EFFECT OF FETAL BOVINE SERUM GLYCOPROTEINS ON THE IN-VITRO PROLIFERATION OF THE OYSTER PARASITE PERKINSUS-MARINUS - DEVELOPMENT OF A FULLY DEFINED MEDIUM

The oyster parasite Perkinsus marinus replicates in our medium consist ing of Dulbecco modified Eagle's medium: Ham's F12 nutrient mixture (1 :1) supplemented with 1-5% fetal bovine serum, with a doubling time of 24 hours during the exponential phase of the culture. Fetal bovine se rum concentrations above 5% dramatically reduced parasite proliferatio n in a dose-dependent manner. We tested the individual effects of the three major protein components of fetal bovine serum (fetuin, transfer rin and albumin) on the replication of the parasite in a serum-free me dium. At the concentrations tested, fetuin enhanced parasite growth, w hereas albumin had a modest positive effect and transferrin was inhibi tory. Proteolytic digestion of fetuin, strongly diminished its growth- enhancing properties, indicating that the overall glycoprotein archite cture may be required for activity. On the contrary, desialylation of fetuin slightly enhanced its growth-promoting activity. The addition o f fetuin at 1.7 mg/ml to the serum-free DME:Ham's F12 medium yielded g rowth rates that are comparable to those obtained with our standard cu lture methodology. This has resulted in a fully defined culture medium that will allow for a rigorous characterization of excretory/secretor y products involved in modulating or blocking the host's humoral and c ellular defense mechanisms.