Supplementary Figure 4: Related to Fig. 4. Expression of the monoclonal MD4 BCR prevents inflammation in Ikzf1^B– mice.

a, Antigen presentation by Ikaros-deficient FO B cells. Splenic CD23⁺ FO B cells from control Ikzf1^B+ mice as well as CD23⁺ (FO B) and CD21^lo/–CD23^– B cells from inflamed Ikzf1^B– mice at the age of 8 weeks were loaded with the OTII peptide before similar numbers of live cells of each B cell type were co-cultured for 4 days at a 1:1 ratio with naïve splenic CD4⁺ OTII TCR-tg Rag2^–/– T cells that were labeled with CellTrace Violet (see Online Methods). The proliferation of T cells (CellTrace Violet dilution) is shown to the left, while the differentiation of naïve T cells (CD44^–CD62L⁺) to activated T cells (CD44⁺CD62L^–) under the control of the Ikaros-deficient CD23⁺ FO or CD21^low/–CD23^– B cells is shown to the right (gated on live Vβ5.1/2⁺ Viability Dye eF780^– cells). b, Immunohistological analysis of spleen sections from 6-week-old MD4 BCR-tg Ikzf1^B+ and MD4 BCR-tg Ikzf1^B– littermates, which were stained with anti-TCRβ (blue, T cells), anti-IgD (green, B cells) and anti-CD169/MOMA-1 (red, metallophilic macrophages) antibodies. c, Expression of the indicated cell surface proteins on FO B cells (CD19⁺CD5^–CD93^–CD21^loCD23⁺) and MZ B cells (CD19⁺CD5^–CD93^–CD21⁺CD23^lo) of MD4 BCR-tg Ikzf1^B+ (purple surface) or MD4 BCR-tg Ikzf1^B– (purple line) littermates, as determined by flow cytometry. For analysis of CD21 (Cr2) expression, FO and MZ B cells were gated as CD19⁺CD5^–CD93^–CD23⁺CD1d^lo and CD19⁺CD5^–CD93^–CD23^loCD1d⁺, respectively. T1 B cells of the MD4 BCR-tg Ikzf1^B+ genotype are shown for comparison. Data in a, b and c are representative of 2, 2 and 3 independent experiments, respectively.