Crustacean haemocytes and haematopoiesis

Crustacean haemocytes play important roles in the host immune response including recognition, phagocytosis, melanization, cytotoxicity and cell-cell communication. 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 defence reactions, for example; in crayfish, the hyaline cells are chiefly involved in phagocytosis, the semigranular cells are the cells active in encapsulation, while the granular cells participate in storage and release of the prophenoloxidase (proPO) system and cytotoxicity. The haematopoietic tissue has been described in several crustacean decapod species and shown to be the haemocyte-producing organ. Tentative stem cells have been shown to be present in this tissue. Using in situ hybridization, we demonstrated that proPO is not present in the haematopoietic tissue of crayfish which suggests that protein expression is different between circulating haemocytes and the cells in the haematopoietic tissue. (C) 2000 Elsevier Science B.V. All rights reserved.