Thymocytes between the beta-selection and positive selection checkpoints are nonresponsive to IL-7 as assessed by STAT-5 phosphorylation.
Interleukin-7 is widely accepted as a major homeostatic factor involved in T cell development. To assess the IL-7 responsiveness of thymocytes involved in selection processes, we used a new sensitive flow cytometry-based assay to detect intracellular phosphorylation of STAT-5 induced by IL-7 in defined mouse thymocyte subsets. Using this method, we found the earliest thymocyte subset (CD4(-)CD8(-)CD25(-)CD44(+)) to contain both IL-7-responsive and nonresponsive cells. Transition through the next stages of development (CD4(-)CD8(-)CD25(+)CD44(+ and -)) was associated with responsiveness of all thymocytes within these populations. Passage of thymocytes through beta-selection resulted in a significant reduction in IL-7 sensitivity. In the next phases of development (TCR(-) and TCR(low)CD69(-)), thymocytes were completely insensitive to the effects of IL-7. STAT-5 phosphorylation in response to IL-7 was again observed, however, in thymocytes involved in the positive selection process (TCR(low)CD69(+) and TCR(intermediate)). As expected, CD4 and CD8 single-positive thymocytes were responsive to IL-7. These findings delineate an IL-7-insensitive population between the beta-selection and positive selection checkpoints encompassing thymocytes predicted to die by neglect due to failure of positive selection. This pattern of sensitivity suggests a two-signal mechanism by which survival of thymocytes at these checkpoints is governed.
Van De Wiele
C Justin
CJ
Department of Surgery, University of Oklahoma College of Medicine, Tulsa, OK 74135, USA.
Marino
Julie H
JH
Murray
Bryce W
BW
Vo
Stephen S
SS
Whetsell
Michael E
ME
Teague
T Kent
TK
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology; D002469:Cell Separation; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004306:Dose-Response Relationship, Immunologic; D015536:Down-Regulation / Q000276:immunology; D005260:Female; D005434:Flow Cytometry; D015333:Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; D015851:Interleukin-7 / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008894:Milk Proteins; D010766:Phosphorylation; D011506:Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D020395:Receptors, Interleukin-7 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D050826:Suppressor of Cytokine Signaling Proteins; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic / Q000276:immunology
D004268:DNA-Binding Proteins; D015851:Interleukin-7; D008894:Milk Proteins; D011506:Proteins; D020395:Receptors, Interleukin-7; C472529:SOCS4 protein, mouse; D050799:STAT5 Transcription Factor; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; C415350:interleukin-7 receptor, alpha chain