Increased expression of cytosolic phospholipase A2, 5-lipoxygenase and 5-lipoxygenase-activating protein in rat peritoneal macrophages during ovalbumin-induced sensitization

Background Macrophages are involved in immediate hypersensitivity reactions by their ability to release leukotrienes involved in the symptomatology of allergy. To date it is unknown whether this ability to secrete leukotriene s has been favoured by modifications, occurring during the sensitization ph ase, of the enzymes involved in leukotriene metabolism. Objective We used ovalbumin-sensitized rats to study the expression of cyto solic phospholipase A2 (cPLA2). 5-lipoxygenase (5-LO) and 5-lipoxygenase-ac tivating protein (FLAP) in peritoneal macrophages during active sensitizati on. We compared basal and challenged (PMA, A23187 and allergen) arachidonic acid (AA) metabolism of macrophages from control (cPM) and sensitized (sPM ) rats. Then we tested, in cultured cPM, whether IL-4, the predominant cyto kine of sensitization process, could reproduce the enzymatic modifications occurring in macrophages during sensitization. Methods cPLA2, 5-LO and FLAP expression was assessed by Western blotting. T he arachidonic acid (AA) metabolism study was performed after incorporation of tritiated AA in macrophages and analysis of secreted tritiated eicosano ids. Results Ovalbumin-sensitization of rats increased cPLA2, 5-LO and FLAP expr ession in peritoneal macrophages. These increased expressions were not para lleled by modifications of basal and PMA- or A23187-stimulated AA metabolis m of sPM. However, when macrophages encountered the specific allergen for a second time, sPM secreted higher levels of leukotrienes than cPM. IL-4 ind uced FLAP expression in cPM but had no effect on cPLA2 and 5-LO expression. Conclusion Active sensitization of rats induces an increase, in peritoneal macrophages, of the enzymes involved in leukotriene metabolism. The increas ed leukotriene secretion of sPM in response to ovalbumin challenge may be f avoured by this increased expression of cPLA2, 5-LO and FLAP that, however, is not able to lead to modifications of macrophage AA metabolism in any ci rcumstance. Our results also suggest that IL-4 is not the major element ori ginating the enzymatic modification induced by sensitization in peritoneal macrophages.