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Title: Inducible versus constitutive immunity: Examining effects of colony infection on glucose oxidase and Defensin-1 production in honey bees

Author
item LOPEZ-URIBE, MARGARITA - Pennsylvania State University
item FITZGERALD, ANDREA - University Of North Carolina
item Simone-Finstrom, Michael

Submitted to: Royal Society Open Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2017
Publication Date: 5/31/2017
Citation: Lopez-Uribe, M.M., Fitzgerald, A., Simone-Finstrom, M. 2017. Inducible versus constitutive immunity: Examining effects of colony infection on glucose oxidase and Defensin-1 production in honey bees. Royal Society Open Science. 4:170224. doi:10.1098/rsos170224.

Interpretive Summary: Honey bees rely on a variety of defense mechanisms to reduce disease infection and spread throughout the colony. Hygienic behavior, resin collection, and production of antimicrobial compounds are some examples of defenses that bees use against parasites. Many of these defenses rely on the collective action of multiple individuals to prevent, reduce or eradicate pathogens—often referred as social immunity. Honey bees produce several antimicrobial secretions that help sterilize food (e.g., honey) and larval diet. Whether or not nurse bees increase in the amount of these compounds, glucose oxidase (GOX) and defensin-1 (Def1) in particular, when the colony is infected by pathogens is currently unclear. This research aimed to address that question see to what level two of these compounds are produced in response to colony level infections. We conclude that GOX and Def1 are prophylactically included in larval diet and are not increased in response to pathogen exposure. Colony variation in level of these antimicrobial compounds was noted and these factors should be considered when investigating immunity at the individual and colony level in social insects.

Technical Abstract: Honey bees use a variety of defense mechanisms to reduce disease infection and spread throughout the colony. Many of these defenses rely on the collective action of multiple individuals to prevent, reduce or eradicate pathogens—often referred as 'social immunity'. Glucose oxidase (GOX) and some antimicrobial peptides (e.g. Defensin-1 or Def1) are secreted by the hypopharyngeal gland of adult bees on larval food for their antiseptic properties. Because workers secrete these compounds to protect larvae, they have been used as “biomarkers” for social immunity. The aim of this study was to investigate if GOX and Def1 are induced after pathogen exposure to determine whether its production by workers is the result of a collective effort to protect the brood and colony in response to a pathogen challenge. Specifically, we quantified GOX and Def1 in honey bee adults before and after colony-level bacterial infection by American Foulbrood (AFB, Paenibacillus larvae). Overall, our results indicate that levels of GOX and Def1are not induced in response to pathogenic infections. We therefore conclude that GOX and Def1 are highly constitutive and co-opted as mechanisms of social immunity, and these factors should be considered when investigating immunity at the individual and colony level in social insects.