Issue published March 15, 2000

W e have recently shown that a single injection of mature, antigen-pulsed, human dendritic cells (DCs) rapidly elicits CD4⁺ and CD8⁺ T-cell immunity in vivo. The DCs were pulsed with 2 foreign proteins, keyhole limpet hemocyanin (KLH) and tetanus toxoid (TT), as well as an HLA A2.1-restricted influenza matrix peptide (MP). Responses to all 3 antigens peaked at 30–90 days after immunization and declined thereafter. To determine if the foreign helper proteins (TT and KLH) were essential for CD8⁺ T-cell responses to the viral peptide, we reinjected 3 of the HLA-2.1 subjects with mature DCs pulsed with MP alone. All 3 volunteers showed a rapid boost in MP-specific immunity, and freshly sampled blood from 1 contained cytolytic T cells. In all 3 subjects, CD8⁺ T-cell responses to booster DCs were faster and of greater magnitude than the responses to the first DC injection. Importantly, the T cells that proliferated after booster DC treatment secreted interferon-γ upon challenge with much lower doses of viral peptide than those elicited after the first injection, indicating a higher functional avidity for the ligand. These data begin to outline the kinetics of T-cell immunity in response to DCs and demonstrate that booster injections of mature DCs enhance both qualitative and quantitative aspects of CD8⁺ T-cell function in humans.This article may have been published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org. J. Clin. Invest. 105:R9–R14 (2000).

I nhibitors of acyl CoA:cholesterol acyltransferase (ACAT) have attracted considerable interest as a potential treatment for atherosclerosis. Currently available inhibitors probably act nonselectively against the two known ACATs. One of these enzymes, ACAT1, is highly expressed in macrophages in atherosclerotic lesions, where it contributes to foam-cell formation. In this study, we examined the effects of selective ACAT1 deficiency in two mouse models of atherosclerosis. In the setting of severe hypercholesterolemia caused by deficiency in apoE or the LDL receptor (LDLR), total ACAT1 deficiency led to marked alterations in cholesterol homeostasis and extensive deposition of unesterified cholesterol in the skin and brain. Bone marrow transplantation experiments demonstrated that ACAT1 deficiency in macrophages was sufficient to cause dermal xanthomas in hyperlipidemic LDLR-deficient mice. ACAT1 deficiency did not prevent the development of atherosclerotic lesions in either apoE-deficient or LDLR-deficient mice, despite causing relatively lower serum cholesterol levels. However, the lesions in ACAT1-deficient mice were atypical in composition, with reduced amounts of neutral lipids and a paucity of macrophages in advanced lesions. Although the latter findings may be associated with increased lesion stability, the marked alterations in cholesterol homeostasis indicate that selectively inhibiting ACAT1 in the setting of severe hyperlipidemia may have detrimental consequences.

A dhesive interactions play an important role in inflammation by promoting leukocyte attachment and extravasation from the vasculature into the peripheral tissues. However, the importance of adhesion molecules within the extracellular matrix–rich environment of peripheral tissues, in which cells must migrate and be activated, has not been well explored. We investigated the role of the major collagen-binding integrins, α1β1 and α2β1, in several in vivo models of inflammation. mAb’s against murine α1 and α2 were found to significantly inhibit effector phase inflammatory responses in animal models of delayed-type hypersensitivity (DTH), contact hypersensitivity (CHS), and arthritis. Mice that were α1-deficient also showed decreased inflammatory responses in the CHS and arthritis models when compared with wild-type mice. Decreased leukocyte infiltration and edema formation accompanied inhibition of antigen-specific models of inflammation, as nonspecific inflammation induced by croton oil was not inhibited. This study demonstrates the importance in vivo of α1β1 and α2β1, the collagen-binding integrins, in inflammatory diseases. The study also extends the role of integrins in inflammation beyond leukocyte attachment and extravasation at the vascular endothelial interface, revealing the extracellular matrix environment of peripheral tissues as a new point of intervention for adhesion-based therapies.

D uring embryonic development, insulin-like growth factor-II (IGF-II) participates in the regulation of islet growth and differentiation. We generated transgenic mice (C57BL6/SJL) expressing IGF-II in β cells under control of the rat Insulin I promoter in order to study the role of islet hyperplasia and hyperinsulinemia in the development of type 2 diabetes. In contrast to islets from control mice, islets from transgenic mice displayed high levels of IGF-II mRNA and protein. Pancreases from transgenic mice showed an increase in β-cell mass (about 3-fold) and in insulin mRNA levels. However, the organization of cells within transgenic islets was disrupted, with glucagon-producing cells randomly distributed throughout the core. We also observed enhanced glucose-stimulated insulin secretion and glucose utilization in islets from transgenic mice. These mice displayed hyperinsulinemia, mild hyperglycemia, and altered glucose and insulin tolerance tests, and about 30% of these animals developed overt diabetes when fed a high-fat diet. Furthermore, transgenic mice obtained from the N1 backcross to C57KsJ mice showed high islet hyperplasia and insulin resistance, but they also developed fatty liver and obesity. These results indicate that local overexpression of IGF-II in islets might lead to type 2 diabetes and that islet hyperplasia and hypersecretion of insulin might occur early in the pathogenesis of this disease.

R educed production of nitric oxide (NO) in the cirrhotic liver results from a defect in hepatic endothelial cell nitric oxide synthase (ecNOS) and appears to contribute to the high intrahepatic resistance and portal hypertension typical of cirrhosis. Therefore, we postulated that targeting a heterologous NOS isoform to sinusoidal endothelial cells or other perisinusoidal cells, such as hepatic stellate cells, would counter the defect in NO production and reduce resistance to blood flow. Recombinant adenovirus (Ad) carrying the neuronal NOS gene (nNOS) targeted liver sinusoidal endothelial cells, stellate cells, and hepatocytes more efficiently than the corresponding cells in cirrhotic livers, but transduction rates were substantial even in cirrhotic animals. Expression of nNOS in each liver cell type, whether from normal or injured liver, caused increased NO production and inhibited endothelin-1–induced contractility of perisinusoidal stellate cells. Finally, in 2 different in vivo models of cirrhosis and portal hypertension, transduction of livers with recombinant Ad.nNOS significantly reduced intrahepatic resistance and portal pressure. The data highlight the feasibility of gene transfer to diseased liver and hepatic cells and demonstrate the potential of a novel therapy for portal hypertension caused by cirrhosis.

E xcess or loss of body fat can be associated with infertility, suggesting that adequate fat mass is essential for proper reproductive function. Leptin is an adipocyte-derived hormone that is involved in the regulation of food intake and energy expenditure, and its synthesis and secretion are markedly increased in obesity. Short-term administration of leptin accelerates the onset of puberty in normal mice and corrects the sterility of leptin-deficient ob/ob mice. These findings suggest a role for leptin as an endocrine signal between fat depots and the reproductive axis, but the effect of hyperleptinemia on the initiation and maintenance of reproductive function has not been elucidated. To address this issue, we examined the reproductive phenotypes of female transgenic skinny mice with elevated plasma leptin concentrations comparable to those in obese subjects. With no apparent adipose tissue, female transgenic skinny mice exhibit accelerated puberty and intact fertility at younger ages followed by successful delivery of healthy pups. However, at older ages, they develop hypothalamic hypogonadism characterized by prolonged menstrual cycles, atrophic ovary, reduced hypothalamic gonadotropin releasing hormone contents, and poor pituitary luteinizing hormone secretion. This study has demonstrated for the first time to our knowledge that accelerated puberty and late-onset hypothalamic hypogonadism are associated with chronic hyperleptinemia, thereby leading to a better understanding of the pathophysiological and therapeutic implication of leptin.

T he first and the rate-limiting enzyme of heme biosynthesis is δ-aminolevulinate synthase (ALAS), which is localized in mitochondria. There are 2 tissue-specific isoforms of ALAS, erythroid-specific (ALAS-E) and nonspecific ALAS (ALAS-N). To identify possible mitochondrial factors that modulate ALAS-E function, we screened a human bone marrow cDNA library, using the mitochondrial form of human ALAS-E as a bait protein in the yeast 2-hybrid system. Our screening led to the isolation of the β subunit of human ATP-specific succinyl CoA synthetase (SCS-βA). Using transient expression and coimmunoprecipitation, we verified that mitochodrially expressed SCS-βA associates specifically with ALAS-E and not with ALAS-N. Furthermore, the ALAS-E mutants R411C and M426V associated with SCS-βA, but the D190V mutant did not. Because the D190V mutant was identified in a patient with pyridoxine-refractory X-linked sideroblastic anemia, our findings suggest that appropriate association of SCS-βA and ALAS-E promotes efficient use of succinyl CoA by ALAS-E or helps translocate ALAS-E into mitochondria.

A topic individuals are predisposed to mounting vigorous Th2-type immune responses to environmental allergens. To determine the factors responsible, animal models that closely mimic natural modes of allergen exposure should prove most informative. Therefore, we investigated the role of IL-4, a known Th2-promoting cytokine, in generation of Th2 responses after exposure of either the skin or airway to soluble protein. Compared with wild-type (WT) mice, IL-4–deficient (IL-4^–/–) mice showed markedly impaired Th2 activation after primary exposure to inhaled ovalbumin (OVA), with decreased OVA-specific IgG1 and IgE, and significantly fewer eosinophils in bronchoalveolar lavage (BAL) fluid after airway challenge. In contrast, IL-4^–/– mice initially exposed to epicutaneous (e.c.) OVA mounted Th2 responses equivalent to responses in WT mice, with high numbers of eosinophils in BAL fluid. Because Th2 responses were not induced by e.c. OVA exposure in Stat6^–/– mice (mice lacking signal transducer and activator of transcription 6), the role of IL-13 was tested. In vivo depletion of IL-13 prevented Th2 responses induced by e.c. OVA exposure in IL-4^–/– mice. These data demonstrate a marked difference in the IL-4 dependence of Th2 responses generated at two anatomic sites of natural allergen encounter and identify the skin as a particularly potent site for Th2 sensitization.

E ffective therapeutic interventions and clinical care of adults infected with HIV-1 require an understanding of factors that influence time of response to antiretroviral therapy. We have studied a cohort of 118 HIV-1–infected subjects naive to antiretroviral therapy and have correlated the time of response to treatment with a series of virological and immunological measures, including levels of viral load in blood and lymph node, percent of CD4 T cells in lymph nodes, and CD4 T-cell count in blood at study entry. Suppression of viremia below the limit of detection, 50 HIV-1 RNA copies/mL of plasma, served as a benchmark for a successful virological response. We employed these correlations to predict the length of treatment required to attain a virological response in each patient. Baseline plasma viremia emerged as the factor most tightly correlated with the duration of treatment required, allowing us to estimate the required time as a function of this one measure.

I n this study we have examined the mechanism of platelet aggregation under physiological flow conditions using an in vitro flow-based platelet aggregation assay and an in vivo rat thrombosis model. Our studies demonstrate an unexpected complexity to the platelet aggregation process in which platelets in flowing blood continuously tether, translocate, and/or detach from the luminal surface of a growing platelet thrombus at both arterial and venous shear rates. Studies of platelets congenitally deficient in von Willebrand factor (vWf) or integrin α_IIbβ₃ demonstrated a key role for platelet vWf in mediating platelet tethering and translocation, whereas integrin α_IIbβ₃ mediated cell arrest. Platelet aggregation under flow appears to be a multistep process involving: (a) exposure of vWf on the surface of immobilized platelets; (b) a reversible phase of platelet aggregation mediated by the binding of GPIbα on the surface of free-flowing platelets to vWf on the surface of immobilized platelets; and (c) an irreversible phase of aggregation dependent on integrin α_IIbβ₃. Studies of platelet thrombus formation in vivo demonstrate that this multistep adhesion mechanism is indispensable for platelet aggregation in arterioles and also appears to promote platelet aggregate formation in venules. Together, our studies demonstrate an important role for platelet vWf in initiating the platelet aggregation process under flow and challenge the currently accepted view that the vWf-GPIbα interaction is exclusively involved in initiating platelet aggregation at elevated shear rates.

G enetic factors are believed to influence the development of arterial thromboses. Because integrin α_IIbβ₃ plays a crucial role in thrombus formation, we analyzed receptor adhesive properties using Chinese hamster ovary and human kidney embryonal 293 cells overexpressing the Pl^A1 or Pl^A2 polymorphic forms of α_IIbβ₃. Soluble fibrinogen binding was no different between Pl^A1 and Pl^A2 cells, either in a resting state or when α_IIbβ₃ was activated with anti-LIBS6. Pl^A1 and Pl^A2 cells bound equivalently to immobilized fibronectin. In contrast, significantly more Pl^A2 cells bound to immobilized fibrinogen in an α_IIbβ₃-dependent manner than did Pl^A1 cells. Disruption of the actin cytoskeleton by cytochalasin D abolished the increased binding of Pl^A2 cells. Compared with Pl^A1 cells, Pl^A2 cells exhibited a greater extent of polymerized actin and cell spreading, enhanced tyrosine phosphorylation of pp125^FAK, and greater fibrin clot retraction. These adhesion differences appear to depend on a signaling mechanism sensitive to receptor occupancy. Thus, the Pl^A2 polymorphism altered integrin-mediated functions of adhesion, spreading, actin cytoskeleton rearrangement, and clot retraction.

W e performed genetic immunization of outbred NMRI mice, using a cDNA encoding the human thyrotropin receptor (TSHr). All mice produced antibodies capable of recognizing the recombinant receptor expressed at the surface of stably transfected Chinese hamster ovary (CHO) cells, and sera from most of the immunized mice blocked TSH-dependent stimulation of cAMP accumulation in cells expressing the TSHr. Five out of 29 female mice showed sign of hyperthyroidism including elevated total T4 and suppressed TSH levels. The serum of these mice contained thyroid-stimulating activity, as measured in a classic assay using CHO cells expressing recombinant TSHr. In contrast, only 1 male out of 30 had moderately elevated serum total T4 with undetectable TSH values. The hyperthyroid animals had goiters with extensive lymphocytic infiltration, characteristic of a Th2 immune response. In addition, these animals displayed ocular signs reminiscent of Graves’ ophthalmopathy, including edema, deposit of amorphous material, and cellular infiltration of their extraocular muscles. Our results demonstrate that genetic immunization of outbred NMRI mice with the human TSHr provides the most convincing murine model of Graves’ disease available to date.

W e assessed the effect of modified antigen presenting cells (APCs) expressing high levels of Fas ligand (APC-FasL) on post-viral chronic inflammatory disease. FasL-deficient B6-gld/gld mice infected with murine cytomegalovirus (MCMV) cleared the virus from their lungs, kidneys, and livers within 2 weeks of infection. However, inflammation persisted in these organs for more than 8 weeks, with a chronically increased T-cell response to MCMV-infected APCs and production of autoantibodies. Administration of APC-AdFasL at 4 weeks suppressed this inflammation and diminished the T-cell response and autoantibody production. APC-AdFasL that had been transfected with ultraviolet-irradiated MCMV were more effective than uninfected APC-AdFasL in ameliorating the chronic inflammation. APC-AdFasL migrated preferentially to the spleen, where they triggered apoptosis of lymphocytes in the marginal zone of the spleen. These results confirm that Fas-mediated apoptosis is not required for clearance of virus, but is required for down-modulation of the virally induced chronic inflammatory response. This organwide effect of APC-AdFasL appears to be mediated by elimination of activated T lymphocytes in the spleen before their emigration to the target organs.

W e examined the effect on osteoclast formation of disrupting the prostaglandin G/H synthase genes PGHS-1 and-2. Prostaglandin E₂ (PGE₂) production was significantly reduced in marrow cultures from mice lacking PGHS-2 (PGHS-2^–/–) compared with wild-type (PGHS-2^+/+) cultures. Osteoclast formation, whether stimulated by 1,25-dihydroxyvitamin D₃ (1,25-D) or by parathyroid hormone (PTH), was reduced by 60–70% in PGHS-2^–/– cultures relative to wild-type cultures, an effect that could be reversed by providing exogenous PGE₂. Cultures from heterozygous mice showed an intermediate response. PGHS inhibitors caused a similar drop in osteoclast formation in wild-type cultures. Co-culture experiments showed that supporting osteoblasts, rather than osteoclast precursors, accounted for the blunted response to 1,25-D and PTH. This lack of response appeared to result from reduced expression of RANK ligand (RANKL) in osteoblasts. We cultured spleen cells with exogenous RANKL and found that osteoclast formation was 50% lower in PGHS-2^–/– than in wild-type cultures, apparently because the former cells expressed high levels of GM-CSF. Injection of PTH above the calvaria caused hypercalcemia in wild-type but not PGHS-2^–/– mice. Histological examination of bone from 5-week-old PGHS-2^–/– mice revealed no abnormalities. Mice lacking PGHS-1 were similar to wild-type mice in all of these parameters. These data suggest that PGHS-2 is not necessary for wild-type bone development but plays a critical role in bone resorption stimulated by 1,25-D and PTH.