ENHANCEMENT OF LEUKOTRIENE B-4 RELEASE IN STIMULATED ASTHMATIC NEUTROPHILS BY PLATELET-ACTIVATING-FACTOR

Background - The role of platelet activating factor (PAF) in asthma re mains controversial. The priming effect of PAF on leukotriene B-4 (LTB 4) release, 5-lipoxygenase activity, and intracellular calcium levels in asthmatic neutrophils was examined. Methods - LTB4 and other lipoxy genase metabolites in neutrophils obtained from 17 asthmatic patients and 15 control subjects were measured by reverse phase-high performanc e liquid chromatography (RP-HPLC). Intracellular calcium levels were m onitored using the fluorescent probe fura-2. Results - The mean (SD) b asal LTB4 release from neutrophils was not significantly different bet ween the two groups (0.05 (0.01) vs 0.03 (0.02) ng/10(6) cells); howev er, when stimulated with calcium ionophore A23187 (2.5 mu M), neutroph ils from asthma patients released more LTB4 than cells from control su bjects (15.7 (1.2) vs 9.9 (1.6) ng/10(6) cells). Although PAF alone di d not alter LTB4 release, it enhanced the response to subsequent A2318 7 stimulation. This effect was observed following treatment for five m inutes with PAF at concentrations >1.0 mu M. The maximal effect was se en with 5.0 mu M PAF+2.5 mu M A23187 (62.7 (2.2) vs 18.6 (2.3) ng/10(6 ) cells). Pretreatment with PAF also increased 5-lipoxygenase activity and intracellular calcium levels in neutrophils fi om asthmatic patie nts to a greater extent than in those from non-asthmatic patients. Con clusions - These findings indicate that, in neutrophils from asthmatic patients, PAF enhances LTB4 release and increases 5-lipoxygenase acti vity and intracellular calcium to a greater extent than in neutrophils from non-asthmatic patients.