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D Lo

Publications and source records attributed to D Lo.

At least 73 records · Page 4Linked to original sources
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↗
PubMed1994

The detection of the c-myc and ras oncogenes in nasopharyngeal carcinoma by immunohistochemistry.

Forty-one paraffin embedded specimens of primary nasopharyngeal carcinoma (NPC) were examined to investigate the expression of c-myc and ras oncogenes. Sections were stained with the monoclonal antibodies myc 1-9E10 or ras Y13-259 and binding was detected using the ABC method. The intensity of staining for each tumour was assessed as nil, moderate or intense. The results indicated that 9 (22%) had intense staining for the c-myc oncogene, 28 (68%) had moderate staining and only 4 (10%) showed no staining. For the ras oncogene, 8 (19%) had intense staining, 22 (54%) moderate staining and 11 (27%) showed no staining. The patient's clinical data indicated no correlation between the expression of either c-myc or ras p21 and age, sex, smoking, tumour stage, antibody titre to EBV, or family history. No correlation was found between ras p21 expression and survival; however, overexpression of the c-myc oncogene correlated with a poor prognosis (p < 0.05). This study is consistent with investigations demonstrating that c-myc expression correlates with poor survival in head and neck tumours.

Adult↗
PubMed1993

Immunoglobulin gamma 2b transgenes inhibit heavy chain gene rearrangement, but cannot promote B cell development.

Transgenic mice with a gamma 2b transgene were produced to investigate whether gamma 2b can replace mu in the development of B lymphocytes. Transgenic gamma 2b is present on the surface of B cells. Young transgenic mice have a dramatic decrease in B cell numbers, however, older mice have almost normal B cell numbers. Strikingly, all gamma 2b-expressing B cells in the spleen also express mu. The same is true for mice with a hybrid transgene in which the mu transmembrane and intracytoplasmic sequences replace those of gamma 2b (gamma 2b-mumem). The B cell defect is not due to toxicity of gamma 2b since crosses between gamma 2b transgenic and mu transgenic mice have normal numbers of B cells. Presence of the gamma 2b transgene strongly enhances the feedback inhibition of endogenous heavy chain gene rearrangement. Light chain genes are expressed normally, and the early expression of transgenic light chains does not improve B cell maturation. When the endogenous mu locus is inactivated, B cells do not develop at all in gamma 2b transgenic mice. The data suggest that gamma 2b cannot replace mu in promoting the developmental maturation of B cells, but that it can cause feedback inhibition of heavy chain gene rearrangement. Thus, the signals for heavy chain feedback and B cell maturation appear to be different.

Animals↗
PubMed1993

Clonal deletion of V beta 5+ T cells by transgenic I-E restricted to thymic medullary epithelium.

A variety of cell types expressing MHC class II molecules is known to function as APC in vitro. We employed the Ig kappa gene enhancer and promoter to target the class II E alpha gene, and thereby I-E, exclusively to B cells to address their APC function in vivo. Although transgenic I-E was expressed on B lymphocytes, we unexpectedly obtained I-E on thymic medullary epithelium but not macrophages and at low frequency on dendritic cells. Using these transgenic mice, we constructed bone marrow irradiation chimeras with I-E expressed only on medullary epithelium, in order to determine the role of this cell type in tolerance by clonal deletion in the thymus. Although it is accepted that bm-derived cells play a primary role in deletion, and thymic epithelium can delete clones to a lesser degree, the role of cortical vs medullary thymic epithelium has not been directly dissected. We demonstrate that medullary epithelium alone can tolerize by partial deletion of I-E-reactive V beta 5+ T cells. These results indicate a role for medullary epithelium in deletion during the later stages of thymic development, and support the notion that positive and negative selection of developing T cells can occur in distinct temporal and anatomic compartments.

Animals↗
PubMed1993

Interference with major histocompatibility complex class II-restricted antigen presentation in the brain by herpes simplex virus type 1: a possible mechanism of evasion of the immune response.

Host survival of herpes simplex virus type 1 (HSV-1) infection depends on the establishment of latent infections in both peripheral and central nervous systems. Strains of HSV-1 that are successful in escaping the immune response produce a lethal infection. We now report a possible mechanism of immune response evasion used by HSV-1. After intraocular inoculation of mice, HSV-1 strain F established a latent infection in the brain, whereas strain KOS did not. The immune response to HSV-1 infection (strains KOS and F) in the brain was characterized by induction of major histocompatibility complex class II expression and recruitment of CD4+ and CD8+ cells to highly restricted sites of intracerebral viral infection. Major histocompatibility complex class II antigen expression was primarily intracellular in strain KOS infection centers and at the cell surface in strain F infection centers. We propose that major histocompatibility complex class II-restricted viral-antigen presentation to T cells is interrupted during strain KOS infections, thereby allowing KOS infection to evade T-cell-mediated events that would normally protect the host from a lethal infection. Immunocompromised mice (athymic or irradiate mice) could not survive strain F infections; however, latent F infections were established in irradiated mice reconstituted with naive lymph node and spleen cells. These data suggest that class II-restricted presentation of viral antigens is required for the control of HSV-1 infections in the nervous system.

Animals↗
PubMed1993

Antigen-presenting cells in adoptively transferred and spontaneous autoimmune diabetes.

Histological techniques were used to identify antigen-presenting cells (APC) in adoptively transferred diabetes in NOD mice and Ins-HA transgenic mice, and in spontaneously diabetic NOD mice. In adoptively transferred disease, CD4+ T cells and F4/80+ macrophages dominated early infiltrates. By contrast, in spontaneously developing diabetes in NOD mice, lymphocytic infiltrates appeared to be well organized around a network of VCAM-1+ NLDC-145+ ICAM-1+ dendritic cells. Thus, the primary APC spontaneous autoimmune disease appears to be the strongly stimulatory dendritic cell rather than the normally resident macrophage. Next, we used chimeric animals to demonstrate that insulitis and diabetes could occur even when responding T cells were unable to recognize islet-specific antigen directly on beta cells. Altogether, the results demonstrate that immune-mediated damage does not require direct contact between CD4+ T cells and beta cells. Moreover, despite the induction of ICAM-1, VCAM-1, and class II on vascular endothelium near islet infiltrates, these experiments show that recruitment of lymphocytes occurs even when antigen presentation is not possible on vascular endothelium.

Amino Acid Sequence↗
PubMed1993

Cryptococcus neoformans in tropical northern Australia: predominantly variant gattii with good outcomes.

BACKGROUND: Infection with Cryptococcus neoformans is common in the Northern Territory of Australia. Disease is life threatening and treatment is prolonged and often complicated by the need for surgery and difficulties with medical therapy. AIMS: To document incidence, demography, risk factors, clinical features and outcomes of infection and to determine differences between gattii and neoformans varieties. METHODS: Case records of all patients (n = 35) diagnosed with cryptococcal infection at the Royal Darwin Hospital between 1976 and 1992 were reviewed retrospectively. Current status of patients was ascertained. Variety identification of isolates was determined by growth in canavanine-glycine-bromthymol blue agar. RESULTS: Of the 35 patients, 23 had meningitis, ten had pneumonia, one had a dermal infection and one had fungaemia with no obvious focus. Twelve (52%) meningitis cases and two (20%) pneumonia cases had no predisposing disease. Thirteen (57%) meningitis cases had concomitant pulmonary cryptococcosis. Twenty-nine patients with Aboriginal and six were Caucasian, with a relative risk for Aboriginals compared with non-Aboriginals of 20.6 (95% CI 8.6-49.5). Arnhemland was the commonest location of infection, with an annual incidence in Aboriginals of 0.14/1000. Fourteen (78%) of 18 isolates tested were C. neoformans var. gattii. Management was characterised by the frequent need for adjunctive surgery and prolonged or repeat courses of systemic antifungal therapy. Despite this, long-term outcomes are encouraging with a mortality of 14% overall and 9% in meningitis patients. The river red gum (Eucalyptus camaldulensis) has a limited distribution in Arnhemland and ongoing studies are seeking alternative environmental sources of C. neoformans var. gattii.

Adolescent↗
PubMed1992

Two subsets of epithelial cells in the thymic medulla.

Information was sought on the features of epithelial cells in the murine thymic medulla. The expression of major histocompatibility complex (MHC) molecules on medullary epithelium was defined by light microscopy with the aid of bone marrow chimeras and MHC-transgenic mice. A proportion of medullary epithelial cells was found to show conspicuously high expression of conventional MHC (H-2) class I (K, D, L) and class II (I-A, I-E) molecules. These cells express a high density of the Y-Ae epitope, a complex of an E alpha peptide and I-Ab molecules found on typical bone marrow-derived cells. MHC+ medullary epithelial cells show limited expression of I-O molecules, a class of atypical nonpolymorphic MHC-encoded class II molecules present on B cells. Other medullary epithelial cells express a high density of I-O molecules but show little or no expression of typical MHC class I or II molecules. MHC and I-O expression thus appear to subdivide medullary epithelial cells into two phenotypically distinct subsets. This applies in adults. In the embryonic thymus most medullary epithelial cells express both types of molecules.

Animals↗
PubMed1992

Peripheral tolerance to an islet cell-specific hemagglutinin transgene affects both CD4+ and CD8+ T cells.

To study the basis for immunological tolerance of peripheral tissue-specific antigens, a transgenic mouse line was established that expresses the influenza hemagglutinin (HA) on pancreatic islet beta cells (Ins-HA transgenic mice). When followed up to 14 months of age, Ins-HA transgenic mice did not develop spontaneous autoimmune disease. Upon immunization with HA-expressing viruses, high titers of HA-specific circulating antibody were detected; however, T cell responses by both the T helper and T cytolytic compartment were markedly reduced as compared with transgene-negative littermates, and no evidence could be found for islet infiltrates. Adoptive transfer of histocompatible lymphocytes from transgene-negative mice plus virus into irradiated Ins-HA hosts resulted in islet inflammation dominated by CD4+ T cells, indicating that the HA antigen was accessible to activated T cells. These results suggest that T cells can be rendered tolerant of antigens expressed outside the thymus.

Amino Acid Sequence↗
PubMed1992

Among naive precursor cell subpopulations only progenitors of memory B cells originate germinal centers.

Immunization leads to the generation of both antibody-forming cells (AFC) and memory B cells which are thought to arise in germinal centers within lymphoid follicles. The findings that the precursors to memory B cells reside in the J11Dlo subpopulation of the spleens in non-immune mice and that this subpopulation is distinct from conventional AFC precursors, including CD5+ B cells, suggest that the precursors of germinal centers might also reside in the J11Dlo subpopulation. To test this hypothesis, SCID mice were repopulated with CD4+ carrier-primed T cells and T-depleted J11Dlo, J11Dhi or CD5+ B cells and immunized with a hapten-carrier conjugate. Only the J11Dlo population was enriched for cells that produced germinal centers. Thus, the subpopulation of precursors that generates memory B cells also originates germinal centers.

Animals↗