Defects in apoptosis can cause autoimmune disease. Loss-of-function mutations in the ‘death receptor’ FAS impair the deletion of autoreactive lymphocytes in the periphery, leading to progressive lymphadenopathy and systemic lupus erythematosus-like autoimmune disease in mice (Faslpr/lpr (mice homozygous for the lymphoproliferation inducing spontaneous mutation)) and humans. The REL/nuclear factor-κB (NF-κB) transcription factors regulate a broad range of immune effector functions and are also implicated in various autoimmune diseases. We generated compound mutant mice to investigate the individual functions of the NF-κB family members NF-κB1, NF-κB2 and c-REL in the various autoimmune pathologies of Faslpr/lpr mutant mice. We show that loss of each of these transcription factors resulted in amelioration of many classical features of autoimmune disease, including hypergammaglobulinaemia, anti-nuclear autoantibodies and autoantibodies against tissue-specific antigens. Remarkably, only c-REL deficiency substantially reduced immune complex-mediated glomerulonephritis and extended the lifespan of Faslpr/lpr mice. Interestingly, compared with the Faslpr/lpr animals, Faslpr/lprnfkb2−/− mice presented with a dramatic acceleration and augmentation of lymphadenopathy that was accompanied by severe lung pathology due to extensive lymphocytic infiltration. The Faslpr/lprnfkb1−/− mice exhibited the combined pathologies caused by defects in FAS-mediated apoptosis and premature ageing due to loss of NF-κB1. These findings demonstrate that different NF-κB family members exert distinct roles in the development of the diverse autoimmune and lymphoproliferative pathologies that arise in Faslpr/lpr mice, and suggest that pharmacological targeting of c-REL should be considered as a strategy for therapeutic intervention in autoimmune diseases.
Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that affects approximately three million people worldwide.1 The disease is characterised by dysregulated humoral, cellular and innate immune responses. Although milder forms of SLE (and certain other autoimmune diseases) can be controlled with immunosuppressive drugs, the chronic inflammation and tissue damage, in particular to the kidney resulting in lupus nephritis, is a major cause of morbidity and mortality.1 Severe autoimmune kidney disease requiring dialysis or transplantation occurs in 10%–30% of SLE patients.1 Current therapeutic options are not focused on specific molecular targets and have many side effects leading to substantial complications. For example, the immune suppression resulting from several currently used therapeutics causes increased susceptibility to infection and certain cancers (for example, Epstein-Barr Virus (EBV)-associated B-cell lymphoma).2 Hence, there is a need to identify molecular targets for novel therapies that improve the treatment of SLE and related autoimmune diseases.
Autoimmune diseases arise due to breakdown of immunological tolerance resulting in potently destructive immune responses against self-antigens. Several mechanisms safeguard immunological tolerance. These include removal of autoreactive T- and B-lymphoid cells by BIM (BCL-2 Interacting Mediator of Cell Death, Bcl2L11 [BCL2-Like 11])-mediated apoptosis, both during their development in the thymus3 or in the bone marrow4 and as mature cells in the periphery,4 dampening the responsiveness of mature lymphocytes (anergy)5 and control of effector T cells by regulatory T cells (Tregs).5 As apoptosis has a critical role in lymphocyte selection and immune cell homeostasis, defects in its regulation have emerged as a cause of autoimmune disease.5 FASL/FAS-mediated apoptosis signalling (known as the ‘death receptor’ or ‘extrinsic’ cell death pathway) imposes a critical barrier against autoimmune disease and lymphadenopathy.6 Expression of the death receptor FAS (also called APO-1 or CD95) is virtually ubiquitous, presumably to allow FASL-mediated killing of many cell types, when infected or stressed.6 In contrast, FASL expression is restricted to activated T cells and natural killer cells, with its activity subject to posttranslational control (for example, proteolytic conversion of membrane bound into secreted FASL).6, 7
Mice bearing spontaneously acquired or gene-targeting-induced loss-of-function mutations in Fas (for example, Faslpr/lpr, Fas−/−), FasL (for example, FasLgld/gld, FasL−/−) or those that lack membrane-bound FASL (FasLΔm/Δm), as well as humans with mutations in Fas (reviewed in Strasser et al.6), develop progressive lymphadenopathy and autoantibody-mediated pathology. The lymphadenopathy is characterised by large numbers of ‘unusual’ non-malignant, double negative (DN) T cells (TCRα/β+CD3+CD4−CD8−B220+), which are thought to be previously activated CD8+ T cells that have accumulated due to defective FASL/FAS-mediated apoptosis.6 Experiments with Faslpr/lpr (mice homozygous for the lymphoproliferation inducing