Figure 2.

CD69 expression by CD4 CD8 DP thymocytes is triggered by biologically relevant TCR-MHC–peptide contact. Young adult OT-I TCR transgenic/RAG-1°/β2m° thymi were cut into fragments and cultured with or without exogenous peptides (20 μM) and exogenous β2m to allow the reconstitution of K^b–peptide complexes as described (28). CD69 expression was determined 24 h later. Data on thymocyte selection and mature T cell activation are from references 28, 34–36. K_d (off/on) values are listed in the text.