Tlr9 deficiency equally increases MYD88^L265P B-cell proliferation and differentiation into IgM plasmablast in vivo. (A) Flow cytometric analysis of the spleens of Rag1^−/− recipient mice 11 days after transplantation of transduced B cells. Plots show concatenated data from 3 recipients per treatment: B220 vs IgM plots show the mean percentage of live spleen lymphocytes falling within the indicated IgM⁺ B-cell gate; CD19 vs EGFP plots are gated on the IgM⁺ B cells and show the percentage of EGFP-expressing cells with either high or low levels of CD19 expression. (B) Total number of live EGFP⁺ cells in the spleen of each recipient mouse. (C) Percentage of CD19^low cells among live EGFP⁺ cells in the spleen of each recipient mouse. Total number of live CD19^high EGFP⁺ (D) and CD19^low EGFP⁺ (E) cells in the spleen of each recipient mouse. Data are representative of 3 independent experiments. (F) Flow cytometric analysis as performed in panel A; plots show concatenated data from 4 recipients per treatment: CD19 vs EGFP plots are gated on live cells and show the percentage of EGFP expressing cells with either high or low levels of CD19 expression; histograms display CD138 and B220 expression and are gated on either CD19^high or CD19^low EGFP⁺ cells. (G) Plots show CD138 and IgM expression on live EGFP⁺ cells as analyzed in panel F. (H) Sera IgM and IgG measured by ELISA from groups of Rag1^−/− recipient mice on the day of flow cytometric analysis. Statistical analysis by unpaired Student t-test. *P < .05; **P < .01; ***P < .001.