The stem cell antigens Sca-1 and Sca-2 subdivide thymic and peripheral T lymphocytes into unique subsets.
Stem cell Ag 1 and 2 (Sca-1 and Sca-2), so named due to their expression by mouse bone marrow stem cells, were evaluated for expression by populations of cells within the thymus. Immunohistochemical analysis demonstrated that Sca-1 was expressed by cells in the thymic medulla and by some subcapsular blast cells, as well as by the thymic blood vessels and capsule. Sca-2 expression, which was limited to the thymic cortex, could be associated with large cycling thymic blast cells. Both Sca-1 and Sca-2 were expressed on a sub-population of CD4-CD8- thymocytes, and this subpopulation was entirely contained within the Ly-1lo progenitor fraction of cells. Sca-1 expression by a phenotypically mature subset of CD4+CD8- thymocytes was also noted. Conversely, Sca-2 expression was observed on a phenotypically immature or nonmature subpopulation of CD4-CD8- thymocytes. MEL-14, an antibody that defines functional expression of a lymphocyte homing molecule, identified a small population of thymocytes that contained all four major thymic subsets. Sca-2 split the MEL-14hi thymocyte subset into two Sca-2+ non-mature/immature phenotype fractions and two Sca-2- mature phenotype fractions. In peripheral lymphoid organs, Sca-1 identified a sub-population of mature T lymphocytes that is predominantly CD4+CD8-, in agreement with the thymic distribution of Sca-1. Peripheral T cells of the CD4-CD8+ phenotype were predominantly Sca-1-. In contrast, Sca-2 did not appear to stain peripheral T lymphocytes, but recognized only a subset of B lymphocytes which could be localized by immunohistochemistry to germinal centers. Thus, expression of Sca-1 is observed throughout T cell ontogeny, whereas Sca-2 is expressed by some subsets of thymocytes, including at least one half of thymic blasts, but not by mature peripheral T lymphocytes.
Spangrude
G J
GJ
Department of Pathology, Stanford University School of Medicine, CA 94305.
Aihara
Y
Y
Weissman
I L
IL
Klein
J
J
D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis; D000954:Antigens, Surface / Q000032:analysis; D015815:Cell Adhesion Molecules; D002453:Cell Cycle; D002454:Cell Differentiation; D007150:Immunohistochemistry; D008221:Lymphoid Tissue / Q000032:analysis; D051379:Mice; D008810:Mice, Inbred C57BL; D010641:Phenotype; D013194:Staining and Labeling; D013234:Stem Cells / Q000145:classification*; D013535:Suspensions; D013601:T-Lymphocytes / Q000145:classification* / Q000166:cytology; D013950:Thymus Gland / Q000166:cytology*
D000945:Antigens, Differentiation, T-Lymphocyte; D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D013535:Suspensions