Differentiation of crocodilian granulocytes using histochemical techniques

Abstract

Blood smears from 54 crocodiles of three breeds (Crocodylus siamensis, C. porosus, and crossbred) were examined after Wright-Giemsa staining. Detection for alkaline phosphatase and peroxidase activities were performed. Four types of granulocytes are distinguished: heterophil, eosinophil, basophil and azurophil. Heterophils with the size of 9-10 µm have an oval eccentric nucleus with mostly spiculate granules and a few tear drop-shaped granules. Heterophils contain both alkaline phosphatase and peroxidase. Eosinophils with the size of 8-9 µm have a round or oval eccentric nucleus. The round, rod- and few tear drop-shaped and spiculate granules are packed in the cytoplasm. Eosinophils are strongly peroxidase positive, but devoid of alkaline phosphatase. Basophils are 9 - 11 µm with a centrally located round nucleus. Their cytoplasm is full of round granules of various sizes and contains neither alkaline phosphatase nor peroxidase activity. A fourth type of granulocyte (8-10 µm) has a centrally located round, oval or kidney shaped nucleus, and a small amount of azurophilic granules. The cytoplasm of this cell gives very strong alkaline phosphatase activity, but no peroxidase is detected. Morphological and physiological characteristics of this questionable leukocyte suggest the possibility that this cell is azurophil. All agranulocytes (monocytes and lymphocytes) and thrombocytes are devoid of both alkaline phosphatase and peroxidase activities.