CD45RA−RO+subset is the major population of dividing thymocytes in the human

摘要

AbstractCD45, or leukocyte common antigen, is expressed in different isoforms on different subsets of thymocytes, suggesting its involvement in the process of T cell development in the thymus. We report studies on CD45 isoform expression on human thymocytes at various stages of development using three‐color flow cytometric analysis and cell cycle analysis. Among CD45RO+cells 18.4 were in S+G2/M phase and represented more than 80 of the dividing cells in the thymus. Among the CD45RO−cells 10.9 were also in cell cycle. Because the CD45RO+population is almost exclusively CD45RA−, the CD45RA−RO+subset constitutes the major portion of dividing cells in the thymus. Both the CD1highand the CD3−populations were actively cycling. However, the former was almost 100 and the latter only 50 CD45RA−RO+. Dividing CD45RA−RO+cells contain, therefore, many cells that have not yet expressed the CD3/T cell receptor complex and presumably have not yet undergone selective procedures. These results are hard to reconcile with the previously presented hypothesis that CD45RO represents a marker for cells that are destined to die in the thymus. Instead, these results suggest an alternative possibility that CD45RO+cells may contain cells that can mature and, thus, also constitute the thymic gener