Overlay histogram showing THP-1 (human monocytic leukemia cell line) cells stained with ab15691 (red line). The cells were fixed with 80% methanol (5 minutes) and then permeabilized with 0.1% PBS-Tween for 20 minutes. The cells were then incubated in 1x PBS / 10% normal goat serum / 0.3M glycine to block non-specific protein-protein interactions. The cells were then incubated with the antibody (ab15691, 10 µl/1 x 10⁶ cells) for 30 minutes at 22ºC. Isotype control antibody (black line) was mouse IgG2b (FITC) (ab91368, 10 µl/1 x 10⁶ cells) used under the same conditions. Acquisition of >5,000 events was performed. This antibody gave a positive signal in THP-1 cells fixed with 4% paraformaldehyde (10 minutes)/permeabilized in 0.1% PBS-Tween used under the same conditions.