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

J Immunol. 2004 Apr 1;172(7):4235-44. doi: 10.4049/jimmunol.172.7.4235.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 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
  • STAT5 Transcription Factor
  • Signal Transduction / genetics
  • Signal Transduction / immunology*
  • 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

Substances

  • DNA-Binding Proteins
  • Interleukin-7
  • Milk Proteins
  • Proteins
  • Receptors, Interleukin-7
  • SOCS4 protein, mouse
  • STAT5 Transcription Factor
  • Suppressor of Cytokine Signaling Proteins
  • Trans-Activators
  • interleukin-7 receptor, alpha chain