PLATELET-ACTIVATING-FACTOR INCREASES LEUKOTRIENE B-4 RELEASE IN STIMULATED ALVEOLAR MACROPHAGES FROM ASTHMATIC-PATIENTS

This study was designed to examine further the role of platelet-activa ting factor (PAF) in asthma, comparing leukotriene B-4 (LTB4) release, 5-lipoxygenase activity and intracellular calcium levels ([Ca2+](i)) in macrophages, LTB4 and other lipoxygenase metabolites in macrophages in bronchoalveolar lavage fluids obtained from 23 asthmatic patients and 20 control subjects were measured by reverse-phase high-performanc e liquid chromatography, [Ca2+](i) was monitored using the fluorescent probe fura-2. The basal LTB4 release of resting macrophages was not d ifferent between groups (0.02+0.01 versus 0.05+/-0.02 ng.10(-6) cells) . When stimulated with calcium ionophore A23187 (25 mu M), homever, ma crophages from asthmatic patients released more LTB4 than cells from c ontrol subjects (30.2+/-3.4 versus 13.7+/-2.1 ng.10(-6) cells). Althou gh PAF alone did not alter LTB4 release, it enhanced the response to s ubsequent A23187 stimulation, This effect was noted following short tr eatment (i.e., 5 min) at concentrations of greater than or equal to 1. 0 mu M PAF, with the maximal effect noted after treatment with 5.0 mu M PAF + 2.5 mu M A23187 (105.1+/-6.7 versus 15.3+/-2.6 ng.10(-6) cells ). Treatment of macrophages with PAF also increased 5-lipoxygenase act ivity and [Ca2+](i) more in cytosols from asthmatic patients than in c ytosols from control subjects. These findings support a role of intrac ellular calcium in the activation of 5-lipoxygenase which, in turn, au gments the release of leukotriene B-4. Because levels of platelet-acti vating factor may be increased in the lung during asthma and can incre ase the subsequent release of a chemotactic mediator leukotriene B-4,B - from macrophages, these findings suggest that platelet-activating fa ctor may prime the constitutive cells of the lung to augment inflammat ory effects important in the pathogenesis of asthma.