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Original Article |
Correspondence to: Yoshimoto Katsura, Department of Immunology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto 606-8507, Japan. Tel:81-75-751-3842 Fax:81-75-751-4648 E-mail:katsura{at}frontier.kyoto-u.ac.jp.
We have established a new clonal assay system that can evenly support the development of T and natural killer (NK) cells. With this system, we show that all T cell progenitors in the earliest CD44+CD25-Fc
RII/III- fetal thymus (FT) cell population retain NK potential, and that the NK lineagecommitted progenitors (p-NK) also exist in this population. T cell lineagecommitted progenitors (p-T), which are unable to generate NK cells, first appear at the CD44+CD25- Fc
RII/III+ stage in day 12 FT. The proportion of p-T markedly increases during the transition from the CD44+CD25- stage to the CD44+CD25+ stage in day 14 FT. On the other hand, p-NK preferentially increase in number at the CD44+CD25- stage between days 12 and 14 of gestation. The production of p-NK continues up to the CD44+CD25+ stage, but ceases before the rearrangement of T cell receptor ß chain genes. It was further shown that the CD44+CD25- CD122+ population of day 14 FT exclusively contains p-NK. These results indicate that the earliest T cell progenitor migrating into the FT is T/NK bipotent, and strongly suggest that the bipotent progenitor continuously produces p-NK and p-T until the CD44+CD25+ stage.
Key Words: T cell, natural killer cell, hematopoietic stem cell, thymus, clonal assay
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