A Leukocyte Lipid Up-Regulates the Avidity of Lymphocyte Function-Associated Antigen-1

An acidic lipid termed leukocyte adhesion lipid (LAL) was isolated from PMA stimulated lymphoid and myeloid cell lines HL60, Jurkat, K562 and U937 but not from unstimulated cells or PMA treated Cos7 cells. LAL treated peripheral blood leukocytes (PBL) adhered strongly to IL-1β activated human umbilical vein endothelial cells (HUVEC), and the interaction could be inhibited by antibodies to intercellular adhesion molecule (ICAM-1) or lymphocyte function-associated antigen-1 (LFA-1). Leukocytes treated with LAL maintained the high avidity state of LFA-1 for at least 1 hr whereas the avidity of LFA-1 in PMA treated cells declined after 30 min. LAL was stable to heat (100°C, 10 min), alkaline phosphatase and proteinase K treatments. Chemical analysis suggested that LAL contained unsaturated lipids. Our findings provide evidence for the involvement of lipids in LFA-1 activation.