Morphology, cytochemistry and immunocytochemistry of the circulating granulocytes of the loggerhead sea turtle Caretta caretta

The eosinophils and heterophils of loggerheads display a similar rounded shape, an eccentric 32 and elongated or slightly lobulated nucleus and a cytoplasm full of acidophilic pleomorphic granules. The characterization of the different types of granulocytes from nine Mediterranean loggerheads (Caretta caretta), based on cytochemical and immunocytochemical reactions and ultrastructural studies, is reported. On the basis of their positivity after myeloperoxidase, alkaline phosphatase and chloroacetate esterase reactions (typical of mammalian neutrophils), the granulocytes were classified as heterophils, while those myeloperoxidase-negative, major basic protein-positive granulocytes (like mammalian eosinophils), displaying a weak expression of interleukin 5 (a growth and differentiation factor, activator and chemoattractant for eosinophils), were classified as eosinophils. The immunocytochemical and TEM studies allowed the identification of these two granulocyte types, both of which show an eosinophilic reaction with May-Grünwald-Giemsa, periodic acid-Schiff and neutral red staining-positivity.