The production of ROS (reactive oxygen species) in response to pathogen detection is a rapid, nonspecific response that is evolutionarily conserved from nematodes to humans. ROS serve as direct and indirect effectors of innate and adaptive immunity. In Caenorhabditis elegans, a ROS burst is observed during infection and is mediated by the dual oxidase BLI-3, which produces H2O2. RNAi (RNA interference) to reduce the amount of BLI-3 results in a significant increase in susceptibility to pathogens, suggesting BLI-3 has a role in the immune response. However, H2O2 by itself is not a potent antimicrobial and in other systems is converted to a more potent oxidant by an affiliated peroxidase. During my work, I have characterized a group of previously unstudied peroxidases in C. elegans and determined their involvement in the host immune response to Enterococcus faecalis. In particular, I focused on SKPO-1 (ShkT-containing peroxidase) and how it contributes to the host immune response with respect to BLI-3.
By RNAi and skpo-1 mutant analysis, I determined that SKPO-1 is involved in the host immune response during E. faecalis infection. By tissue-specific RNAi, I determined that SKPO-1 is functionally active in the hypodermis and required for wild type resistance to infection. Additionally, by immunohistochemistry, I observed that SKPO-1 is only expressed in the hypodermis and that its protein levels do not change in response to E. faecalis. In support of SKPO-1 acting as a peroxidase, I observed a significant increase in H2O2 levels when expression of the gene was reduced by RNAi. The increased H2O2 was observed only during infection and was BLI-3-dependent. Thus, I have characterized a likely BLI-3/SKPO-1 system, potentially similar to the oxidative burst systems present in higher eukaryotes.
Potential Roles of Peroxidases in Caenorhabditis Elegans Innate Immunity