Activation of Lyn and Btk is not dependent on FCS in medium. HMC-1.1 and HMC-1.2 cells were kept in 1% or 10% FCS for 4 hours. Thereafter, the expression of Lyn, p-Lyn^Tyr507, p-Src^Tyr416, Btk, and p-Btk^Tyr223 were analyzed by Western blotting. β-actin served as loading control.