Neurodegeneration in autoimmune MRL-lpr mice as revealed by Fluoro Jade B staining

As in many humans suffering from lupus erythematosus, the development of systemic autoimmunity and inflammation in Fas-deficient MRL-lpr mice is accompanied by CNS dysfunction of unknown etiology. Experimental studies revealed infiltration of lymphoid cells into the choroid plexus, reduced neuronal complexity, retarded brain growth, and enlargement of cerebral ventricles. Moreover, an increased presence of cells with nicked-DNA (TUNEL+ cells) in the periventricular areas suggested accelerated apoptosis in brain cells of MRL-lpr mice. However, direct evidence that the dying cells were neurons was lacking. For this purpose, we presently use Fluoro-Jade B (FJB), a novel fluorescent dye which has high affinity for dying neurons (both apoptotic and necrotic). As expected, in comparison to the control groups, the brains of diseased, 5-month-old MRL-lpr mice showed increased numbers of FJB-positive (+) cells in cortical and periventricular regions. The FJB+ cells were significantly more numerous than TUNEL+ cells, and only approximately 7% co-localized with TUNEL. Immunostaining for CD4 and CD8 markers did not correlate with the number of FJB+ cells, suggesting that T-lymphocyte infiltration into the brain tissue is not a reliable predictor of neuronal demise. Conversely, indices of systemic autoimmunity (splenomegaly and high serum anti-nuclear antibody levels) were associated with increased FJB+ cell numbers in brains of autoimmune MRL-lpr mice, supporting the causal link between autoimmunity and neurodegeneration. Taken together, the above results suggest that factors other than T-cell infiltration and cell death mechanisms other than Fas-mediated apoptosis dominate neuronal degeneration in lupus-prone MRL-lpr mice.