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Biomedical subjects

R L Yung

Publications and source records attributed to R L Yung.

13 recordsLinked to original sources
PubMed2000

TRAIL (Apo2 ligand) and TWEAK (Apo3 ligand) mediate CD4+ T cell killing of antigen-presenting macrophages.

The human marrow produces approximately 1010 monocytes daily, and this production must be balanced by a similar rate of destruction. Monocytes/macrophages can undergo apoptosis after activating CD4+ T cells, suggesting one mechanism that may contribute to macrophage homeostasis. Previous reports indicate that Fas-Fas ligand interactions are the principle molecules mediating this response. However, D10, an Iak-restricted cloned Th2 line, will similarly induce apoptosis in Ag-presenting macrophages, and D10 cells lack Fas ligand. To confirm that D10 cells kill macrophages through Fas-independent pathways, D10 cells were shown to kill MRL lpr/lpr (Iak) macrophages in an Ag-dependent fashion, indicating additional mechanisms. Recent reports demonstrate that TNF-related apoptosis-inducing ligand (TRAIL), interacting with Apo2, and TNF-like weak inducer of apoptosis (TWEAK), interacting with Apo3, will induce apoptosis in some cells. Using Abs to TRAIL and an Apo3-IgG Fc fusion protein, we demonstrated that D10 cells express both TRAIL and TWEAK. The Apo3 fusion protein, but not human IgG, inhibited D10-induced macrophage apoptosis, as did anti-TRAIL. Further studies demonstrated that AE7, a cloned Th1 line, and splenic T cells express TWEAK, TRAIL, and Fas ligand, and inhibiting these molecules also inhibited macrophage killing. These results indicate that D10 cells induce macrophage apoptosis through TRAIL- and TWEAK-dependent pathways. Because normal T cells also express these molecules, these results support the concept that T cells have multiple pathways by which to induce macrophage apoptosis. These pathways may be important in immune processes such as macrophage homeostasis as well as in down-regulation of immune responses and elimination of macrophages infected with intracellular organisms.

Animals↗
PubMed2000

Changes in immune function with age.

Aging is associated with a decline in immune function in humans and animals. The primary defects appear to reside in the T-cell compartment. Improving understanding of the mechanisms underlying the general decline in immune functions with age may enhance our ability to prevent and treat age-associated illnesses. Development of biomarker(s) of immune senescence may eventually help clinicians to identify subpopulations of the elderly who are at risk for infections, malignancies, and possibly autoimmune diseases.

Aged↗
PubMed2000

LFA-1 overexpression and T cell autoreactivity: mechanisms.

Overexpressing LFA-1 (CD11a/CD18) on antigen specific CD4+ T cells makes the cells proliferate to normally subthreshold stimuli, including self-Ia molecules without specific antigen. The mechanisms by which this occurs are unknown, but potentially include transmission of an increased costimulatory signal, overstabilization of normally low affinity TCR-Ia interactions, or both. A role for increased costimulatory signaling was tested by culturing control and CD18-transfected antigen-specific T cells clones with anti-CD3 and anti-CD11a. Minimal calcium fluxes were detected, but increased protein tyrosine phosphorylation was observed in the transfectants. However, the proliferative response to graded amounts of these antibodies were identical in the transfectants and controls, suggesting that increased signaling alone was insufficient to cause the increased responsiveness. To test for overstabilization, transfected and control clones were cultured with syngeneic Mø with or without antigen. The transfected but not control cells downregulated TCR expression in response to Mø alone, thus demonstrating successful TCR signaling to a low affinity interaction. These results indicate that LFA-1 overexpression permits TCR signal transmission to a normally subthreshold stimulus presented by Mø, consistent with overstabilization. LFA-1 overexpression also causes increased tyrosine phosphorylation, but this alone is not sufficient to cause a proliferative response to low level stimuli.

Animals↗
PubMed1996

Ligand recognition by murine anti-DNA autoantibodies. II. Genetic analysis and pathogenicity.

Although anti-DNA autoantibodies are an important hallmark of lupus, the relationships among anti-DNA structure, reactivity, and pathogenicity have not been fully elucidated. To further investigate these relationships, we compare the variable genes and primary structure of eight anti-DNA mAbs previously obtained from an MRL/MpJ-lpr/lpr mouse along with the ability of three representative mAbs to induce nephritis in nonautoimmune mice using established adoptive transfer protocols. One monospecific anti-single-stranded (ss) DNA (11F8) induces severe diffuse proliferative glomerulonephritis in nonautoimmune mice whereas another anti-ssDNA with apparently similar in vitro binding properties (9F11) and an anti-double-stranded DNA (4B2) are essentially benign. These results establish a murine model of anti-DNA-induced glomerular injury resembling the severe nephritis seen in lupus patients and provide direct evidence that anti-ssDNA can be more pathogenic than anti-double-stranded DNA. In vitro binding experiments using both protein-DNA complexes and naive kidney tissue indicate that glomerular localization of 11F8 may occur by recognition of a planted antigen in vivo. Binding to this antigen is DNase sensitive which suggests that DNA or a DNA-containing molecule is being recognized.

Amino Acid Sequence↗
PubMed1995

Mechanism of drug-induced lupus. I. Cloned Th2 cells modified with DNA methylation inhibitors in vitro cause autoimmunity in vivo.

Treating activated CD4+ T cells with DNA methyltransferase inhibitors modifies gene expression and induces autoreactivity. Adoptive transfer of viable polyclonal autoreactive cells causes a lupus-like disease, most likely because of one or more effector functions expressed by the autoreactive cells. However, the number of potential effector mechanisms expressed by polyclonal cells is large. To more readily identify responsible mechanisms, we asked if autoimmunity can be induced by using the conalbumin-reactive, cloned Th2 cell line D10.G4.1, treated with 5-azacytidine (5-azaC) or procainamide (Pca). Treated, but not untreated, cells responded to syngeneic APCs without Ag, overexpressed LFA-1, spontaneously lysed syngeneic macrophages, and secreted relatively large amounts of IL-6, small amounts of IL-4, and no detectable IL-2 nor IFN-gamma. Adoptive transfer of treated, but not untreated, cells induced a severe immune complex glomerulonephritis, pulmonary alveolitis, central nervous system abnormalities including fibrinoid necrosis, karyorrhexis, and meningitis, and bile duct proliferation with periportal inflammatory cell infiltration resembling primary biliary cirrhosis. Anti-ssDNA, anti-dsDNA, and anti-histone Abs were also found. These experiments demonstrate that modification of this cloned T cell line with DNA methyltransferase inhibitors is sufficient to cause an autoimmune disease, with features of lupus as well as autoimmune liver disease. The results also raise the possibility that macrophage lysis, IL-6 secretion, and LFA-1 overexpression could contribute to the disease process. This system may be useful in testing the role of these and other pathologic mechanisms in the development of specific autoimmune lesions.

Animals↗
PubMed1995

New concepts in the pathogenesis of drug-induced lupus.

Although the importance of DNA methylation in normal cellular development and hereditary disease states has been appreciated for some time, the role of environmental agents in causing DNA methylation abnormalities and the effects of DNA hypomethylation on T cells have only recently been examined. This review summarizes current knowledge about the role of DNA methylation in regulating T function and gene expression and highlights a novel mechanism causing autoimmunity, in which epigenetic modification of T cell DNA by environmental agents plays an important role in triggering lupus-like diseases. The observations that DNA methylation inhibitors modify gene expression and induce autoreactivity in cloned, Ag-specific CD4+ cells in vitro, that the modified cells cause autoimmunity in vivo, and that similar changes are found in patients with active lupus provide a new approach to understanding how some forms of autoimmunity develop and may lead to new and more effective treatments.

Acetylation↗
PubMed1994

Lymphocyte function-associated antigen 1 overexpression and T cell autoreactivity.

OBJECTIVE: To determine if DNA methylation inhibitors make T cells autoreactive by inducing lymphocyte function-associated antigen type 1 (LFA-1) (CD11a/CD18) overexpression. METHODS: T cell clones were treated with 3 distinct DNA methylation inhibitors or were stably transfected with a CD18 cDNA in a mammalian expression vector, and the effects on LFA-1 expression and activation requirements were examined. RESULTS: LFA-1 overexpression, caused by DNA methylation inhibitors or by transfection, correlates with the development of autoreactivity. CONCLUSION: LFA-1 overexpression may contribute to T cell autoreactivity.

Azacitidine↗
PubMed1994

Role of T cell DNA methylation in lupus syndromes.

Current theories postulate that exposure to certain environmental agents will induce lupus in genetically predisposed individuals. However, the mechanisms by which environmental agents interact with the immune system to trigger lupus is unclear. Recent work has shown that some environmental agents associated with lupus, such as procainamide, hydralazine and ultraviolet light, will inhibit T cell DNA methylation, increase LFA-1 expression and induce autoreactivity. In addition, T cells isolated from patients with active lupus have hypomethlated DNA, diminished DNA methyltransferase activity and overexpress LFA-1 on an autoreactive subset of cells which spontaneously lyses autologous macrophages. More recent work has shown that the adoptive transfer of murine T cells made autoreactive with DNA methylation inhibitors is sufficient to cause a lupus-like disease in otherwise healthy syngeneic recipients. Together, these results support a new model of autoimmunity, in which certain environmental agents modify T cells by inhibiting DNA methylation and altering expression of certain genes, thereby inducing autoreactivity. The autoreactive cells then interact with the host to produce a lupus-like disease.

Azacitidine↗
PubMed1994

Drug-induced lupus.

Recent years have seen promising developments in both our appreciation of the spectrum of autoimmune phenomena associated with DIL as well as our understanding of the pathogenesis of this disease. From our present knowledge, it seems likely that the cause of DIL is multifactorial, and that the disease manifestations depend on both the drugs involved as well as predisposing host factors. The present availability of an animal model of DIL promises to further our understanding of the role of drugs and other environmental factors in this disorder. It is hoped that further studies will provide additional understanding of the pathogenesis of these lupus-like diseases and possibly bring us one step closer to providing more rational and effective treatments for patients with idiopathic lupus.

Anticonvulsants↗
PubMed1993

Treating activated CD4+ T cells with either of two distinct DNA methyltransferase inhibitors, 5-azacytidine or procainamide, is sufficient to cause a lupus-like disease in syngeneic mice.

Human antigen-specific CD4+ T cells become autoreactive after treatment with various DNA methylation inhibitors, including 5-azacytidine, procainamide, and hydralazine. This suggests a mechanism that could contribute to the development of some forms of autoimmunity. In this report we have asked whether T cells treated with DNA methylation inhibitors can induce autoimmunity. Murine CD4+ T cells were treated with 5-azacytidine or procainamide and were shown to respond to syngeneic antigen-presenting cells, similar to CD4+ human T cell clones treated with these drugs. Functional characterization demonstrated that cells treated with either drug spontaneously lysed syngeneic macrophages and secreted IL-4, IL-6, and IFN-gamma. Adoptive transfer of 5-azacytidine- or procainamide-treated cells into unirradiated syngeneic recipients induced an immune complex glomerulonephritis and IgG anti-DNA and antihistone antibodies. These experiments demonstrate that T cells treated with either of two distinct DNA methyltransferase inhibitors are sufficient to induce a lupus-like disease. It is possible that the lysis of macrophages, together with the release of cytokines promoting B cell differentiation, contributes to the autoantibody production and immune complex deposition. These results suggest that environmental agents that inhibit DNA methylation could interact with T cells in vivo to produce a lupus-like illness, a mechanism that could have relevance to drug-induced and idiopathic lupus.

Animals↗