Surface Mo1 (CD11b/CD18) glycoprotein is up-modulated by neutrophils recruited to sites of inflammation in vivo.

Inasmuch as the recruitment of polymorphonuclear leukocytes (PMNs) to inflammatory foci in vivo involves adhesion-dependent events (e.g., margination, diapedesis, and directed migration), we sought to characterize the relationship between the local accumulation of PMNs in sterile peritonitis and their surface expression of the adhesion-promoting plasma membrane glycoprotein, Mo1 (CD11b/CD18). In an immunofluorescence analysis of PMNs isolated from rats injected intraperitoneally with sterile 1% glycogen solution, we detected a significant enhancement of surface Mo1 expression by exudative peritoneal PMNs. In contrast, no significant rise in Mo1 expression was noted over time by circulating intravascular PMNs (isolated simultaneously). However, these intravascular PMNs had the capacity to increase their surface Mo1 density upon exposure to peritoneal fluid supernatant at 37 degrees C. These results demonstrate that PMNs at sites of inflammation in vivo do up-modulate their surface expression of the adhesion-promoting Mo1 glycoprotein during their recruitment from the circulating, intravascular leukocyte pool.