The regulation of murine lupus

The MRL/lpr mouse strain as a model for neuropsychiatric systemic lupus erythematosus

To date, CNS disease and neuropsychiatric symptoms of systemic lupus erythematosus (NP-SLE) have been understudied compared to end-organ failure and peripheral pathology. In this review, we focus on a specific mouse model of lupus and the ways in which this model reflects some of the most common manifestations and potential mechanisms of human NP-SLE. The mouse MRL lymphoproliferation strain (a.k.a. MRL/lpr) spontaneously develops the hallmark serological markers and peripheral pathologies typifying lupus in addition to displaying the cognitive and affective dysfunction characteristic of NP-SLE, which may be among the earliest symptoms of lupus. We suggest that although NP-SLE may share common mechanisms with peripheral organ pathology in lupus, especially in the latter stages of the disease, the immunologically privileged nature of the CNS indicates that early manifestations of particularly mood disorders maybe derived from some unique mechanisms. These include altered cytokine profiles that can activate astrocytes, microglia, and alter neuronal function before dysregulation of the blood-brain barrier and development of clinical autoantibody titres.

Interferon regulatory factor-1 gene deletion decreases glomerulonephritis in MRL/lpr mice

To investigate the role of interferon regulatory factor-1 (IRF-1) in the development of lupus nephritis, IRF-1(-/-) genotype mice were bred onto the MRL/lpJfas(lpr) (MRL/lpr) background. We examined kidney mesangial cell function and disease progression. Endpoints evaluated included inflammatory mediators, autoantibody production, immune complex deposition, renal pathology, T cell subset analysis, and duration of survival. Mesangial cells cultured from IRF-1(-/-) mice produced significantly lower levels of nitric oxide and IL-12 but not TNF-alpha when stimulated with LPS + IFN-gamma. IRF-1(-/-) mice showed less aggravated dermatitis compared to the wild-type mice. Anti-double-stranded DNA production and proteinuria were significantly decreased in IRF-1(-/-) mice compared to IRF-1(+/+) mice. IgG and C3 deposition as well as glomerulonephritis were decreased in IRF-1(-/-) mice at 26 wk of age compared to the IRF-1(+/+) mice. Splenic CD4- CD8- CD44+ T cells were decreased while CD4+ CD25+ T cells were increased in the IRF-1(-/-) mice when compared to IRF-1(+/+) mice. Survival rates (ED50) were 22 wk for IRF-1(+/+) mice and 45 wk for IRF-1(-/-) mice. These findings suggest an important role of IRF-1 in mediating renal disease in MRL/lpr mice.

Prevention of autoimmune hearing loss in MRL/lpr mice by bone marrow transplantation

We examined the effects of bone marrow transplantation (BMT) on immune-mediated inner ear diseases in MRL/Mp-lpr/lpr (MRL/lpr) mice, which manifest not only lupus nephritis but also sensorineural hearing loss (SNHL) at the age of 20 weeks. These mice were treated with cyclophosphamide (CY) and irradiation (5 Gy x 2), followed by the transplantation of bones plus bone marrow cells from allogeneic normal C57BL/6 mice at the age of 12 weeks. Hematolymphoid cells were reconstituted with donor-derived cells 3 months after BMT. Thus-treated MRL/lpr mice showed neither lupus nephritis nor SNHL even 24 weeks after BMT. No pathological findings were observed in either glomeruli or cochleae. These findings suggest that BMT can be used to prevent the development of autoimmune SNHL in MRL/lpr mice.

Autoreactive T cells in murine lupus: origins and roles in autoantibody production

The conventional paradigm to explain systemic lupus erythematosus (SLE) is that disease results from tissue deposition of pathogenic autoantibodies and immune complexes, secondary to activation of autoreactive B cells in the context of help from alphabeta T cells. Recent work in murine lupus has confirmed this notion and demonstrated that autoantigen-specific alphabeta T cells are absolutely required for full penetrance of disease, with such autoreactive alphabeta T cells, even in Fas-intact mice, likely arising from defects in peripheral tolerance. These studies have also revealed a network of regulation that also involves nonclassical pathogenic and downregulatory alphabeta and gammadelta T cells, suggesting that the lupus immune system involves more complex interactions than the conventional paradigm suggests.

Ultrastructural pathology in the stria vascularis of the MRL-Fasl(lpr) mouse

The MRL-Fas(lpr) mouse, a model of multisystemic, organ nonspecific autoimmune disease, has been proposed as a model of immune-mediated inner ear disease. A preliminary study employing light microscopy indicated that it develops cochlear pathology that appeared most striking in the stria vascularis, where cells underwent edema and degeneration. However, other structures, including the inner and outer hair cells and the supporting cells, also appeared to display pathology. The current study analyzed cochlear ultrastructure using transmission electron microscopy to better delineate the cochlear lesions found in these animals. MRL-Fas(lpr) animals were allowed to develop systemic disease (20 weeks old) and then had auditory brainstem response (ABR) thresholds determined. Animals were then killed and their cochleas prepared for electron microscopy. Age-matched MRL-+/+ and BALB/c mice served as controls. Results indicated that MRL-Fas(lpr) mice demonstrated elevated ABR thresholds. In contrast to a preliminary report, the cochlear pathology was observed exclusively in the stria vascularis, where cells demonstrated hydropic degeneration. Strial capillary structure was normal as were the rest of the cellular cochlear constituents. No inflammatory infiltrate was noted. These studies confirm that the MRL-Fas(lpr) mouse develops cochlear abnormalities focused in the stria vascularis. Whether the mechanism of the cellular degeneration involves autoimmune, genetic, or uremic processes has yet to be determined.

Effects of immunosuppression on the development of cochlear disease in the MRL-Fas(lpr) mouse

OBJECTIVES

The MRL-Fas(lpr) mouse, an animal that spontaneously develops multisystemic autoimmune disease, has been proposed as model of immune-mediated inner ear disease. Previous studies revealed that this mouse manifested elevated auditory brainstem response thresholds, hydropic degeneration of strial cells, and antibody deposition within strial capillaries. As the etiology of the observed strial disease may be immune, genetic, or uremic, a study was designed to attempt to delineate between these possible etiologic factors.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Dexamethasone, which is known to suppress autoantibody production and glomerulonephritis in these animals, was administered systemically on a daily basis to experimental animals, beginning at 6 weeks of age. Control animals received no treatment. Animals were allowed to age, with control animals predictably manifesting systemic disease at 20 weeks of age, at which point all animals were sacrificed.

RESULTS

Animals receiving dexamethasone treatment manifested a significant reduction in serum immunoglobulin levels, lymphoid hyperplasia, and a significant improvement in the level of renal function. However, morphologic analysis revealed a persistence of strial disease despite the elimination of strial antibody deposition.

CONCLUSION

The results of this experiment support the hypothesis that genetic mechanisms may be responsible for the observed strial disease. Further studies are under way to confirm these findings.

Antibody deposition in the stria vascularis of the MRL-Fas(lpr) mouse

The MRL-Fas(lpr) mouse, a model of multisystemic, organ non-specific autoimmune disease, has been proposed as a model of immune-mediated inner ear disease. Preliminary studies indicate that it develops cochlear pathology focused in the stria vascularis including intracellular edema and degeneration which develops in the absence of an inflammatory infiltrate but in the presence of antibody deposition. It was thus hypothesized that the antibodies found in the stria were mediating a direct pathologic effect on this structure, without recruiting classical inflammatory mediators. It was further hypothesized that the antibodies deposited within the stria would be derived from the non-complement fixing isotypes and subclasses, which are known to be able to mediate direct pathologic effects on target tissues. This study utilized immunohistologic techniques to identify the antibody isotypes and subclasses deposited within the stria vascularis of the MRL-Fas(lpr) mouse. Results indicate that all antibody isotypes and subclasses can be identified within the stria vascularis in the absence of complement. Thus, antibody deposition was not restricted to non-complement fixing antibodies. While it is possible that antibodies are mediating direct pathologic effects within the stria, the non-specific nature of the antibody deposition may indicate that these antibodies are not responsible for the observed pathology. Rather, other mechanisms, such as metabolic and genetic etiologies, must also be considered.

Perforin Protects Against Autoimmunity in Lupus-Prone Mice

The roles of cytolytic regulatory mechanisms in the immune system of lupus-prone mice were examined in perforin-deficient animals bearing functional or defective (lpr) Fas Ag (CD95). Perforin-deficient Fas+ animals developed accelerated autoimmunity, characterized by increased hypergammaglobulinemia, autoantibody production, and immune deposit-related end-organ disease compared with perforin-intact counterparts. In comparison, perforin-deficient lpr animals had accelerated mortality compared with perforin-intact lpr mice, associated with the abnormal accumulation of CD3+CD4−CD8− αβ T cells in conjunction with unaltered hypergammaglobulinemia, autoantibody production, and immune complex renal disease. These results indicate that cytolytic lymphoid regulation plays critical roles in the immune homeostasis of lupus-prone animals, and identify perforin-mediated cytotoxicity as a specific mechanism in the regulation of systemic autoimmunity.