TLR7 and MyD88 signaling is required for ABC accumulation. (A) Average percentage of ABCs among B cell in spleen of young (12-16 weeks old) and aged (> 12 months old) C57BL/6, IFNR^−/−, and TLR7^−/−, MyD88^−/− female mice. (B) Average percentage of ABCs among B cells in spleen of young (8-12 weeks old) C57BL/6 female mice after 30 immunizations with vehicle or the indicated TLR agonist. (C) Anti-Smith IgG autoantibodies were measured by ELISA in serum of mice chronically injected with TLR agonists. (D) Average percentage of ABCs among B cells in spleen of young (8-12 weeks old) C57BL/6 female mice after 30 immunizations with indicated TLR agonist. (E) Average percentage of ABCs among B cells in spleen of young (12-week-old) BXSB male and female mice. (F) Bone marrow chimeras possessing wild-type or TLR7^−/− B cells were treated with vehicle or TLR7 agonist for 2 months, and the percentage of ABCs in the spleen was determined by flow cytometric analysis. Bars represent mean (± SEM) of at least 10 mice per group. *P < .05 (Student 2-tailed t test).