The Functional Paradox of CD43 in Leukocyte Recruitment: A Study Using CD43-deficient Mice

Although there is considerable evidence implicating a role for CD43 (leukosialin) in leukocyte cell–cell interactions, its precise function remains uncertain. Using CD43-deficient mice (CD43(−/−)) and intravital microscopy to directly visualize leukocyte interactions in vivo, we investigated the role of CD43 in leukocyte–endothelial cell interactions within the cremasteric microcirculation under flow conditions. Our studies demonstrated significantly enhanced leukocyte rolling and adhesion after chemotactic stimuli in CD43(−/−) mice compared with wild type mice. Using an in vitro flow chamber, we established that the enhanced rolling interactions of CD43(−/−) leukocytes, primarily neutrophils, were also observed using immobilized E-selectin as a substrate, suggesting that passive processes related to steric hindrance or charge repulsion were likely mechanisms. Despite increased adhesion and rolling interactions by CD43(−/−) leukocytes, we uncovered a previously unrecognized impairment of CD43(−/−) leukocytes to infiltrate tissues. Oyster glycogen–induced neutrophil and monocyte infiltration into the peritoneum was significantly reduced in CD43(−/−) mice. In response to platelet activating factor, CD43(−/−) leukocytes were impaired in their ability to emigrate out of the vasculature. These results suggest that leukocyte CD43 has a dual function in leukocyte–endothelial interactions. In addition to its role as a passive nonspecific functional barrier, CD43 also facilitates emigration of leukocytes into tissues.