Comparison of transcriptional changes of immune genes to experimental challenge in the honey bee (Apis mellifera)

Honey bee colony losses of the last decade have been alarming. Besides the most critical factors, such as parasites and pathogens, losses have been claimed to be linked to immunodeficiency. For the evaluation of this suggestion powerful immunological tests are required. The aim of this study was to obtain further data to characterize common markers of immunity with respect to their experimental practicability. Honey bees were challenged by mechanical and pathogen-like stressors. These were wounding and the injection of buffers and acute bee paralysis virus (ABPV), lipopolysaccharides, lipoteichoic acid, Paenibacillus larvae suspensions and petidoglycan. All experiments were conducted with bees in hoarding cages at a laboratory scale. Immune reactions were quantified by inhibition zone assays and by expression analysis of the genes coding for abaecin, apidaecin, defensin1, hymenoptaecin, hopscotch, Toll and prophenoloxidase. Wounding and injections led to significant immune responses, but the addition of pathogen derived material to the injection solutions did not result in a prominent or specific increase of the defense reactions. A significant upregulation was found for abaecin, defensin1, apidaecin and hymenoptaecin, which was the most responsive gene, showing a 270-fold upregulation after P larvae injection. The upregulation of each of these effector genes was strongly correlated with each other and with Toll, but not with hopscotch or prophenoloxidase.