Precursors of functional MHC class I- or class II-restricted CD8alphaalpha(+) T cells are positively selected in the thymus by agonist self-peptides

Immunity. 2002 Mar;16(3):355-64. doi: 10.1016/s1074-7613(02)00284-4.


The origin and specificity of alphabeta TCR(+) T cells that express CD8alphaalpha have been controversial issues. Here we provide direct evidence that precursors of functional CD8alphaalpha T cells are positively selected in the thymus in the presence of agonist self-peptides. Like conventional positive selection, this agonist selection process requires functional TCR alpha-CPM, whereas it is independent of CD8beta expression. Furthermore, CD8alphaalpha expression on mature, agonist-selected T cells does not imply selection by MHC class I, and CD8alphaalpha(+) T cells can be either class I or class II restricted. Our data define a distinct agonist-dependent, positive selection process in the thymus, and they suggest a function for CD8alphaalpha distinct from the conventional TCR coreceptor function of CD8alphabeta or CD4.

Publication types

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

MeSH terms

  • Animals
  • Antigen Presentation*
  • CD8 Antigens / immunology*
  • CD8-Positive T-Lymphocytes / immunology*
  • Histocompatibility Antigens Class I / immunology
  • Histocompatibility Antigens Class II / immunology
  • Mice
  • Mice, Transgenic
  • Thymus Gland / immunology*


  • CD8 Antigens
  • CD8 antigen, alpha chain
  • Histocompatibility Antigens Class I
  • Histocompatibility Antigens Class II