Effect of Tetramicra brevifilum (Microspora) infection on respiratory-burst responses of turbot (Scophthalmus maximus L.) phagocytes

In vitro assays were performed to investigate microsporidian-induced intrac ellular and extracellular production of reactive oxygen species (ROS) by pe ritoneal-exudate adherent (PEA) cells from turbot. ROS production was quant ified using the fluorescent reagents OxyBURST Green H2HFF BSA (extracellula r) and OxyBURST Green H(2)DCFDA succinimidyl ester (intracellular). Five da ys before assay, the cells had been elicited in vivo by intraperitoneal inj ection of sodium thioglycollate or spores of Tetramicra brevifilum. Elicita tion with spores led to a marked increase in the proportion of neutrophils among PEA cells. PEA cells from normal turbot showed considerable extracell ular and intracellular ROS production in response to microsporidian spores. By contrast, PEA cells from microsporidian-infected turbot showed consider ably reduced extracellular and intracellular ROS production in response to microsporidian spores. Extracellular ROS production was affected by the add ition of infected turbot serum to the assay medium, regardless of whether t he PEA cells had been obtained from normal or infected fish. The presence o f microsporidian-infected turbot serum significantly reduced intracellular ROS production by PEA cells elicited with microsporidian spores. These resu lts suggest that (a) microsporidian spores partially suppress the repirator y-burst response of turbot phagocytes; and (b) infected turbot serum contai ns substances capable of modulating the respiratory-burst response of turbo t phagocytes to microsporidian spores. (C) 2001 Academic Press.