Apolipophorin-III and the interactions of lipoteichoic acids with the immediate immune responses of Galleria mellonella

We investigated the effects of lipoteichoic acids, surface components of Gr am-positive bacteria, on the hemocytes and phenoloxidase activity in last i nstar Galleria mellonella larvae, as well as the binding of apolipophorin-I II, an insect lipid-binding protein, to lipoteichoic acids. Binding of apol ipophorin-III to lipoteichoic acid was studied using an assay based on 1,9- dimethylmethylene blue. Apolipophorin-III bound the lipoteichoic acids from Bacillus subtilis, Enterococcus hirae, and Streptococcus pyogenes and to i ntact cells of E. hirae. E. hirae lipoteichoic acid promoted the binding of apolipophorin-III to the cells of this species. All lipoteichoic acids tes ted caused a dose- and time-dependent drop in the total counts of hemocytes and, depending on the species of lipoteichoic acid, partial or complete de pletion of plasmatocytes. Granulocyte counts were not affected. Apolipophor in-III prevented partially the loss of plasmatocytes due to B. subtilis lip oteichoic acid. All three lipoteichoic acids studied activated phenoloxidas e in vitro; injections of B. subtilis lipoteichoic acid into the larvae ele vated the phenoloxidase activity, whereas injections of E. hirae or S. pyog enes lipoteichoic acid, or apolipophorin-III alone, suppressed it. Apolipop horin-III decreased the activation of phenoloxidase by B. subtilis lipoteic hoic acid. (C) 2000 Academic Press.