Insect cell stimulation by LPS requires the activity of cell‐released proteases

The hemocyte line BTI‐EA‐1174‐A from the lepidopteran insect Estigmene acraea responds to bacterial lipopolysaccharide (LPS) by an enhanced phagocytic reaction and a dose‐dependent increase of lysozyme release [Wittwer et al., Dev Comp Immunol 21 :323 (1997)]. This paper provides evidence for a strong proteolytic activity in cell culture supernatants occuring after addition of LPS (1 mg/ml). The proteolysis is caused by cell‐released proteases and seems to be necessary for cell activation. Its inhibition by α 2 ‐macroglobulin results in a dose‐dependent reduction in cellular response strength. Phagocytic reactions, as well as lysozyme release, are lowered to about half in the presence of 0.0001 mg/ml α 2 ‐macroglobulin. A nearly complete abolishment of activation was achieved with final concentrations of 1.0 mg/ml α 2 ‐macroglobulin. The data presented allow us to conclude that the LPS‐triggered proteolytic activity is an important part of the activation process; it occurs outside of the cells and delivers immune response activating factors. Arch. Insect Biochem. Physiol. 39:91–97, 1998. © 1998 Wiley‐Liss, Inc.