A model of the differential control of neutrophil degranulation by the chemotactic agents fMLP and PAF. Both fMLP and PAF induce PLA₂ and PLC activation via G-protein–linked serpentine receptors. PLC may regulate β₂-integrin–mediated adhesion by modulating local calcium fluxes. AA may be required for CD11b/CD18 cycling (de novo expression and activation), a process necessary for prolonged neutrophil adhesion and migration. Signaling via the fMLP receptor but not the PAF receptor also mobilizes FLAP, which in turn activates five lipoxygenase (5LO). LTB₄ is synthesized by the action of 5LO on arachidonic acid. Details are not shown, but the intermediate metabolite LTA₄ may also be transformed by intercellular pathways. The binding of LTB₄ to a specific G-protein–linked serpentine receptor activates PLD, the action of which generates PA from membrane phospholipids. Signals from PA and ligand-bound CD11b/CD18 are integrated in an unknown manner (▪) that results in granule mobilization, fusion with the outer cell membrane, and release of contents into the extracellular environment (see text for abbreviations).