Identification and characterization of peritoneal cavity B1d and B1d²³⁺ cells. (A) Left panel: Subfractionation of WT peritoneal cavity CD19⁺CD11b⁻CD5⁻ cells by anti-CD23. The abundance of the 2 subsets is shown as the mean percentage of total CD19⁺CD11b⁻CD5⁻ cells. Right panels: Overlaid CCL2^AF647 uptake profiles of WT (black) and D6-deficient (KO, gray) CD23⁺ and CD23⁻ subsets, referred to as ‘FO’ and B1d, respectively. Proportion of D6^active ‘FO’ B cells is indicated. (B) Surface immunophenotype of WT peritoneal cavity ‘FO’ and B1d B cells. Data show average mean fluorescence intensity (MFI) ± SEM. (C) Comparison of size of WT peritoneal cavity ‘FO’, B1d, and CD11b⁺ B1 (B1a/b) cells by forward scatter (FSC; left panel), and microscopic measurements of nuclear and cellular diameter (middle and right panels) of FACS-sorted peritoneal cavity cells. (D-E) Production of IL-10, IgM, and anti-PC Abs by FACS-sorted, cultured CD11b⁺ B1 (B1a/b), B1c, B1d, and ‘FO’ cells. Data show means ± SEM of data generated from 3 repeat experiments. ND indicates not detected. (F) Overlaid forward scatter (FSC; left panel) and surface CD19 (right panel) of WT peritoneal cavity D6-active and D6-negative CD19⁺CD11b⁻CD5⁻CD23⁺ ‘FO’ cells. (G) Surface immunophenotype of WT peritoneal cavity D6-active and D6-negative CD19⁺CD11b⁻CD5⁻CD23⁺ ‘FO’ cells shown as the average mean fluorescence intensity (MFI) ± SEM. (H) Production of IgM by FACS-sorted, cultured CD19⁺CD11b⁻CD5⁻CD23⁺ cells in the absence (−) or presence (+) of their D6-active subset. Flow cytometric profiles are representative of data from at least 3 mice per genotype per experiment, with experiments repeated at least 3 times. *P < .05; **P < .01; ***P < .001.