Innate Immune system of the honey bee (Apis mellifera)
Insects, lacking an adaptive immune system, have developed an efficient strategy for combating microbial infections (“innate immune response”). For a successful defence against invading pathogens, the cooperation between cellular and humoral immune reactions is necessary. Cellular mechanisms include phagocytosis, nodulation and melanin formation, whereas the humoral response is characterized by the activation of the phenoloxidase cascade and by the rapid and transient expression of several genes encoding antimicrobial peptides.
Innate immune response of insects. Figure: Olaf Gimple, BEEgroup
Although many features are conserved in most insects, individual species have adapted their defence strategies to their specific environment.
As social insects with a very high population density, honey bees offer a unique possibility to study the immune status of individuals with respect to their developmental stage (larva, pupa, adult) and to their caste-specific activities (queen, drone, nurse and forager workers).
We have established the technique for the in vitro rearing of larvae and pupae that enables us to study their immune response after the application of various pathogens under controlled and sterile conditions.
Honey bee workers challenged with non-pathogenic and pathogenic microorganisms at different developmental stages. Figure: Olaf Gimple. BEEgroup
The defence reactions of bees against microbial infections are studied on different levels:
• Differential protein expression (proteomic analysis) by one-and two-dimensional gel electrophoresis in combination with mass spectrometry
• Differential gene expression (transcriptional analysis) by semi-quantitative RT-PCR
• Cell-free protein synthesis of antimicrobial peptides/immune-related proteins and functional analyses
• Determination of genotypes (patrilines) by microsatellite analyses
• Gene-silencing by double-stranded RNA interference
All of these studies are greatly facilitated by the availability of the complete genome sequence of A. mellifera (Honeybee Genome Sequencing Consortium. 2006. Nature 443, 931-949).
The discovery of novel classes of antimicrobial peptides, immune-related proteins will offer a chance to strengthen the bee’s immune response and to improve bee health.