The Activin Branch Ligand Daw Regulates the Immune Response and Lipid Metabolism against the Serine Carboxypeptidase.

Despite impressive advances in the broad field of innate immunity, our understanding of the molecules and signaling pathways that control the host immune response to nematode infection remains incomplete. We have shown recently that Transforming Growth Factor-β (TGF-β) signaling in the fruit fly is activated by nematode infection and certain TGF-β superfamily members regulate the anti-nematode immune response. Here, we investigate the effect of an entomopathogenic nematode infection factor on host TGF-β pathway regulation and immune function. We find that serine carboxypeptidase activates the Activin branch in adults and the immune deficiency pathway in Activin-deficient flies, it affects hemocyte numbers and survival in flies deficient for Activin signaling, and causes increased intestinal steatosis in Activin-deficient flies. Thus, insights into the signaling pathways and metabolic processes interacting with pathogenicity factors will be applicable to entomopathogenic nematode infection of important agricultural insect pests and vectors of disease.