Changes in the apolipophorin III in Galleria mellonella larvae treated with Pseudomonas aeruginosa exotoxin A

In the present study, we have demonstrated a correlation in time between changes in the amount of apolipophorin III (apoLp-III) in the fat body and hemocytes of Galleria mellonella larvae challenged with Pseudomonas aeruginosa exotoxin A (exoA). An increase in the amount of apoLp-III was detected 1–8 h after the challenge; then, a temporary decrease was observed after 15 h followed by an increase in the level of apoLp-III, however to a different extent. The profile of apoLp-III forms in the hemolymph, hemocytes, and fat body of the exoA-challenged larvae was analyzed using two-dimensional electrophoresis (IEF/SDS-PAGE) and immunoblotting with anti-apoLp-III antibodies. Two apoLp-III forms differing in isoelectric point values estimated at ∼ 6.5 and ∼ 6.1 in the hemolymph and ∼ 6.5 and ∼ 5.9 in the hemocytes as well as one isoform with pI ∼ 6.5 in the fat body with an additional apoLp-III-derived polypeptide with estimated pI ∼ 6.9 were detected in the control insects. The injection of exoA caused a significant decrease in the abundance of both apoLp-III isoforms in the insect hemolymph. In the hemocytes, a decrease in the amount of the pI ∼ 5.9 isoform was detected, while the major apoLp-III isoform (pI ∼ 6.5) remained unchanged. In addition, appearance of an additional apoLp-III-derived polypeptide with an estimated pI ∼ 5.2 was observed. Interestingly, there were no statistically significant differences in the amount of the main isoform in the fat body between the control and exoA-challenged insects, but the polypeptide with pI ∼ 6.9 disappeared completely. It should be noted that the decrease in the amount of apoLp-III and other proteins was especially noticeable at the time points when exoA was detected in the studied tissues.