Role and Importance of Phenoloxidase in Insect Hemostasis

In response to microbial infection, insects mount several defense reactions including the induction of proteolytic cascades that lead to localized melanization and coagulation. Melanization requires the activation of prophenoloxidase (proPO) to its active form phenoloxidase (PO), a key enzyme that leads to the formation of melanin at wound sites and around intruding microorganisms in the hemolymph. Clotting is critical in limiting hemolymph loss and initiating wound healing following injury; it quickly acts to form a solid barrier against infection by immobilizing microorganisms and promoting their killing. Recent advances in Drosophila and other insects imply a possible link between PO and the coagulation system, although the exact molecular mechanisms controlling this interaction appear to be complex and are still not well defined. The development of hemolymph experimental techniques in Drosophila larvae together with proteomic analysis have further led to the identification of proPO as a cross-linking component that is involved in the hardening and melanization of clots. However, clot PO activity varies between insect species and life stages, depending on physiological and ecological conditions. Here we review Received: August 29, 2010 Accepted after revision: October 12, 2010 Published online: November 6, 2010 Journal of Innate Immunity Dr. Ioannis Eleftherianos Department of Biological Sciences The George Washington University 336 Lisner Hall, 2023 G Street NW, Washington, DC 20052 (USA) Tel. +1 202 994 0876, Fax +1 202 994 6100, E-Mail ioannise @ gwu.edu © 2010 S. Karger AG, Basel 1662–811X/11/0031–0028$38.00/0 Accessible online at: www.karger.com/jin D ow nl oa de d by : 54 .7 0. 40 .1 1 11 /1 9/ 20 17 1 :2 0: 54 P M