Nancy C. Kirkiles-Smith

Interferon-gamma elicits arteriosclerosis in the absence of leukocytes.

Atherosclerosis and post-transplant graft arteriosclerosis are both characterized by expansion of the arterial intima as a result of the infiltration of mononuclear leukocytes, the proliferation of vascular smooth muscle cells (VSMCs) and the accumulation of extracellular matrix. They are also associated with the presence of the immunomodulatory cytokine interferon-γ (IFN-γ). Moreover, in mouse models of atheroma formation or allogeneic transplantation, the serological neutralization or genetic absence of IFN-γ markedly reduces the extent of intimal expansion. However, other studies have found that exogenous IFN-γ inhibits cultured VSMC proliferation and matrix synthesis, and reduces intimal expansion in response to mechanical injury. This discrepancy is generally explained by the idea that IFN-γ either directly activates macrophages, or, by increasing antigen presentation, indirectly activates T cells within the lesions of atherosclerosis and graft arteriosclerosis. These activated leukocytes are thought to express the VSMC-activating cytokines and cell-surface molecules that cause the observed arteriosclerotic responses. Here we have inserted pig and human arteries into the aorta of immunodeficient mice, and we show that IFN-γ can induce arteriosclerotic changes in the absence of detectable immunocytes by acting on VSMCs to potentiate growth-factor-induced mitogenesis.

TRAIL Induces Apoptosis and Inflammatory Gene Expression in Human Endothelial Cells

Human TRAIL can efficiently kill tumor cells in vitro and kill human tumor xenografts in mice with little effect on normal mouse cells or tissues. The effects of TRAIL on normal human tissues have not been described. In this study, we report that endothelial cells (EC), isolated from human umbilical veins or human dermal microvessels, express death domain-containing TRAIL-R1 and -R2. Incubation with TRAIL for 15 h causes ∼30% of cultured EC to die, as assessed by propidium iodide uptake. Death is apoptotic, as assessed by Annexin V staining, 4′,6′-diamidino-2-phenylindole staining, and DNA fragment ELISA. EC death is increased by cotreatment with cycloheximide but significantly reduced by caspase inhibitors or transduced dominant-negative Fas-associated death domain protein. In surviving cells, TRAIL activates NF-κB, induces expression of E-selectin, ICAM-1, and IL-8, and promotes adhesion of leukocytes. Injection of TRAIL into human skin xenografts promotes focal EC injury accompanied by limited neutrophil infiltration. These data suggest that TRAIL is an inducer of tissue injury in humans, an outcome that may influence antitumor therapy with TRAIL.

Antibody to human leukocyte antigen triggers endothelial exocytosis.

Although antibodies to HLA play a role in the pathogenesis of diseases processes such as rejection of transplanted organs, the precise mechanisms by which antibodies cause tissue injury are not completely understood. We hypothesized that antibodies to host tissues cause inflammation in part by activating endothelial exocytosis of granules that contain prothrombotic mediators such as von Willebrand Factor (VWF) and proinflammatory mediators such as P-selectin. To test this hypothesis, we treated human endothelial cells with murine monoclonal antibody W6/32 to HLA class I and then measured exocytosis by the release of VWF and the externalization of P-selectin. Antibody to HLA activates endothelial exocytosis in a dose-dependent manner over time. The biologically active complement split product, C5a, adds a slight but significant increase to antibody induction of exocytosis. Antibody to HLA alone or with C5a did not damage the cells. Cross-linking of HLA appears to play a role in the ability of antibody to activate exocytosis, because the W6/32 monovalent Fab fragment did not activate VWF release, but the bivalent F(ab′)2 was effective in triggering exocytosis. To explore the in vivo effects of antibody upon graft injury, we infused W6/32 F(ab′)2 antibody to human HLA into severe combined immunodeficient/beige mice that had been transplanted with human skin grafts. Antibody to HLA activated exocytosis and inflammation in human skin grafts. Our data show that antibody to host antigens can activate human endothelial cell exocytosis and leukocyte trafficking. By triggering vascular inflammation, antibody activation of exocytosis may play a role in transplant rejection.

Interleukin-11 up-regulates survivin expression in endothelial cells through a signal transducer and activator of transcription-3 pathway.

Interleukin-11 (IL-11) reduces injury both in vivo and in vitro, but the mechanisms are unknown. Stimulation of serum- and growth factor-deprived HUVEC with IL-11 increased survivin mRNA and protein expression levels in a dose-dependent manner, with maximal induction at 50 to 100 ng/ml of IL-11. Survivin mRNA expression peaked after 3 to 6 hours of IL-11 treatment and decreased by 24 hours. Survivin protein expression was maximal at 6 hours of treatment and remained elevated through 24 hours. Survivin induction may be mediated by activation of protein kinase B/Akt, but IL-11 failed to activate this pathway in HUVEC. IL-11 did activate signal transducer and activator of transcription (STAT)-3 and IL-11 failed to induce survivin expression in HUVEC transduced with a dominant-negative STAT3 mutant, whereas control-transduced HUVEC responded normally. An IL-11 transgene caused increased survivin mRNA expression in mice compared with control littermates. Intradermal injection of IL-11 (500 ng) into human skin xenografts on immunodeficient mice up-regulated survivin protein in microvascular endothelium and epithelial keratinocytes. We conclude that IL-11 induces expression of survivin, an antiapoptotic protein, in vitro and in vivo, and identify STAT3 as a critical mediator of this response.

Comparison of human fetal liver, umbilical cord blood, and adult blood hematopoietic stem cell engraftment in NOD-scid/γc−/−, Balb/c-Rag1−/−γc−/−, and C.B-17-scid/bg immunodeficient mice

Immunodeficient mice bearing components of a human immune system present a novel approach for studying human immune responses. We investigated the number, phenotype, developmental kinetics, and function of developing human immune cells following transfer of CD34(+) hematopoietic stem cell (HSC) preparations originating from second trimester human fetal liver (HFL), umbilical cord blood (UCB), or granulocyte colony-stimulating factor-mobilized adult blood (G-CSF-AB) delivered via intrahepatic injection into sublethally irradiated neonatal NOD-scid/gammac(-/-), Balb/c-Rag1(-/-)gammac(-/-), and C.B-17-scid/bg mice. HFL and UCB HSC provided the greatest number and breadth of developing cells. NOD-scid/gammac(-/-) and Balb/c-Rag1(-/-)gammac(-/-) harbored human B and dendritic cells as well as human platelets in peripheral blood, whereas NOD-scid/gammac(-/-) mice harbored higher levels of human T cells. NOD-scid/gammac(-/-) mice engrafted with HFL CD34(+) HSC demonstrated human immunological competence evidenced by white pulp expansion and increases in total human immunoglobulin following immunization with T-dependent antigens and delayed-type hypersensitivity-infiltrating leukocytes in response to antigenic challenge. In conclusion, we describe an encouraging base system for studying human hematopoietic lineage development and function utilizing human HFL or UCB HSC-engrafted NOD-scid/gammac(-/-) mice that is well suited for future studies toward the development of a fully competent humanized mouse model.

Human Effector Memory CD4 + T Cells Directly Recognize Allogeneic Endothelial Cells In Vitro and In Vivo

The frequency of circulating alloreactive human memory T cells correlates with allograft rejection. Memory T cells may be divided into effector memory (TEM) and central memory (TCM) cell subsets, but their specific roles in allograft rejection are unknown. We report that CD4+ TEM (CD45RO+CCR7−CD62L−) can be adoptively transferred readily into C.B-17 SCID/bg mice and mediate the destruction of human endothelial cells (EC) in vascularized human skin grafts allogeneic to the T cell donor. In contrast, CD4+ TCM (CD45RO+CCR7+CD62L+) are inefficiently transferred and do not mediate EC injury. In vitro, CD4+ TEM secrete more IFN-γ within 48 h in response to allogeneic ECs than do TCM. In contrast, TEM and TCM secrete comparable amounts of IFN-γ in response to allogeneic monocytes (Mo). In the same cultures, both TEM and TCM produce IL-2 and proliferate in response to IFN-γ-treated allogeneic human EC or Mo, but TCM respond more vigorously in both assays. Blockade of LFA-3 strongly inhibits both IL-2 and IFN-γ secretion by CD4+ TEM cultured with allogeneic EC but only minimally inhibits responses to allogeneic Mo. Blockade of CD80 and CD86 strongly inhibits IL-2 but not IFN-γ production by in response to allogeneic EC or Mo. Transduction of EC to express B7-2 enhances allogeneic TEM production of IL-2 but not IFN-γ. We conclude that human CD4+ TEM directly recognize and respond to allogeneic EC in vitro by secreting IFN-γ and that this response depends on CD2 but not CD28. Consistent with EC activation of effector functions, human CD4+ TEM can mediate allogeneic EC injury in vivo.

Interleukin (IL)-1 promotes allogeneic T cell intimal infiltration and IL-17 production in a model of human artery rejection

Interleukin (IL) 1α produced by human endothelial cells (ECs), in response to tumor necrosis factor (TNF) or to co-culture with allogeneic T cells in a TNF-dependent manner, can augment the release of cytokines from alloreactive memory T cells in vitro. In a human–mouse chimeric model of artery allograft rejection, ECs lining the transplanted human arteries express IL-1α, and blocking IL-1 reduces the extent of human T cell infiltration into the artery intima and selectively inhibits IL-17 production by infiltrating T cells. In human skin grafts implanted on immunodeficient mice, administration of IL-17 is sufficient to induce mild inflammation. In cultured cells, IL-17 acts preferentially on vascular smooth muscle cells rather than ECs to enhance production of proinflammatory mediators, including IL-6, CXCL8, and CCL20. Neutralization of IL-17 does not reduce T cell infiltration into allogeneic human artery grafts, but markedly reduces IL-6, CXCL8, and CCL20 expression and selectively inhibits CCR6+ T cell accumulation in rejecting arteries. We conclude that graft-derived IL-1 can promote T cell intimal recruitment and IL-17 production during human artery allograft rejection, and suggest that targeting IL-1 in the perioperative transplant period may modulate host alloreactivity.

Alloantibody and Complement Promote T Cell–Mediated Cardiac Allograft Vasculopathy Through Noncanonical Nuclear Factor-κB Signaling in Endothelial Cells

Background— Cardiac allograft vasculopathy is the major cause of late allograft loss after heart transplantation. Cardiac allograft vasculopathy lesions contain alloreactive T cells that secrete interferon-&ggr;, a vasculopathic cytokine, and occur more frequently in patients with donor-specific antibody. Pathological interactions between these immune effectors, representing cellular and humoral immunity, respectively, remain largely unexplored. Methods and Results— We used human panel reactive antibody to form membrane attack complexes on allogeneic endothelial cells in vitro and in vivo. Rather than inducing cytolysis, membrane attack complexes upregulated inflammatory genes, enhancing the capacity of endothelial cells to recruit and activate allogeneic interferon-&ggr;––producing CD4+ T cells in a manner dependent on the activation of noncanonical nuclear factor-&kgr;B signaling. Noncanonical nuclear factor-&kgr;B signaling was detected in situ within endothelial cells both in renal biopsies from transplantation patients with chronic antibody-mediated rejection and in panel-reactive antibody––treated human coronary artery xenografts in immunodeficient mice. On retransplantation into immunodeficient hosts engrafted with human T cells, panel-reactive antibody––treated grafts recruited more interferon-&ggr;––producing T cells and enhanced cardiac allograft vasculopathy lesion formation. Conclusions— Alloantibody and complement deposition on graft endothelial cells activates noncanonical nuclear factor-&kgr;B signaling, initiating a proinflammatory gene program that enhances alloreactive T cell activation and development of cardiac allograft vasculopathy. Noncanonical nuclear factor-&kgr;B signaling in endothelial cells, observed in human allograft specimens and implicated in lesion pathogenesis, may represent a target for new pharmacotherapies to halt the progression of cardiac allograft vasculopathy.

IL-11 Protects Human Microvascular Endothelium from Alloinjury In Vivo by Induction of Survivin Expression

IL-11 can reduce tissue injury in animal models of inflammation but the mechanism(s) is unknown. When C.B-17 SCID/beige mice bearing human skin grafts are injected i.p. with human PBMC allogeneic to the donor skin, infiltrating T cells destroy human microvessels by day 21. Intradermal injection of human IL-11 (500 ng/day) delays the time course of graft microvessel loss without reducing the extent of T cell infiltration. Protective actions of IL-11 are most pronounced on day 15. IL-11 has no effect on T cell activation marker, effector molecule, cytokine expression, or endothelial ICAM-1 expression. IL-11 up-regulates the expression of survivin, a cytoprotective protein, in graft keratinocytes and endothelial cells. Topical application of survivin antisense oligonucleotide down-regulates survivin expression in both cell types and largely abrogates the protective effect of IL-11. We conclude that in this human transplant model, IL-11 exerts a cytoprotective rather than anti-inflammatory or immunomodulatory effect mediated through induction of survivin.

Interferon-γ Induces X-linked Inhibitor of Apoptosis-associated Factor-1 and Noxa Expression and Potentiates Human Vascular Smooth Muscle Cell Apoptosis by STAT3 Activation

Interferon (IFN)-γ actions on the vessel wall play an important role in the pathogenesis of arteriosclerosis, yet the contribution of different IFN-γ signaling pathways to the phenotypic modulation of vascular smooth muscle cells (VSMCs) are poorly understood. We investigated the effects of IFN-γ on VSMCs and arteries through interactions involving signal transducer and activator of transcription (STAT) proteins. In addition to STAT1 activation, IFN-γ consistently phosphorylated STAT3 in human VSMCs but weakly or not at all in human endothelial cells or mouse VSMCs. STAT3 activation resulted in nuclear translocation of this transcription factor. By selectively inhibiting STAT3 and not STAT1 signaling, we identified a number of candidate IFN-γ-inducible, STAT3-dependent gene products by microarray analysis. Results for selected genes, including the pro-apoptotic molecules X-linked inhibitor of apoptosis associated factor-1 (XAF1) and Noxa, were verified by real time quantitative reverse transcription-PCR and immunoblot analyses. IFN-γ-induced STAT3 and STAT1 signaling in VSMCs demonstrated reciprocal inhibition. STAT3 activation by IFN-γ sensitized VSMCs to apoptosis triggered by both death receptor- and mitochondrial-mediated pathways. Knock down of XAF1 and Noxa expression inhibited the priming of VSMCs to apoptotic stimuli by IFN-γ. Finally, we confirmed the in vivo relevance of our observations using a chimeric animal model of immunodeficient mice bearing human coronary artery grafts in which the expression of XAF1 and Noxa as well as the pro-apoptotic effects induced by IFN-γ were dependent on STAT3. The data suggest STAT1-independent signaling by IFN-γ via STAT3 that promotes the death of human VSMCs.