Hemocyte activation and nodule formation in the giant keyhole limpet, Megathura crenulata

The giant keyhole limpet, Megathura crenulata, lives in rocky intertidal and subtidal environments along the Southern California coast, where it is exposed to viruses, bacteria, and other potential pathogens. We demonstrate that when exposed to bacteria or latex beads, hemocytes from specimens of M. crenulata in vivo and in vitro immediately become adhesive and form nodules. The rapid activation of hemocytes suggests a role for an array of recognition proteins, and inhibition of nodulation by the tripeptide Arg–Gly–Asp indicates that integrins are involved. The morphological changes involved with nodule formation include the rapid extension of lamellipodia, phagocytosis of particles, and compaction of the hemocyte aggregates. The number of nonadherent hemocytes rapidly decreases as aggregates form. The elimination of bacteria is due to a dynamic hemocyte response, rather than antibacterial factors in the plasma. These findings are compared to work on other gastropods and expand the current knowledge on the immune response of molluscs, such as M. crenulata, which is increasing in importance as they continue to be raised in aquaculture for pharmacological use.