Differential Release of Mediators From Human Basophils: Differences in Arachidonic Acid Metabolism Following Activation by Unrelated Stimuli

We have examined the release of histamine and LTC 4 from purified human basophils challenged with several different stimuli, both physiological and nonphysiological. Basophils (n=16) challenged with 0.1 μg/ml anti‐IgE released 38±4% of their available histamine and 39±12 ng LTC 4 /10 9 basophils within 15‐30 min. F‐Met peptide (n=8) caused the release of 54±8% histamine and 42±25 ng LTC 4 /10 6 basophils within a period of 2‐6 min. C5a caused the release of 22±3% histamine from selected donors but failed to initiate any LTC 4 release unless combined with D 2 O or 5 mM extracellular calcium. The two nonphysiological stimuli A23187 and TPA caused extensive histamine release, 67±8 and 82±11%, respectively, and while A23187 initiated a large and rapid release of leukotriene, TPA failed to release any LTC 4 even when combined with D 2 O or 2‐5 mM extracellular calcium. Increased concentrations of extracellular calcium enhanced anti‐IgE and f‐Met peptide induced release of LTC 4 but inhibited the A23187 induced release of leukotriene. A single peak of immunoreactive leukotriene C 4 that comigrated with the authentic standard was identified using HPLC followed by radioimmunoassay. No LTD 4 or LTE 4 could be detected. Purified human basophils incubated with 0.2 μM [ 3 H]AA incorporated 290 pmol/10 6 cells, or 32±5% of the available label within 60 min. The [ 3 H]AA was taken principally into the phospholipids (73±5%), with 20±3% as neutral lipid, and only 5±2% remaining as the free acid. Three phospholipid subclasses, phosphatidylcholine, PC (24±2%), phosphatidylinositol, PI (22±1%), and phosphatidytethanolamine, PE (15±3%), accounted for the majority of the incorporated [ 3 H]AA while the remainder of the phospholipids accounted for less than 5% of the total cpm. HPLC analysis of the lipid mediators released during stimulation with 0.1 μg/ml anti‐IgE revealed [ 3 H]LTC 4 (2.4±1.0%), [ 3 H]5HETE (1.0±0.1%), unmetabollzed [ 3 H]AA (91±2%), and an unidentified peak (3.4±1.4%). The unknown metabolite eluted with the prostaglandins, was inhibited by indomethacin, and appeared to have a relatively high specific activity. It may thus represent an artifact of the labeling procedure rather than a novel basophil‐derived prostaglandin.