Non-specific responses of Turbot (Scophthalmus maximus L.) adherent cells to microsporidian spores

We investigated non-specific responses of turbot spleen- and pronephros-res ident adherent cells to spores of fish microsporidians, and the effects of the glucocorticoid dexamethasone (DX) on these responses. On average, 65% o f adherent cells from the spleen and pronephros showed esterase activity la s characteristic of macrophages); 32% showed peroxidase activity las charac teristic of neutrophils), and 19% of peroxidase-positive cells were capable of phagocytosing microsporidian spores. A significantly higher proportion of adherent cells showed phagocytic activity when viable spores were the ta rget than when non-viable spores were the target. Microsporidian spores sti mulated adherent cells to produce reactive oxygen and nitrogen intermediate s (ROIs and RNIs), though less effectively than the other stimulants tested . Adherent cells exposed to viable spores produced significantly less intra cellular superoxide than adherent cells exposed to non-viable spores. Daily injection of fish with DX over 6 days significantly inhibited both phagocy tosis of microsporidian spores and spore-induced ROI production, and simila r effects were observed when adherent cells were exposed to DX in vitro. (C ) 2000 Elsevier Science B.V. All rights reserved.