Figure 6. Low SHM IgM⁺ GC B Cell Clones Persist in the Absence of FcγRIIB on FDCs.

(A) Experimental setup to label and follow 564Igi-induced, autoreactive GC B cells. B6 or FcγRIIB^−/− mice were lethally irradiated and subsequently received a 1:2 mixture of 564Igi and Aicda^CreERT2EYFP BM or a 1:2 mixture of B6 and Aicda^CreERT2EYFP BM. After 9 weeks, mice were tamoxifen induced (tamox) and splenic EYFP⁺ GC B cells were sorted at days 7 or 14 post-tamoxifen.

(B) Gating strategy used to sort EYFP⁺ GC B cells. Cells were gated on forward versus side scatter (FSC/SSC) for lymphocytes, singlets, and live-dead stain negative cells before the indicated gates.

(C) Frequency of EYFP⁺ GC B cells relative to measured B220⁺ B cell population in indicated chimeras and naive Aicda^CreERT2-EYFP mice (naiv) and 564Igi mice at the 1 week post-tamoxifen time point. Recip, recipient; KO, FcγRIIB^−/−. All of the chimeras received 2 parts Aicda^CreERT2-EYFP (not shown) and 1 part 564Igi (+564) or 1 part B6 (+B6). Pooled data from 3 independent experiments. n = 6 mice for 564Igi+Aicda^CreERT2 EYFP chimeras, 4 mice for B6+Aicda^CreERT2EYFP recipients, naive Aicda^CreERT2EYFP, and 564Igi mice. Error bars represent SDs.

(D and E) The number of nucleotide mutations (D) or amino acid mutations (E) in the VDJ region from EYFP⁺ GC B cell heavy chains obtained from 564Igi+Aicda^CreERT2EYFP mixed BM chimeras 1 week post-tamoxifen. Sequences from three mice per group.

(F and G) Nucleotide mutations (F) or amino acid mutations (G) 2 weeks post-tamoxifen treatment. Sequences from two mice per group. Kruskal-Wallis with Dunn’s post hoc testing. The number of sequences analyzed for this figure is listed in Table S1.