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 proteins that are synthesized largely in the fatbody. kappa B-like motifs upstream of the immune protein genes bind the Cecropia immunoresponsive factor (CIF), and confer high levels of inducible expression. We have extended our studies and sought evidence that oxygen-derived active species might modulate the expression of the immune protein genes and 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 expression of the attacin genes, both in vivo and in vitro. A general stimulant of oxidative stress, H2O2, stimulated expression of these genes and the weak immune response to wounding was greatly augmented by administration of H2O2. These responses were largely or entirely inhibited by dithiothreitol and by N-acetylcysteine. Nonspecific responses were excluded since immune genes failed to respond to albumin or starch, and the expression of a non-immunoresponsive gene was not affected. Electrophoretic mobility-shift assays showed that H2O2 and bacteria, when administered in vitro, could activate CIF in fatbody cells and that dithiothreitol and N-acetylcysteine prevented this process. Our data suggest that the induction of the immune protein genes is mediated through the activation of CIF, contingent upon thiol oxidation induced by oxidative stress.