ENDOTOXIN-INDUCED MACROPHAGE GENE-EXPRESSION DEPENDS ON PLATELET-ACTIVATING-FACTOR

Background: The development of multiple organ failure in septic patien ts is due to a systemic inflammation orchestrated by macrophages (M ph i). Elucidation and control of the mechanism involved in M phi activat ion in sepsis is crucial to improving survival. An early event of M ph i activation involves the hydrolysis of membrane phospholipid by phosp holipase A(2) (PAL(2)) and subsequent generation of platelet-activatin g factor (PAF). Objective: We designed this study to test the hypothes is that M phi gene expression depends on PAF. Design: Rabbit alveolar M phi were obtained by bronchoalveolar lavage and were stimulated with 10 ng/mL of Escherichia coli endotoxin lipopolysaccharide (LPS), PAF (1 mu mol/L), LPS+/-CV3988 (10 mu mol/L), a PAF receptor antagonist, o r LPS+/-PLA(2) inhibitors: AACOCF(3) (50 mu mol/L) or manoalide (10 mu mol/L). After 4 hours of incubation, M phi tumor necrosis factor (TNF ) messenger RNA (mRNA) expression was assessed by Northern blot analys es. The TNF production in the M phi supernatant was measured by L929 b ioassays. Results: The LPS-stimulated M phi expressed increased levels of TNF mRNA and produced an enormous amount of TNF. CV3988, a PAF ant agonist, inhibited LPS-induced TNF mRNA. Furthermore, inhibiting PAF p roduction with AACOCF(3), or manoalide, also inhibited LPS-induced M p hi TNF mRNA expression. The effect of PAF depends on changes in intrac ellular calcium concentration. Inhibitors of calcium flux attenuated t he PAF effects on LPS-stimulated M phi. Conclusions: Our data suggest that LPS-induced M phi gene expression is mediated by PAF. It is likel y that modulation of PAF production or activity may be beneficial in d own-regulating the overactivity of Mb in sepsis.