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Fatty acid composition of immune-associated tissues of Spodoptera exigua
Immune mediators play crucial roles in amplifying the emergency signals with massive amounts of de novo synthesized mediators and relaying the specific recognition signals to the immune-associated target tissues. Eicosanoids are the representative immune mediators and synthesized from a polyunsaturated fatty acid (PUFA), arachidonic acid. Compared to mammalian systems, insects have relatively low levels of arachidonic acid in the biological membranes. This has raised a fundamental issue that eicosanoids may be not significant in insect system. Our previous chemical analysis suggests that the hemocytes of Spodoptera exigua have less than 5% arachidonic acid. We postulated that S. exigua may store arachidonic acid in other tissues, such as fat body. This analysed fatty acid compositions of two immune-associated tissues using a gas chromatography (GC) eguipped with FID detector or GC-MS. Our analysis of PUFA in the immune tissues suggests that insects maintain a low level of PUFA including arachidonic acid due to its evolutionary origin from the paleozoic era at which the oxygen level was 35%, compared to the present era 21%.
