INTERACTION OF PHAGOCYTOSED BONAMIA SP (HAPLOSPORIDIA) WITH HEMOCYTESOF OYSTERS TIOSTREA-CHILENSIS

The interaction between the haplosporidian pathogen Bonamia sp. and th e haemocytes of oysters Tiostrea chilensis was studied ultrastructural ly and using ultracytochemistry for the lysosomal hydrolases, beta-gly cerophosphatase (beta-GPase), cytidine monophosphatase (CMPase), thiam ine pyrophosphatase (TPPase), and beta-galactosidase. Although fine an d coarse granulocytes, serous (brown) cells and hyalinocytes were pres ent, agranular precursors of fine granulocytes (progranulocytes), degr anulated coarse granulocytes, hyalinocytes and serous cells commonly p hagocytosed Bonamia sp. A sequence of infection from initial occupatio n of tight phagosomes to formation of an enlarged phagosome or parasit ophorous vacuole (PV), which sometimes broke down, occurred in all inf ected haemocytes. Enlargement of the phagosome membrane to eventually form a PV coincided with formation of bilaminar vesicles in the lipoid bodies of parasites and their release from an indented area of the pa rasite surface. Too few infected granulocytes were observed to determi ne whether phagosome modification blocked lysosome-phagosome fusion. V esicular CMPase and TPPase were produced by agranular haemocytes conta ining phagocytosed Bonamia sp. and passed into tight phagosomes. Despi te some endocytosis of these enzymes by Bonamia sp., very few parasite s appeared dense or moribund. From the orientation of lipoid bodies to ward the phagosome lumen, and release of beta-GPase into the lumen fro m the lipoid bodies, parasite hydrolytic enzymes in lipoid bodies may function in parasite nutrition, by extracellular digestion of host hae mocyte cytoplasm.