Chemotaxis of Mercenaria mercenaria hemocytes to bacteria in vitro

Hemocytes of the hard clam Mercenaria mercenaria migrate toward secreted bacterial products in vitro by chemotaxis (i.e., by detection of an increasing chemical gradient of attractant). The attractants produced by Escherichia coli are peptides or small proteins. Clam hemocytes also migrate toward formyl-methionyl-leucyl-phenylalanine (fMLF), a mammalian neutrophil chemoattractant produced by bacteria, but not toward the related compound formyl-methionyl-valine. Migration of hemocytes to fMLF was blocked with the neutrophil fMLF receptor antagonist, t-Boc-MLF, suggesting that the hemocytes possess this receptor and that the response is receptor-mediated. However, fMLF is not the major bacterial chemoattractant for clam hemocytes, as t-Boc-MLF did not block migration of these cells to secreted bacterial chemoattractants.