HEMOLYMPH IMMUNE PROTEINS PROTECT THE INSECT BODY CAVITY FROM INVADING BACTERIA

Injections of living, non-pathogenic Enterobacter cloacae into the bod y cavity of Galleria mellonella provoked the insect's cion-self respon se system to produce antibacterial activity that eliminated the bacter ial infection, Immunized larvae of Galleria contained no E. cloacae in haemolymph within 24 hr post-infection and they transmitted normally to pupae, Parallel to this protective immunity, antibacterial activity of cecropin-like polypeptides and manifold increased innate titer of haemolymph lysozyme were shown in vaccinated insects. Application of a ctinomycin D or cycloheximide in an induction phase of antibacterial r esponse at a dose of 0.25 x LD(50) demonstrably reduced the lysozyme t iter and entirely prevented (except for actinomycin-treated pupae) the synthesis of cecropin-like antibacterial activity, In insects with im paired antibacterial immunity, the immunizing bacteria multiplied to t he titer of almost 10(9) cells/ml of haemolymph, causing death in near ly 100% of larvae due to E. cloacae bacteriaemia, No bacteriaemia of E . cloacae could be induced in larvae given actinomycin D (or cyclohexi mide) in an effector phase of immune response when the antibacterial p roteins begin to be synthesized in invaded insects. For the expression of cell-free immunity in Galleria ia, there is a requirement for the de novo synthesis of antibacterial immune proteins that normally prote ct the insect body cavity from invading bacteria, The anti-cecropin ag ent from Heterohabditis bacteriophora selectively destroyed the induci ble antibacterial immunity, thereby allowing the immunizing bacteria t o grow in Galleria. This implies that the cecropin antibacterial activ ity is primarily responsible for the elimination of E. cloacae and oth er bacterial invaders from the insect body cavity.