Flow cytometric analysis of CD4 expression on Rhesus macaque (Macaca mulatta) peripheral blood lymphocytes. Whole blood was stained with either FITC Mouse Anti-Human CD4 (Cat. No. 550628; solid line histogram) or FITC Mouse IgG1 κ Isotype Control (Cat. No. 556649; dashed line histogram). Erythrocytes were lysed with BD Pharm Lyse™ Lysing Buffer (Cat. No. 555899). Fluorescence histograms depicting CD4 (or Ig isotype control expression) were derived from gated events with the forward and side light-scatter characteristics of viable lymphocytes.