Crustacean haemocytes and haematopoiesis

Crustacean haemocytes play important roles in the host immune response incl uding recognition, phagocytosis, melanization, cytotoxicity and cell-cell c ommunication. Classification of the haemocyte types in decapod crustaceans is based mainly on the presence of cytoplasmic granules into hyaline cells, semigranular cells, and granular cells. Each cell type is active in defenc e reactions, for example; in crayfish, the hyaline cells are chiefly involv ed in phagocytosis, the semigranular cells are the cells active in encapsul ation, while the granular cells participate in storage and release of the p rophenoloxidase (proPO) system and cytotoxicity. The haematopoietic tissue has been described in several crustacean decapod species and shown to be th e haemocyte-producing organ. Tentative stem cells have been shown to be pre sent in this tissue. Using in situ hybridization, we demonstrated that proP O is not present in the haematopoietic tissue of crayfish which suggests th at protein expression is different between circulating haemocytes and the c ells in the haematopoietic tissue. (C) 2000 Elsevier Science B.V. All right s reserved.