Lipopolysaccharide-binding protein of Bombyx mori participates in a hemocyte-mediated defense reaction against gram-negative bacteria

BmLBP is a lipopolysaccharide-binding protein in B. mori and participates i n bacterial clearance in vivo. Here, we investigated the function of BmLBP more specifically. More than 90% of injected gram-negative rough strains to which BmLBP binds were removed from the plasma within 30 min post-injectio n, whereas it required 8h for the clearance of smooth strains to which BmLB P does not bind. Observation of the hemocoel after the injection of Escheri chia coli rough strain showed that melanized nodules were formed at 30 min post-injection when the clearance of injected E. coli cells had occurred. F luorescence microscope observation revealed that E. coli cells were actuall y trapped in the nodules formed in vivo. Furthermore, plasma pre-treated E. coli rough cells (BmLBP bound) added to hemocytes isolated in vitro caused vigorous hemocyte aggregations with the bacteria, while plasma pretreated smooth cells did not. The formation of aggregates was inhibited by anti BmL BP serum pre-treatment, suggesting that BmLBP causes the clearance of bacte ria by promoting hemocyte nodule formation. (C) 1999 Elsevier Science Ltd. All rights reserved.