ACTIVATION OF THE BETA(2) INTEGRIN MAC-1 (CD11B CD18) BY AN ENDOGENOUS LIPID MEDIATOR OF HUMAN NEUTROPHILS AND HL-60 CELLS/

beta(2) integrins (CD11/CD18) play a key role in the adhesion, activat ion, migration and phagocytosis of human neutrophils, In order to exer t their functions, beta(2) integrins require activation, which results in an enhancement of ligand affinity, This functional up-regulation i s probably due to a conformational change of the beta(2) integrins, bu t the mechanisms of inside-out signaling that trigger this activation are still under investigation, In the present study, the effect of cel lular lipids on the affinity state of beta(2) integrins was investigat ed, Lipids were extracted from human neutrophils and HL-60 cells after stimulation with IL-8 or phorbol ester, respectively, The extracts we re purified by anion exchange chromatography and/or HPLC fractionation , The lipid extracts induced the adhesion of neutrophils to fibrinogen and, in a cell-free assay system, the binding of C3bi-coated zymosan- particles by purified beta(2) integrin Mac-1 (CD11b/CD18). The integri n up-regulating activity was resistant to ester hydrolysis, eluted as one particular HPLC-fraction, and showed an absorption maximum at 194/-2 nm, Taken together, these data support the concept that activated neutrophils and HL-60 cells can generate an endogenous lipid mediator, which up-regulates ligand binding activity of beta(2) integrins.