Lipid-mediator synthesis in peritoneal macrophages from mice injected with immunostimulants.

The metabolism of bioreactive lipid mediators was studied in two types of activated macrophages (M phi). We compared the capacity of resident and activated M phi to release, upon a zymosan challenge, cyclooxygenase and lipoxygenase products as well as PAF-acether (platelet-activating factor) and its 2-lyso precursor. Activated M phi were obtained from mice injected intraperitoneally either with nonviable C74 streptococci (St-M phi) or with trehalose dimycolate, a defined immunostimulant isolated from Mycobacterium tuberculosis (TDM-M phi). Both activated populations exhibited common features: conversion of endogenous [14C]arachidonic acid into prostaglandin E2 and thromboxane A2 rather than into prostaglandin I2 and low biosynthesis of PAF-acether, probably due to an impairment of the acetylation step. However, contrary to St-M phi, TDM-M phi did not display a marked overall reduction of arachidonate metabolism. In addition, as compared to resident M phi, TDM-M phi presented a ratio of thromboxane B2/6-ketoprostaglandin F1 alpha 30-fold higher, a better conversion of leukotriene C to leukotriene D and a higher capacity to release the PAF-acether they synthesize. These macrophages thus seem to be valuable tools for studying the formation of mediators and for determining specific markers of an activated state.