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Biomedical subjects

J D Mountz

Publications and source records attributed to J D Mountz.

At least 73 records · Page 4Linked to original sources
PubMed1996

Inhibition of Nur77/Nurr1 leads to inefficient clonal deletion of self-reactive T cells.

The Nur77/Nurr1 family of DNA binding proteins has been reported to be required for the signal transduction of CD3/T cell receptor (TCR)-mediated apoptosis in T cell hybridomas. To determine the role of this family of DNA-binding proteins in thymic clonal deletion, transgenic (Tg) mice bearing a dominant negative mutation were produced. The transgene consisted of a truncated Nur77 (deltaNur77) gene encoding the DNA-binding domain of Nur77 ligated to a TCR-beta enhancer resulting in early expression in thymocytes. Apoptosis of CD4+CD8+ thymocytes mediated by CD3/TCR signaling was greatly inhibited in the deltaNur77 Tg mice, compared with non-Tg littermates, after treatment with anti-CD3 or anti-TCR antibody in vivo and in vitro. Clonal deletion of self-reactive T cells was investigated in deltaNur77-Db/HY TCR-alpha/beta double Tg mice. There was a five-fold increase in the total number of thymocytes expressing self-reactive Db/HY TCR-alpha/beta in the deltaNur77-TCR-alpha/beta double Tg male mice. Deficient clonal deletion of self-reactive thymocytes was demonstrated by a 10-fold increase in the CD4+CD8+ thymocytes that expressed Tg TCR-alpha/beta. There was an eightfold increase in the CD8+, Db/HY TCR-alpha/beta T cells in the lymph nodes (LN) of delta Nur77-Db/HY TCR-alpha/beta double Tg compared with Db/HY TCR-alpha/beta Tg male mice. In spite of defective clonal deletion, the T cells expressing the Tg TCR were functionally anergic. In vivo analysis revealed increased activation and apoptosis of T cells associated with increased expression of Fas and Fas ligand in LN of deltaNur77-Db/HY TCR-alpha/beta double male mice. These results indicate that inhibition of Nur77/Nurr1 DNA binding in T cells leads to inefficient thymic clonal deletion, but T cell tolerance is maintained by Fas-dependent clonal deletion in LN and spleen.

Animals↗
PubMed1996

The role of programmed cell death as an emerging new concept for the pathogenesis of autoimmune diseases.

Activation-induced apoptosis is a primary mechanism for downmodulation of an immune response leading to immune homeostasis and deletion of T cells with specificities which may be harmful. These include deletion of T cells with self-specificities (autospecific) and excessively high affinity for foreign antigen which may lead to an excessively heightened immune response and septic shock. Surface molecules involved in activation-induced apoptosis involve Fas and Fas ligand (FasL), as well as the T-cell receptor (TCR) which modulates the expression and function of these molecules. Fas signaling mechanisms include the hematopoietic cell phosphatase (HCP) and sphingomyelinase, while TCR-signaling mechanisms include Nur77 and fyn kinase and unknown molecules that modulate expression of FasL. Apoptosis signals are further modulated by inhibitors or inducers of apoptosis including Bcl-2, p53, and interleukin-1 beta converting enzyme (ICE). Further understanding of the interaction of these molecules in autoimmune disease may lead to more specific therapies for immunosuppression tailored to the genetic or environmentally induced, activation-induced apoptosis defect in patients.

Animals↗
PubMed1996

Autoimmune disease results from multiple interactive defects in apoptosis induction molecules and signaling pathways.

Activation induced cell death (AICD) plays a critical role in eliminating autoimmune cells and limiting inflammation after activation. The two major signaling molecules for AICD are the Fas and TNF-R pathways of apoptosis. Defective Fas apoptosis in lpr/lpr mice results in a compensatory increase in TNF-R/TNF-mediated apoptosis. TNF/TNF-R has been shown to be a compensatory pathway of apoptosis in T cells and macrophages of lpr/lpr mice. Therefore, early production of TNF/TNF-R limit an immune response by inducing AICD in the absence of an intact Fas/Fas ligand apoptosis pathway. However, increased TNF production in lpr mice also lead to increased susceptibility to septic shock and autoimmune disease such as arthritis. Therefore TNF production during an inflammatory response can downmodulate this response, but this also results in the failure to downmodulate TNF production leading to septic shock and arthritis. A second pathway of AICD is mediated by Nur77 after T cell stimulation through the CD3 molecule. Mice with defective Nur77 signaling undergo AICD using the Fas-Fas ligand pathway to eliminate autoreactive T cells. A third defect of AICD is observed in HCP-mutant me/me (motheaten) mice which develop autoimmune disease related to defective Fas apoptosis signaling. Therefore, multiple interactive pathways play a role in limiting development of autoimmunity.

Animals↗
PubMed1995

Increased susceptibility of fas mutant MRL-lpr/lpr mice to staphylococcal enterotoxin B-induced septic shock.

MRL-lpr/lpr mice are defective in the fas Ag/APO-1 apoptosis gene (CD95). Using the hepatotoxin D-galactosamine (D-GalNH2), we demonstrate that MRL-lpr/lpr mice have an increased susceptibility to staphylococcal enterotoxin B (SEB)-induced lethal shock, which causes them to exhibit the septic shock-like behaviors of fur ruffling and listlessness, and death occurs within 8 to 18 h. SEB susceptibility is greater in V beta 8.2 TCR transgenic MRL-lpr/lpr mice than in nontransgenic mice. In studies designed to elucidate the molecular pathways of SEB-induced septic shock, we found that C57Bl/6.Ab0/Ab0, MHC class II-deficient "C2D" mice, but not C57Bl/6-(+/+) mice, are nonresponsive to challenge with SEB. C2D mice, backcrossed with the fas mutation resulting in double-knockout C2D;lpr/lpr mice, are more susceptible to challenge with SEB/D-GalNH2. The LD50s for C57Bl/6.C3H-gld/gld "fas ligand-mutant mice" challenged with SEB/D-GalNH2 were comparable to C57Bl/6.MRL-lpr/lpr and MRL-lpr/lpr mice, suggesting that reciprocal mutations in either fas or fas ligand increases susceptibility to bacterial superantigens (SAGs). SEB-induced lethal shock can be reversed by treatment with Abs to V beta 8 TCR, MHC class II Ia+, IL-2, and TNF-alpha, by the immunosuppressant cyclosporin A, or by treatment with carbocyclic nucleoside analogues. These data indicate that SAG-induced septic shock is dependent on interactions with the TCR and MHC class II Ags, and they also suggest a critical role for a functional fas and/or fas ligand in resistance to SAG-induced septic shock.

Animals↗
PubMed1995

Differential expression of human Fas mRNA species upon peripheral blood mononuclear cell activation.

Human Fas/Apo-1 is a cell-surface protein that mediates apoptosis upon ligation with Fas ligand. The gene lies on the long arm of chromosome 10, consists of nine exons, and spans more than 26 kb of DNA. We previously reported the presence of a Fas variant mRNA, designated as Fas delta TM, in human peripheral blood mononuclear cells. Fas delta TM is generated by alternative splicing of the intact exon 6, which encodes the Fas transmembrane domain. In the present study, we describe three novel forms of Fas mRNA that are generated by alternative splicing of exons 3, 4, 6 and 7. These three mRNA variants undergo a frameshift and produce truncated polypeptides because of the appearance of a stop codon in the altered open reading frame. On activation of the peripheral blood mononuclear cells, a decreased expression of alternatively spliced Fas mRNA species correlated with increased cell-surface expression of Fas. These results suggest that differential expression of alternatively spliced Fas mRNAs may play a role in regulation of Fas function via regulation of the production of the membrane-bound and the soluble, secreted Fas protein products.

Alternative Splicing↗
PubMed1995

Prevention of age-related T cell apoptosis defect in CD2-fas-transgenic mice.

T cell dysfunction and thymic involution are major immunologic abnormalities associated with aging. Fas (CD95) is a bifunctional molecule that is critical for apoptosis and stimulation during T cell development, but the role of Fas during aging has not been determined. Fas expression and function on T cells from old (22-26-mo-old) mice was compared with young (2-mo-old) mice and old CD2-fas-transgenic mice. Fas expression and ligand-induced apoptosis were decreased on T cells from old mice compared with young mice. This correlated with an age-related increase in CD44+Fas- T cells. There was a marked decrease in the proliferation of T cells from old mice after anti-CD3 stimulation compared with young mice. Anti-CD3-stimulated T cells from young mice exhibited increased production of interleukin (IL)-2 and decreased production of interferon-gamma and IL-10 compared with old mice. There was an age-related decrease in the total thymocyte count from 127 +/- 10 cells in young mice compared with 26 +/- 8 x 10(6) in old mice. In 26-mo-old CD2-fas-transgenic mice, Fas and CD44 expression, Fas-induced apoptosis, T cell proliferation, and cytokine production were comparable to that of the young mice. These results suggest that T cell senescence with age is associated with defective apoptosis, and that the CD2-fas transgene allows maintenance of Fas apoptosis function and T cell function in aged mice comparable to that of young mice.

Aging↗
PubMed1995

Characterization of human Fas gene. Exon/intron organization and promoter region.

Ligation of the Fas cell-surface molecule induces apoptosis. Defective Fas-mediated apoptosis has been associated with spontaneous autoimmunity in mice. Using human Fas/Apo-1 cDNA as a probe, we have molecularly cloned and characterized the human Fas chromosomal gene. The gene consists of nine exons and spans more than 26 kilobases of DNA. The lengths of introns vary from > 14 kilobases at the 5' end of the gene to 152 base pairs upstream of the exon encoding the transmembrane domain. The domain structure of the human Fas is encoded by an exon or a set of exons. Primer extension analysis revealed three major transcription initiation sites. The promoter region lacked canonical "TATA" and "CAAT" boxes but was a "GC-rich" sequence, and contained consensus sequences for AP-1, GF-1, NY-Y, CP-2, EBP20, and c-myb. These data provide the first characterization of the human Fas gene and insight into its regulatory region.

Amino Acid Sequence↗
PubMed1995

Fibromyalgia in women. Abnormalities of regional cerebral blood flow in the thalamus and the caudate nucleus are associated with low pain threshold levels.

OBJECTIVE: To determine if regional cerebral blood flow (rCBF) in the left and right hemithalami or the left and right heads of the caudate nucleus is abnormal in women with fibromyalgia (FM). METHODS: Resting-state rCBF in the hemithalami and left and right heads of the caudate nucleus of 10 untreated women with FM and 7 normal control women was measured by single-photon-emission computed tomography. Pain threshold levels at tender and control points also were assessed in both the women with FM and the controls. RESULTS: The rCBF in the left and right hemithalami and the left and right heads of the caudate nucleus was significantly lower in women with FM than in normal controls (P = 0.01, P = 0.003, P = 0.01, and P = 0.02, respectively). Compared with controls, the women with FM also were characterized by significantly lower cortical rCBF (P = 0.001) and lower pain threshold levels at both tender points (P = 0.0001) and control points (P = 0.0001). CONCLUSION: The findings of low rCBF and generalized low pain thresholds support the hypothesis that abnormal pain perception in women with FM may result from a functional abnormality within the central nervous system.

Adult↗
PubMed1995

Autoimmunity, apoptosis defects and retroviruses.

Autoimmunity and AIDS both share the common feature of increased expression of retroviral protein products and abnormal apoptosis of immune cells (81). This leads to a more global immunomodulatory defect (82-84). The challenge in the future will be to devise compounds that can either regulate the effect of the retroviral products on apoptosis, or that can inhibit apoptosis pathways in order to restore normal immune system function.

Amino Acid Sequence↗
PubMed1995

Defective expression of hematopoietic cell protein tyrosine phosphatase (HCP) in lymphoid cells blocks Fas-mediated apoptosis.

Protein tyrosine dephosphorylation after Fas cross-linking occurred in Fas apoptosis-sensitive CEM-6 cells but not in Fas apoptosis-resistant MOLT-4 cells, and apoptosis in the CEM-6 cells could be inhibited by the protein tyrosine phosphatase inhibitor, pervanadate. The time course and level of dephosphorylation were correlated with increased hematopoietic cell protein tyrosine phosphatase (HCP) activity, but not with the activity of two other tyrosine phosphatases. The level of expression of HCP was correlated with Fas apoptosis function in eleven human and murine Fas-positive lymphoid cell lines. Expression of recombinant HCP in the MOLT-4 cell line converted this Fas apoptosis-resistant cell line to Fas apoptosis sensitive. HCP-mutant mev/mev mice exhibited increased expression of Fas but decreased Fas-mediated apoptosis function in lymphoid organs after anti-mouse Fas antibody treatment in vivo. Thus, HCP-mediated protein dephosphorylation is involved in the delivery of the Fas apoptosis signal in lymphoid cells.

Animals↗
PubMed1995

A fas antigen receptor mutation allows development of toxic shock syndrome toxin-1-induced lethal shock in V beta 8.2 T-cell receptor transgenic mice.

Recombinant toxic shock syndrome toxin-1 (rTSST-1) administered to MRL-lpr/lpr TCR V beta 8.2 transgenic mice at doses of 0.1 microgram/mouse resulted in 100% mortality. This was an unexpected finding since TSST-1 does not activate V beta 8.2 T cells. In contrast, control mice heterozygous at the lpr locus and also for the transgene (MRL-lpr/+; V beta 8.2/0) survived doses of superantigen 100 times higher. The transgenic mice which succumbed to rTSST-1 challenge exhibited histopathology of the liver consistent with toxic shock (generalized inflammation and hepatocellular necrosis) as well as substantially elevated serum TNF-alpha, IL-2, and IL-6 cytokine levels. Splenic T cells derived from transgenic mice stimulated with rTSST-1 in vitro did not undergo detectable proliferation as measured in a standard mitogen assay. However, PCR amplification of cDNA prepared from the V beta 8.2 splenocytes revealed the presence of minor populations of TSST-1-reactive V beta elements (i.e. V beta 3 and V beta 15). Furthermore, an expansion of the V beta 3 and V beta 15 T-cell families was detected by PCR assay of spleen cell cultures stimulated with rTSST-1. These results suggested that the exquisite sensitivity of the MRL-lpr/lpr V beta 8.2 transgenic animals to rTSST-1 was not dependent exclusively on T-cell proliferation but was augmented by the influence of a defective fas antigen receptor expressed in homozygous lpr mice. To test this hypothesis more directly, we compared the sensitivity of MRL-lpr/lpr mice (not carrying the V beta 8.2 transgene) to MRL-+/+ mice. The MRL-lpr/lpr fas antigen-defective mice were substantially more susceptible to rTSST-1 challenge. Mice carrying the lpr mutation on another genetic background (C57BL/6.C3H-lpr/lpr) were also more sensitive to rTSST-1 challenge than were C57BL/6.C3H-+/+ mice. Although induction of toxic shock is clearly associated with T-cell proliferation, defects in fas antigen receptor or ligand may also contribute substantively to superantigen-mediated lethal shock by still undefined mechanisms.

Adenine↗
PubMed1994

Protection from Fas-mediated apoptosis by a soluble form of the Fas molecule.

Fas is an apoptosis-signaling receptor molecule on the surface of a number of cell types. Molecular cloning and nucleotide sequence analysis revealed a human Fas messenger RNA variant capable of encoding a soluble Fas molecule lacking the transmembrane domain because of the deletion of an exon encoding this region. The expression of soluble Fas was confirmed by flow cytometry and immunocytochemical analysis. Supernatants from cells transfected with the variant messenger RNA blocked apoptosis induced by the antibody to Fas. Levels of soluble Fas were elevated in patients with systemic lupus erythematosus, and mice injected with soluble Fas displayed autoimmune features.

Amino Acid Sequence↗
PubMed1994

Correction of accelerated autoimmune disease by early replacement of the mutated lpr gene with the normal Fas apoptosis gene in the T cells of transgenic MRL-lpr/lpr mice.

MRL-lpr/lpr mice develop a generalized autoimmune disease which includes increased autoantibody production, glomerulonephritis, and development of lymphadenopathy. The lpr genetic defect has been identified as a mutation in the Fas apoptosis gene that results in low expression of Fas mRNA. To determine the significance of the lpr mutation and T cells in the development of the autoimmune disease, we constructed transgenic MRL-lpr/lpr mice using a full-length murine Fas cDNA under the regulation of the T-cell-specific CD2 promoter and enhancer. Here we show that the early correction of the lpr gene defect in T cells eliminates glomerulonephritis and development of lymphadenopathy and decreases the levels of autoantibodies. In this model, early correction of the lpr defect in T cells is sufficient to eliminate the acceleration of autoimmune disease even in the presence of B cells and other cells that express the mutant lpr gene.

Animals↗
PubMed1994

T cell influence on superantigen-induced arthritis in MRL-lpr/lpr mice.

OBJECTIVE: To define the influence of the T cell receptor (TCR) and the lpr autoimmune gene on the induction and progression of superantigen-induced arthritis in V beta 8 transgenic MRL-lpr/lpr mice. METHODS: The time to onset and the extent of synovial hyperplasia after the induction of arthritis by intraarticular injection of staphylococcal enterotoxin B (SEB) were compared in mice having T cells that bear the V beta 8 transgene alone (V beta 8 TCR transgenic MRL-+/+), the lpr gene without the V beta 8 gene (nontransgenic MRL-lpr/lpr), both the V beta 8 gene and the lpr gene (V beta 8 transgenic MRL-lpr/lpr), or neither gene (nontransgenic MRL-+/+). Synovial hyperplasia was compared in SEB-injected V beta 8 transgenic MRL-lpr/lpr mice after treatment with cyclosporin A (CSA), anti-V beta 8 and anti-CD4 monoclonal antibodies, and in V beta 8 transgenic MRL-lpr/lpr mice after injection of a non-V beta 8-reactive superantigen, staphylococcal enterotoxin A (SEA). RESULTS: At day 30, increased synovial cells were observed in all SEB-treated mice, but the increase was greatest in the V beta 8 transgenic MRL-lpr/lpr mice. T cell involvement was indicated by the inability of either heat-denatured SEB or SEA to induce severe arthritis, the reduction in the severity of the arthritis on systemic treatment with CSA or anti-V beta 8, and the correlation of synovial hyperplasia with in vitro SEB reactivity of T cells. CONCLUSION: These observations suggest that superantigens can induce chronic arthritis and that the induction and progression of the arthritis requires an underlying T cell defect in anergy induction in addition to exposure to the superantigen.

Animals↗
PubMed1994

Autoimmune disease. A problem of defective apoptosis.

Human autoimmune diseases share the common feature of an imbalance between the production and destruction of various cell types including lymphocytes (SLE), synovial cells (RA), and fibroblasts (scleroderma). Patients with SLE have increased levels of soluble Fas that inhibit proper apoptosis of lymphocytes. In animal models of autoimmune diseases, mutations of genes involved in apoptosis including Fas, Fas ligand, and the hematopoietic cell phosphatase gene have been identified. Oncogenes, including bcl-2, p53, and myc, that regulate apoptosis are also expressed abnormally. Potent inducers of apoptosis including steroids, azathioprine, cyclophosphamide, and methotrexate are the most efficacious therapies for autoimmune disease currently known. Specific therapies that induce apoptosis without incurring side effects should improve treatment of autoimmune disease.

Antigens, Surface↗