Myd88^L252P and Cd79b^Y195H cooperate to promote IgM⁺ PB and PC output from spontaneous splenic GCs. (A) Percentages of CD45.2 follicular B cells (FoB), IgM^– or IgM⁺ GCBs, PBs, or PCs in unimmunized spleens of mixed BM chimeras that were generated with a mixture of 20% Cr2-cre Myd88^L252P/+Cd79b^Y195H/+ (Myd88/Cd79b) or control BM (CD45.2) and 80% WT CD45.1/2 eight weeks after irradiation. Example gating scheme is depicted in supplemental Figure 2A. (B) Intracellular fluorescence-activated cell sorting for 5-bromo-2′-deoxyuridine (BrdU) incorporation in IgM^– or IgM⁺ GCBs from spleens of control or Myd88/Cd79b mixed BM chimeras that were treated intraperitoneally with BrdU 30 minutes before euthanasia. Frequency of (C) or BrdU incorporation in (D) IgM⁺ GCBs, IgM⁺ PBs, or IgM⁺ PCs in spleens of unimmunized control or Myd88/Cd79b mice that were 6 to 9 months old. (E) Frequency of tdTomato⁺ cells among IgM⁺ or IgM^– GCs, PBs, PCs, or MBCs in S1pr2-creERT2 Rosa26^{LSLtdTomato/+} Myd88^L252P/+ Cd79b^Y195H/+ or control mice 14 days after Cre induction by tamoxifen. Example gating for tdTomato is shown in supplemental Figure 2B. Data in panel A are from one experiment representative of three with 7 and 8 mice per group, respectively; data in panel B are from one experiment representative of two with 7 and 8 mice per group; data in panel C are pooled data from 8 independent experiments with 19 and 16 mice per group; data in panel D are pooled data from 4 independent experiments with 7 and 5 mice per group; data in panel E are pooled from 5 independent experiments with a total of 8 and 9 mice per group. *P < .05, **P < .01, ***P < .001, ****P < .0001, paired two-tailed t test for data in panel A comparing populations from the same mice and in panel B; and unpaired two-tailed t test for data in panel A comparing populations between mice and in panel E.