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Mol. Cell. Biol., Mar 1996, 1074-1084, Vol 16, No. 3
M Rincon and RA Flavell
The ability of thymocytes to express cytokine genes changes during the
different stages of thymic development. Although CD4- CD8- thymocytes are
able to produce a wide spectrum of cytokines in response to a T- cell
receptor (TcR)-independent stimulus, as they approach the double- positive
(DP) CD4+ CD8+ stage, they lose the ability to produce cytokine. After the
DP stage, thymocytes become single-positive CD4+ or CD8+ thymocytes which
reacquire the ability to secrete cytokines. In an attempt to understand the
molecular basis of this specific regulatin, we use AP-1-luciferase and
newly generated NFAT-luciferase transgenic mice to analyze the
transcriptional and DNA-binding activities of these two transcription
factors that are involved in the regulation of cytokine gene expression.
Here, we show that both AP-1 and NFAT transcriptional activities are not
inducible in the majority of DP cells but that during the differentiation
of DP cells to the mature single-positive stage, thymocytes regain this
inducibility. Subpopulation analysis demonstrates that this inducibility is
reacquired at the DP stage before the down-modulation of one of the
coreceptors. Indeed AP-1 inducibility, just like the ability to express the
interleukin-2 gene, is reacquired during the differentiation of DP TcRlow
CD69low heat-stable antigen (HSA)high thymocytes to DP TcRhigh CD69high
HSAhigh cells, which is considered to be the consequence of the first
signal that initiates positive selection. We therefore propose that the
inability of DP thymocytes to induce AP-1 and NFAT activities is one of the
causes for the lack of cytokine gene expression at this stage and that this
inducibility is reacquired at the latest stage of DP differentiation as a
consequence of positive selection. This could be a mechanism to prevent the
activation of DP thymocytes before selection has taken place.
Copyright © 1996, American Society for Microbiology
Regulation of AP-1 and NFAT transcription factors during thymic selection of T cells
Section of Immunobiology, Yale University, School of Medicine, New Haven, Connecticut 06510, USA.
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