Accumulating B cells are derived from the recirculating lymphocyte pool. (A) Splenic follicular (CD19⁺CD23⁺CD21⁺) and marginal zone (CD19⁺CD23^loCD21^hi) B-cell populations were quantified following IFA treatment. Data are pooled from 2 experiments. (B) Blood B cells were enumerated by flow cytometry. Data are pooled from 2 independent experiments. (C) Single axillary and inguinal lymph nodes were pooled and analyzed together with mesenteric lymph nodes by flow cytometry. Data are pooled from 2 independent experiments. (D) Splenic IgD⁺ cells were sorted by FACS and labeled with Cell Tracker Orange before IV injection. Data are from 2 experiments. (E) Two weeks after splenectomy mice were challenged with IFA for bone marrow analysis. In additional experiments intact or splenectomized mice were treated with FTY-720 immediately prior to IFA. Data are from 2 or 3 experiments. (F) B-cell blood counts are compared between the data from (B) and splenectomized mice. Data are pooled from 2 experiments.