Insects have an innate immune system that protects against infections by pathogens and parasites. The overall goal of this project is to investigate proteins in insect hemolymph plasma that participate in different aspects of insect immunity. Previous work from this laboratory has established the lepidopteran insect, Manduca sexta, as a model system well suited for biochemical characterization of the complex functions of hemolymph proteins. We plan to investigate three aspects of immunity that are mediated by plasma proteins. (1) We will characterize interactions of plasma proteins with peptidoglycan from Gram-negative and Gram- positive bacteria that trigger activation of a serine protease, thereby initiating protease cascades that result in activation of phenoloxidase and the Toll pathway. (2) We will investigate how the redox environment of hemolymph is regulated during an immune response and test a hypothesis that immune proteins may be regulated by thiol modifications. (3) Mammals have well-characterized mechanisms for depriving invading microorganisms of iron; however, immune-related iron-withholding in insects is still poorly understood. We will use M. sexta as a model for discovering conserved iron-withholding mechanisms in insects. The fundamental biochemical knowledge gained as a result of this research is expected to stimulate better understanding of regulation of protease cascade pathways and molecules in insect hemolymph that contribute to oxidative modulation during immunity, and lead to understanding of how iron influences human disease transmission by insect vectors. This supplement will fund an undergraduate student from an underrepresented group to gain research experience and training by participating in the project.