CYTOCHEMICAL CHARACTERIZATION OF LEUKOCYTES FROM THE SEAWATER TELEOST, GILTHEAD SEABREAM (SPARUS-AURATA L)

The cytochemical characterization of head-kidney and peripheral blood leucocytes of gilthead seabream (Sparus aurata L.) was studied by ligh t and electron microscopy. Neutrophilic granulocytes show some cytopla smic granules, which are positive for alkaline phosphatase and peroxid ase but acid phosphatase negative. The scarce granules found in the cy toplasm of the circulating neutrophils and their cytochemical features seem to be indicative of an immature stage. Acidophils are also alkal ine phosphatase and peroxidase positive at pH 11.0. They are strongly positive for acid phosphatase and acid phosphatase activity may thus b e considered a cytochemical marker to characterize and differentiate n eutrophilic from acidophilic granulocytes in this fish species. Three granule populations are characterized in the cytoplasm of the gilthead seabream acidophils: the first is positive only for peroxidase and th e second contains a dense core with acid and alkaline phosphatase acti vities, surrounded by a thin peroxidase positive electron-dense halo. The third granule type contains an eccentric core, which is strongly p ositive for acid and alkaline phosphatase and peroxidase. As regards t heir cytochemical features, the first and second granule types seem to correspond respectively to the azurophilic and specific granules foun d in acidophils of mammals and could be involved in phagocytic process es, thus playing an important microbicidal role in this species. The m onocytes, monocyte-macrophages and macrophages show different cytochem ical features. The first have scarce acid phosphatase-positive lysosom es, while blood monocyte-macrophages and macrophages are positive for acid and alkaline phosphatases and for peroxidase; the monocyte-macrop hages show scarce lysosomes.