Analysis of the attraction of haemocytes from Mytilus edulis by molecules of bacterial origin

Boyden chamber assays were performed to test the stimulatory effect of different bacterial products on the migratory activity of Mytilus haemocytes. The results indicate that these blood cells exhibit chemotactic as well as chemokinetic reactions. Lipopolysaccharides (LPS) from both Serratia marcescens and Escherichia coli stimulated the migration of cells through the membrane of the Boyden chamber when LPS was present in the lower compartment only. In contrast, addition of LPS to the lower as well as to the upper chamber did not increase the rate of migrating cells. Thus, LPS seemed to act as a chemotaxis-stimulating substance. Further analysis indicated that complete LPS molecules are required for cell stimulation because this did not occur when either the lipid or polysaccharide moieties of LPS were tested alone. Unlike LPS, the formylated tripeptide N-FMLP stimulated random cell migration. The peptide, which is released by bacteria, induced a higher haemocyte motility when present in both wells of the Boyden chamber than in tests where it was added to the lower compartment only. This chemokinetic response was not stimulated by the tetrapeptide N-FMLPLys. These findings demonstrate that bacterial products may elicit chemotactic and/or chemokinetic reactions in haemocytes from an invertebrate, and that the type of reaction that occurs is dependent upon the nature of the molecules presented.