Adipokinetic hormone enhances laminarin and bacterial lipopolysaccharide-induced activation of the prophenoloxidase cascade in the African migratory locust, Locusta migratoria

Induced hyperlipaemia and immune challenge in locusts

“…Co-injection of Lom-AKH-II with laminarin also results in a dose-dependent prolonging of phenoloxidase activity in the haemolymph, but this hormone is less potent in this effect than AKH-I (Goldsworthy et al, 2002a). Passive immunisation experiments have been undertaken using IgG prepared against Lom-AKH-II (data not shown), and give similar results to those shown here for AKH-I.…”

“…The possibility remains, of course, that the release of AKH-III is responsible for the changes in lipid metabolism induced by the immunogens, but this is considered very unlikely: the three AKHs in Locusta are thought to be released together (Harthoorn et al, 1999;Flanigan and Gade, 1999), and AKH-III is present in the corpora cardiaca in the least quantities of the three neurohormones (Oudejans et al, 1991;Oudejans et al, 1993). It is interesting to note that the particular preparation of LPS used here had unusual biological activity, in that it was able to activate prophenoloxidase in the haemolymph when injected alone: other commercial preparations of LPS from a variety of bacteria, including Pseudomonas, were reported to have no effect on the phenoloxidase activity in the haemolymph unless co-injected with AKH (Goldsworthy et al, 2002a). A fresh sample of Pseudomonas LPS was purchased and tested for it's ability to activate prophenoloxidase when injected alone, and was completely ineffective in doing so (data not shown), which is consistent with the results presented earlier (Goldsworthy et al, 2002a).…”

“…It is interesting to note that the particular preparation of LPS used here had unusual biological activity, in that it was able to activate prophenoloxidase in the haemolymph when injected alone: other commercial preparations of LPS from a variety of bacteria, including Pseudomonas, were reported to have no effect on the phenoloxidase activity in the haemolymph unless co-injected with AKH (Goldsworthy et al, 2002a). A fresh sample of Pseudomonas LPS was purchased and tested for it's ability to activate prophenoloxidase when injected alone, and was completely ineffective in doing so (data not shown), which is consistent with the results presented earlier (Goldsworthy et al, 2002a). Therefore, the physiological effects of commercial preparations of LPS should be interpreted with some caution, as in our experience, there are differences in physiological effects and in potency between preparations and between batches.…”

“…The most wellknown effects are lipid mobilisation and activation of glycogen phosphorylase in the fat body to provide energy for migratory flight (for review see Goldsworthy, 1990), although other actions include inhibition of the synthesis of protein, fatty acid and mRNA (Lee and Goldsworthy, 1995;Kodrik and Goldsworthy, 1994). Recently, however, it has been shown that in locusts injection of AKH can also influence immune responses (Goldsworthy et al, 2002a;Goldsworthy et al, 2003a;Goldsworthy et al, 2003b;Mullen and Goldsworthy, 2003). The orthopteran prophenoloxidase system is apparently located within haemocytes (Brehelin et al, 1989) and is activated by a serine protease cascade (Ashida, 1990) in response to recognition of non-self material within the haemocoel, and produces effector molecules such as cytotoxic quinones (for review see Ashida and Brey, 1998).…”

“…The orthopteran prophenoloxidase system is apparently located within haemocytes (Brehelin et al, 1989) and is activated by a serine protease cascade (Ashida, 1990) in response to recognition of non-self material within the haemocoel, and produces effector molecules such as cytotoxic quinones (for review see Ashida and Brey, 1998). Activation of prophenoloxidase in response to injection of immunogens such as bacterial lipopolysaccharide (LPS) or β-1,3 glucan (laminarin) is influenced by coinjection of AKH-I: prolonging the activation of prophenoloxidase in the haemolymph in response to laminarin and enabling an activation of prophenoloxidase in response to LPS (Goldsworthy et al, 2002a). Another aspect of the immune response, nodule formation, is also enhanced by co-injection of AKH-I with an immunogen such as LPS (Goldsworthy et al, 2003a).…”