Hepatic stellate cells undermine the allostimulatory function of liver myeloid dendritic cells via STAT3-dependent induction of IDO

Hepatic stellate cells (HSCs) are critical for hepatic wound repair and tissue remodeling. They also produce cytokines and chemokines that may contribute to the maintenance of hepatic immune homeostasis and the inherent tolerogenicity of the liver. The functional relationship between HSCs and the professional migratory APCs in the liver, that is, dendritic cells (DCs), has not been evaluated. In this article, we report that murine liver DCs colocalize with HSCs in vivo under normal, steady-state conditions, and cluster with HSCs in vitro. In vitro, HSCs secrete high levels of DC chemoattractants, such as MΙP-1α and MCP-1, as well as cytokines that modulate DC activation, including TNF-α, IL-6, and IL-1β. Culture of HSCs with conventional liver myeloid (m) DCs resulted in increased IL-6 and IL-10 secretion compared with that of either cell population alone. Coculture also resulted in enhanced expression of costimulatory (CD80, CD86) and coinhibitory (B7-H1) molecules on mDCs. HSC-induced mDC maturation required cell-cell contact and could be blocked, in part, by neutralizing MΙP-1α or MCP-1. HSC-induced mDC maturation was dependent on activation of STAT3 in mDCs and, in part, on HSC-secreted IL-6. Despite upregulation of costimulatory molecules, mDCs conditioned by HSCs demonstrated impaired ability to induce allogeneic T cell proliferation, which was independent of B7-H1, but dependent upon HSC-induced STAT3 activation and subsequent upregulation of IDO. In conclusion, by promoting IDO expression, HSCs may act as potent regulators of liver mDCs and function to maintain hepatic homeostasis and tolerogenicity.

Dendritic cells promote macrophage infiltration and comprise a substantial proportion of obesity-associated increases in CD11c+ cells in adipose tissue and liver

Obesity-associated increases in adipose tissue (AT) CD11c(+) cells suggest that dendritic cells (DC), which are involved in the tissue recruitment and activation of macrophages, may play a role in determining AT and liver immunophenotype in obesity. This study addressed this hypothesis. With the use of flow cytometry, electron microscopy, and loss-and-gain of function approaches, the contribution of DC to the pattern of immune cell alterations and recruitment in obesity was assessed. In AT and liver there was a substantial, high-fat diet (HFD)-induced increase in DC. In AT, these increases were associated with crown-like structures, whereas in liver the increase in DC constituted an early and reversible response to diet. Notably, mice lacking DC had reduced AT and liver macrophages, whereas DC replacement in DC-null mice increased liver and AT macrophage populations. Furthermore, delivery of bone marrow-derived DC to lean wild-type mice increased AT and liver macrophage infiltration. Finally, mice lacking DC were resistant to the weight gain and metabolic abnormalities of an HFD. Together, these data demonstrate that DC are elevated in obesity, promote macrophage infiltration of AT and liver, contribute to the determination of tissue immunophenotype, and play a role in systemic metabolic responses to an HFD.

IL-27 production and STAT3-dependent upregulation of B7-H1 mediate immune regulatory functions of liver plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are highly specialized APCs that, in addition to their well-recognized role in anti-viral immunity, also regulate immune responses. Liver-resident pDCs are considerably less immunostimulatory than those from secondary lymphoid tissues and are equipped to promote immune tolerance/regulation through various mechanisms. IL-27 is an IL-12 family cytokine that regulates the function of both APCs and T cells, although little is known about its role in pDC immunobiology. In this study, we show that mouse liver pDCs express higher levels of IL-27p28 and EBV-induced protein 3 (Ebi3) compared with those of splenic pDCs. Both populations of pDCs express the IL-27Rα/WSX-1; however, only liver pDCs significantly upregulate expression of the coregulatory molecule B7 homolog-1 (B7-H1) in response to IL-27. Inhibition of STAT3 activation completely abrogates IL-27-induced upregulation of B7-H1 expression on liver pDCs. Liver pDCs treated with IL-27 increase the percentage of CD4(+)Foxp3(+) T cells in MLR, which is dependent upon expression of B7-H1. pDCs from Ebi3-deficient mice lacking functional IL-27 show increased capacity to stimulate allogeneic T cell proliferation and IFN-γ production in MLR. Liver but not spleen pDCs suppress delayed-type hypersensitivity responses to OVA, an effect that is lost with Ebi3(-/-) and B7-H1(-/-) liver pDCs compared with wild-type liver pDCs. These data suggest that IL-27 signaling in pDCs promotes their immunoregulatory function and that IL-27 produced by pDCs contributes to their capacity to regulate immune responses in vitro and in vivo.

Selective expansion of allogeneic regulatory T cells by hepatic stellate cells: role of endotoxin and implications for allograft tolerance

Hepatic stellate cells (HSCs) may play an important role in hepatic immune regulation by producing numerous cytokines/chemokines and expressing Ag-presenting and T cell coregulatory molecules. Due to disruption of the endothelial barrier during cold-ischemic storage and reperfusion of liver grafts, HSCs can interact directly with cells of the immune system. Endotoxin (LPS), levels of which increase in liver diseases and transplantation, stimulates the synthesis of many mediators by HSCs. We hypothesized that LPS-stimulated HSCs might promote hepatic tolerogenicity by influencing naturally occurring immunosuppressive CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs). Following their portal venous infusion, allogeneic CD4(+) T cells, including Tregs, were found closely associated with HSCs, and this association increased in LPS-treated livers. In vitro, both unstimulated and LPS-stimulated HSCs upregulated Fas (CD95) expression on conventional CD4(+) T cells and induced their apoptosis in a Fas/Fas ligand-dependent manner. By contrast, HSCs induced Treg proliferation, which required cell-cell contact and was MHC class II-dependent. This effect was augmented when HSCs were pretreated with LPS. LPS increased the expression of MHC class II, CD80, and CD86 and stimulated the production of IL-1α, IL-1β, IL-6, IL-10 and TNF-α by HSCs. Interestingly, production of IL-1α, IL-1β, IL-6, and TNF-α was strongly inhibited, but that of IL-10 enhanced in LPS-pretreated HSC/Treg cocultures. Adoptively transferred allogeneic HSCs migrated to the secondary lymphoid tissues and induced Treg expansion in lymph nodes. These data implicate endotoxin-stimulated HSCs as important immune regulators in liver transplantation by inducing selective expansion of tolerance-promoting Tregs and reducing inflammation and alloimmunity.

The STATus of PD-L1 (B7-H1) on tolerogenic APCs

Expression by DCs of co-inhibitory molecules such as programmed death ligand-1 (PD-L1/B7-H1/CD274), a member of the B7 superfamily, is crucial for the downregulation of T-cell responses and the maintenance of immune homeostasis. Exposure of immature DCs to danger-associated molecular patterns (DAMPS) or pathogen-associated molecular patterns (PAMPs) generally results in their maturation and acquisition of immunostimulatory function. However, exposure of DCs to TLR ligands early during their differentiation can inhibit further differentiation and confer tolerogenic properties on these APCs. A report in this issue of The European Journal of Immunology reveals that early inhibition of human DC differentiation from blood monocytes by TLR agonists is associated with a tolerogenic phenotype and Treg generation. The tolerogenic function of these APCs is dependent on MAPK-induced IL-6 and IL-10 production, which drives STAT-3-mediated PD-L1 expression. These observations link IL-10 and IL-6 to PD-L1 expression, providing a new dimension to the anti-inflammatory properties of these cytokines. These findings also have implications for understanding the inherent function of DCs in non-lymphoid tissues such as the liver and lung, where they are exposed to PAMPs that are found constitutively in the local microenvironment.

DAP12 promotes IRAK-M expression and IL-10 production by liver myeloid dendritic cells and restrains their T cell allostimulatory ability

Freshly isolated hepatic dendritic cells (DC) are comparatively immature, relatively resistant to maturation, and can downmodulate effector T cell responses. Molecular mechanisms that underlie these properties are ill defined. DNAX-activating protein of 12 kDa (DAP12) is an ITAM-bearing transmembrane adaptor protein that integrates signals through several receptors, including triggering receptor expressed on myeloid cells-1, -2, and CD200R. Notably, DC propagated from DAP12-deficient mice exhibit enhanced maturation in response to TLR ligation. Given the constitutive exposure of liver DC to endotoxin draining from the gut, we hypothesized that DAP12 might regulate liver DC maturation. We show that DAP12 is expressed by freshly isolated liver, spleen, kidney, and lung myeloid DC. Moreover, inhibition of DAP12 expression by liver DC using small interfering RNA promotes their phenotypic and functional maturation, resulting in enhanced TNF-α, IL-6, and IL-12p70 production, reduced secretion of IL-10, and enhanced CD4(+) and CD8(+) T cell proliferation. Furthermore, DAP12 silencing correlates with decreased STAT3 phosphorylation in mature liver DC and with diminished expression of the IL-1R-associated kinase-M, a negative regulator of TLR signaling. These findings highlight a regulatory role for DAP12 in hepatic DC maturation, and suggest a mechanism whereby this function may be induced/maintained.

Molecular regulation of hepatic dendritic cell function and its relation to liver transplant outcome

Studies on liver interstitial dendritic cells (DC) indicate that the maturation and function of these important antigen-presenting cells may be suppressed by continual exposure to microbial products from the gut, in particular, bacterial lipopolysaccharide. New evidence is emerging for a role of specific intracellular regulators of signal transduction and of cytokines in the hepatic microenvironment, which may contribute to a hyporesponsive state in liver DC. Analysis of signaling molecule expression within DC in liver transplant tissue is likely to uncover its relation to allograft outcome.

Mammalian target of rapamycin inhibition and alloantigen-specific regulatory T cells synergize to promote long-term graft survival in immunocompetent recipients

Minimization of immunosuppression and donor-specific tolerance to MHC-mismatched organ grafts are important clinical goals. The therapeutic potential of regulatory T cells (Tregs) has been demonstrated, but conditions for optimizing their in vivo function posttransplant in nonlymphocyte-depleted hosts remain undefined. In this study, we address mechanisms through which inhibition of the mammalian target of rapamycin (Rapa) synergizes with alloantigen-specific Treg (AAsTreg) to permit long-term, donor-specific heart graft survival in immunocompetent hosts. Crucially, immature allogeneic dendritic cells allowed AAsTreg selection in vitro, with minimal expansion of unwanted (Th17) cells. The rendered Treg potently inhibited T cell proliferation in an Ag-specific manner. However, these AAsTreg remained unable to control T cells stimulated by allogeneic mature dendritic cells, a phenomenon dependent on the release of proinflammatory cytokines. In vivo, Rapa administration reduced danger-associated IL-6 production, T cell proliferation, and graft infiltration. Based on these observations, AAsTreg were administered posttransplant (day 7) in combination with a short course of Rapa and rendered >80% long-term (>150 d) graft survival, a result superior to that achieved with polyclonal Treg. Moreover, graft protection was alloantigen-specific. Significantly, long-term graft survival was associated with alloreactive T cell anergy. These findings delineate combination of transient mammalian target of Rapa inhibition with appropriate AAsTreg selection as an effective approach to promote long-term organ graft survival.

NOD2 ligation subverts IFN-alpha production by liver plasmacytoid dendritic cells and inhibits their T cell allostimulatory activity via B7-H1 up-regulation

The nucleotide-binding oligomerization domain (NOD)2/CARD15 protein, which senses muramyl dipeptide (MDP), a product of bacterial peptidoglycan, appears to play an important role in regulating intestinal immunity. Although the liver is exposed to gut-derived MDP, the influence of NOD2 ligation on hepatic APC, in particular dendritic cells (DC), is unknown. Freshly isolated mouse liver and spleen plasmacytoid (p)DC expressed higher levels of NOD2 message than conventional myeloid (m)DC. Following MDP stimulation in vivo, liver pDC, but not mDC, up-regulated expression of IFN regulatory factor 4 (IRF-4), a negative regulator of TLR signaling, and induced less allogeneic T cell proliferation and IFN-gamma production. The adoptive transfer of liver pDC from MDP-treated mice failed to prime allogeneic T cells in vivo. By contrast, splenic DC IRF-4 levels and T cell stimulatory activity remained unchanged. Liver pDC from MDP-stimulated mice also displayed greater IkappaBalpha, cell surface B7-H1, and B7-H1 relative to CD86 than control liver pDC. No similar effects were observed for liver mDC or spleen DC. Absence of B7-H1 on liver pDC reversed the inhibitory effect of MDP. After ex vivo stimulation with LPS or CpG, liver pDC but not mDC from MDP-treated animals secreted less IL-12p70, IL-6, and TNF-alpha and induced weaker allogeneic T cell proliferation than those from controls. Moreover, CpG-stimulated liver pDC from MDP-treated mice secreted less IFN-alpha than their splenic counterparts, and systemic levels of IFN-alpha were reduced in MDP-treated animals after CpG administration. These findings suggest that differential effects of NOD2 ligation on liver pDC may play a role in regulating hepatic innate and adaptive immunity.

Dendritic cell immunobiology in relation to liver transplant outcome

The unique immunologic environment of the liver, together with its anatomic location downstream of the gut, influences the maturation and function of its interstitial dendritic cell (DC) populations. These well-equipped, antigen-presenting cells play critical roles in regulation of innate and adaptive immunity. New information is emerging about the molecular regulation of liver DC maturation and function, and their tolerogenic potential, while new insight is being gained regarding interactions between liver DC and other immune effector cell populations (NK, NKT cells) in addition to T cells. During transplantation, factors that affect liver DC biology include ischemia-reperfusion injury, liver regeneration, viral infection and the actions of anti-inflammatory and immunosuppressive drugs. Herein, we review the molecular and cell biology of hepatic DC populations in relation to the regulation of alloimmune responses and liver transplant outcome.

Host-derived plasmacytoid dendritic cells prolong cardiac allograft survival and regulate alloreactive T cell responses via B7 homolog-1 (141.28)

This study evaluated the contribution of the inhibitory molecule B7 homolog-1 (B7-H1) to the regulation of alloimmune responses by pDC. mPDCA-1+ splenic pDC from wild type (WT) or B7-H1 knockout (KO) mice were pulsed with donor antigen (Ag). Cell phenotype was analyzed for Ag-presenting and co-regulatory molecules and T cell allostimulatory capacity was assessed in mixed leukocyte reaction (MLR). WT or KO pDC pulsed with donor Ag were injected into syngeneic mice and CD4+ T cells were purified 7 days later for secondary MLR. T cell proliferation was assessed by 3H-thymidine incorporation and cytokines quantified by ELISA. BALB/c hearts were transplanted into untreated C57BL/6 controls or into mice receiving syngeneic pDC pulsed with donor Ag 7 days before grafting. pDC expressed low levels of CD40, CD80, CD86, MHC I/II, and B7-H1 and showed poor CD4+ T cell stimulatory capacity compared to conventional myeloid DC. pDC from KO mice exhibited greater T cell stimulatory capacity compared to WT controls. T cells from mice given immature, donor Ag-pulsed KO pDC showed greater proliferation and secreted more IFN-γ in secondary MLR compared to WT controls. Recipient-derived, immature WT pDC pulsed with donor Ag prolong allograft survival. These results reveal that B7-H1 on pDC contributes to regulation of alloreactive T cell responses. This work was funded by the transplantation immunology training grant NIAID T32 AI 074490.

DAP12 renders liver dendritic cells resistant to maturation (91.14)

Liver APC are constitutively exposed to gut-derived LPS, yet are refractory to LPS-induced maturation. We and others have hypothesized that resistance to LPS in liver DC reflects molecular inhibition of NF-κB activation. DNAX-activating protein of 12kDa (DAP12), a transmembrane adaptor protein, dampens co-stimulatory molecule and cytokine expression associated with inhibition of NF-κB in myeloid (m)DC. In this study, we evaluated the function of DAP12 in mDC (CD11c+CD11b+NK1.1-B220-) purified from livers or spleens of Fms-like tyrosine kinase 3 ligand (10 μg/day/10d)-mobilized C57BL/10 mice (in which DC populations were enriched), then cultured overnight with LPS. To test the hypothesis that DAP12 impairs LPS-induced maturation of liver mDC, DAP12 was silenced with siRNA (400nM) 2h prior to LPS stimulation. Liver mDC did not upregulate CD80, CD86, B7-H1 (PD-L1), B7RP or IL-12 to the extent of splenic mDC in response to LPS. Silencing DAP12 enhanced expression of CD80, CD86, IL-12 and the Th1-polarizing molecule, Delta4, but not B7-H1 or B7RP in liver and spleen mDC in response to LPS. These effects were more pronounced in liver mDC. We conclude that the comparatively immature state of liver mDC may be regulated, in part, by DAP12. Supported by American Liver Foundation and American Transplantation Society Fellowships and NIH RO1AI60994.

Combined mTOR inhibition and post-transplant infusion of alloantigen-specific Treg promotes long-term graft survival in otherwise unmanipulated hosts (141.42)

Protocols that achieve donor-specific tolerance of MHC-mismatched organ grafts remain an unmet clinical goal. We report a strategy that combines post-transplant administration of alloAg-specific Treg (AAsTreg) with inhibition of the mammalian target of rapamycin (Rapa) (mTOR) to promote long-term, donor-specific heart graft survival.

AAsTreg selection was achieved by co-culture of CD4+CD25+ Treg with immature dendritic cells (DC) in the presence of conditioned media. This rendered cells that potently inhibited T cell proliferation in an Ag-specific manner. However, AAsTreg remained unable to control T cell activation when stimulated by mature DC, - a phenomenon dependent on IL-6 release. Exploiting the in vivo inhibitory effects of Rapa on inflammatory cytokine (IL-6) production, T cell proliferation and graft infiltration, AAsTreg were administered post-transplant (d7) in combination with short-term Rapa. AAsTreg exerted a pro-tolerogenic effect: >80% long-term graft survivors [LTS] (MST>150d). Polyclonal Treg exerted an inferior protective effect: 40% LTS (MST=45d). Moreover, the pro-tolerogenic effect was Ag-specific as AAsTreg selected against third party DC failed to prolong graft survival. Significantly, LTS exhibited alloreactive T cell anergy. Thus, combination of mTOR inhibition with AAsTreg is an effective, clinically-applicable approach to promote long-term graft survival.

Allostimulatory activity of bone marrow-derived plasmacytoid dendritic cells is independent of indoleamine dioxygenase but regulated by inducible costimulator ligand expression

We investigated the role of two key immunoregulatory molecules, indoleamine dioxygenase (IDO) and inducible costimulator ligand (ICOSL), in determining the function of bone marrow (BM)-derived plasmacytoid (p)DC, which offer the potential for therapy of allograft rejection. pDC generated from BM of wild-type (WT) or IDO knockout (KO) C57BL/6 mice were used to stimulate T-cell proliferation and interferon-gamma (IFN-gamma) production in response to alloantigen (alloAg) via the direct or indirect pathways. In some experiments, pDC were first activated by exposure to CpG +/- CTLA4Ig for IDO induction via B7 ligation. Although IDO KO pDC induced enhanced T-cell responses compared with WT pDC, the use of the IDO inhibitor 1-methyltryptophan (1-MT) demonstrated that the inferior stimulatory capacity of WT pDC was not caused by the production of functional IDO, even under IDO-inducing conditions. The DNAX-activating protein of 12 kDa (DAP12), which inhibits functional IDO expression, was expressed in BM-pDC. DAP12 silencing increased the T-cell stimulatory capacity of WT pDC, but only in the presence of 1-MT. Compared with WT pDC, activated IDO KO DC expressed much lower levels of ICOSL. Moreover, when ICOSL was blocked on WT pDC, T-cell proliferation resembled that induced by IDO KO pDC, and interleukin (IL)-10 secretion in MLR was markedly decreased. These findings implicate ICOSL-induced IL-10, but not IDO in the regulation of BM-derived pDC function.

Poor allostimulatory function of liver plasmacytoid DC is associated with pro-apoptotic activity, dependent on regulatory T cells

BACKGROUND/AIMS

The liver is comparatively rich in plasmacytoid (p) dendritic cells (DC), - innate immune effector cells that are also thought to play key roles in the induction and regulation of adaptive immunity.

METHODS

Liver and spleen pDC were purified from fms-like tyrosine kinase ligand-treated control or lipopolysaccharide-injected C57BL/10 mice. Flow cytometric and molecular biologic assays were used to characterize their function and interaction with naturally occurring regulatory T cells (Treg).

RESULTS

While IL-10 production was greater for freshly isolated liver compared with splenic pDC, the former produced less bioactive IL-12p70. Moreover, liver pDC expressed a low Delta4/Jagged1 Notch ligand ratio, skewed towards T helper 2 cell differentiation/cytokine production, and promoted allogeneic CD4(+)T cell apoptosis. T cell proliferation in response to liver pDC was, however, enhanced by blocking IL-10 function at the initiation of cultures. In the absence of naturally occurring CD4(+)CD25(+) regulatory T cells, similar levels of T cell proliferation were induced by liver and spleen pDC and the pro-apoptotic activity of liver pDC was reversed.

CONCLUSIONS

The inferior T cell allostimulatory activity of in vivo-stimulated liver pDC may depend on the presence and function of Treg, a property that may contribute to inherent liver tolerogenicity.

IL-1beta-driven ST2L expression promotes maturation resistance in rapamycin-conditioned dendritic cells

Maturation resistance and tolerogenic properties can be conferred on human and murine dendritic cells (DC), crucial regulators of T cell responses, by exposure to rapamycin (RAPA), a "tolerance-sparing" immunosuppressive agent. Mechanisms underlying this acquired unresponsiveness, typified by diminished functional responses to TLR or CD40 ligation, have not been identified. We report that in vitro and in vivo conditioning of murine myeloid DC with RAPA elicits the de novo production of IL-1beta by otherwise phenotypically immature DC. Interestingly, IL-1beta production promotes overexpression of the transmembrane form of the IL-1R family member, IL-1R-like 1, also know as ST2 on RAPA-conditioned DC (RAPA-DC). ST2 is the recently identified receptor for IL-33, a cytokine favoring Th2 responses. In addition, transmembrane ST2, or ST2L, has been implicated as a potent negative regulator of TLR signaling. RAPA-DC generated from ST2-/- mice exhibited higher levels of costimulatory molecules (CD86) than wild-type RAPA-DC. Consistent with its regulatory function, IL-1beta-induced ST2L expression suppressed the responsiveness of RAPA-DC to TLR or CD40 ligation. Thus, as a result of their de novo production of IL-1beta, RAPA-DC up-regulate ST2L and become refractory to proinflammatory, maturation-inducing stimuli. This work identifies a novel mechanism through which a clinically important immunosuppressant impedes the capacity of DC to mature and consequently stimulate effector/adaptive T cell responses.

Dendritic cells, the liver, and transplantation

Interstitial liver dendritic cells (DCs) exhibit phenotypic diversity and functional plasticity. They play important roles in both innate and adaptive immunity. Their comparatively low inherent T cell stimulatory ability and the outcome of their interactions with CD4(+) and CD8(+) T cells, as well as with natural killer (NK) T cells and NK cells within the liver, may contribute to regulation of hepatic inflammatory responses and liver allograft outcome. Liver DCs migrate in the steady state and after liver transplantation to secondary lymphoid tissues, where the outcome of their interaction with antigen-specific T cells determines the balance between tolerance and immunity. Systemic and local environmental factors that are modulated by ischemia-reperfusion injury, liver regeneration, microbial infection, and malignancy influence hepatic DC migration, maturation, and function. Current research in DC biology is providing new insights into the role of these important antigen-presenting cells in the complex events that affect liver transplant outcome.

Regulation of the NFAT pathway discriminates CD4+CD25+ regulatory T cells from CD4+CD25- helper T cells

CD4(+)CD25(+) regulatory T cells (Tregs) are potent modulators of immune responses. The transcriptional program distinguishing Tregs from the CD4(+)CD25(-) Th cells is unclear. NFAT, a key transcription factor, is reported to interact with forkhead box p3, allowing inhibitory and activating signals in T cells. In the current study, we hypothesize that distinctive NFAT regulation in Tregs as compared with Th cells, may contribute to specific functions of these cells. Tregs express basal levels of cytoplasmic NFATc1 and NFATc2. In contrast to Th cells, anti-CD3-mediated T cell activation did not induce nuclear translocation of NFATc1 or NFATc2 in Tregs. This effect was associated with altered regulation for NFAT in Tregs that included reduced calcium flux, diminished calcineurin activation, and increased activity of glycogen synthase kinase-3beta, a negative regulatory kinase for NFAT in Tregs relative to Th cells. These data suggested that NFAT inhibition in Th cells may induce regulatory function. Indeed, pharmacologically mediated NFAT inhibition induced Th cells to function as Tregs, an effect that was mediated by induction of membrane-bound TGF-beta on Th cells. Collectively, these data suggest that maintaining NFAT at basal levels is a part of the transcriptional program required for Tregs.

Pulmonary immunity to viral infection: adenovirus infection of lung dendritic cells renders T cells nonresponsive to interleukin-2

Adenovirus (Ad) infection has been identified as predisposing hosts to the development of pulmonary disease through unknown mechanisms. Lung dendritic cells (DCs) are vital for initiating pulmonary immune responses; however, the effects of Ad infection on primary lung DC have not been studied. In contrast to the effects on bone marrow- and monocyte-derived DCs, the current study shows that Ad infection of murine BALB/c lung DCs in vitro and in vivo suppresses DC-induced T-cell proliferation. The effect of Ad on DCs was not due to a downregulation of major histocompatibility complex or costimulatory molecules. Analysis of the production of interleukin-12 (IL-12), alpha interferon (IFN-alpha), and IFN-gamma by the Ad-infected DCs shows no significant differences over noninfected control lung DCs. Ad-induced suppression was not due to a deficiency of IL-2 or other DC-secreted factors and was dependent on viral protein synthesis, as UV irradiation of Ad abrogated the suppressive effect. Results suggest that Ad-infected DCs induce T cells to be nonresponsive to IL-2 during primary coculture, as the addition of IL-2 in secondary cultures recovered T-cell proliferation. In vivo studies supported in vitro results showing that Ad infection resulted in lung T cells with decreased proliferative ability. This study demonstrates that Ad infection induces local immunoincompetence by altering DC-T-cell interactions.

The phenotype and function of lung dendritic cells

Dendritic cells (DCs) are central to the integration of innate and adaptive immunity. In contrast to B and T lymphocytes, DCs have retained many of the pattern recognition receptors and are thus uniquely able to sense stimuli such as tissue damage, necrosis, and bacterial and viral infection. Also, immature DCs respond to danger signals in the environment, which leads to their maturation, upon which DCs differentiate and acquire the ability to direct the development of the primary immune response. The ability of lung DCs to elicit specific CD4 and CD8 T lymphocyte responses have made them attractive targets for vaccine development strategies in the treatment and prevention of diseases such as allograft rejection responses, allergy, and asthma, as well as autoimmune disease and cancer.

Role of autoimmunity in organ allograft rejection: a focus on immunity to type V collagen in the pathogenesis of lung transplant rejection

Lung transplantation is the only definitive treatment modality for many forms of end-stage lung disease. However, the lung is rejected more often than any other type of solid organ allograft due to chronic rejection known as bronchiolitis obliterans (BO). Indeed, BO is the primary reason why the 5- and 7-yr survival rates are worse for the lung than for any other transplanted organ. Alloimmunity to donor antigens is established as the primary mechanism that mediates rejection responses. However, newer immunosuppressive regimens designed to abrogate alloimmune activation have not improved survival. Therefore, these data suggest that other antigens, unrelated to donor transplantation antigens, are involved in rejection. Utilizing human and rodent studies of lung transplantation, our laboratory has documented that a native collagen, type V collagen [col(V)], is a target of the rejection response. Col(V) is highly conserved; therefore, these data indicate that transplant rejection involves both alloimmune and autoimmune responses. The role of col(V) in lung transplant rejection is described in this review article. In addition, the potential role of regulatory T cells that are crucial to modulating autoimmunity and alloimmunity is also discussed.

Tetrabenazine fails to antagonize a behavioral effect of cocaine in rhesus monkeys

For research and therapeutic purposes, a cocaine antagonist is an important drug development goal. The vesicular monoamine transport inhibitor tetrabenazine was tested for interaction with cocaine using food-reinforced responding in rhesus monkeys as an assay. Both tetrabenazine and cocaine suppressed food-maintained behavior individually. However, a low-dose tetrabenazine pretreatment did not alter the rate-suppressing effects of cocaine and cocaine did not alter the rate-suppressing effects of a high dose tetrabenazine pretreatment. Because tetrabenazine interacts with the monoamine oxidase inhibitor deprenyl in this assay, we conclude that cocaine does not produce an effect through vesicular catecholamines in this assay.

Titer-dependent antagonism of cocaine following active immunization in rhesus monkeys

Immunization may be a useful pharmacokinetic antagonist therapy for cocaine users. Three rhesus monkeys were immunized with a cocaine:bovine serum albumin conjugate in alum and later with complete and incomplete Freund's adjuvants. Monkeys developed cocaine-binding antibodies (as measured by enzyme-linked immunosorbent assay) after immunization with alum; greater antibody titers developed after immunization with Freund's adjuvants. The response rate-decreasing effect of cocaine diminished in proportion to antibody titer; there was no substantial change in the rate-decreasing effect of bupropion. Plasma cocaine concentrations increased in proportion to antibody titer. Immunizations were well tolerated and had no effect on response rates. These data suggest that the antibody response to a cocaine antigen can produce a specific pharmacokinetic shift in cocaine distribution sufficient to antagonize a behavioral effect of the drug, and can do so with minimal side effects.