PROLONGED E-SELECTIN INDUCTION BY MONOCYTES POTENTIATES THE ADHESION OF FLOWING NEUTROPHILS TO CULTURED ENDOTHELIAL-CELLS

We investigated the hypothesis that the infiltration of monocytes into inflamed tissue or damaged vessels would induce a secondary accumulat ion of neutrophils. Confluent human umbilical vein endothelial cells ( HUVEC) acid blood monocytes (0.5 or 0.05 monocytes/endothelial cell) w ere co-incubated for 4 or 24 h. The adhesion of neutrophils flowing ov er HUVEC was then analysed by video microscopy. Co-incubation caused u p to a 40-fold increase in neutrophil adhesion, dependent upon monocyt e/HUVEC ratio and duration of incubation. At the lower monocyte/HUVEC ratio, rolling adhesion alone was induced after 4 h co-incubation; how ever, the full repertoire of rolling, immobilization and migration of neutrophils was observed at all other combinations of co-culture ratio and exposure time. After maximal stimulation by monocytes, antibody b lockade of the neutrophil integrin CD18 inhibited neutrophil arrest an d migration and revealed underlying rolling adhesion. Rolling was supp orted by endothelial E-selectin as demonstrated by the almost total ab olition of adhesion by a blocking antibody. In a direct comparison, mo nocytes, tumour necrosis factor alpha (TNF-alpha) and interleukin-1 be ta (IL-1 beta) were assessed fur their ability to induce endothelial e xpression of E-selectin. E selectin was significantly increased by all agents at 4 h, but monocytes alone were able to maintain high levels of E-selectin expression for 24 h. We conclude that monocytes carl ind uce prolonged neutrophil adhesion and migration by activating endothel ial cells and causing expression of E-selectin.