Quantifying CD73⁻ and CD73⁺ memory B cells. Combined data from five experiments showing the numbers of PE-specific (A) GC cells, IgM⁺ CD73⁻ and CD73⁺ memory cells (B), or swIg⁺ CD73⁻ and CD73⁺ memory cells (C) at the indicated time points after injection. (D) Combined data from multiple experiments showing the numbers of CD73⁻ and total (CD73⁻ + CD73⁺) PE-specific memory cells and at days 6, 10, and 30. The mean and SEM (n = 3–6) are shown for A–D. (E) Combined data from two experiments showing the numbers of IgM⁺ CD73⁻, IgM⁺ CD73⁺, swIg⁺ CD73⁻, and swIg⁺ CD73⁺ memory cells 60 d after injection with 1.5, 15, or 150 µg PE in CFA or 15 µg PE adsorbed to alum. To account for unstimulated naive cells contaminating the IgM⁺ CD73⁻ population, the mean number of PE-specific cells found in unimmunized animals was subtracted from the IgM⁺ CD73⁻ population. The means and SEM (n = 3–6) are shown.