Science Serving Maryland's Coasts
Robert Anderson, Ph.D.
Chesapeake Biological Laboratory
Chemotactic Rresponse of Mercenaria mercenaria Hemocytes to Labyrinthilomycota spp. In Vitro
Labyrinthilomycota spp. (or "Laby") is an unnamed species of the same phylum as the clam parasite QPX (quahog parasite unknown). QPX disease has been shown to cause mass mortalities in the clam (Mercenaria mercenaria). Research was conducted to determine if the cell-mediated immune system of M. mercenaria responds to this potential pathogen via chemotaxis, defined as directional migration of blood cells (hemocytes) along a concentration gradient of substances secreted by Laby. Test substances (i.e., live Laby cells, cell-free culture media, dead or lysed Laby cells, concentrated Laby proteins from culture media) were placed in the bottom of a blind-well chamber and clam hemocytes were placed in the top well, with a 5 micron pore size polycarbonate membrane separating the two wells. After an hour incubation, membranes were fixed, stained, and mounted, and cells were counted under 400x for the top and bottom sides of the membrane to determine the number of cells migrating through the membrane towards the putative chemoattractant. This information was used to calculate a chemotactic index, to compare control and experimental data. Preliminary results indicate that the presence of Laby cells does increase hemocytic chemotaxis, and that this response is dose-dependent. Results also indicate that hemocytes are responding more to a secreted chemoattractant, possibly protein, than to the Laby cell surface components. It is suggested that Laby cells secrete a mix of proteins, some that are attractive and some that are inhibitory to the clam chemotactic response. Since Laby is closely related to QPX, conclusions drawn from these experiments may be applicable to QPX as well.
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