To distinguish between these two possibilities, we directly investigated whether constitutive activation of Btk had the capacity to change the B-cell Cabozantinib cost fate in the 3-83μδ Tg system. The 3-83μδ Tg encodes an antibody specific for MHC class I of the H-2Kk,b haplotype 29. On a non-autoreactive background, the expression of the 3-83μδ BCR commits B cells to the follicular or MZ subsets in the spleen. In these 3-83μδ BCR Tg mice only B cells that have edited their BCR are able to differentiate into

CD5+ B-1 B cells: all peritoneal B220lowCD5+ B-1 B cells have lost the 3-83μδ BCR specificity detected by the 54-1 anti-idiotypic antibody (Fig. 4A). We generated 3-83μδ Tg E-Btk-2 and EY-Btk-5 mice on the non-autoreactive H2-Kd background. As expected, in the spleen of these mice all conventional B220highCD5− B cells had high 54.1 reactivity. However, B220lowCD5+ B cells had lost their 54.1 reactivity (Fig. 4B), while surface Ig μ and κ expression levels were similar (data not shown). These results indicate that 3-83μδ Tg E-Btk-2 and EY-Btk-5 B220lowCD5+ B-1 B cells in the spleen had undergone receptor editing. We therefore conclude that the presence of the E-Btk-2

or EY-Btk-5 Tg did not change the follicular versus selleckchem B-1 B-cell subset choice. Instead, the increased proportions of splenic CD5+ B cells in E-Btk-2 and EY-Btk-5 mice most likely resulted from increased expansion or survival of B-1 B cells. The presence of the E-Btk-2 and EY-Btk-5 Tg also did not change the MZ B-cell subset choice in VH81X Tg mice, which carried a VH81X Tg encoding an Ig heavy chain favoring MZ B-cell development 30. As shown in Fig. 5A and B cells recognized by the 35-1 anti-idiotypic antibody are efficiently selected into the MZ B-cell compartment

in VH81X WT, but not in VH81X Tg Btk-deficient spleens (Fig. 5B). Splenic 35-1+ CD19+ B cells from VH81X E-Btk-2 Tg mice expressed similar CD5 levels as those from VH81X WT, lacked the B220low phenotype characteristic for CD5+ B cells and, importantly, had a CD21high/CD23low MZ phenotype similar to those of VH81X WT mice (Fig. 5A). ID-8 Moreover, in contrast to E-Btk-2 mice (which had few MOMA-1+ macrophages and no MZ B cells in the spleen), in E-Btk-2 mice that carried a VH81X Tg splenic architecture was corrected: EY-Btk-2 VH81X double Tg spleens contained IgM+ B cells within and outside rims of brightly staining MOMA-1+ macrophages (Fig. 5A; right panels). Collectively, these findings show that MZ cell fate was maintained in the presence of constitutive active Btk, indicating that the VH81X BCR specificity is dominant over the increased BCR signal strength generated by the E-Btk-2 Tg.