The blood contains multiple distinct progenitor populations with clonogenic B and T lineage potential.
The thymus is seeded by bone marrow-derived progenitors that circulate in the blood. Multiple cell types can be found in the thymus early after i.v. administration or in steady state, but most fail to satisfy the known characteristics of true T progenitors. Cells that do conform to classical definitions retain multilineage potential, but surprisingly, cannot make B cells. Because acquisition of the T lineage fate among noncommitted progenitors is a lengthy process, the absence of B cell potential in early thymocytes suggests that B and T lineages diverge prethymically. To test this suggestion, we screened numerous presumptive progenitor populations for T cell growth and differentiation potential, as well as for clonogenic T or B cell development. We find that blood and marrow each contain multiple distinct subsets that display growth and differentiation potential consistent with being canonical T progenitors. Assessment of clonogenic potential further shows that although all blood and marrow populations have high T cell cloning potential, no T/non-B cells are apparent. These data suggest that either true thymic reconstitution potential derives from a small T/non-B cell subset of one of these populations, or that most of the cells defined as canonical progenitors within the thymus do not, in fact, reside in the mainstream of T progenitor differentiation.
Umland
Oliver
O
The Scripps-Florida Research Institute, 5353 Parkside Drive, Jupiter, FL 33458, USA.
Mwangi
William N
WN
Anderson
Bradley M
BM
Walker
Juliette C
JC
Petrie
Howard T
HT
D000818:Animals; D000067696:Ataxin-1; D000067528:Ataxins; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D002454:Cell Differentiation; D019070:Cell Lineage; D002999:Clone Cells / Q000737:chemistry / Q000166:cytology / Q000276:immunology; D006412:Hematopoietic Stem Cells / Q000737:chemistry / Q000166:cytology / Q000276:immunology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009419:Nerve Tissue Proteins / Q000032:analysis; D009687:Nuclear Proteins / Q000032:analysis; D019009:Proto-Oncogene Proteins c-kit / Q000032:analysis; D020395:Receptors, Interleukin-7 / Q000032:analysis; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology; D051941:fms-Like Tyrosine Kinase 3 / Q000032:analysis
D000067696:Ataxin-1; D000067528:Ataxins; C000593750:Atxn1 protein, mouse; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D020395:Receptors, Interleukin-7; C497971:Flt3 protein, mouse; D019009:Proto-Oncogene Proteins c-kit; D051941:fms-Like Tyrosine Kinase 3