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 leukotrienes has been favoured by modifications, occurring during the sensitization phase, of the enzymes involved in leukotriene metabolism.


OBJECTIVE
We used ovalbumin-sensitized rats to study the expression of cytosolic phospholipase A2 (cPLA2), 5-lipoxygenase (5-LO) and 5-lipoxygenase-activating protein (FLAP) in peritoneal macrophages during active sensitization. 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 cytokine 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. The arachidonic acid (AA) metabolism study was performed after incorporation of tritiated AA in macrophages and analysis of secreted tritiated eicosanoids.


RESULTS
Ovalbumin-sensitization of rats increased cPLA2, 5-LO and FLAP expression in peritoneal macrophages. These increased expressions were not paralleled by modifications of basal and PMA- or A23187-stimulated AA metabolism of sPM. However, when macrophages encountered the specific allergen for a second time, sPM secreted higher levels of leukotrienes than cPM. IL-4 induced FLAP expression in cPM but had no effect on cPLA2 and 5-LO expression.


CONCLUSIONS
Active sensitization of rats induces an increase, in peritoneal macrophages, of the enzymes involved in leukotriene metabolism. The increased leukotriene secretion of sPM in response to ovalbumin challenge may be favoured 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 circumstance. Our results also suggest that IL-4 is not the major element originating the enzymatic modification induced by sensitization in peritoneal macrophages.
Escoubet-Lozach
L
L
Université Paul Sabatier UPRES EA 2405, Macrophages, Médiateurs de l'Inflammation et Interactions Cellulaires, CHU Rangueil, 1 Avenue Jean Poulhès, 31403 Toulouse cedex 4, France.
M'Rini
C
C
Rey
A
A
Béraud
M
M
Lepert
J C
JC
Courtade
M
M
Frisach
M F
MF
Pipy
B
B
D058927:5-Lipoxygenase-Activating Proteins; D000818:Animals; D001094:Arachidonate 5-Lipoxygenase / Q000096:biosynthesis* / Q000378:metabolism; D016718:Arachidonic Acid / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002352:Carrier Proteins / Q000096:biosynthesis*; D002478:Cells, Cultured; D003600:Cytosol / Q000201:enzymology*; D007279:Injections, Subcutaneous; D015847:Interleukin-4 / Q000096:biosynthesis / Q000494:pharmacology; D017737:Macrophages, Peritoneal / Q000201:enzymology* / Q000276:immunology*; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis*; D010047:Ovalbumin / Q000008:administration & dosage / Q000276:immunology*; D010741:Phospholipases A / Q000096:biosynthesis* / Q000378:metabolism; D054467:Phospholipases A2; D051381:Rats; D011914:Rats, Inbred BN; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D058927:5-Lipoxygenase-Activating Proteins; C548594:Alox5ap protein, rat; D002352:Carrier Proteins; D008565:Membrane Proteins; D015847:Interleukin-4; D016718:Arachidonic Acid; D000001:Calcimycin; D010047:Ovalbumin; D001094:Arachidonate 5-Lipoxygenase; D010741:Phospholipases A; D054467:Phospholipases A2; D013755:Tetradecanoylphorbol Acetate