An Immunologic Approach to Cell Cycle Analysis of the Stem Cell
The development of specific tools and methodologies to probe the nature of cell differentiation and proliferation in multicellular organisms is a crucial and essential step in the development of our capabilities to obtain definitive answers to these funda
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The development of specific tools and methodologies to probe the nature of cell differentiation and proliferation in multicellular organisms is a crucial and essential step in the development of our capabilities to obtain definitive answers to these fundamental biologic problems. For the hematopoietic system, the colony assay technique introducted by Till and McCulloch (27) for pluripotent stem cells or CFU-s, the in vitro assays for unipotent myeloid [CFU-c (3)], erythroid [CFU-e (25)], and, recently, megakaryocytic [CFU-m (16, 21)] progenitors, as well as cell separation techniques (12, 17), provide us with invaluable tools for addressing ourselves to the nature of hematopoietic cell regulation. Another fruitful methodology has been immunologic in nature. The finding by Reif and Allen (22) of a specific membrane-bound antigen on the surface of thymocytes (i.e., the theta or thy-1 antigen) leads one to speculate about the possible existence of other specific blood cell antigens. Since Reif and Allen noted that the theta antigen was also found in homogenates of adult brain, Golub (7) has prepared a potent anti-theta serum by immunizing animals with brain tissue rather than with thymus. This not only produced an antiserum with antitheta activity, but one which has, since, also been shown to be selectively cytotoxic to other hemic cells, such as mature erythrocytes (8), the pluripotent stem cell (9), and perhaps B-cells as well (5). With selective tissue absorption it can be shown that the cytotoxic activity for each of these cells is due to a different antibody in the anti-brain serum. All four of the above cell-specific antigens must therefore be expressed by the brain itself. For those interested in stem cell kinetics, the observation of a specific stem cell antigen is of obvious interest. This interest was intensified by the experiment reported by van den Engh and Golub (28) which showed that the stem cell antigen was lost during the step(s) in differentiation leading to the myeloid progenitor cell: although present on almost all CFU-s, the antigen could not be detected on CFU-c. With some modification in technique, this important observation appears to have been recently confirmed (24). If further confirmation of this apparent specificity is forthcoming, it would appear that the use of the anti-brain antiserum will offer a new dimension to cell kinetics studies. For example, there is one school of thought that envisions the CFU-s as a more closely related progenitor ofthe CFU -c (2, 11, 31) than of the erythroid progenitor, CFU-e (10). If this is the
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11 S. J. Baum et al. (eds.), Experimental Hematology Today © Springer Science+Business Media New York 1977
An Immunologic Approach to Cell Cycle Analysis of the Stem Cell Francis C. Monette, Peter Q. Eichacker, William Byrt, Robert I. Garver, Michael J. Gilio, and John B. DeMello.
Characterization of the Multipotential Stem Cell (CFU-s)
case and CFU-s do indeed have a parent-toprogeny relationship with CFU-c, then, extrapolating back to van den Engh and Golu
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