Haemocytes of the clam Tapes philippinarum (Adams & Reeve, 1850): morphofunctional characterisation

Tapes philippinarum is a bivalve mollusc of the Pacific Ocean, successfully imported for human consumption into the northern Adriatic Sea (Europe). Fo r better knowledge of its considerable adaptive ability in comparison with similar autochthonous species, a morpho-functional characterisation of its haemocytes was carried out with the establishment of short-term cell cultur es (60 min at 25 degrees C). Various methods of cytochemical staining ident ified four cell types in the haemolymph: granulocytes (48.05% +/- 1.43), hy alinocytes (32.18% +/- 0.99), haemoblasts (18.97% +/- 0.63) and serous cell s (0.8% +/- 0.19). The granulocytes, possessing cytoplasmic granules with d iffering dye affinity, included basophils, neutrophils and acidophile. Such granules stained vitally with Neutral Fed, and correspond to lysosomes. Hy drolytic and oxidative enzymes were mainly detectable after stimulation in the presence of yeast cells. Both granulocytes and hyalinocytes were positi ve for alkaline phosphatase, non-specific esterase, peroxidase, and cytochr ome C oxidase, whereas only granulocytes were positive for beta -glucuronid ase, acid esterase, and arylsulphatase. Both cell types were competent phag ocytes towards yeast and plasma had an opsonising effect. Moreover, the res piratory burst accompanied phagocytosis with superoxide anion production, r ecognisable through cytoplasmic deposits of formazan after treatment with n itro blue tetrazolium. Haemoblasts were small undifferentiated cells which, due to their morphology and positivity to the anti-CD34 antibody, show the typical features of stem cells. Serous cells, probably arising from Keber' s gland and belonging to another differentiation pathway, contained non-sul phate acid mucopolysaccharides and play an important role in early defence mechanisms, taking part in the formation of clots. (C) 2000 Academic Press.