The level of apoLp-III in fat body, hemocytes and plasma from Galleria mellonella larvae infected with Pseudomonas aeruginosa was studied. It was found that the amount of 18kDa
protein present in fat body and hemocytes decreased progressively with time after
infection. In the case of plasma, an increase in apoLp-III content was observed during the first 19h after
infection and then decreased significantly after prolonged
infection time. The decreased level of apoLp-III in plasma 24h after
infection was accompanied by the appearance of smaller than 18kDa immunoreactive
polypeptides. Four intermediate forms with molecular mass of, respectively, 15, 13.3, 12 and 9.5kDa were detectable. The size of
polypeptides detected in experiments performed in vivo is comparable with the degradation products of apoLp-III produced by
serine protease IV in vitro. In addition, the total proteolytic activity of plasma increased progressively during
infection time. The results of our studies suggest that a significant part of total proteolytical activity in the plasma of infected G. mellonella larvae can be attributed to
proteases produced by P. aeruginosa during pathogenesis. We discuss the possibility that
protease IV of P. aeruginosa is responsible for apoLp-III degradation in vivo.