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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.

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.

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.

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.

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.

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.

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.