Dual phase priming by IL-3 for leukotriene C₄ generation in human basophils: Difference in characteristics between acute and late priming effects

Previous studies have suggested that enhancement of mediator release from human basophils by IL-3 occurs in at least two phases, and the current studies further characterize the signaling changes that accompany these two phases of the basophil in response to IL-3. The test stimulus for these studies was anaphylatoxin split product of C component (C5a), which does not induce leukotriene C4 release without prior IL-3 treatment. Functionally, IL- 3 priming occurs after 5 min, disappears by 2 h, and returns by 18 h. In contrast, the kinetics of cytosolic phospholipase A₂ (cPLA₂) and extracellular signal-regulated kinase CERK1/2) phosphorylation, induced by IL-3, do not show the second rise by 18 h. The kinetics of cPLA₂ and ERK1/2 phosphorylation following stimulation with C5a are the same for cells that were not treated with IL-3 as for those treated for 18 h, i.e., a lag in phosphorylation of cPLA₂ and ERK1/2 lasting 30 s before its eventual rise. Previous studies showed that a 5-min treatment with IL-3 induced little change in the C5a-induced cytosolic calcium response, while 24 h of treatment resulted in a marked and sustained cytosolic calcium elevation during the C5a-induced response. The first phase of the IL-3 priming effect (5-15 min of treatment) was unaffected by cycloheximide, while the second phase (18 h) was inhibited. These data suggest that early IL-3 priming results from preconditioning cPLA₂, i.e., causing its phosphorylation, while late priming results from a qualitative change in the cytosolic calcium response.