CD73 expression identifies most GC-derived memory B cells. (A) Representative flow cytometry plots from WT:Bcl6^−/− mixed chimeras showing the expression of CD73 on PE-specific WT and Bcl6^−/− IgM⁺ and swIg⁺ memory populations 30 d after injection, and the naive PE-specific cells found in uninjected mice. (B) Combined data from two experiments showing the numbers of PE-specific WT and Bcl6^−/− CD73⁻ and CD73⁺ memory populations 31 d after injection. (C) Numbers of PE-specific CD73⁻ and CD73⁺ memory populations 31 d after injection, treated with or without anti-CD40L beginning on day 5. The bars in B and C indicate the means. P-values are shown for the indicated comparisons.