Experimental infection of acute bee paralysis virus induces differential responses of selected honey bee immune genes, independent of varroa resistance.

Honeybees (Apis mellifera) have a complex immune system, with both innate and social immunity. The mite-resistant honeybee population from Gotland, Sweden, is well-known for their independent resistance to Varroa destructor mites and tolerance to virus infections, particularly deformed wing virus and acute bee paralysis virus (ABPV). However, the immune mechanisms underlying their virus tolerance remains unclear. Adult bees from this mite-resistant (MR) and a mite-susceptible (MS) control population were orally inoculated with either ABPV or a mock inoculum, in a laboratory time-course experiment. Two representative genes from five major immune signalling pathways, previously shown to respond to viral infections, were quantified using RT-qPCR. The genes exhibited distinct responses to ABPV inoculation, with some genes showing clear treatment-related differential expression between 24 and 48 h post-inoculation while other genes remained unaffected. However, there was no difference in the expression patterns between MR and MS populations. These findings suggest that the enhanced virus tolerance of the Gotland mite-resistant population is not due to differential regulation of the immune genes examined here. They also highlight the dynamic nature of immune gene expression, refine hypotheses for further studies of honeybee virus tolerance and motivate more comprehensive molecular analyses of a selection of these samples.