Parasite Evasion of Host: Perkinsus marinus /Eastern Oyster as a Model Interaction

1. Parasite Evasion of Host: Perkinsus marinus/Eastern Oyster as a Model Interaction G. Burreson www.disease-watch.com/.../ CD/index/images/pm.jpg Christina Panko

2. Introduction Disease induction: www.nwfsc.noaa.gov/.../ ec/ecotox/immuno2.jpg Pathogen: protozoan parasite Perkinsus marinus Host: eastern oyster, Crassostrea virginica Environmental factors: temperature and salinity

3. History

4. Pathogen 80% infection of oysters in the Gulf of Mexico and along the U.S. Atlantic coast Favorable environmental conditions are temp >20◦C and salinity >15ppt Depletes host energy resources causing decreased growth and reproduction and increased mortality Rapidly proliferates and spreads via hemolymph (oyster blood) through tissues causing deterioration and organ failure www.jaxshells.org/ guide.htm

5. S. Bower www.disease-watch.com/.../ CD/index/images/pm.jpg www.vims.edu/env/research/ shellfish/gallery.html

6. Host Innate immune system, both humoral and cell-mediated Humoral=lectins, lysozyme, and uncharacterized hemolymph proteins Cell-mediated=hemocytes (main effector cells) Hemocytes function in wound repair, shell repair, internal defense mechanisms, excretion, and nutrient digestion and transport Phagocytosis is the main effector function of hemocytes

7. Hemocyte Phagocytosis Fluorescent bead engulfed by hemocyte

8. P. marinus/hemocyte Recognition and Eventual Phagocytosis Conjugate cell surface receptors mediate pathogen entry into the hemocyte Hemocytes have both membrane-bound and soluble lectins with specificity for galactose residues Coincidentally, P. marinus has cell-surface ligands composed of galactose Lectin recognition of non-self induces binding between the conjugate receptors on hemocytes and P. marinus. Once bound, signal transduction occurs and the hemocyte receives signals to activate a cellular response (i.e. phagocytosis) Soluble lectins in the circulating hemolymph may enhance cell surface receptor recognition through opsonization (flag to mark particles as foreign and facilitate their recognition and phagocytic removal)

9. P. marinus Engulfed by a Hemocyte Contrary to other protozoan parasites, P. marinus adapted a mechanism to gain entry into hemocytes by specifically presenting cell surface ligands that are rapidly recognized by the hemocyte cell surface lectins When hemocytes phagocytose P. marinus, it facilitates rapid intracellular proliferation S. Bower www.disease-watch.com/.../ CD/index/images/pm.jpg

10. Oxygen-dependent Defense Pathway Reactive Oxygen Intermediates

11. P. marinus Secreted/Excreted Scavenging Enzymes P. marinus subverts an array of intracellular toxic ROI’s through an “offensive response” before a host defensive challenge Enzymes: 1. Superoxide dismutase (SOD)--catalyzes the oxidation and reduction of superoxide to oxygen and hydrogen peroxide 2. Ascorbate dependent peroxidase (APX)—may potentially convert hydrogen peroxide to water 3. Protein phosphatases (PP)—may destabilize NADPH oxidase(remove phosphate group) Collectively the P. marinus SODs, APXs, and PPs may provide an advantage for the parasite to evade the host

12. P. marinus SOD, APX and PP Subvert Reactive Oxygen Intermediates

13. Significance • Design more insightful therapeutic targets • Apply therapies in aquaculture to rebuild commercial output and potentially restore wild populations 3. Serve as a model of intracellular parasite evasion of host that parallels human intracellular parasites (i.e. Malaria parasite)

14. Summary 1. Disease induction- role of host/pathogen/environment 2. Role of the innate immune system (vertebrate and invertebrate) 3. P. marinus/hemocyte recognition and phagocytosis 4. ROI pathway (similar to human neutrophils) 5. Scavenging enzymes that subvert ROI’s