Leukotriene B₄ levels from stimulated neutrophils from healthy and allergic subjects: effect of platelets and exogenous arachidonic acid

Abstract

Leukotriene B4 (LTB4) levels were measured in peripheral blood neutrophils from allergic and healthy donors after stimulation by calcium ionophore A 23187. This level was higher in neutrophils from allergic subjects than in neutrophils from healthy subjects in the presence as well as in the absence of exogenous arachidonic acid. Platelets from allergics increased LTB4 levels from neutrophils from allergics but not levels in those from healthy donors. Moreover, platelets from healthy subjects reduced LTB4 in neutrophils from both groups. These results suggest that biochemical differences exist in neutrophils and platelets from allergics which contribute to changes in arachidonic acid metabolism via the 5-lipoxygenase pathway. In addition, they support the concept that platelets may play an important role in the regulation of neutrophil LTB4 levels, possibly by affecting the 5-lipoxygenase activity during the course of allergic inflammatory reactions.

Platelets Abrogate Leukotriene B4 Generation by Human Blood Neutrophils Stimulated with Monosodium Urate Monohydrate or f-Met-Leu-Phe In Vitro

“…This persistent inhibition of neutrophil LTB 4 synthesis by platelets in the presence of MSUM indicates that adenosine was not responsible for the inhibitory effect and suggests that another platelet product is involved in such an effect. This pattern is reminiscent of (a) a significant inhibition by platelets of the LTB 4 synthesis from A23187-stimulated neutrophils (Hosni et al, 1991), of (b) the absence of effect of adenosine on LTB 4 synthesis by neutrophils activated by ionophore A23187 as previously reported (Krump et al, 1997), and of (c) the absence of inhibition by adenosine of phospholipase D stimulated by MSUM in human neutrophils (Thibault et al, 2000).…”

“…Thrombinactivated platelets are also able to increase LTB 4 synthesis by human blood neutrophils stimulated with fMLP, PAF, or C5a through a mechanism independent of platelet 12-LOX and COX, possibly through plateletderived AA (Palmantier and Borgeat, 1991), or to increase LTB 4 synthesis by rabbit blood neutrophils stimulated with fMLP through AA originating from platelets (Evangelista et al, 1999). However, human platelets added to neutrophils in the presence of ionophore A23187 can slightly increase LTB 4 accumulation while decreasing that of 5-HETE (McCulloch et al, 1992) or can decrease LTB 4 synthesis (Maderna et al, 1993), an effect not observed in allergic patients (Hosni et al, 1991). These controversial data prompted us to study the effect of human platelets on blood neutrophils to verify whether the platelet inhibitory effect on LTB 4 formation could be demonstrated in conditions using pathophysiologic agonists such as fMLP and MSUM.…”

“…AAderived metabolites were purified and assayed by RP-HPLC as described (Hosni et al, 1991). Briefly, the LiChrospher 100 RP-18 column was isocratically eluted with MeOH/ACN/water/acetic acid (250:300:400:4) at a flow rate of 0.8 ml/min to separate the dihydroxy derivatives (LTB 4 , ⌬6-trans-LTB 4 , 12-epi-⌬6-trans-LTB 4 , 20-OH-LTB 4 , and 5S,12S-diHETE) monitored at 270 nm.…”

“…Platelets from healthy subjects also have the capacity to modulate neutrophil superoxide anion production and chemiluminescence depending on the stimulus used in vitro (Carulli et al, 1995;Colli et al, 1996). However, platelets from uremic or allergic patients are altered and are unable to decrease the production of superoxide anion (Carulli et al, 1995) or LTB 4 by A23187-activated neutrophils (Hosni et al, 1991). Circulating platelets bind to neutrophils, and platelet-neutrophil complexes have been demonstrated in whole blood (Rinder et al, 1991).…”

“…Besides their phlogogenic activity through interactions with neutrophils, platelets can counterbalance neutrophil activation. Platelets from healthy donors can reduce LTB 4 synthesis in A23187-stimulated neutrophils from allergics (Hosni et al, 1991). Thus, unactivated platelets might act as a natural inhibitor of LTB 4 formation by neutrophils in diseases such as bacterial infection or arthritis.…”