Repeated 0.5-Gy γ-ray irradiation attenuates autoimmune manifestations in MRL-lpr lpr mice

Purpose: MRL-lpr lpr mice, a model for various autoimmune diseases, were repeatedly irradiated with 0.5 Gy of γ-rays, and changes in their autoimmune manifestations were investigated. Materials and methods: MRL-lpr lpr mice at 13 weeks of age were maintained in plastic cages and exposed whole-body to 0.5 Gy γ-ray irradiation from a 137Cs source 5 times per week for 4 weeks, from the time they were 13 weeks old until they reached 17 weeks old. Changes of autoimmune manifestations were examined 3 weeks later at the 20th week. Results: Splenomegaly, lymphadenopathy, and proteinuria in MRL-lpr lpr mice were clearly ameliorated by a total dose of 10 Gy (0.5 Gy day×5 days week for 4 weeks). Histologically severe disease-specific damage to the kidney and the salivary gland, i.e., glomerulonephritis and sialoadenitis, was also improved after irradiation. CD3+ CD4− CD8− CD45R B220+ T cell numbers, which proliferate abnormally in MRL-lpr lpr mice, were significantly decreased by the irradiation, possibly through induction of apoptosis. The elevated NO2− and NO3− (NOx−) production by macrophages of MRL-lpr lpr mice was lowered by the irradiation. The irradiation also prolonged the life span of MRL-lpr lpr mice. These phenomena may contribute to the amelioration of autoimmune manifestations in MRL-lpr lpr mice exposed to repeated small-doses of γ-rays. Conclusions: Repeated small-dose γ-ray exposure ameliorates the autoimmune manifestations in MRL-lpr lpr model mice.