TRANSCRIPTION OF IMMUNE GENES IN THE GIANT SILKMOTH, HYALOPHORA-CECROPIA IS AUGMENTED BY H2O2 AND DIMINISHED BY THIOL REAGENTS

Insects have an effective humoral immune system, residing in immune pr oteins that are synthesized largely in the fatbody. kappa B-like motif s upstream of the immune protein genes bind the Cecropia immunorespons ive factor (CIF), and confer high levels of inducible expression. We h ave extended our studies and sought evidence that oxygen-derived activ e species might modulate the expression of the immune protein genes an d the activation of CIF after the administration of different inducers . Mitogens, like arachidonic acid, phorbol esters, phytohemagglutinin, bacteria, and components of microbial cell envelopes stimulate expres sion of the attacin genes, both in vivo and in vitro. A general stimul ant of oxidative stress, H2O2, stimulated expression of these genes an d the weak immune response to wounding was greatly augmented by admini stration of H2O2. These responses were largely or entirely inhibited b y dithiothreitol and by N-acetylcysteine. Nonspecific responses were e xcluded since immune genes failed to respond to albumin or starch, and the expression of a non-immunoresponsive gene was not affected. Elect rophoretic mobility-shift assays showed that H2O2 and bacteria, when a dministered in vitro, could activate CIF in fatbody cells and that dit hiothreitol and N-acetylcysteine prevented this process. Our data sugg est that the induction of the immune protein genes is mediated through the activation of CIF contingent upon thiol oxidation induced by oxid ative stress.