T-cell receptor beta-chain gene rearrangement and expression during human
thymic ontogenesis
A Bonati, P Zanelli, S Ferrari, A Plebani, B Starcich, M Savi and TM Neri
Institute of Medical Pathology, University of Parma, Italy.
T-cell receptor (TCR) beta-chain proteins appear early (approximately 15th
week of gestation) during human thymic ontogenesis. These beta- chain
proteins, which appear before terminal deoxynucleotidyl transferase (TdT),
could be an expression of a fully rearranged (V-D- J), incompletely
rearranged (D-J), or germline TCR beta-chain gene. The aims of this study,
performed from the 15th week onward, were the following: (1) to investigate
whether or not TCR beta gene rearranges at an early stage during human
thymic ontogenesis; (2) to investigate whether complete presumptive
functional (1.3 kb) TCR beta gene transcript is present at these early
stages of development, or if incomplete (1 kb) or germ-line (1.1 kb)
transcripts are expressed; (3) to examine the phenotype of TCR beta-chain+
cells with two-color fluorescence using monoclonal antibody (MoAb) beta F1
and MoAbs that recognize CD1, CD2, CD3, CD4, CD8, CD5, and CD7 antigens
(rabbit anti- calf TdT antiserum was used to detect TdT); and (4) to
demonstrate whether or not beta gene N-diversity regions are detectable as
early as the 15th week and whether or not N-nucleotide insertions correlate
to TdT expression. Fifteen- to 22-week fetal thymuses and pediatric
thymuses were investigated. We demonstrated that TCR beta-chain gene
rearranged as early as the 15th week in human thymus and that a complete
functional TCR beta gene transcript was expressed at these early stages of
human development. No other analyses to date have investigated TCR beta
gene expression in early human thymus using molecular biology techniques.
No significant differences were detectable between phenotypic analysis of
fetal and pediatric samples, except for TdT expression, which appeared
after the 20th week. Essentially all mCD3+ (OKT3+) cells were beta-chain+
at the different weeks investigated. A significant percentage of CD1+ cells
were beta- chain+, and the percentage increased along with the age of
development. After the 20th week, we identified three main populations:
TdT+, cCD3+, beta F-(early thymic precursors); TdT+, CD1+, beta F1+
(intermediate maturity cortical thymocytes); and TdT-, mCD3+, beta F1++
(mature medullary thymocytes). Given these values, we may consider
beta-chain expression an ordered process. beta gene N-nucleotide insertions
were correlated to TdT expression, since N-regions increased considerably
after the 20th week. A further increase of N-nucleotide insertions was
detected from the 22nd week to the 32nd week.
Volume 79,
Issue 6,
pp. 1472-1483,
03/15/1992
Copyright © 1992 by The American Society of Hematology
