Human whole blood was fixed, lysed, and permeabilized as per the Cell Signaling Technology Flow Alternate Protocol and stained using Tri-Methyl-Histone H3 (Lys4) (C42D8) Rabbit mAb (Alexa Fluor ® 647 conjugate). The forward/side-scatter lymphocyte gate was applied to a histogram depicting the mean fluorescence intensity of Tri-Methyl-Histone H3 (Lys4) (blue histogram) versus that of a concentration-matched Rabbit (DA1E) mAb IgG XP ® Isotype Control (Alexa Fluor ® 647 Conjugate) #2985 (red histogram).