The hemocytes of Polyandrocarpa misakiensis: morphology and immune-related activities.

A preliminary study of the hemocytes of developing buds of the compound ascidian Polyandrocarpa misakiensis was carried out at the light microscope level for a better understanding of their biological role. Similarly to other ascidians, P. misakiensis immunocytes are represented by phagocytes and morula cells. Phagocytes include hyaline amoebocytes and round, giant phagocytes, the former the probable precursors of the latter. Hyaline amoebocytes showed high macropinocytotic activity in the presence of bacteria, whereas yeast cells were ingested by phagocytosis. Morula cells contain the enzyme phenoloxidase inside their vacuoles, probably stored as pro-enzyme, which is released upon the recognition of non-self. Together with macrogranular leukocytes, morula cells were the most abundant hemocyte-types which stresses the importance of these cells in Polyandrocarpa biology. Macrogranular leukocytes are frequently found inside the vacuoles of phagocytes and were recognized by a polyclonal antibody raised against an opsonin purified from the colonial ascidian Botryllus schlosseri, which suggests that a similar lectin can be involved in the interaction between these cells and phagocytes.