Thymocytes between the beta-selection and positive selection checkpoints are nonresponsive to IL-7 as assessed by STAT-5 phosphorylation

• Published in: The Journal of immunology (1950) 2004-04, Vol.172 (7), p.4235-4244
• Main Authors: Van De Wiele, C Justin, Marino, Julie H, Murray, Bryce W, Vo, Stephen S, Whetsell, Michael E, Teague, T Kent
• Format: Article
• Language: English
• Subjects: Animals; Cell Differentiation - genetics; Cell Differentiation - immunology; Cell Separation; Cell Survival - genetics; Cell Survival - immunology; DNA-Binding Proteins - metabolism; Dose-Response Relationship, Immunologic; Down-Regulation - immunology; Female; Flow Cytometry; Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; Interleukin-7 - pharmacology; Mice; Mice, Inbred C57BL; Milk Proteins; Phosphorylation; Proteins - antagonists & inhibitors; Proteins - genetics; Receptors, Interleukin-7 - antagonists & inhibitors; Receptors, Interleukin-7 - biosynthesis; Receptors, Interleukin-7 - genetics; Signal Transduction - genetics; Signal Transduction - immunology; STAT5 Transcription Factor; Suppressor of Cytokine Signaling Proteins; T-Lymphocyte Subsets - cytology; T-Lymphocyte Subsets - immunology; T-Lymphocyte Subsets - metabolism; Thymus Gland - cytology; Thymus Gland - immunology; Thymus Gland - metabolism; Trans-Activators - metabolism; Transcription, Genetic - immunology
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.172.7.4235

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.