Abstract
The sequential appearance of the thymocyte subpopulations and TCR gene messages occurred in the thymus of AKR mice (H-2k, Mlsa) from 7 to 14 days after sublethal irradiation. The thymocytes on day 7 after irradiation were composed of a large number of CD4+CD8+ blast-like cells and a relatively high proportion of CD4-CD8- cells (15 to 25%) but few CD3highCD4+CD8-/CD4-CD8+ cells. Approximately 22% of the CD4-CD8- cells were CD3high and -27% of the CD3highCD4-CD8- cells (-6% of whole CD4-CD8- cells) were F23.1+. The thymocytes on day 7 expressed a large amount of gamma- and delta-chain gene transcripts but reduced levels of alpha- and beta-chain gene transcripts. The V gene repertoire of 18 functional beta-chain cDNA derived from the thymocytes on day 7 was compared with those of 20 functional beta-chain cDNA derived from the thymocytes on day 14 which were composed of a large number of CD3lowCD4+CD8+ small-sized cells and a small number of CD3highCD4+CD8- cells. It is noteworthy that the distribution of V beta genes expressed in the thymocytes on day 7 was much the same as that in the thymocytes on day 14 but significantly different from that in normal BALB/c thymocytes as previously described. Interestingly, neither V beta 8.1 nor V beta 6 genes, which are important for recognition of the product of the Mlsa locus, was detected in these two cDNA libraries. These results suggest that clonal selection of TCR V beta repertoire, irrespective of positive or negative selection, appears to occur at the early stage of T cell differentiation, i.e., on the blast-like CD4+CD8+ thymocytes.
- Copyright © 1989 by American Association of Immunologists
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