B Lymphopoiesis in the Thymus

Department of Developmental Biology , Stanford University, Stanford, California, United States
The Journal of Immunology (Impact Factor: 4.92). 06/2000; 164(10):5221-6. DOI: 10.4049/jimmunol.164.10.5221
Source: PubMed


The thymus has been regarded as the major site of T cell differentiation. We find that in addition to alphabeta and gammadelta T cells, a significant number (approximately 3 x 104 per day) of B220+IgM+ mature B cells are exported from the thymus of C57BL/6 mice. Of these emigrating B cells, we estimate that at least approximately 2 x 104 per day are cells which developed intrathymically, whereas a maximum of approximately 0.8 x 104 per day are cells which circulated through the thymus from the periphery. The thymus possesses a significant number of pro-B and pre-B cells that express CD19, VpreB, lambda5, and pax-5. These B cell progenitors were found in the thymic cortex, whereas increasingly mature B cells were found in the corticomedullar and medullary regions. Other lymphoid cells, including NK cells and lymphoid dendritic cells, are not exported from the thymus at detectable levels. Thus, the thymus contributes to the formation of peripheral pools of B cells as well as of alphabeta and gammadelta T cells.

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Available from: William H. Carr, Jul 10, 2014
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    • "However, mature B cells are clearly present in thymus although in low frequencies (Akashi et al., 2000;Cukrowska et al., 1996a;Sinkora et al., 2000a). The presence of B cells in the thymus is sometimes explained as a consequence of marginal B cell lymphopoiesis occurring in the thymus (Akashi et al., 2000;Perera et al., 2013) or as a consequence of B cells immigration into the thymus (Cukrowska et al., 1996a;Sinkora et al., 2000a). Our earlier results showed that IgM þ B cells are present within porcine thymus in the frequencies of ~1% from all thymocytes (Sinkora et al., 2000a). "
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    • "Based upon previous reports on intrathymic B lymphopoiesis (Akashi et al., 2000), we considered that Aire expression might be an intrinsically programmed feature of an intrathymically differentiating B lineage. Around one third of CD19 + thymic B cells were surface IgM – IgD – and thereby resembled B cell precursors in the BM (Figure 2A). "
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    • "Subsequently, phycoerythrin staining demonstrated that approximately 3 × 104 cells/day emigrate from the adult mice thymus, showing a T cell-unrelated phenotype. These emigrant cells express IgM and B220 molecules and are therefore characterized as mature B cells [49]. In the same study, it was demonstrated that the majority of thymic B cells matured in the thymus, and only a minority of this population constituted infiltrated B cells. "
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