Infection of honey bees with acute bee paralysis virus does not trigger humoral or cellular immune responses

We have studied the responses of honey bees at different life stages (Apis mellifera) to controlled infection with acute bee paralysis virus and have identified the haemolymph of infected larvae and adult worker bees as the compartment where massive propagation of ABPV occurs. Insects respond with a broad spectrum of induced innate immune reactions to bacterial infections, whereas defence mechanisms based on RNA interference play a major role in antiviral immunity. In this study, we have determined that honey bee larvae and adult workers do not produce a humoral immune reaction upon artificial infection with ABPV, in contrast to control individuals challenged with Escherichia coli. ABPV-infected bees produced neither elevated levels of specific antimicrobial peptides (AMPs), such as hymenoptaecin and defensin, nor any general antimicrobial activity, as revealed by inhibition-zone assays. Additionally, adult bees did not generate melanised nodules upon ABPV infection, an important cellular immune function activated by bacteria and viruses in some insects. Challenge of bees with both ABPV and E. coli showed that innate humoral and cellular immune reactions are induced in mixed infections, albeit at a reduced level.