In response to bacteria or trauma, insects produce a battery of antibacterial peptide or polypeptide such as cecropin, diptericin, attacin and defensin, the synthesis of which are induced in the fat body and secreted into the hemolymph where they act synergistically to kill the invading microorganisms. The insect host defence system shares common basic characteristics of the mammalian acute phase response, especially in the aspect of the coordinating gene expression, where similar cis-regulatory and inducible transactivator appear to play major roles.