20-Hydroxyecdysone Modulates Gene-Specific Immune Response to Metarhizium anisopliae Infection in Drosophila melanogaster S2 Cell Culture

The interplay between innate immunity and other signaling pathways remains a central focus in immunological research, with considerable ongoing investigation. Of particular interest are studies exploring the influence of the hormonal system on the innate immunity of Drosophila melanogaster. In this study, we performed a comprehensive analysis of the combined effects of the insect hormone 20-hydroxyecdysone (20E) and spores from the fungus Metarhizium anisopliae on the innate immune response in D. melanogaster S2 cell culture, addressing this interaction for the first time. Our results demonstrate that, compared to cells exposed solely to M. anisopliae spores, pretreatment with 20E followed by fungal challenge led to a reduction in the transcription of antimicrobial peptide genes CecropinA1 and Drosocin. In contrast, expression of the Metchnikowin (Mtk) gene was upregulated. No significant alterations were observed in the transcription levels of Drosomycin or in genes encoding key receptors, transcription factors, or other components of innate immune signaling pathways. Furthermore, knockdown of the transcription factor Relish markedly decreased Mtk expression, highlighting its central role in hormone-modulated antifungal immunity. These findings reveal complex hormonal-immune crosstalk that differentially regulates AMP gene expression in Drosophila.