ADHESION MOLECULES ARE UP-REGULATED ON DENDRITIC CELLS ISOLATED FROM HUMAN BLOOD

This study investigated whether the high expression of adhesion molecu les on enriched preparations of circulating dendritic cells (DCs) was an intrinsic property of the cells or whether it was a consequence of the procedure used to isolate them from blood. Expression of the beta 1, beta 2 integrins (CD11/CD18 family) and other adhesion molecules on DCs in whole blood was compared with that on isolated DCs. Dendritic cells were identified by flow cytometry as leucocytes that were positi ve for human leucocyte antigen (HLA)-DR, but negative for CD3, CD14, C D16, CD19 and CD56. In contrast to a minority of DCs in whole blood, t he majority of isolated DCs expressed the beta 2 integrins and there w ere a greater number of cells bearing CD44, CD54 and some of the beta 1 integrins (notably CD49b, CD49d, CD49e and CD29). An increase in the proportion of DCs bearing adhesion molecules was generally apparent a t the isolation stage when mononuclear cells, which had been incubated overnight, were centrifuged on a metrizamide gradient to enrich for c ells of low density, Inclusion of an inhibitor of protein glycosylatio n and exocytosis (brefeldin A) at all stages of separation partially p revented an increase in the percentage of DCs bearing CD18, C29 and C5 4 whereas the inclusion of cycloheximide (an inhibitor of polypeptide synthesis) interfered with increases in the percentage of cells bearin g CD29 and CD54. Neither of these antagonists had an effect on the int ensity of adhesion molecule expression. We suggest that some of the ad hesion-dependent functions of isolated DCs are caused, in part, by an upregulation of surface adhesion molecules induced by the enrichment p rocedure.