Modulation of the in vitro activity of European sea bass (Dicentrarchus labrax L.) phagocytes by the myxosporean parasite Sphaerospora dicentrarchi (Myxosporea : Bivalvulida)

Several in vitro studies were performed to study the cellular reaction of E uropean sea bass (Dicentrarchus labrax L.) against Sphaerospora dicentrarch i. Head kidney phagocytes were obtained from parasitised (P) and non-parasi tised (NP) fish. The production of superoxide anion (O-2(-)), tested by the NET method, was higher in P than in NP fish. The addition of increasing am ounts of sea bass serum (SBS) produced a gradual increment of the respirato ry burst with SBS from parasitised animals (P-SBS), whereas this increment reached a plateau at lower concentration with SBS from nonparasitised ones (NP-SBS). O-2(-) production was higher when adding NP-SBS than with P-SBS o r fetal bovine serum. Heat inactivation of NP-SBS and FBS reduced the respi ratory burst significantly, whereas it did not change the effect of P-SBS. The number of NET-positive cells after particulate stimulation was signific antly higher using S. dicentrarchi spores than using SRBC, but lower than w ith phorbol myristate acetate. Phagocytes primed overnight with spore extra cts produced higher amounts of O-2(-) than those LPS-primed or non-primed o nes. A similar percentage of phagocytosis was detected using glutaradehyde fixed spores and SRBC. Most of the phagocytes engulfed three or more SRBC, where as most of the phagocytes engulfed only one spore. Complement mediated opso nisation by NP-SBS may occur, as the phagocytic index was reduced when the serum was heat inactivated. (C) 2000 Academic Press.