Stimulus-dependent leukotriene release from human basophils: A comparative study of C5a and fmet-leu-phe

Previous studies of human basophil mediator release have noted that the bacterial peptide fmet-leu-phe and the anaphylatoxin C5a induce comparable levels of histamine release while only fmet peptide induces leukotriene release. Since 5-lipoxygenase metabolism of arachidonic acid is calcium dependent, we examined the characteristics of the human basophil [Ca⁺⁺](i) response which folows its activation by either fmet peptide or C5a. While the peak [Ca⁺⁺](i) response was essentially identical for these two stimuli, fmet peptide induced a prolonged increase in [Ca⁺⁺](i) while C5a stimulated only a transient increase in [Ca⁺⁺](i) that was essentially over within 2 minutes of adding the stimulus. Simultaneous addition of EDTA with fmet peptide revealed the two phases of the [Ca⁺⁺](i) response and demonstrated that leukotriene release was dependent on an elevated [Ca⁺⁺](i) level in the 2-5 minutes following challenge. Enhancement of leukotriene release induced by C5a by agents such as staurosporine and interleukin-3 also produced a [Ca⁺⁺](i) kinetic curve which resembled fmet peptide. Single cell studies of the [Ca⁺⁺](i) response could detect no subpopulations of cells which responded preferentially to fmet peptide or C5a, eliminating the possibility that the ability of fmet peptide to induce leukotriene was a result of its action on a functionally distinct population of basophils.