IL-3 alters free arachidonic acid generation in C5a-stimulated human basophils

IL-3 is known to enhance the secretion of several mediators from human basophils activated by receptor-mediated stimuli. IL-3 can cause a qualitative change in the mediator release pattern for C5a-mediated stimulation; without IL-3, C5a causes no leukotriene release whereas in the presence of IL-3, significant leukotriene occurs. This study examines the influence of a 15-min pretreatment of basophils with IL-3 (10 ng/ml) on several signal transduction events. Basophils stimulated with C5a typically displayed only a transient cytosolic Ca2+ response [Ca2+]i, attributed to the release of intracellular calcium stores. IL-3 had sporadic, statistically nonsignificant, effects on the peak of this initial response as well as inconsistent effects on the generation of a second phase in the [Ca2+]i response (i.e., that which is caused by the influx of extracellular Ca2+). IL-3 also had no effect on resting [Ca2+]i levels. Challenge of basophils in the presence of EGTA had little effect on the amount of leukotrienes generated. This maneuver did not influence the initial transient elevation of [Ca2+]i. Although basophil leukotriene release is usually slow, after exposure to IL-3 it was found that leukotriene release occurred rapidly, during the brief window of time (0 to 45 s) in which the [Ca2+]i transient occurred. These results suggested that the generation of AA was accelerated by pretreatment with IL-3. Subsequent mass measurements of free AA by gas chromatography-mass spectroscopy showed: 1) IL-3 itself caused no free AA generation; 2) without IL-3, C5a stimulated little or no free AA generation; and 3) in the presence of IL-3, C5a generated substantial levels of free AA at an accelerated rate. A similar acceleration in the rate of free AA generation, without any apparent increase in the amount, occurred in IL-3-primed basophils stimulated with FMLP. Additional studies showed that IL-3 had no effects on whole cell ATP levels and that the kinase inhibitor, staurosporine, did not inhibit the ability of IL-3 to cause enhanced responses to C5a. We conclude that the primary effect of a short period of pretreatment with IL-3 is to couple the generation of free AA to C5a-mediated stimulation in particular and to accelerate its generation after other stimuli. Enhancements of the [Ca2+]i response, while sporadic and at best modest, may have some influence on enhanced mediator release but did not clearly explain the functional effects of IL-3.