Autoimmune manifestations in old B^A20−/− mice. (A) Analysis of autoantibodies in aged mice. ANA indicates that antinuclear IgG antibodies were detected by ELISA, n(B^A20−/−) = 12, n(control) = 21; αRBC-IgM, antierythrocyte IgM was detected by FACS and represented as mean fluorescence intensity, n(B^A20−/−) = 8, n(control) = 4. IgG and IgM rheumatoid factor (RF) was measured by ELISA; n(B^A20−/−) = 12, n(control) = 11. α-Cardiolipin IgG antibodies were detected by ELISA; n(B^A20−/−) = 12, n(control) = 11. *P < .05 (2-tailed unpaired Student t test). **P < .001 (2-tailed unpaired Student t test). (B) Table depicting the self-reactivity of sera from individual B^A20−/− mice against the indicated organs from Rag2^−/− mice. +, ++, and +++ indicate the severity of autoreactivity; and n.s., not screened. (C) Levels of α-cardiolipin IgG autoantibodies in 3-month-old mice (left panel; n = 8 per genotype) and in 11-month-old mice (right panel; n = 5 per genotype) were detected by ELISA. *P < .05 (1-tailed unpaired Student t test).