Differential release of mediators from human basophils: differences in arachidonic acid metabolism following activation by unrelated stimuli

Abstract

We have examined the release of histamine and LTC4 from purified human basophils challenged with several different stimuli, both physiological and nonphysiological. Basophils (n = 16) challenged with 0.1 micrograms/ml anti-IgE released 38 +/- 4% of their available histamine and 39 +/- 12 ng LTC4/10(6) basophils within 15-30 min. F-Met peptide (n = 8) caused the release of 54 +/- 8% histamine and 42 +/- 25 ng LTC4/10(6) basophils within a period of 2-5 min. C5a caused the release of 22 +/- 3% histamine from selected donors but failed to initiate any LTC4 release unless combined with D2O 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 LTC4 even when combined with D2O or 2-5 mM extracellular calcium. Increased concentrations of extracellular calcium enhanced anti-IgE and f-Met peptide induced release of LTC4 but inhibited the A23187 induced release of leukotriene. A single peak of immunoreactive leukotriene C4 that comigrated with the authentic standard was identified using HPLC followed by radioimmunoassay. No LTD4 or LTE4 could be detected. Purified human basophils incubated with 0.2 microM [3H]AA incorporated 290 pmol/10(6) cells, or 32 +/- 5% of the available label within 60 min. The [3H]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 phosphatidylethanolamine, PE (15 +/- 3%), accounted for the majority of the incorporated [3H]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 micrograms/ml anti-IgE revealed [3H]LTC4 (2.4 +/- 1.0%), [3H]5HETE (1.0 +/- 0.1%), unmetabolized [3H]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.