B lymphopoiesis in the thymus.
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.
Akashi
K
K
Department of Pathology, Stanford University School of Medicine, Stanford, CA, USA. koichi_akashi@dfci.harvard.edu
Richie
L I
LI
Miyamoto
T
T
Carr
W H
WH
Weissman
I L
IL
D000818:Animals; D016175:B-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D002454:Cell Differentiation / Q000276:immunology; D002465:Cell Movement / Q000276:immunology; D016650:Fluorescein-5-isothiocyanate / Q000378:metabolism; D006410:Hematopoiesis / Q000276:immunology*; D007075:Immunoglobulin M / Q000096:biosynthesis; D017493:Leukocyte Common Antigens / Q000096:biosynthesis; D008198:Lymph Nodes / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000378:metabolism; D016692:Receptors, Antigen, T-Cell, gamma-delta / Q000378:metabolism; D013154:Spleen / Q000166:cytology; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism
D007075:Immunoglobulin M; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016692:Receptors, Antigen, T-Cell, gamma-delta; D017493:Leukocyte Common Antigens; D016650:Fluorescein-5-isothiocyanate