Interaction of hemocytes and prophenoloxidase system of fifth instar nymphs of Acheta domesticus with bacteria.

The hemocytes to which bacteria adhere were defined and the contribution of the prophenoloxidase system of fifth instar nymphs of Acheta domesticus to adhesion were examined. The physicochemical parameters affecting hemocyte and phenoloxidase activity were determined. Both plasmatocytes and granular cells responded to bacteria, the latter cells entrapping the microorganisms on filopodial extensions. The optimum pH for hemocyte adhesion to glass slides was 6.5, the granular cells being the most sensitive hemocyte type. Although hydrophobic resin beads and positively-charged beads favoured hemocyte attachment, these parameters did not contribute to differential bacterial adhesion to hemocytes. Activation of phenoloxidase was neither enhanced nor inhibited by 0.1 and 1 mg/ml of laminarin or zymosan nor by dead Bacillus subtilis. However, live B. subtilis activated the enzyme and dead Xenorhabdus nematophilus inhibited enzyme activation. Serine protease components of the prophenoloxidase system had opsonic properties for B. subtilis but not for X. nematophilus. Phenoloxidase activity was enhanced by Ca(2+) and Mg(2+) and inhibited by SO(2-)(4).