(A) Expression of RAG in DWEYS tetramer-binding cells requires the presence of circulating dsDNA in the plasma. BALB/c naive splenocytes were adoptively transferred to Rag2^–/– mice. Three weeks later, the recipient mice were immunized with DWEYS-MAP as described in Figure 3. From day 9 through day 15 following immunization, 500 μg active or heat-inactivated bovine DNase I were administered to the mice. Tetramer-reactive cells were sorted on day 16, and Rag1 and Rag2 were analyzed by qPCR. (B) Soluble 10-2–BSA induces RAG in the spleen of mice immunized with 10-2–KLH. (C and D) Receptor revision is induced in antigen-reactive B cells by soluble 10-2–BSA. BALB/c mice were immunized with 10-2–KLH in CFA on day 0 and boosted with 10-2–KLH in incomplete Freund adjuvant on day 7. On days 13, 14, and 15, 1 mg of 10-2–BSA or BSA were administered. qPCR analysis for the mRNA of l chain (Igl-V1) was done on 10-2–tetramer reactive cells, and nonreactive naive B cells were sorted on day 16 (C). Data (mean ± SEM) are representative of 2 independent experiments. Serum levels of Igλ were measured by ELISA (D). Five mice were included in each group. The experiment was repeated twice. **P < 0.01, 2-tailed Student’s t test.