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Biomedical subjects

G Morahan

Publications and source records attributed to G Morahan.

At least 19 recordsLinked to original sources
PubMed2004

Deficient IL-12p70 secretion by dendritic cells based on IL12B promoter genotype.

Interleukin-12 (IL-12), a heterodimeric cytokine, is important in the generation of a Th1-biased immune response. Several polymorphisms have been described in IL12B, the gene encoding the p40 subunit of IL-12. A bi-allelic polymorphism within the IL12B promoter region has been reported to show association with diseases as diverse as severe childhood asthma and fatal cerebral malaria. In order to define the molecular basis for these disease associations, we investigated the secretion of IL-12 by human monocyte-derived dendritic cells. Homozygotes for the IL12B promoter polymorphism showed a 10-fold difference in median p70 secretion in response to CD40 ligation. Remarkably, this difference resulted from the inability of most allele 1 homozygotes to secrete heterodimeric IL-12. In contrast, most of the donors homozygous for allele 2 had detectable secretion. These findings are important for the understanding of the highly complex regulation of IL-12 secretion, and its consequent impact on disease susceptibility, in humans.

Asthma↗
PubMed2003

HLA genes associated with autoimmunity and progression to disease in type 1 diabetes.

Insulin dependent diabetes mellitus (type I DM) is caused by an autoimmune process which culminates in destruction of pancreatic beta cells with resultant loss of insulin production. Preceding the clinical diagnosis of type I DM is a preclinical stage characterized by autoantibodies to insulin, glutamic acid decarboxylase (GAD) and a tyrosine phosphatase-like molecule (IA-2). We have studied both HLA class I and class 2 allele distributions in diabetic probands and autoantibody positive individuals in members of 452 families recruited for the Australian type I diabetes DNA repository. The results demonstrate that progression to autoimmunity as measured by the appearance of autoantibodies is strongly associated with the class 2 alleles DRB1*03 and DRB*04 and with DRB1*03/04 heterozygosity. In contrast, the progression to clinical disease appears associated with class I alleles A24, A30 and B18 while A1, A28, B14 and B56 appear negatively associated. The class 2 alleles appear to have a minimal role in the progression from autoantibody positivity to clinical disease. These results are consistent with the view that CD4+ T cells responding to peptides in the context of class 2 molecules are responsible for initiating autoantibody production, while the destruction of islet cells leading to clinical expression of the disease is the function of CD8+ T cells recognizing relevant peptides in the context of class I molecules.

Alleles↗
PubMed2003

Definition of polymorphisms in the gene encoding the interleukin-12 receptor B1 subunit: testing linkage disequilibrium with Type I diabetes susceptibility.

The cytokine interleukin (IL)-12 is bound by a heterodimeric receptor and mediates a range of immunological activities, in particular, favouring the development of uncommitted T cells to the Th1 phenotype. Genes encoding elements of the IL-12 pathway are therefore good candidates for mediating susceptibility or resistance to a range of immune disorders, including Type I diabetes. We made a systematic search for variants in the human gene encoding the low-affinity IL-12 receptor, IL12RB1. Four single-nucleotide polymorphisms and two microsatellite polymorphisms were defined. We also tested these IL12RB1 alleles for involvement in Type I diabetes susceptibility, testing 131 families. Although suggestive evidence for linkage to a susceptibility gene was found, none of the IL12RB1 variants we defined demonstrated preferential transmission in these families.

Diabetes Mellitus, Type 1↗
PubMed2002

Polymorphisms in the Il12b gene affect structure and expression of IL-12 in NOD and other autoimmune-prone mouse strains.

Interleukin (Il)-12 is a heterodimeric cytokine composed of 35 and 40 kD chains that plays a key role in the induction of Th1 cells, a T cell subset involved in many autoimmune diseases. We report here the cDNA sequence encoding the IL-12 p40 subunit from the autoimmune-prone non-obese diabetic (NOD) mouse, which spontaneously develops type 1 diabetes. Compared with the C57BL/6 sequence, there are two base changes that lead to amino acid replacements. Other autoimmune-prone strains, but not the diabetes-resistant NOR strain, share the same allele as NOD. We found both trans- and cis- allele-dependent effects on levels of basal and induced IL-12p40 expression. Furthermore, we show that one of these changes results in a structural change in the p40 molecule, as evidenced by the failure of a monoclonal antibody to bind NOD IL-12. These findings have implications for the predisposition to autoimmune responses in NOD and other autoimmune-prone mouse strains.

Animals↗
PubMed2002

A promoter polymorphism in the gene encoding interleukin-12 p40 (IL12B) is associated with mortality from cerebral malaria and with reduced nitric oxide production.

Interleukin-12 (IL-12) is an important regulatory cytokine in infection and immunity. Administration of IL-12 may reduce complications of severe malaria in rodents. Polymorphisms in IL12B, the gene encoding the IL-12 p40 subunit, influence the secretion of IL-12 and susceptibility to Type 1 diabetes. We therefore investigated whether IL12B polymorphisms may affect the outcome of severe malaria. Homozygosity for a polymorphism in the IL12B promoter was associated with increased mortality in Tanzanian children having cerebral malaria but not in Kenyan children with severe malaria. Furthermore, homozygotes for the IL12B promotor polymorphism had decreased production of nitric oxide, which is in part regulated by IL-12 activity. These studies suggest that IL12B polymorphisms, via regulation of IL-12 production, may influence the outcome of malaria infection in at least one African population.

Animals↗
PubMed2001

Identification of a T1D susceptibility gene.

It is not known what causes type 1 diabetes (T1D) which affects over 1 million people in the U.S. alone. Each year, 30,000 young people in the U.S. develop this disease and depend on insulin injections thereafter. Because of the huge cost to the individual, the family, and to society in increased health care costs, it is important to find what makes these people susceptible. The disease process itself is clear: the individual's immune system, the T lymphocytes in particular, attack and destroy the body's insulin-producing cells. But how and why this autoimmune process starts or proceeds unregulated is still not known.

Animals↗
PubMed2001

Linkage disequilibrium of a type 1 diabetes susceptibility locus with a regulatory IL12B allele.

Type 1 diabetes (T1D; or insulin-dependent diabetes mellitus, IDDM) is an autoimmune disease with both genetic and environmental components. In addition to the human leukocyte antigen (HLA) complex, the single major genetic contributor of susceptibility, an unknown number of other unidentified genes are required to mediate disease. Although many loci conferring susceptibility to T1D have been mapped, their identification has proven problematic due to the complex nature of this disease. Our strategy for finding T1D susceptibility genes has been to test for human homologues of loci implicated in diabetes-prone NOD (non-obese diabetic) mice, together with application of biologically relevant stratification methods. We report here a new susceptibility locus, IDDM18, located near the interleukin-12 (IL-12)p40 gene, IL12B. Significant bias in transmission of IL12B alleles was observed in affected sibpairs and was confirmed in an independent cohort of simplex families. A single base change in the 3' UTR showed strong linkage disequilibrium with the T1D susceptibility locus. The IL12B 3' UTR alleles showed different levels of expression in cell lines. Variation in IL-12p40 production may influence T-cell responses crucial for either mediating or protecting against this and other autoimmune diseases.

3' Untranslated Regions↗
PubMed2001

Effect of localized cytokine dysregulation: accelerated rejection of IL-2-expressing skin grafts.

Transgenic mice were created in which a sheep keratin promoter directed the expression of IL-2 into the dermis. These KIL-2 transgenic mice were used to investigate the effects of localized IL-2 dysregulation on immune responses. Peripheral tolerance to skin antigens was not broken by in situ IL-2 expression because syngeneic KIL-2 skin grafts were not rejected. However, MHC Class I-disparate skin grafts from KIL-2 donors were rejected faster (median survival time (MST) 12 days) than grafts of non-transgenic littermate skin (MST 18 days). In contrast, the kinetics of KIL-2 H-Y-disparate skin graft rejection (MST 14 days) did not differ significantly from controls (MST 16 days), suggesting that upregulation of IL-2 at the effector site could affect CD4+ T cell- independent, but not CD4+ T cell-dependent, responses. No effect on rejection kinetics was observed when wild type allogeneic skin was grafted onto transgenic mice that expressed bcl2 constitutively in their lymphocytes (MST of 14 days, both sets), indicating that this was not simply due to increased longevity of T cells within the IL-2 expressing graft. We therefore suggest that aberrant expression of IL-2 can accelerate helper-independent CD8+ T cell responses by increasing proliferation and/or differentiation of cytolytic T cells at the effector site.

Animals↗
PubMed2001

A locus affecting immunoglobulin isotype selection (Igis1) maps to the MHC region in C57BL, BALB/c and NOD mice.

We have previously shown that H2b mice with B10 or BALB genetic backgrounds have higher basal levels of IgG2a than H2k and H2d congenic strains and, hence, have low IgG1/IgG2a ratios, which is consistent with a T1 cytokine milieu. The phenotypic marker of the high IgG2a levels, denoted immunoglobulin isotype-1 (Igis1) was provisionally mapped telomeric of IEbeta using MHC recombinant mice. In addition, data from B10.A(2R), B10.A(1R) and B10.A(18R) mice indicated that Igis1 may lie in a 27 kb region between G7b (Sm-X5) and G7c. In the present study we confirm that Igis1 is in the H2 region using BALB and B10 congenic F2 mice. H2bb F2 mice had higher IgG2a levels than the H2dd parental strains. H2bd F1 and F2 mice on the B10 background produced IgG2a levels comparable with the H2bb parental strain, indicating that the b allele was dominant. In contrast, the H2bd F1 and F2 mice on the BALB background produced IgG2a levels between those of the H2bb and H2dd parental strains, indicating codominance of the b and d alleles. This suggests that a background gene influences regulation of IgG2a levels by Igis1. Non-obese diabetic (NOD) mice (KdIAg7IEnu11Db), which can develop type 1 diabetes, had higher levels of IgG2a than NOD-H2d congenic mice. Thus, Igis1 affects isotype selection in the presence of non-MHC diabetes genes. As type 1 diabetes is associated with T1 responses, Igis1 may affect susceptibility to this condition.

Animals↗
PubMed2000

Localization of Idd11 using NOD congenic mouse strains: elimination of Slc9a1 as a candidate gene.

Type 1 diabetes is a multigenic autoimmune disease, the genetic basis for which is perhaps best characterized in the nonobese diabetic (NOD) mouse model. We previously located a NOD diabetes susceptibility locus, designated Idd11, on mouse Chromosome (Chr) 4 by analyzing diabetic backcross mice produced after crossing NOD/Lt with the nondiabetic resistant strain C57BL/6 (B6) strain. In order to confirm Idd11 and further refine its location, three NOD congenic mouse strains with different B6 derived intervals within Chr 4 were generated. Two of the congenic strains had a significant decrease in the cumulative incidence of diabetes compared with NOD/Lt control mice. The third NOD congenic strain, containing a B6 interval surrounding the Slc9a1 locus, was not protected against diabetes. These results define a new distal boundary for Idd11 and eliminate the Slc9a1 gene as a candidate. The Idd11 locus has now been definitively mapped to a 13cM interval on mouse Chr 4.

Alleles↗
PubMed2000

A study of graft versus host disease using bile duct implants under the kidney capsule.

BACKGROUND/AIMS: Graft versus host disease (GVHD) following histoincompatible bone marrow transplantation may be modelled experimentally using irradiated metallothionein promoter-H-2Kb transgenic mice (MET-Kb mice), reconstituted with syngeneic non-transgenic spleen and lymph node (LN) cells. In this model, inflammation peaks at 3 weeks post-reconstitution, but resolves by 3 months, and is focussed on portal tracts and bile ducts (BD). The aim of this study was to determine if transgene-expressing hepatocytes play a role in the immune response, why portal tracts are selectively targeted, and which cell types are involved. METHODS: Intrahepatic BD (IHBD) with attached hepatocytes, or extrahepatic BD (EHBD) devoid of hepatocytes, were isolated from MET-Kb mice and implanted under the kidney capsule of transgenic (syngeneic) and congenic (allogeneic) mice. Three weeks post-implantation, BD were scored histologically for rejection or survival, and stained for various cell-surface molecules. RESULTS: Generally, IHBD survived better than EHBD, and T cells were the predominant infiltrating cell type in both implants. Both types of implants undergoing rejection expressed intercellular adhesion molecule-1 (ICAM-1) and leukocyte function antigen-1 (LFA-1) at high density; BD and the underlying kidney parenchyma also expressed class I and II major histocompatibility complex (MHC). CONCLUSIONS: The rejection of both groups of implants by congenic recipients suggests that BD from MET-Kb mice express the transgene, but the reason for the selective targeting of portal tracts rather than transgene-expressing hepatocytes remains unclear. One possible explanation is that dendritic cells/antigen-presenting cells (DC/APC) in portal tracts, which express high levels of MHC and co-stimulatory molecules, are the primary targets, and that BD are infiltrated and destroyed as 'bystanders'.

Animals↗
PubMed2000

Complete primary structure, chromosomal localisation, and definition of polymorphisms of the gene encoding the human interleukin-12 p40 subunit.

Owing to the importance of interleukin (IL)-12 in regulating immune responses, we have determined the complete genomic sequence and organization of the gene encoding its p40 subunit. The genomic sequence was determined and was compared to cDNA sequences to derive exon/intron boundaries. Unusually, both the first and last of the eight exons of this gene are not translated. An extensive search identified several polymorphisms in IL-12p40, including repeat elements in introns 2 and 4 and a polymorphic Taql site in the 3'UTR. However, no polymorphisms were found which could result in amino acid substitutions. This finding places constraints on any preferential involvement of alleles of IL-12p40 in contributing to autoimmune, inflammatory or infectious diseases.

Chromosome Mapping↗
PubMed2000

Differential and genetically separable associations of leptin with obesity-related traits.

OBJECTIVE: The extent to which leptin protects against obesity is unknown. By intercrossing New Zealand obese mice with lean C57BL/6J mice, we have separated the genes controlling leptin and other weight-related phenotypes. This has allowed us to determine whether hyperleptinaemia is associated with reduced food intake and increased physical activity in mice spanning a large range in body weight. METHODS: Plasma leptin, glucose and insulin, body weight, food intake, running wheel activity, and four adipose depots were measured in 587 adult F2 and backcross mice RESULTS: When mice were categorized by adiposity, a plot of food intake vs leptin illustrated a U-shaped curve. Food intake decreased as leptin levels rose to approximately 15 ng/ml, beyond which the relationship reversed. A negative relationship was observed between activity and leptin with a maximal decrease in activity once leptin reached approximately 15 ng/ml. CONCLUSION: Leptin has differential responses to food intake and activity, suggesting that it has limited potential to defend against obesity. A genetic defect in leptin sensitivity is unlikely to be the primary cause of obesity in these mice, since hyperleptinaemia was not coinherited with both hyperphagia and inactivity as body weight increased.

Adipose Tissue↗
PubMed1999

The molecular characterisation of a novel tetraspanin protein, TM4-B(1).

TM4-B is a novel member of the Tetraspanin superfamily and displays characteristics typical of the superfamily. It bears significant homology to other superfamily members and is most similar to Tspan-1. This molecule is broadly expressed in most human tissues and cell lines including neural and bone marrow derived tissues. TM4-B was mapped to the q34 region on human chromosome 9.

Amino Acid Sequence↗
PubMed1998

Structure and chromosomal mapping of the TNF-alpha inducible endothelial protein 1 (Edp1) gene in the mouse.

EDP1 was identified as a human gene activated transcriptionally by tumour necrosis factor alpha in endothelial cells. Here we have characterised the mouse Edp1 gene. We show that the gene encodes a highly conserved protein and describe its intron/exon structure. The presence of related genes in the sequence databases suggests that Edp1 is part of a gene family. Fine mapping of the gene in the mouse genome indicates that, as expected from its location on human chromosome 17, the mouse Edp1 gene maps to mouse chromosome 11. However, surprisingly, the gene does not map to the expected region of mouse chromosome 11 suggesting that a change in the order of genes has occurred within a conserved linkage group.

Adaptor Proteins, Signal Transducing↗
PubMed1997

T cell tolerance and autoimmunity.

Many T cells with auto-aggressive potential are deleted in the thymus. Although some of these escape to the general circulation, they do not usually damage organs such as the pancreas. To investigate the mechanisms preventing autoimmunity, we generated transgenic mice expressing known genes under the control of various promoters. We found that the occurrence of autoaggression depended on factors such as the precursor frequency of responding T cells, their state of activation, their accessibility to the autoantigen, the physicochemical properties of the autoantigen, the possibility of priming by environmental antigens which mimic the target antigen, and some inflammatory reaction in the target site.

Animals↗