Abstract
This paper is focused on eicosanoid signaling in insect immunology. We begin with eicosanoid biosynthesis through the actions of phospholipase A2, responsible for hydrolyzing the C18 polyunsaturated fatty acid, linoleic acid (18:2n-6), from cellular phospholipids, which is subsequently converted into arachidonic acid (AA; 20:4n-6) via elongases and desaturases. The synthesized AA is then oxygenated into one of three groups of eicosanoids, prostaglandins (PGs), epoxyeicosatrienoic acids (EETs) and lipoxygenase products. We mark the distinction between mammalian cyclooxygenases and insect peroxynectins, both of which convert AA into PGs. One PG, PGI2 (also called prostacyclin), is newly discovered in insects, as a negative regulator of immune reactions and a positive signal in juvenile development. Two new elements of insect PG biology are a PG dehydrogenase and a PG reductase, both of which enact necessary PG catabolism. EETs, which are produced from AA via cytochrome P450s, also act in immune signaling, acting as pro-inflammatory signals. Eicosanoids signal a wide range of cellular immune reactions to infections, invasions and wounding, including nodulation, cell spreading, hemocyte migration and releasing prophenoloxidase from oenocytoids, a class of lepidopteran hemocytes. We briefly review the relatively scant knowledge on insect PG receptors and note PGs also act in gut immunity and in humoral immunity. Detailed new information on PG actions in mosquito immunity against the malarial agent, Plasmodium berghei, has recently emerged and we treat this exciting new work. The new findings on eicosanoid actions in insect immunity have emerged from a very broad range of research at the genetic, cellular and organismal levels, all taking place at the international level.
Highlights
Immune reactions to invasions, infections and wounds are critical fitness traits in organisms, generally, and as the papers in this Special Issue illustrate, insects as well
This paper lies in the context of a Special Issue devoted to insect immunology, which obviates a broad description of insect immunity
Interest in eicosanoid actions in invertebrates appears to be growing as new knowledge on eicosanoid signaling in insect immunity has emerged since drafting our last review
Summary
Infections and wounds are critical fitness traits in organisms, generally, and as the papers in this Special Issue illustrate, insects as well. We shift focus onto specific eicosanoid actions in insect immunity These include clearing bacterial infections from hemolymph circulation, nodulation, hemocyte spreading and release of prophenoloxidase (PPO) from specific lepidopteran hemocytes. Park and Kim [11] revealed the broad biological significance of PLA2 actions in insect immunity with their discovery that eicosanoid treatments rescued beet armyworms, Spodoptera exigua, from lethal infections of the bacterium Xenorhabdus nematophila. They discovered that the bacterium somehow inhibited necessary PLA2 activity, required to release PUFAs from PLs for eicosanoid biosynthesis [12]. While there has been considerable progress on insect PLA2s, much more new knowledge is necessary on the biology, physiology, biochemistry and molecular biology of insect PLA2s
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
