2a). The B220+ CD43− fraction can be further subdivided based on surface IgM and IgD expression into pre-B (IgM− IgD−), immature

(IgM+ IgD−) or mature (IgM+ IgD+) B cells29 (Fig. 2a). We found that WT and dnRAG1 mice exhibited Dinaciclib molecular weight a similar percentage and absolute number of B220+ CD43+ B cells, but the more mature B220+ CD43− B-cell subset was slightly lower in dnRAG1 mice compared with WT mice because of a significant reduction of mature B cells (Fig. 2a,b; see Supplementary material, Table S2). Taken together, these data suggest that dnRAG1 expression impairs B-cell development in the bone marrow at the immature-to-mature B-cell transition. Upon reaching the immature stage, B cells migrate to the spleen to complete their maturation, progressing through phenotypically and functionally distinct transitional stages during this process.30,31 Splenic B220hi B cells can be initially segregated based on the differential expression of AA4.1 (CD93) into transitional (B220hi AA4.1+) and mature (B220hi AA4.1−) subsets. Transitional cells can be further classified into subsets based on the CB-839 concentration differential expression of surface IgM and CD23.32 T1 B cells (IgMhi CD23lo) are considered as immature B cells that have recently emigrated from

the bone marrow, which can differentiate into T2 B cells (IgMhi CD23hi).32 A third transitional B-cell subset, T3 (IgMlo CD23+), is thought to consist of immature B cells that have been rendered anergic by encounter with self-antigen.31,33 The mature B-cell population can be further subdivided by the differential expression of CD21 and CD23

into follicular (CD21int CD23−) and marginal zone (MZ; CD21hi CD23+) B-cell subsets.31 Consistent with observations in the bone marrow, dnRAG1 mice exhibit a significant reduction in the number of splenic transitional (B220hi AA4.1+) B cells compared with WT mice, because of a significant loss of cells in the T2 and T3 subsets (Fig. 2a,b; see Supplementary material, Table S2). In dnRAG1 mice, the mature B220hi AA4.1−subset is also significantly reduced relative to WT mice, with most of the difference attributed Adenosine triphosphate to a significant decrease in follicular B cells, but not MZ B cells (Fig. 2a,b). To explain the lack of an apparent defect in early B-cell maturation and in T-cell development in dnRAG1 mice, we used qPCR to detect total RAG1 transcript in various tissues and compare the relative abundance of RAG1 transcript between normal and dnRAG1 mice after normalizing to an internal calibrator (β-actin). From these experiments, we found that splenic RAG1 transcript levels are about 120-fold higher in dnRAG1 mice compared with normal littermates, but little difference was observed in thymus, bone marrow, lymph node, or liver (Fig. 3a,b).