Impaired IgM response in Stat1^−/− MZ B cells in response to TLR stimulation in vitro and in vivo . MZ B (A) or FO B (B) cells of WT and Stat1^−/− mice were treated with or without 1 µg/ml Pam3CSK4 (Pam), 2 µg/ml LPS, 10 µg/ml R848, or 1 µg/ml CpG for 4 d (n = 3–5). Results represent three experiments. Same as in A, except MZ B cells of WT and (C) Ifnar1^−/− or (D) Ifngr1^−/− mice were stimulated with the indicated TLR agonists for 4 d. Secreted IgM in the culture supernatant was measured by ELISA (n = 2–5). Results represent two to three experiments. (E) WT and Stat1^−/− mice were intravenously injected with 25 µg LPS for 0, 3, and 5 d (n = 5). Results represent three experiments. (F) MZ B cells of WT or Stat1^−/− mice (2 × 10⁶ each) were adoptively transferred into RBP-J CKO mice for 1 d, and then 25 µg LPS was intravenously injected for the indicated times. Total serum IgM of the treated mice was measured by ELISA (n = 4). Results represent two experiments. All values are shown as the means ± SD. *, P < 0.05; **, P < 0.01, Student’s t test.