Immune defenses in bumble bees

Bumble bees, like other insect species are able to identify self as distinct from non-self and exclude invading organisms that might cause disease or death. The protective mechanisms of bumble bees are considered to be functional analogies of vertebrate immune mechanisms insofar as they have similar effects but are of a totally different origin and chemical composition. The bumble bee protects itself against infections and parasitic invasions by physical barriers as well as processes analogous to phagocytosis, cell-mediated immune responses and humoral immunity. The anatomical structures of the bumble bee form natural barriers to infection. The major structures are the integument, the respiratory system consisting of spiracles and tracheae, and the digestive tract, including the midgut epithelium and the peritrophic membrane. The cellular reaction is a recognition of self from non-self together with pattern recognition molecules, phagocytosis, cellular encapsulation and nodule formation. among the immune proteins that mimic antibody molecules are lysozyme, defensins, the phenoloxidase system and inducible molecules of antibacterial activity such as apidaecins, abaecin and hymenoptaecin. These antibacterial immune proteins appear about 2 hours after exposure to the bacteria and reach peak levels 24 hours later. It has been suggested that phagocytosed bacteria or bacteria destroyed by lysozyme release cell-wall components that stimulate the fat body and haemocytes to produce and secrete antibacterial immune proteins.