The expanded IgD⁺ population is composed mostly of naive, nonproliferating, B-2 lineage cells. (A) The cellular phenotype of bone marrow IgD⁺ cells was determined by flow cytometry 12 hours following IFA injection. Representative flow plots are shown. CD11b⁺ and CD43⁺ cells were enumerated across 2 independent experiments. (B) Fixed and permeablized bone marrow cells were stained with DAPI and B-cell makers to analyze cell cycle. Shown is a representative histogram comparing naive and IFA mice at 12 hours. The percentage of IgD⁺ cells in each cell cycle phase was tabulated and is graphed, n = 5 in each group and error bars are SEM. (C) Bone marrow populations were stained for intracellular Ki67. A representative histogram for IgD⁺ and progenitor populations is shown. The experiment was repeated twice.