Immunolocalization of prophenoloxidase among hemocytes of the silkworm, Bombyx mori

Silkworm (Bombyx mori) hemocytes were fixed immediately after collection. Thin sections of the hemocytes were stained by an indirect immunogold staining method using rabbit anti-prophenoloxidase/IgG as a primary antibody and colloidal gold coated with goat anti-rabbit/IgG as a secondary antibody. Electron micrographs of the sections revealed that only plasmatocytes and oenocytoids have prophenoloxidase both in cytoplasm and nucleus whereas granulocytes, spherulocytes and prohemocytes do not have appreciable amounts of the proenzyme. Cytoplasmic inclusions of oenocytoids also contain the proenzyme. A wide variety of concentrations of prophenoloxidase was observed among oenocytoids. Plasmatocytes appeared to have less prophenoloxidase than any oenocytoids. Once materials in the granules of granulocyte were discharged into the plasma and formed coagula, they cross-reacted with antiprophenoloxidase/IgG, suggesting that prophenoloxidase was trapped in the coagula by unknown mechanisms. This observation is discussed in relation to the dispute concerning the presence of prophenoloxidase or phenoloxidase in the granulocyte.