ADHESION OF FLOWING LEUKOCYTES TO IMMOBILIZED PLATELETS

Adhesion of neutrophils, lymphocytes and promyelocytic HL60 cells was compared in a flow-based model in which a monolayer of activated plate lets formed the adhesive substrate. Each type of leucocyte formed P-se lectin-mediated rolling attachments on the platelet surface under phys iologically relevant flow conditions. Lymphocytes adhered less, and HL 60 in similar numbers, compared to neutrophils, whereas the lymphocyte s and HL60 cells rolled much more rapidly. Sulphated, sialylated sacch aride(s) were implicated as ligand(s) for P-selectin for all leucocyte s, but L-selectin (borne by neutrophils and lymphocytes, but not HL60 cells) appears to be a major presenter of ligand for neutrophils alone . T cells enriched from peripheral blood lymphocytes adhered in greate r numbers than B cells. Differentiation of HL60 cells to neutrophil-li ke cells (induced by DMSO) caused cell volume to decrease and surface expression of integrin adhesion molecules to increase, but only a smal l percentage of cells were converted to an L-selectin-bearing phenotyp e. Differentiated cells showed evidence of stabilization of adhesion w ith increasing stress and a marked reduction in rolling velocity. Thes e studies indicate that cell differentiation may be accompanied by alt eration of adhesive behaviour, resulting from changes in physical char acteristics as well as surface properties. Moreover, results suggest t hat P-selectin could promote lymphocyte attachment to endothelium in a cute inflammatory conditions and possibly mediate lymphocyte-platelet interaction during thrombosis.