Figure 5.

Activation of Erk2 does not require costimulation. (A) DP thymocytes were stimulated with anti-CD3 with or without anti-CD28, and cell lysates were tested after different periods of stimulation for Erk2 activity by in vitro i.p. kinase reaction using MBP as a substrate. (B) In addition, DP thymocytes were stimulated for 5 min with anti-CD3 with or without anti-CD28 and analyzed for JNK activity in a solid state kinase reaction using GST–c-Jun (1–223) as a substrate (Upper) or Erk2 activity as in A (Lower). The numbers underneath the lanes represent the fold induction compared with samples treated with only crosslinker, calculated from quantification obtained by phosphorimager.