SERUM-PROTEINS FACILITATE NEUTROPHIL INDUCTION OF ENDOTHELIAL-LEUKOCYTE ADHESION MOLECULE-1

Background. Although the individual actions of neutrophils and serum p roteins such as complement in acute inflammation are well characterize d, less is known about their effects in combination. We investigated t he combined effects of neutrophil contact and active serum proteins on the expression of endothelial leukocyte adhesion molecule 1 (ELAM-1). Methods. Confluent monolayers of human umbilical vein endothelial cel ls were incubated with neutrophils in the presence and absence of fres h human serum. Flow cytometry was used to assess expression of endothe lial intercellular adhesion molecule 1 (ICAM-1) and ELAM-1. In additio n neutrophils were retained in a semipermeable insert, which allowed t heir secretions to contact the endothelium but restricted neutrophil-e ndothelial contact. Results, ELAM-1 expression was significantly incre ased on the cells coincubated with neutrophils and fresh human serum ( 25.8%; p < 0.01). There was no significant change in ELAM-1 expression on endothelial cells incubated with fresh human serum alone (3.9%; p > 0.01) or in those incubated with neutrophils and heat-inactivated se rum (9.3 %; p > 0.01). In the absence of neutrophil contact, ELAM-1 ex pression was increased only in the presence of fresh human serum (9.6% ; p < 0.05). Conclusions, These findings suggest that serum proteins m ay potentiate the volume or potency of neutrophil-derived diffusable m ediators of ELAM-1 expression. These effects are eliminated with the h eat inactivation of serum proteins, implicating a heat sensitive media tor such as the complement cascade.