Inhibition of Notch2-mediated marginal zone B-cell development by DNMAML1 but not Dtx1. C57BL/6 mice were lethally irradiated and reconstituted with BM cells transduced with MigR1, Mig DNMAML1, and Mig Dtx1. Analysis was performed at least 6 weeks after transplantation. (A) Expression of sIgM and CD21 in GFP^- and GFP⁺ spleen cells. A selective loss of sIgM^hi CD21^hi B cells is observed in the GFP⁺ fraction of DNMAML1-transduced mice (arrowheads). (B) Analysis of CD21 and CD23 profiles among GFP^- and GFP⁺ sIgM⁺ cells, showing the selective loss of 2 distinct populations of cells after transduction with DNMAML1. sIgM⁺CD21^hiCD23^low cells (^*) are marginal zone B cells. sIgM⁺CD21^hiCD23^int cells(^**) were originally thought to be a subset of transitional B cells referred to as T2 or cycling T2 B cells,²⁵  but their exact nature is controversial. The decrease in GFP⁺ relative to GFP^- MZB and cycling T2 B cells observed in DNMAML1 mice was statistically significant (P < .05). The slight increase observed in mice transduced with Mig Dtx1 was not statistically significant when compared to Mig R1 mice. (C) Analysis of AA4⁺ transitional B cell subsets as defined by a combination of sIgM and CD23 staining.²⁶  Results are representative of 2 independent experiments with at least 3 mice. The numbers in the quadrants and above the brackets indicate the percentage of cells.