Barrier immune effectors are maintained during transition from nurse to forager in the honey bee.

Foragers facilitate horizontal pathogen transmission in honey bee colonies, yet their systemic immune function wanes during transition to this life stage. In general, the insect immune system can be categorized into mechanisms operating at both the barrier epithelial surfaces and at the systemic level. As proposed by the intergenerational transfer theory of aging, such immunosenescence may result from changes in group resource allocation. Yet, the relative influence of pathogen transmission and resource allocation on immune function in bees from different stages has not been examined in the context of barrier immunity. We find that expression levels of antimicrobial peptides (AMPs) in honey bee barrier epithelia of the digestive tract do not follow a life stage-dependent decrease. In addition, correlation of AMP transcript abundance with microbe levels reveals a number of microbe-associated changes in AMPs levels that are equivalent between nurses and foragers. These results favor a model in which barrier effectors are maintained in foragers as a first line of defense, while systemic immune effectors are dismantled to optimize hive-level resources. These findings have important implications for our understanding of immunosenescence in honey bees and other social insects

Differences in AMP expression based on level s of DWV and of all bacteria are similar in nurse and foragers.

<p>Correlation of levels of <i>Apidaecin</i> (n = 92), with levels of DWV (A) and <i>Defensin 1</i> (B) and <i>Apidaecin</i> (C), with levels of all bacteria (16S RNA).</p

Broad range of AMP production in midgut barrier epithelium.

<p>Individual levels of the six honey bee AMPs (<i>Abaecin (n = 91), Hymenoptaecin (n = 91), Defensin 1 (n = 92)</i>, <i>Defensin 2 (n = 91), Apidaecin</i> (<i>n = 92)</i>, and <i>Apisimin</i> (<i>n = 92)</i>) and the immune signaling protein <i>Relish</i> (<i>n = 91)</i> relative to <i>β-actin</i> in midgut tissue from both nurses and foragers from multiple hives. Boxes show 1st and 3rd interquartile range with line denoting medians. Whiskers encompass 95% of the individuals. Outliers are denoted with filled circles.</p

Nurse and forager AMP expression in fatbody tissue.

<p>Individual levels of the six honey bee AMPs relative to <i>β-actin</i> in abdominal tissue for Nurse and Foragers, as assessed by behavior and location cues, for <i>Abaecin</i> (A), <i>Hymenoptaecin</i> (B), <i>Defensin 1</i> (C), <i>Defensin 2</i> (D), <i>Apidaecin</i> (E), and <i>Apisimin</i> (F) from trials 3 and 4. Boxes show 1st and 3rd interquartile range with line denoting medians. Whiskers encompass 95% of the individuals. Outliers are denoted with filled circles.</p

Similar midgut barrier AMP expression in nurse and forager stages.

<p>Individual levels of the six honey bee AMPs relative to <i>β-actin</i> in midgut tissue for Nurses (n = 46) and Foragers (n = 45), as assessed by behavior and location cues, for <i>Abaecin</i> (A), <i>Hymenoptaecin</i> (B), <i>Defensin 1</i> (C), <i>Defensin 2</i> (D), <i>Apidaecin</i> (E), and <i>Apisimin</i> (F) from the six trials. Boxes show 1st and 3rd interquartile range with line denoting medians. Whiskers encompass 95% of the individuals. Outliers are denoted with filled circles.</p

NFκB-family transcriptional activators of the Toll and Imd pathways are similar in nurses and foragers.

<p>Individual levels of <i>Relish</i> (A) and <i>Dorsal-like 1a</i> (B) relative to <i>β-actin</i> in midgut tissue from Nurses (n = 23) and Foragers (n = 22) from trials 1, 3, and 5. Boxes show 1st and 3rd interquartile range with line denoting medians. Whiskers encompass 95% of the individuals. Outliers are denoted with filled circles.</p

Differences in AMP expression between <i>Nosema</i> infected and non-infected bees are similar in nurse and foragers.

<p>Levels of the six honey bee AMPs (<i>Abaecin</i> (n = 91), <i>Hymenoptaecin</i> (n = 91), <i>Defensin 1</i> (n = 92), <i>Defensin 2</i> (n = 91), <i>Apidaecin</i> (n = 92), and <i>Apisimin</i> (n = 92) relative to <i>β-actin</i> in midgut tissue from bees that were positive (+) or negative (−) for <i>Nosema ceranae</i> (A). Levels of <i>Abaecin</i> (B) and <i>Apidaecin</i> (C) relative to <i>β-actin</i> in midgut tissue from bees that were positive (+) or negative (−) for <i>Nosema ceranae</i> for all bees and split into nurses and foragers. Boxes show 1st and 3rd interquartile range with line denoting medians. Whiskers encompass 95% of the individuals. Outliers are denoted with filled circles.</p