Overlapping and asymmetric functions of TCR signaling during thymic selection of CD4 and CD8 lineages.
TCR signaling plays a central role in directing developmental fates of thymocytes. Current models suggest TCR signal duration directs CD4 versus CD8 lineage development. To investigate the role of TCR signaling during positive selection directly, we switched signaling off in a cohort of selecting thymocytes and followed, in time, their subsequent fate. We did this using an inducible Zap70 transgenic mouse model that allowed Zap70-dependent signaling to be turned on and then off again. Surprisingly, loss of TCR signaling in CD4(+)CD8(lo) thymocytes did not prevent their development into committed CD4 single positives (SPs), nor their continued maturation to HSA(lo) SPs. However, numbers of CD4 SPs underwent a substantial decline following loss of Zap70 expression, suggesting an essential survival role for the kinase. Termination of TCR signaling is considered an essential step in CD8 lineage development. Loss of Zap70 expression, however, resulted in the rapid death of CD8 lineage precursor thymocytes and a failure to generate CD8 SPs. Significantly, extending the window of Zap70 expression was sufficient for generation and export of both CD4 and CD8 T cells. These data reveal a parallel requirement for TCR-mediated survival signaling, but an asymmetric requirement for TCR-mediated maturation signals.
Division of Immune Cell Biology, Medical Research Council National Institute for Medical Research, London NW7 1AA, United Kingdom.
Charles
C
Sinclair
Division of Immune Cell Biology, Medical Research Council National Institute for Medical Research, London NW7 1AA, United Kingdom benedict.seddon@ucl.ac.uk.
Benedict
B
Seddon
D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D016923:Cell Death / Q000235:genetics / Q000276:immunology; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D005786:Gene Expression Regulation / Q000235:genetics / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000276:immunology*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*; D051746:ZAP-70 Protein-Tyrosine Kinase / Q000235:genetics / Q000276:immunology
D011948:Receptors, Antigen, T-Cell; D051746:ZAP-70 Protein-Tyrosine Kinase; C497262:Zap70 protein, mouse