In vitro phagocytosis of Escherichia coli and release of lipopolysaccharide by adhering hemocytes of the silkworm, Bombyx mori.

A primary culture containing adhering hemocytes mainly granular cells from the silkworm, Bombyx mori, was used to investigate in vitro phagocytosis of Escherichia coli. Phagocytosis was confirmed to occur in this system by microscopic observation. Lipopolysaccharide (LPS) concentration in the culture medium was measured by a Limulus test and a higher LPS concentration was detected in phagocytosis-occurred samples than in control samples, which omitted either E. coli cells or adhering hemocytes. Moreover, it was found that LPS containing sample but not control samples strongly induces gene expression of cecropin B, an antibacterial protein. These results suggest that bacterial cell wall components like LPS released by phagocytosis play an important role in the induction of insect antibacterial proteins.