Ecdysone Titer Determined by 3DE-3β-Reductase Enhances the Immune Response in the Silkworm

Although recent studies have demonstrated that 20-hydroxyecdysone (20E), one of the two most important hormones for development, could promote the insect innate immune response, how insects regulate 20E titer to affect the immunity after suffering pathogen attack remains unknown. In this study, to our knowledge, we first found that 20E titer was significantly elevated after bacterial infection in the domesticated silkworm, Bombyx mori. Furthermore, the elevated 20E enhanced the silkworm innate immune system against invading bacteria via ecdysone receptor. During immune response, the expression of the silkworm 3-dehydroecdysone-3 beta-reductase (3DE-3 beta-reductase) that converts 3DE released from prothoracic glands into ecdysone was induced. RNA interference experiments suggested that 3DE-3 beta-reductase is essential to upregulate the 20E titer after bacterial infection. The rescue experiments showed that injection with the recombinant 3DE-3 beta-reductase protein can significantly elevate the 20E concentration and modulate the expressions of the silkworm immune-related genes. Taken together, 20E titer determined by 3DE-3 beta-reductase enhances the silkworm defense against the bacterial infection. Thus, our findings reveal an important role of the 20E synthesis pathway from 3DE in enhancing the silkworm immune response and have profound implications for the understanding of interaction mechanisms between insect hormone and immunity.