Chemotactic migration triggers IL-8 generation in neutrophilic leukocytes

Neutrophils recovered from inflammatory exudates possess increased levels o f IL-8, but exposure of neutrophils to chemoattractants results in only a m odest stimulation of IL-8 generation. This study was undertaken to explore the hypothesis that IL-8 generation in these cells is dependent upon the pr ocess of migration. Neutrophils synthesized up to 30 times as much IL-8 dur ing migration in response to a gradient of diverse chemoattractants than th ey did when stimulated directly by the attractants in the absence of a grad ient. This IL-8 response was dependent on migration since it was not observ ed in cells exposed to concentration gradients of chemoattractants under co nditions that prevented cell movement. While actinomycin-D (I mu g/ml) had little influence on the generation of IL-8 during chemotaxis, the protein s ynthesis inhibitor cycloheximide (10 mu g/ml) markedly blunted the accumula tion of cell-associated IL-8, suggesting that new protein synthesis from pr eexisting mRNA was responsible for the effect. Consistent with this interpr etation, migrating cells incorporated over 10 times as much [H-3]leucine in to IL-8 as did nonmotile neutrophils exposed to chemoattractants. A substan tial portion of the IL-8 generated during chemotaxis was released upon subs equent metabolic stimulation. Thus, the IL-8 synthesized during chemotaxis is uniquely positioned to exert a regulatory influence on inflammatory proc esses governed by neutrophilic leukocytes responding to inflammatory and in fectious stimuli.