Apolipophorin-III in Galleria mellonella potentiates hemolymph lytic activity

Heat-inactivated serum of non-immune Galleria mellonella larvae enhanced the lytic activity of larval cell-free hemolymph against Micrococcus lysodeikticus. The increase in bacterial lysis was due to a 17.2 kDa protein known previously to bind to bacterial lipopolysaccharides. The protein enhanced the lytic activity of insect cell-free hemolymph and hen lysozyme in vitro and insect hemolymph in vivo. The hydrophobic protein, which adhered to M. lysodeikticus, was identified by its amino acid sequence homology as apolipophorin-III. The titer of apolipophorin-III in 200-250 mg last instar larvae was 8.7 mg/ml of hemolymph. Apolipophorin-III did not bind to lysozyme. A possible mode of action of apolipophorin-III with lysozyme in the insect is proposed.