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D Lo

Publications and source records attributed to D Lo.

At least 73 records · Page 4Linked to original sources
PubMed1997

RelB regulation of chemokine expression modulates local inflammation.

The resolution of acute inflammation is incompletely understood but presumably requires the elimination of both inflammatory cells and production of inflammatory cytokines. In the case of recruited bone-marrow-derived inflammatory cells such as granulocytes and macrophages, their short life span helps eliminate these cells and the cytokines they produce. By contrast, resident permanent cells such as fibroblasts require other mechanisms to stop the production of chemokines generated in response to inflammatory triggers such as lipopolysaccharide. Here we demonstrate that RelB is an important regulator of chemokine expression in fibroblasts, thereby playing a key role in the resolution of acute inflammation. Activation of normal fibroblasts by lipopolysaccharide induced a transient production of chemokines, closely followed by induction of RelB expression. However, stimulated RelB-/- fibroblasts exhibited dramatic persistent induction of seven chemokines (RANTES, MIP-1 alpha, MIP-1 beta, MIP-2, IP-10, JE/MCP-1, and KC/CINC). The persistent overexpression of chemokines correlated with increased NF- kappa B binding as well as with increased p50, p65/RelA, and I kappa B alpha expression. Transfection of RelB cDNA into RelB-deficient fibroblasts reversed the lipopolysaccharide-induced chemokine overexpression. In vivo, activated RelB-/- fibroblasts dramatically increased recruitment of granulocytes into tissues. In view of the apparent role of RelB in the resolution of acute inflammation in tissues and previous work showing a requirement for RelB in the initiation of immune responses through the differentiation of antigen-presenting cells, RelB may be an important factor regulating the transition from innate to adaptive immunity.

Animals↗
PubMed1996

Unopposed positive selection and autoreactivity in mice expressing class II MHC only on thymic cortex.

The normal development of T cells in the thymus requires both positive and negative selection. During positive selection, thymocytes mature only if their T-cell receptors react with some specificity to host major histocompatibility complex (MHC) and host peptides. During negative selection, thymocytes die if their T-cell receptors react with too high an affinity to the presenting cell, self MHC, and peptides to which they are exposed. These two processes are important for the development of the T-cell repertoire and the acquisition of self-tolerance, but their precise location and temporal relationship are not known. We have used the keratin 14 (K14) promoter to re-express a class II MHC antigen (I-Ab) in class II-negative mice. The transgenic I-A molecule is expressed only on thymic cortical epithelium; thymic medullary epithelium and bone-marrow-derived cells are I-A negative. CD4+ cells are positively selected in K14 mice, but clonal deletion does not ocur in K14 mice or in relB-negative mice, which lack a thymic medulla. The K14 CD4 cells are autoreactive, as they proliferate extensively to and specifically lyse I-Ab-positive target cells. These autoreactive cells make up 5% of the peripheral CD4 T cells, providing and estimate of the minimal frequency of positively selected cells that must subsequently undergo negative selection for self-tolerance to be preserved. Thus positive and negative selection occur in anatomically distinct sites.

Animals↗
PubMed1996

CD8(+) T cell-mediated spontaneous diabetes in neonatal mice.

Transgenic mice that express the influenza virus hemagglutinin (HA) on pancreatic islet beta cells (ins-HA) demonstrate tolerance of HA even after immunization with influenza virus. Surprisingly, when Ins-HA mice were mated with a transgenic mouse expressing a TCR specific for an epitope of HA that is restricted by MHC class I H-2Kd (Clone-4 TCR), the resulting double transgenic (Ins-HA x Clone-4 TCR)F1 neonates developed spontaneous autoimmune diabetes immediately after birth and died within 10 days. This represents a unique situation in which all safeguards within the immune system that normally maintain tolerance of self-antigens in the neonate are insufficient.

Animals↗
PubMed1996

Animal models of human disease. Transgenic and knockout models of autoimmunity: Building a better disease?

The development of transgenic and knockout technologies has driven an explosion in new animal models of disease. These engineered diseases are a departure from previous animal models in that pathological syndromes are created from a priori assumptions about how disease pathogenesis could develop. Such models have been useful in providing new information on the functions of effector molecules such as cytokines, and in following the behavior of lymphocytes in vivo. However, the contrived nature of the systems might generate false information, unless validated by careful reference to human disease and spontaneous disease in other animal models.

Animals↗
PubMed1995

lambda 5, but not mu, is required for B cell maturation in a unique gamma 2b transgenic mouse line.

gamma 2b transgenic mice have a severe B cell defect, apparently caused by strong feedback inhibition of endogenous H-gene rearrangement coupled with an inability of gamma 2b to provide the survival/maturation functions of mu. A unique gamma 2b transgenic line, named the C line, was found to permit B cell development. When the C line is crossed with a mu-membrane knockout line, gamma 2b+ B cells develop in the homozygous knockout. In contrast, a transgenic line representative of all the other gamma 2b lines is completely B cell deficient when mu-mem is deleted. Strikingly, the C phenotype is dominant in C x other gamma 2b transgenic line crosses. There is no evidence for higher gamma 2b transgene expression or other position effects on the transgene in the C mouse. The sequences of the three gamma 2b transgene copies in the C line are identical to that of the original transgene. These results have led to the conclusion that in the C line the transgene integration constitutively induces a gene whose expression can replace mu. To more clearly delineate the stage at which the altered phenotype of the C line is expressed, C mice were crossed onto a lambda 5 knockout background. In the absence of lambda 5, the C line produces no B cells. Since it was also found that gamma 2b can associate with the surrogate light chain (sL; lambda 5/Vpre-B), the crosses between C line gamma 2b mice and lambda 5 knockout mice suggest that gamma 2b/sL is required for B cell maturation in this mouse line. Thus, gamma 2b alone is unable to replace mu for pre-B cell survival/maturation; however, in combination with an unknown factor and the sL, gamma 2b can provide these nurturing functions.

Alleles↗
PubMed1995

Expression of relB is required for the development of thymic medulla and dendritic cells.

Dendritic cells (DC) derived from bone marrow are critical in the function of the immune system, for they are the primary antigen-presenting cells in the activation of T-lymphocyte response. Their differentiation from precursor cells has not been defined at a molecular level, but recent studies have shown an association between expression of the relB subunit of the NF-kappa B complex and the presence of DC in specific regions of normal unstimulated lymphoid tissues. Here we show that relB expression also correlates with differentiation of DC in autoimmune infiltrates in situ, and that a mutation disrupting the relB gene results in mice with impaired antigen-presenting cell function, and a syndrome of excess production of granulocytes and macrophages. Thymic UEA-1+ medullary epithelial cells from normal mice show striking similarities to DC and, interestingly, these cells are also absent in relB mutant mice. Taken together, these results suggest that relB is critical in the coordinated activation of genes necessary for the differentiation of two unrelated but phenotypically similar cells (DC and thymic UEA-1+ medullary epithelial cells) and is therefore a candidate for a gene determining lineage commitment in the immune system.

Amino Acid Sequence↗
PubMed1995

Biaxial strain analysis of the porcine aortic valve.

The function of a bioprosthetic heart valve is determined largely by the material properties of the valve cusps. The mechanics of natural and bioprosthetic valve cusps have been studied extensively using uniaxial tensile testing. This type of testing, however, does not duplicate the natural biaxial loading condition. Whole-valve biaxial testing therefore is preferred. The objective of the present study was to investigate the heterogeneity of the valve cusps by mapping out the regional variability of the biaxial strain versus pressure relationship. Whole porcine aortic valves were mounted horizontally, submerged in physiologic saline solution at 37 degrees C, and pressurized in the range of 0 to 130 mm Hg of pressure. The ventricular side of the cusps were marked with black dots and the three-dimensional position of these dots was recorded together with the aortic pressure. By calculating the distance between the dots in the radial and circumferential directions in different regions, the local strain versus pressure relationship was determined. The results showed that the valve cusp material strained by 23% +/- 0.8% in the radial direction and 10.0% +/- 0.5% in the circumferential direction before lock-up. It was also found that while the valve cusp was highly anisotropic in the central region, the basal region was relatively isotropic, and the cusp as a whole was asymmetrical in its distensibility.

Animals↗
PubMed1995

Potent effects of low levels of MHC class II-associated invariant chain on CD4+ T cell development.

Invariant chain (Ii)-negative mice exhibit defects in MHC class II assembly and transport that results in reduced levels of surface class II, altered antigen presentation, and inefficient positive selection of CD4+ T cells. Many CD4+ T cells that do mature in Ii-negative mice express a cell surface phenotype consistent with aberrant positive selection or peripheral activation. Reconstitution of these mice with low levels of either the p31 or p41 form of Ii does not restore transport of the bulk of class II or class II surface expression, but surprisingly does restore positive selection as measured by numbers and surface phenotype of CD4+ T cells. Thus, an Ii-dependent process, independent of effects on class II surface density, appears to be required for normal positive selection of CD4+ T cells.

Animals↗
PubMed1995

Transgenic mice expressing MHC class II molecules with truncated A beta cytoplasmic domains reveal signaling-independent defects in antigen presentation.

The thymic development and peripheral activation of CD4+ T cells are critically dependent upon interactions with MHC class II molecules on the surface of antigen presenting cells (APC). In vitro studies involving transfection of cell lines with mutant MHC molecules have demonstrated that the cytoplasmic domains of class II molecules can be required for efficient antigen presentation. To address the role of class II cytoplasmic domains in physiological, non-transformed APC and in vivo immune responses, we have generated transgenic mice which express only truncated class II A beta molecules lacking the 13 membrane distal residues. In vivo, CD4+ T cell development and immune responses to conventional protein antigens, parasitic infections and skin grafts were indistinguishable between control and transgenic mice. Nevertheless, in vitro, APC from transgenic mice poorly stimulate T cell hybridomas and wild-type in vivo-primed T cells. Neither class II-mediated induction of B7-1 expression nor homotypic aggregation were diminished in transgenic B cells, suggesting that both cAMP and tyrosine kinase signaling pathways remain intact despite truncation of the A beta cytoplasmic domain. Furthermore, chemically-fixed cells from transgenic animals are impaired in their antigen presenting capacity. Thus, in contrast to previous studies with cell lines transfected with truncated class II molecules, these results suggest that signaling-independent mechanisms account for the defective in vitro antigen presenting capacity of physiological APC expressing truncated A beta proteins.

Amino Acid Sequence↗
PubMed1995

Clinical characteristics of subjects with a missense mutation in glucokinase.

The clinical characteristics of subjects with a missense glucokinase mutation, gly299-->arg, were studied in a large pedigree, BX, initially characterized by some members having Maturity Onset Diabetes of the Young (MODY). Glucose tolerance, beta cell function and insulin sensitivity were measured with Homeostasis Model Assessment (HOMA) and with a 'Continuous Infusion of Glucose with Model Assessment' (CIGMA) test. Diabetic complications were clinically assessed. Subjects with glucokinase gly299-->arg were the same age, height, and obesity as the subjects without the mutation. Diabetes was usually asymptomatic at diagnosis and was treated with diet alone in 15 of the 18 subjects. Five of the 11 adult females had been diagnosed when they developed gestational diabetes. The fasting plasma glucose concentrations at the time of study were 4.3-12.6 mmol l-1, with the higher levels being in the more obese (p < 0.05) and in the older subjects (p < 0.05). In subjects with the mutation, beta cell function was impaired, being geometric mean 63% (normal-100%) compared with 126% in the subjects without the mutation (p < 0.001) measured by HOMA and in a subset assessed by CIGMA 59% and 127% (p < 0.01), respectively. There was no difference in fasting insulin concentrations, insulin sensitivity, lipid concentrations or blood pressure between the groups. The haemoglobin A1c was raised (mean 6.5% compared with 5.5% in the subjects without the mutation), but microvascular and macrovascular complications were uncommon. The subjects with the mutation did not have microalbuminuria but had an impaired vibration perception threshold compared with subjects without the mutation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Regulation of CD4 T cell reactivity to self and non-self.

While the thymus may be effective in inducing tolerance to lymphoid associated antigens, it is not as efficient in deleting T cells reactive to peripheral tissue specific antigens. Therefore, to maintain self tolerance to peripheral tissues, post-thymic mechanisms must be invoked. One important way to prevent autoimmune pathology mediated by autoreactive CD4 T cells is the diversion of clones to regulatory Th2 effector cells. However, many different factors contribute in vivo to the decision of stimulated CD4 T cells to develop into Th1 versus Th2 cells. For example, T cell signaling pathways may influence the types of cytokines produced by naive T cells, and studies have provided evidence for a genetic polymorphism among common mouse strains that can significantly influence the early cytokine production in stimulated naive CD4 T cells. The allele carried by the BALB/c strain promotes IL-4 production, and consequently provides resistance to autoimmune diabetes in our transgenic mouse model. In addition, antigen presenting cells can influence the development of stimulated CD4 T cells in part through the production of cytokines such as IL-12. The absorption of IL-12 in vivo can permit the expansion of Th2 type effector cells, and this phenomenon will also protect mice from autoimmunity. Finally, the relative potency of various class II positive antigen presenting cell types can influence the development of autoreactive T cells, with dendritic cells apparently being the strongest stimulator of Th1 responses. Consistent with this notion, a relB knockout mouse, which is missing dendritic cells, appears to drive Th2 development even in response to viral infection. In sum, these various influences over the Th1/Th2 decision in vivo may provide new targets for immunotherapy of autoimmune diseases.

Animals↗
PubMed1994

B7 expression on thymic medullary epithelium correlates with epithelium-mediated deletion of V beta 5+ thymocytes.

Recent evidence suggests that I-E+ thymic epithelium, especially medullary epithelium, can induce partial deletion of superantigen-reactive T cells expressing TcR V beta 5, V beta 11, and V beta 17. To seek further information on this issue, we constructed bone marrow chimeras in which MHC class II I-E is expressed on thymic epithelial cells at various levels and locations; the chimeras were reconstituted with stem cells from TcR V beta 5 transgenic mice. Intrathymic deletion of V beta 5 T cells was restricted to relatively mature T cells (expressing high TcR levels), and the degree of deletion correlated with the density of I-E expression in the thymic medulla rather than in the thymic cortex; selective I-E expression in medullary epithelium caused prominent deletion. Interestingly, immunostaining of normal and chimeric mice revealed that expression of B7 (the ligand for CD28) is largely restricted to a subset of medullary epithelial cells; these cells are I-E+ and co-express a specific carbohydrate bound by the lectin UEA-1. B7 expression was lower in thymuses of class II-deficient mice (A beta b-/-) and T-cell-deficient mice (SCID), suggesting that B7 expression is up-regulated during CD4+ thymocyte selection. In support of this idea, B7 expression in the thymus was restored to a normal level in bone marrow reconstituted SCID mice. Because B7 expression correlates with a costimulatory signal for T cells, selective expression of B7 and related antigens on I-E+ medullary epithelium may explain why these cells play a more prominent role in V beta deletion than cortical epithelium.

Animals↗
PubMed1994

On the various manifestations of spontaneous autoimmune diabetes in rodent models.

Autoimmune (type 1) diabetes mellitus in mouse, rat, and humans shares several features, including T lymphocyte infiltration into pancreatic islets and a dependence on permissive class II major histocompatibility complex (MHC) alleles. We report here on an experimental model involving mice that express influenza hemagglutinin (HA) under the control of the insulin promoter and, at the same time, a transgenic class II MHC-restricted T cell receptor (TcR) specific for an HA peptide. These mice spontaneously develop islet infiltrates resembling those found in NOD mice and most animals become diabetic within 8 weeks of age. Because of the availability of a clonotypic TcR antibody, we can be confident that the Ins-HA transgene does not induce any measurable alterations in the vast majority of T cells with the transgenic TcR in primary and secondary lymphoid organs. Continuous export of large numbers of HA-specific lymphocytes from the thymus was not required for the manifestation of the disease since mice thymectomized at 3 days after birth still developed the disease albeit with smaller infiltrates.

Animals↗
PubMed1994

A role for non-MHC genetic polymorphism in susceptibility to spontaneous autoimmunity.

Peripheral immunological tolerance is traditionally explained by mechanisms for deletion or inactivation of autoreactive T cell clones. Using an autoimmune disease model combining transgenic mice expressing a well-defined antigen, influenza hemagglutinin (HA), on islet beta cells (Ins-HA), and a T cell receptor transgene (TCR-HNT) specific for a class II-restricted HA peptide, we demonstrate that the conventional assumptions do not apply to this in vivo situation. Double transgenic mice displayed either resistance or susceptibility to spontaneous autoimmune disease, depending on genetic contributions from either of two common inbred mouse strains, BALB/c or B10.D2. Functional studies on autoreactive CD4+ T cells from resistant mice showed that, contrary to expectations, neither clonal anergy, clonal deletion, nor receptor desensitization was induced; rather, there was a non-MHC-encoded predisposition toward differentiation to a nonpathogenic effector (Th2 versus Th1) phenotype. T cells from resistant double transgenic mice showed evidence for prior activation by antigen, suggesting that disease may be actively suppressed by autoreactive Th2 cells. These findings shed light on functional aspects of genetically determined susceptibility to autoimmunity, and should lead to new therapeutic approaches aimed at controlling the differentiation of autoreactive CD4+ effector T cells in vivo.

Animals↗
PubMed1994

Discrimination between thymic epithelial cells and peripheral antigen-presenting cells in the induction of immature T cell differentiation.

During their intrathymic migration, immature CD4+ CD8+ thymocytes that express a TCR able to recognize the expressed MHC molecules are positively selected, i.e., complete their differentiation program and become mature T cells. Using the immature CD4+CD8+ T cell line DPK, which can be induced to differentiate in culture, we show here that a subset of isolated thymic epithelial cells, but not peripheral antigen-presenting cells, can induce differentiation, suggesting a unique function of these cells in T cell development. In addition, analysis of activation markers induced by thymic epithelial cells versus specific antigen gives the first direct evidence that positive selection is associated with low level cell activation. In contrast with strict affinity-avidity models of thymic selection, we propose that a specialized antigen-presenting cell environment is an essential contributor to TCR-mediated differentiation in the thymus.

Animals↗