Human peripheral blood lymphocytes stained with ab657 (red line). Human whole blood was processed using a modified protocol based on Chow et al, 2005 (PMID: 16080188). In brief, human whole blood was fixed in 4% formaldehyde (methanol-free) for 10 min at 22ºC. Red blood cells were then lyzed by the addition of Triton X-100 (final concentration - 0.1%) for 15 min at 37ºC. For experimentation, cells were treated with 50% methanol (-20°C) for 15 min at 4ºC. Cells were then incubated with the antibody (ab657, 1μg/1x10⁶ cells) for 30 min at 4ºC. The secondary antibody used was Alexa Fluor® 488 goat anti-mouse IgG (H&L) (ab150113) at 1/2000 dilution for 30 min at 4ºC. Isotype control antibody (black line) was mouse IgG1 [ICIGG1] (ab91353, 1μg/1x10⁶ cells) used under the same conditions. Unlabelled sample (blue line) was also used as a control. Acquisition of >30,000 total events were collected using a 20mW Argon ion laser (488nm) and 525/30 bandpass filter. Gating strategy - peripheral blood lymphocytes.