Histone H2B as a functionally important plasminogen receptor on macrophages

Plasminogen (Pig) facilitates inflammatory cell recruitment, a function that depends upon its binding to Pig receptors (Pig-Rs). However, the Pig-Rs that are critical for cell migration are not well defined. Three previously characterized Pig-Rs (a-enolase, annexin 2, and p11) and a recently identified PIg-R (histone H2B [H2B]) were assessed for their contribution to Pig binding and function on macrophages. Two murine macrophage cell lines (RAW 264.7 and J774A.1) and mouse peritoneal macrophages induced by thioglycollate were analyzed. All 4 PIg-Rs were present on the surface of these cells and showed enhanced expression on the thioglycollate-incluced macrophages compared with peripheral blood monocytes. Using blocking Fab fragments to each PIg-R, H2B supported approximately 50% of the Pig binding capacity, whereas the other Pig-Rs contributed less than 25%. Anti-H2B Fab also demonstrated a major role of this PIg-R in plasmin generation and matrix invasion. When mice were treated intravenously with anti-H2B Fab, perlitoneal macrophage recruitment in response to thioglycollate was reduced by approximately 45% at 24, 48, and 72 hours, with no effect on blood monocyte levels. Taken together, these data suggest that multiple Pig-Rs do contribute to Pig binding to macrophages, and among these, H2B plays a very prominent and functionally important role.