12 administration can improve responses to tumors, the effects of IL-12-based treatments on DC, in particular hepatic DC, remain incompletely understood. In this study, we demonstrate systemic IL-12 administration induces a 2–3 fold increase in conventional, but not plasmacytoid, DC subsets in the liver. Following IL-12 administration, hepatic DC became more phenotypically and functionally mature, resembling the function of splenic DC, but differed as compared to their splenic counterparts in the production of IL-12 following co-stimulation with toll-like receptor (TLR) agonists. Hepatic DCs from IL-12 treated mice acquired enhanced T cell proliferative capabilities similar to levels observed using splenic DCs. Furthermore, IL-12 administration preferentially increased hepatic T cell activation and IFNγ expression in the RENCA mouse model of renal cell carcinoma. Collectively, the data shows systemic IL-12 administration enables hepatic DCs to overcome at least some aspects of the inherently suppressive milieu of the hepatic environment that could have important implications for the design of IL-12-based immunotherapeutic strategies targeting hepatic malignancies and infections.

Alloimmunization to transfused platelets requires priming of CD4+ T cells in the splenic microenvironment in a murine model

BACKGROUND

Alloantibodies are a clinically significant sequelae of platelet (PLT) transfusion, potentially rendering patients refractory to ongoing PLT transfusion support. These antibodies are often IgG class switched, suggesting the involvement of CD4+ T-cell help; however, PLT-specific CD4+ T cells have not been visualized in vivo, and specifics of their stimulation are not completely understood.

STUDY DESIGN AND METHODS

A murine model of alloimmunization to transfused PLTs was developed to allow in vivo assessment and characterization of CD4+ T cells specific for PLT major histocompatibility complex (MHC) alloantigen. PLTs were harvested from BALB/c mice, filter leukoreduced, and transfused into C57BL/6 recipients. PLT-specific CD4+ T-cell responses were visualized by using a T-cell receptor transgenic mouse that detects peptide from donor MHC I presented on recipient MHC II. Antibody responses were determined by indirect immunofluorescence using BALB/c donor targets.

RESULTS

C57BL/6 recipients of BALB/c leukoreduced PLT transfusions produced BALB/c antibodies, with proliferation of antigen-specific CD4+ T cells seen in the spleen but not lymph nodes or liver. Depletion of recipient CD4+ cells or splenectomy independently abrogated the alloantibody response.

CONCLUSION

We report a novel model to study antigen-specific CD4+ T cells during alloimmunization to PLT transfusion. The presented data support a critical role for CD4+ T-cell help in the humoral response to PLT transfusion and establish the spleen as a required microenvironment for effective CD4+ T-cell priming against donor PLT-derived MHC I.

Conventional DCs reduce liver ischemia/reperfusion injury in mice via IL-10 secretion

TLRs are recognized as promoters of tissue damage, even in the absence of pathogens. TLR binding to damage-associated molecular patterns (DAMPs) released by injured host cells unleashes an inflammatory cascade that amplifies tissue destruction. However, whether TLRs possess the reciprocal ability to curtail the extent of sterile inflammation is uncertain. Here, we investigated this possibility in mice by studying the role of conventional DCs (cDCs) in liver ischemia/reperfusion (I/R) injury, a model of sterile inflammation. Targeted depletion of mouse cDCs increased liver injury after I/R, as assessed by serum alanine aminotransferase and histologic analysis. In vitro, we identified hepatocyte DNA as an endogenous ligand to TLR9 that promoted cDCs to secrete IL-10. In vivo, cDC production of IL-10 required TLR9 and reduced liver injury. In addition, we found that inflammatory monocytes recruited to the liver via chemokine receptor 2 were downstream targets of cDC IL-10. IL-10 from cDCs reduced production of TNF, IL-6, and ROS by inflammatory monocytes. Our results implicate inflammatory monocytes as mediators of liver I/R injury and reveal that cDCs respond to DAMPS during sterile inflammation, providing the host with protection from progressive tissue damage.

Distinct populations of metastases-enabling myeloid cells expand in the liver of mice harboring invasive and preinvasive intra-abdominal tumor

The liver is the most common site of adenocarcinoma metastases, even in patients who initially present with early disease. We postulated that immune-suppressive cells in the liver of tumor-bearing hosts inhibit anti-tumor T cells, thereby accelerating the growth of liver metastases. Using models of early preinvasive pancreatic neoplasia and advanced colorectal cancer, aims of this study were to determine immune phenotype, stimulus for recruitment, inhibitory effects, and tumor-enabling function of immune-suppressive cells in the liver of tumor-bearing hosts. We found that in mice with intra-abdominal malignancies, two distinct CD11b(+)Gr1(+) populations with divergent phenotypic and functional properties accumulate in the liver, becoming the dominant hepatic leukocytes. Their expansion is contingent on tumor expression of KC. These cells are distinct from CD11b(+)Gr1(+) populations in other tissues of tumor-bearing hosts in terms of cellular phenotype and cytokine and chemokine profile. Liver CD11b(+)Gr1(+) cells are highly suppressive of T cell activation, proliferation, and cytotoxicity and induce the development of Tregs. Moreover, liver myeloid-derived suppressor cells accelerate the development of hepatic metastases by inactivation of cytotoxic T cells. These findings may explain the propensity of patients with intra-abdominal cancers to develop liver metastases and suggest a promising target for experimental therapeutics.

Fever-range whole-body thermal therapy combined with cisplatin, gemcitabine, and daily interferon-alpha: a description of a phase I-II protocol

PURPOSE

The purpose of the Phase I component of this study was to find the maximally tolerated dose (MTD) of cisplatin administered within a regimen of fever-range whole body thermal therapy (FR-WB-TT), cisplatin, gemcitabine, and low-dose interferon-alpha (IFN-alpha). The Phase II component aimed to assess which cancer diagnoses responded to the regimen, the response rate, and response duration.

MATERIALS AND METHODS

The protocol design derived from a schedule-optimized preclinical regimen. Drugs were administered together, and also with thermal therapy in a schedule that optimized the therapeutic index. Eligible patients were those with therapy-resistant, metastatic or advanced solid malignancies. Beginning at 40 mg/m(2), the cisplatin dose was escalated by 10 mg/m(2) to the maximally tolerated dose (MTD) in successive cohorts of 3 patients. A treatment cycle consisted of cisplatin on day one, followed by thermal therapy and simultaneous gemcitabine 36 hours later; then a second dose of gemcitabine one week later; and daily IFN- alpha.

RESULTS

Thirty-seven patients were treated on protocol. The MTD of cisplatin in the thermochemotherapy regimen was established to be 60 mg/m(2). The dose limiting toxicities (DLT) were peripheral neuropathy and ototoxicity. Complete and partial responses combined were 43%. The therapy improved the quality of life of responding patients.

CONCLUSION

The protocol was well tolerated and was associated with antitumor activity in patients with a variety of advanced metastatic solid tumors. Tumor response occurred with the thermochemotherapy treatment despite treating malignancies that had progressed on the same chemotherapy drugs administered as standard treatment. Notably, good responses were observed in patients with high-grade neuroendocrine and pancreas cancers. This regimen will be tested in a phase II study.

Molecular mechanisms of portal vein tolerance

The liver has been considered as a tolerogenic organ in the sense that favors the induction of peripheral tolerance. The administration of antigens (Ags) via the portal vein causes tolerance, which is termed portal vein tolerance and can explain the occurrence of tolerogenic responses in the liver. Here we discuss the fundamental mechanisms accounting for portal vein tolerance. Antigen-presenting cells (APCs) in the liver, especially dendritic cells and sinusoidal endothelial cells, have limited the ability to produce pro-inflammatory cytokines upon stimulation with endotoxin, an effect that could be due to the continuous exposure to bacterial Ags derived from intestinal microflora. Ag presentation by liver APCs results in T cell tolerance through clonal deletion and selection of regulatory T cells. Thus, APCs with immunosuppressive functions are associated with the achievement of portal vein tolerance via the induction of clonal deletion and generation of regulatory T cells.

Gut-derived commensal bacterial products inhibit liver dendritic cell maturation by stimulating hepatic interleukin-6/signal transducer and activator of transcription 3 activity

Intraorgan dendritic cells (DCs) monitor the environment and help translate triggers of innate immunity into adaptive immune responses. Liver-based DCs are continually exposed, via gut-derived portal venous blood, to potential antigens and bacterial products that can trigger innate immunity. However, somehow the liver avoids a state of perpetual inflammation and protects central immune organs from overstimulation. In this study, we tested the hypothesis that hepatic interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) activity increases the activation/maturation threshold of hepatic DCs toward innate immune signals. The results show that the liver nuclear STAT3 activity is significantly higher than that of other organs and is IL-6-dependent. Hepatic DCs in normal IL-6 wild-type (IL-6(+/+)) mice are phenotypically and functionally less mature than DCs from IL-6-deficient (IL-6(-/-)) or STAT3-inhibited IL-6(+/+) mice, as determined by surface marker expression, proinflammatory cytokine secretion, and allogeneic T-cell stimulation. IL-6(+/+) liver DCs produce IL-6 in response to exposure to lipopolysaccharide (LPS) and cytidine phosphate guanosine oligonucleotides (CpG) but are resistant to maturation compared with IL-6(-/-) liver DCs. Conversely, exogenous IL-6 inhibits LPS-induced IL-6(-/-) liver DC maturation. IL-6/STAT3 signaling influences the liver DC expression of toll-like receptor 9 and IL-1 receptor associated kinase-M. The depletion of gut commensal bacteria in IL-6(+/+) mice with oral antibiotics decreased portal blood endotoxin levels, lowered the expression of IL-6 and phospho-STAT3, and significantly increased liver DC maturation.

CONCLUSION

Gut-derived bacterial products, by stimulating hepatic IL-6/STAT3 signaling, inhibit hepatic DC activation/maturation and thereby elevate the threshold needed for translating triggers of innate immunity into adaptive immune responses. Manipulating gut bacteria may therefore be an effective strategy for altering intrahepatic immune responses.

Tolerogenic dendritic cells and the quest for transplant tolerance

In recent years, there has been a shift from the perception of dendritic cells (DCs) solely as inducers of immune reactivity to the view that these cells are crucial regulators of immunity, which includes their ability to induce and maintain tolerance. Advances in our understanding of the phenotypical and functional plasticity of DCs, and in our ability to manipulate their development and maturation in vitro and in vivo, has provided a basis for the therapeutic harnessing of their inherent tolerogenicity. In this Review, we integrate the available information on the role of DCs in the induction of tolerance, with a focus on transplantation.

Murine liver plasmacytoid dendritic cells become potent immunostimulatory cells after Flt-3 ligand expansion

The liver has unique immunological properties. Although dendritic cells (DCs) are central mediators of immune regulation, little is known about liver DCs. Plasmacytoid DCs (pDCs) are a recently identified subtype of murine liver DC. We sought to define the function of freshly isolated murine liver pDCs. We found that normal liver pDCs were weak in stimulating T cells, yet they possessed a proinflammatory cytokine profile with high tumor necrosis factor-alpha and low IL-10 secretion. To facilitate the investigation of murine liver pDCs, we expanded them in vivo with fms-like tyrosine kinase 3 ligand (Flt3L). After Toll-like receptor-9 ligation, expanded liver pDCs secreted high levels of IFN-alpha and were able to stimulate NK cells, NKT cells, and antigen-specific CD8+ T cells in vitro. In addition, Flt3L expansion alone generated pDCs capable of activating antigen-specific CD8+ T cells in vivo.

CONCLUSION

Unstimulated liver pDCs exist in a latent state with the potential to become potent activators of the innate and adaptive immune systems through their interactions with other immune effectors. Our findings have implications for understanding the role of the liver in tolerance and immunity.

Linking proximal and downstream signalling events in hepatic ischaemia/reperfusion injury

Hepatic I/R (ischaemia/reperfusion) injury occurs in a variety of clinical settings including transplantation, elective liver resections and trauma. One of the challenges in studying the pathophysiology of I/R injury is the fact that the liver plays a central role in a variety of metabolic pathways in addition to governing aspects of immune surveillance and tolerance. The pathways activated in response to insults as varied as toxins, microbial and endogenous ligands and I/R may share common elements. The multiple intracellular signalling cascades involved in this process and the initiating events are still under investigation. Recent work on the role of TLRs (Toll-like receptors) in I/R injury has elucidated some of the more proximal signalling events in the pathway. In addition to the well-established role of signalling molecules such as NO (nitric oxide) in mediating damage or protection following hepatic I/R, more recent studies have focused on the participation of endogenous danger signals or DAMPs (damage-associated molecular patterns) such as HMGB1 (high-mobility group box 1). The complex interplay between HMGB1, TLRs and the many intracellular signalling molecules and pathways is illustrative of how our understanding of hepatic I/R injury is continually evolving.

In vivo expansion of two distinct dendritic cells in mouse livers and its impact on liver immune regulation

Liver transplant tolerance in pigs, rats, and mice has been disclosed for decades, but the underlying mechanisms are not completely understood. Accumulating data indicate that residing dendritic cells (DC) are important in determining direction of immune responses in the liver. However, our knowledge remains very limited due to the difficulties in obtaining sufficient liver DC. Most of the previous studies were dependent on DC propagated in vitro with growth factors and cytokines. In this study, we adopted an approach to transfect genes into the mouse liver by tail vein injection of plasmid DNA. Transfection with plasmid granulocyte-macrophage colony-stimulating factor markedly expanded liver CD11c(+) DC mainly located in portal regions, while liver B220(+) DC were dramatically generated after injection with plasmid interleukin (IL)-3/CD40L largely present in the lobules. Although both were phenotypically mature and strong T-cell stimulators, CD11c(+)DC induced potent T-cell response while B220(+)DC induced T-cell hyporesponsiveness. Administration of CD11c(+)DC accelerated cardiac allograft rejection, while B220(+)DC significantly prolonged graft survival. This hyporesponsiveness is not due to inhibition of DC/T-cell interaction, but rather through an active process of stimulating T-cell apoptosis. Compared to B220(+) DC that expressed messenger RNA of (TLR) 1, 2, 6, 7, and 9, CD11c(+)DC expressed all TLR 1 to 9. TLR 9 ligation stimulated very high IL-12 in CD11c(+) DC, but high IL-10 and no IL-12 in B220(+) DC. In conclusion, through these mechanisms, liver DC may be actively involved in immune regulation in the liver.

Increasing numbers of hepatic dendritic cells promote HMGB1-mediated ischemia-reperfusion injury

Endogenous ligands released from damaged cells, so-called damage-associated molecular pattern molecules (DAMPs), activate innate signaling pathways including the TLRs. We have shown that hepatic, warm ischemia and reperfusion (I/R) injury, generating local, noninfectious DAMPs, promotes inflammation, which is largely TLR4-dependent. Here, we demonstrate that increasing dendritic cell (DC) numbers enhance inflammation and organ injury after hepatic I/R. High-mobility group box 1 (HMGB1), a NF released by necrotic cells or secreted by stimulated cells, is one of a number of ligands promoting TLR4 reactivity. Augmentation of DC numbers in the liver with GM-CSF hydrodynamic transfection significantly increased liver damage after I/R when compared with controls. TLR4 engagement on hepatic DC was required for the I/R-induced injury, as augmentation of DC numbers in TLR4 mutant (C3H/HeJ) mice did not worsen hepatic damage. It is interesting that TLR4 expression was increased in hepatic DC following HMGB1 stimulation in vitro, suggesting a mechanism for the increased liver injury following I/R. It thus appears that functional TLR4 on DC is required for I/R-induced injury. Furthermore, HMGB1 may direct the inflammatory responses mediated by DC, at least in part, by enhancing TLR4 expression and reactivity to it and other DAMPs.

Preoperative granulocyte/macrophage colony-stimulating factor (GM-CSF) increases hepatic dendritic cell numbers and clustering with lymphocytes in colorectal cancer patients

Despite surgery with curative intent, approximately 30% of colorectal carcinoma patients will develop liver metastases during follow-up. Synchronous occult micrometastases, tumor cell shedding into the portal circulation and postoperative immune impairment have all been suggested to facilitate outgrowth of liver metastases. In experimental models, increases in both number of resident macrophages of the liver, the so-called Kupffer cells (KC), and tumoricidal capacity of KC were observed after pretreatment with granulocyte/macrophage colony-stimulating factor (GM-CSF), a potent immuno-stimulatory agent. Following perioperative recombinant human GM-CSF (rhGM-CSF), we previously showed activation of the systemic immune response in the postoperative period, which is normally transiently down-modulated after surgery. Therefore, in this pilot study, effects of preoperative rhGM-CSF administration on the composition of human liver immune cell population were evaluated in patients undergoing surgery for colorectal cancer. No difference in KC numbers of rhGM-CSF-treated patients was observed. Importantly, however, a 6-fold increase in dendritic cell (DC) numbers was observed compared to control patients, as quantified by immunohistochemistry of liver biopsies, taken during laparotomy. Furthermore, direct contact between liver CD8+ cells and DC was significantly enhanced in rhGM-CSF-treated patients. Both increases in DC numbers and DC interaction with CD8+ T cells suggest enhanced immunological activation, which may reduce liver metastases formation and ultimately improve survival after initial colorectal surgery.

Biliary obstruction selectively expands and activates liver myeloid dendritic cells

Obstructive jaundice is associated with immunologic derangements and hepatic inflammation and fibrosis. Because dendritic cells (DCs) play a major role in immune regulation, we hypothesized that the immunosuppression associated with jaundice may result from the functional impairment of liver DCs. We found that bile duct ligation (BDL) in mice expanded the myeloid subtype of liver DCs from 20 to 80% of total DCs and increased their absolute number by >15-fold. Liver myeloid DCs following BDL, but not sham laparotomy, had increased Ag uptake in vivo, high IL-6 secretion in response to LPS, and enhanced ability to activate T cells. The effects of BDL were specific to liver DCs, as spleen DCs were not affected. Expansion of liver myeloid DCs depended on Gr-1(+) cells, and we implicated monocyte chemotactic protein-1 as a potential mediator. Thus, obstructive jaundice selectively expands liver myeloid DCs that are highly functional and unlikely to be involved with impaired host immune responses.

In vivo overexpression of Flt3 ligand expands and activates murine spleen natural killer dendritic cells

Natural killer dendritic cells (NKDC) are a unique class of murine immune cells that possess the characteristics of both natural killer (NK) cells and dendritic cells (DC). Because NKDC are able to secrete IFN-gamma, directly lyse tumor cells, and present antigen to naïve T cells, they have immunotherapeutic potential. The relative paucity of NKDC, however, impedes their detailed study. We have found that in vivo, overexpression of the hematopoietic cytokine Flt3 ligand (Flt3L) expands NKDC in various organs from 2-18 fold. Flt3L expanded splenic NKDC retain the ability to lyse tumor cells and become considerably more potent at activating naïve allogeneic and antigen-specific T cells. Compared to normal splenic NKDC, Flt3L-expanded splenic NKDC have a more mature phenotype, a slightly increased ability to capture and process antigen, and a similar cytokine profile. In vivo, we found that Flt3L-expanded splenic NKDC are more effective than normal splenic NKDC in stimulating antigen-specific CD8 T cells. Additionally, we show that NKDC are able to cross-present antigen in vivo. The ability to expand NKDC in vivo using Flt3L will facilitate further analysis of their unique biology. Moreover, Flt3L-expanded NKDC may have enhanced immunotherapeutic potential, given their increased ability to stimulate T cells.

Overexpression of granulocyte-macrophage colony-stimulating factor in mouse liver enhances the susceptibility of lipopolysaccharide leading to massive apoptosis of hepatocytes

BACKGROUND/AIMS

We examined whether antigen-nonspecific accumulation of dendritic cells (DCs) and macrophages in the liver by the overexpression of granulocyte macrophage-colony stimulating factor (GM-CSF) could prime severe liver injury after LPS injection.

METHODS

We injected a recombinant adenovirus encoding GM-CSF intravenously (AdGM), and LPS was administered 7 days later. Liver histology, serum alanine aminotransferase (ALT) levels and apoptosis of hepatocytes were examined.

RESULTS

Liver histology of the AdGM-primed mice showed marked infiltrates of mononuclear cells (DCs and macrophages) without granuloma formation on day 7. Expression of toll-like receptor-4 on intrahepatic mononuclear cells isolated from AdGM-primed mice was up-regulated. After LPS injection, serum ALT levels in AdGM-primed mice reached about 6000 IU/l at 12 h, and all those mice died within 24 h. Hemorrhagic liver injury with massive apoptosis of hepatocytes was histologically recognized. When AdGM and LPS were injected in FasL-deficient C57BL/6J-gld/gld mice, serum ALT levels were not elevated by the pretreatment with a neutralizing anti-TNF-alpha antibody.

CONCLUSIONS

Our present study provides a new model of severe liver injury, in which antigen-nonspecific accumulation of DCs and macrophages in the liver by overexpressing GM-CSF enhances the susceptibility to LPS, leading to hemorrhagic liver injury with massive hepatocyte apoptosis after LPS injection.

Conventional liver CD4 T cells are functionally distinct and suppressed by environmental factors

The contribution of intrahepatic conventional T cells to the unique immunologic properties of the liver has not been clearly defined. We isolated bulk and CD4 T cells from mouse liver and compared their functions with each other and with their splenic counterparts. Unlike bulk spleen T cells, bulk liver T cells reacted minimally to allogeneic or antigen-loaded syngeneic dendritic cells. However, after exclusion of natural killer T cells (NKTs) and gammadelta T cells by FACS, liver and spleen CD4 T cells actually proliferated to a similar extent upon allogeneic or antigen-specific stimulation. Liver CD4 T cells were more sensitive to interleukin 2 (IL-2) than were spleen CD4 T cells, but had a similar proliferative potential based on their response to CD3 ligation. In addition, activated liver CD4 T cells produced higher levels of IL-4, IL-5, IL-10, and interferon gamma (IFN-gamma) than did splenic CD4 T cells. Therefore, liver CD4 T cells are intrinsically different from spleen CD4 T cells. In vitro, liver or spleen NKTs and gammadelta T cells suppressed liver and spleen CD4 T-cell proliferation in a dose-dependent fashion. In conclusion, unconventional T cells constrain liver CD4 T-cell function. Our findings have implications for pathological conditions of the liver that involve the response of conventional CD4 T lymphocytes.

Natural killer dendritic cells have both antigen presenting and lytic function and in response to CpG produce IFN-gamma via autocrine IL-12

We have isolated rare cells bearing the NK cell surface marker NK1.1, as well as the dendritic cell (DC) marker CD11c, from the spleen, liver, lymph nodes, and thymus of normal mice. These cells possess both NK cell and DC function because they can lyse tumor cells and subsequently present Ags to naive Ag-specific T cells. Interestingly, in response to IL-4 plus either IL-2 or CpG, NKDC produce more IFN-gamma than do DC, or even NK cells. We determined that CpG, but not IL-2, induces NKDC to secrete IFN-gamma via the autocrine effects of IL-12. In vivo, CpG dramatically increases the number of NKDC. Furthermore, NKDC induce greater Ag-specific T cell activation than do DC after adoptive transfer. Their unique ability to lyse tumor cells, present Ags, and secrete inflammatory cytokines suggests that NKDC may play a crucial role in linking innate and adaptive immunity.

Increased and long-term generation of dendritic cells with reduced function from IL-6-deficient bone marrow

The importance of IL-6 in dendritic cell (DC) development and function has not been well defined. To establish the role of IL-6, we studied bone marrow-derived DC (BMDC) and freshly isolated splenic DC from IL-6(-/-)-transgenic mice. We found that although IL-6(-/-) bone marrow had a similar composition to that of wild-type (WT) mice, it generated up to 10 times more DC when cultured in GM-CSF. The difference persisted even when IL-6(-/-) and WT bone marrow were cultured together, excluding the possibility that the effects were simply due to different cytokine microenvironments. In comparison to WT BMDC, IL-6(-/-) BMDC captured at least as much Ag, had an equivalent surface phenotype, and matured similarly in response to LPS or CpG. However, IL-6(-/-) BMDC induced less T cell allostimulation and Ag-specific T cell activation, but only the former was related to their inability to generate IL-6. Although WT bone marrow cultures died within 4 wk, IL-6(-/-) cultures continued to generate BMDC for >120 days, although the BMDC became immature and less functional. In vivo, we found that IL-6(-/-) mice had similar numbers and types of splenic DC as WT mice, both normally and after treatment with either Flt-3 ligand or GM-CSF. These findings demonstrate that IL-6 has profound effects on DC development in vitro, although the number and subtype composition of DC are unaffected by the absence of IL-6 in vivo. Furthermore, secretion of IL-6 is critical to certain DC functions.

Liver sinusoidal endothelial cells are insufficient to activate T cells

Liver sinusoidal endothelial cells (LSEC) have been reported to express MHC class II, CD80, CD86, and CD11c and effectively stimulate naive T cells. Because dendritic cells (DC) are known to possess these characteristics, we sought to directly compare the phenotype and function of murine LSEC and DC. Nonparenchymal cells from C57BL/6 mice were obtained by collagenase digestion of the liver followed by density gradient centrifugation. From the enriched nonparenchymal cell fraction, LSEC (CD45(-)) were then isolated to 99% purity using immunomagnetic beads. Flow cytometric analysis of LSEC demonstrated high expression of CD31, von Willebrand factor, and FcgammaRs. However, unlike DC, LSEC had low or absent expression of MHC class II, CD86, and CD11c. LSEC demonstrated a high capacity for Ag uptake in vitro and in vivo. Although acetylated low-density lipoprotein uptake has been purported to be a specific function of LSEC, we found DC captured acetylated low-density lipoprotein to a similar extent in vivo. Consistent with their phenotype, LSEC were poor stimulators of allogeneic T cells. Furthermore, in the absence of exogenous costimulation, LSEC induced negligible proliferation of CD4(+) or CD8(+) TCR-transgenic T cells. Thus, contrary to previous reports, our data indicate that LSEC alone are insufficient to activate naive T cells.

Identification of GM-CSF in Paneth cells using single-cell RT-PCR

Paneth cells, granule-containing cells located at the bottom of the intestinal crypts, have a role in innate mucosal immunity. We identified the exclusive expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) in Paneth cells using single-cell reverse transcription-polymerase chain reaction and cDNA array. Cytosolic total RNA was aspirated from single Paneth cells and other villous epithelial cells (non-Paneth cells) of rats using capillary micropipettes. In addition to lysozyme, secretory phospholipase A2, defensin, TNF-alpha, and xanthine dehydrogenase genes, cDNA array analysis revealed that the GM-CSF gene is specifically present in Paneth cells, whereas GM-CSF receptor beta-chain mRNA is expressed in Paneth cells and other epithelial cells. There was intense immunohistochemical staining of GM-CSF in Paneth cells but not in other epithelial cells. Treatment of IEC6 cells with GM-CSF enhanced expression of CD80 and CD86. Thus, GM-CSF in Paneth cells might have an important role in mucosal immunity through increasing the expression of costimulatory molecules in epithelial cells.

A role for niches in the development of a multiplicity of dendritic cell subsets

Although most studies on murine dendritic cell (DC) differentiation concentrate on the nature of the DC precursor population and the lineage relationship between DC and other hematopoietic cell types, very little research addresses the nature of the microenvironments necessary for DC hematopoiesis. Evidence supporting a major contribution of niches in DC differentiation within hematopoietic tissues is reviewed. A model is presented that identifies a potential role for multiple hematopoietic niches in DC differentiation. It is proposed that multiple DC subsets develop from one or a small number of DC progenitor types that lodge in various niches within different tissue sites. Implications of a niche-mediated model for differentiation of DC precursors are discussed in the context of both physiological and pathological situations.

Liver Dendritic Cells Are Less Immunogenic Than Spleen Dendritic Cells because of Differences in Subtype Composition

The unique immunological properties of the liver may be due to the function of hepatic dendritic cells (DC). However, liver DC have not been well characterized because of the difficulty in isolating adequate numbers of cells for analysis. Using immunomagnetic bead and flow cytometric cell sorting, we compared freshly isolated murine liver and spleen CD11c+ DC. We found that liver DC are less mature, capture less Ag, and induce less T cell stimulation than spleen DC. Nevertheless, liver DC were able to generate high levels of IL-12 in response to CpG stimulation. We identified four distinct subtypes of liver DC based on the widely used DC subset markers CD8alpha and CD11b. Lymphoid (CD8alpha+CD11b-) and myeloid (CD8alpha-CD11b+) liver DC activated T cells to a similar degree as did their splenic DC counterparts but comprised only 20% of all liver DC. In contrast, the two more prevalent liver DC subsets were only weakly immunostimulatory. Plasmacytoid DC (B220+) accounted for 19% of liver DC, but only 5% of spleen DC. Our findings support the widely held notion that liver DC are generally weak activators of immunity, although they are capable of producing inflammatory cytokines, and certain subtypes potently activate T cells.