Role of H2B in Plg activation. RAW 264.7 cells were dissociated and washed. The cells were either pretreated with anti-H2B, anti–α-enolase, anti–annexin 2, anti-p11, or nonimmune rabbit Fab or left untreated, and then 200 nM Plg was added. After 1 hour, uPA (3 nM) was added with the chromogenic substrate S-2251, and plasmin generation was measured at 405 nm over 2.5 hours.