Cytochemical, immunocytochemical and ultrastructural observations on leukocytes and thrombocytes of fat snook (Centropomus parallelus)

The cytochemical, immunocytochemical and ultrastructural characteristics of leukocytes and thrombocytes in the peripheral blood of the fat snook (Centropomus paralellus) – a fish occurring in Brazil – were investigated. The cytochemical methods were performed to demonstrate four enzymatic reactions – o-toluidine-hydrogen peroxide, naphtol AS-MX phosphate, naphtol AS-BI phosphate and alpha-naphtil acetate to detect myeloperoxidase (MPO), alkaline phosphatase (ALP), acid phosphatase (ACP) and non-specific esterase (α-NAE), respectively – and two non-enzymatic ones – Periodic-Acid Schiff (PAS) and Sudan black B (SBB) to detect the occurrence of glycogen and phospholipids, respectively. Immunocytochemical method utilizing polyclonal rabbit antibody against mammal metalloproteinases (MMPs) 2 and 9 were done. Standard method for Electron Microscopy (EM) was applied for the ultrastructural study. The cytochemical reactions were positive in neutrophils for MPO, ACP, α-NAE, glycogen and phospholipids; in lymphocytes for ACP and α-NAE; in monocytes for ACP and α-NAE and in thrombocytes for ACP, α-NAE and glycogen. Only neutrophils were positive for MMPs 2 and 9, and none of the cells studied were positive for ALP. Ultrastructurally: 1) neutrophil showed a spherical shape with a spherical, indented or lobulated euchromatic nucleus, and cytoplasm containing granules of varied sizes and mitochondria of varied shapes and sizes. The nucleus/cytoplasm relation and the size of granules suggest neutrophil maturation in peripheral blood; 2) lymphocytes showed partially heterochromatic nucleus and minimal cytoplasm; 3) monocytes had long cytoplasmic projections, an indented nucleus, evident nucleolus and cytoplasm with granules of varied sizes and vacuoles; 4) thrombocytes were predominantly elliptical or roughly spherical in shape, had a partially heterochromatic nucleus and cytoplasm containing electron-dense granules, intricate canalicular system and vacuoles occasionally holding phagocytic material.

► Cytochemistry, immunocytochemistry and ultrastructure of leukocytes and thrombocytes of C. parallelus.
► Reactions were performed to demonstrate MPO, ALP, ACP, α-NAE, PAS, SBB and MMPs 2 and 9.
► The positivity for ACP can detect young and mature neutrophils as well as thrombocytes.
► Nucleus/cytoplasm relation and the size of granules suggest neutrophil maturation in peripheral blood.
► Thrombocytes cytoplasm contain vacuoles occasionally holding phagocytic material.