Functional significance of CRLF2 expression. (A) Cytokine withdrawal assay of BaF3 and BaF3-CRLF2 cells infected with either empty vector (EV), mouse FLAG-Jak2 wild-type (wt), or mouse FLAG-Jak2 R683S. Error bars represent SE. (B) Constitutive activation of the Jak/Stat5 pathway in BaF3 and BaF3-CRLF2 cells expressing mouse FLAG-Jak2 wild-type (wt) or R683S, after 5 hours of cytokine deprivation. IL3+ indicates cells harvested after 5 hours of interleukin-3 deprivation followed by 15 minutes of interleukin-3 stimulation. (C) Effect of JAK inhibitor I on growth of BaF3 cells expressing Jak2 R683S and BaF3-CRLF2 cells expressing either wt Jak2 or Jak2 R683S.