Chitosan-induced phospholipase A2 activation and arachidonic acid mobilization in P388D1 macrophages

We have found that chitosan, a polysaccharide present in fungal cell walls, is able to activate macrophages for enhanced mobilization of arachidonic acid in a dose- and time-dependent manner. Studies aimed at identifying the intracellular effector(s) implicated in chitosan-induced arachidonate release revealed the involvement of the cytosolic Group IV phospholipase A2 (PLA2), as judged by the inhibitory effect of methyl arachidonoyl fluorophosphonate but not of bromoenol lactone. Interestingly, priming of the macrophages with lipopolysaccharide renders the cells more sensitive to a subsequent stimulation with chitosan, and this enhancement is totally blocked by the secretory PLA2 inhibitor 3-(3-acetamide)-1-benzyl-2-ethylindolyl-5-oxy-propanesulfonic acid (LY311727). Collectively, the results of this work establish chitosan as a novel macrophage-activating factor that elicits AA mobilization in P388D1 macrophages by a mechanism involving the participation of two distinct phospholipases A2.