Humoral immune response upon mild heat-shock conditions in Galleria mellonella larvae

Larvae of Galleria mellonella exposed to mild heat-shock (38 °C) showed an enhanced humoral immune response after microbial infection in comparison to infected animals grown at 28 °C. This enhanced response was manifested by increased expression of antimicrobial peptide (AMP) genes leading to enhanced antimicrobial activity in the hemolymph. We found an increased level of Hsp90 and changes in the level of a 55 kDa protein recognized by anti-Hsp90 antibodies in fat bodies of infected animals reared at 28 °C as well as in uninfected animals exposed to elevated temperature. Pre-treatment of animals with an inhibitor of Hsp90, 17-DMAG, prior to immunization resulted in increased expression of AMP genes encoding gallerimycin and cecropin at 38 °C. This observation was correlated with the changes in Hsp90 protein and increased level of 55 kDa protein. Also G. mellonella larvae pre-treated with 17-DMAG and exposed to mild heat-shock for 30 min showed an increased survival rate after infection with entomopathogenic bacteria Pseudomonas aeruginosa. We also show the effect of 17-DMAG on the phosphorylation state of ERK MAP kinase. We postulate that Hsp90 may play a significant role in converging pathways involved in the insect immune response and heat-shock.