Tet2 deficiency induces alterations of the proportions of peripheral B-cell populations in old mice. (A) Analysis of splenic B-cell populations in 4-month-old mice. (Left) B220 and CD19 expression analysis on total splenocytes. (Middle) CD23 and CD21 expression in the B220⁺CD19⁺ (B220⁺) gate showing the follicular (FO:CD23⁺CD21/35^medium), marginal zone (MZ: CD23^lowCD21/35^high), and newly formed (CD23⁻CD21/35⁻) B-cell populations. (Right) IgM and IgD staining gated in B220⁺CD19⁺ are also shown. Mice genotypes are indicated on the left-hand side. Histograms show the percentages of populations. (Top left) Average percentage ± standard error of the mean (SEM) of B220⁺ and B220^low populations in total splenocytes. (Bottom) Average percentage ± SEM of FO, MZ, and NF. (Top right) IgM⁺IgD⁻ and IgM⁺IgD⁺ populations in the B220⁺ B-cell compartment (Tet2^+/+ mice, n = 5; Tet2^−/− mice, n = 8). (B) Analysis of B-cell populations in the peritoneum. Peritoneal cell suspensions were stained with B220 and CD19 to define B2 (B220⁺CD19⁺) and B1 (B220^lowCD19⁺) populations. In the B1-cell gate, CD19 and CD5 expressions allow us to define B1a (CD19⁺CD5⁺) and B1b (CD19⁺CD5⁻) subsets. (Tet2^+/+, n = 4; Tet2^−/−, n = 5). The histograms show the average percentage ± SEM of the peritoneum populations. (C) Venn diagram illustrating comparison of upregulated genes in Tet2^−/− abnormal B cells and B1a cells, both with respect to splenic wild-type B cells. The deregulated pathways, as identified using gene set enrichment analyses, are shown at the bottom. SPB1a: B1a population from spleen. PCB1a: B1a population from peritoneum. (Bottom) List of signatures enriched in genes specifically upregulated in Tet2 samples. (D) Same as in panel C but for downregulated genes. (Bottom) List of signatures enriched in genes specifically downregulated in Tet2 samples. *P < .05.