Involvement of both granular cells and plasmatocytes in phagocytic reactions in the greater wax moth, Galleria mellonella

Although it has been previously found by most authors that only plasmatocytes are involved in phagocytosis of non-self in the greater wax moth, Galleria mellonella, in the present study we demonstrate that in vitro, both granular cells and plasmatocytes are involved in this reaction, using monolayers of these haemocytes prepared from larval haemolymph by a differential cell fractionation method. The adhesion of granular cells to glassware and phagocytosis by granular cells of FITC-labelled silica beads were both greatly reduced by the presence of p-NPGB, a serine proteinase inhibitor, which is known to inhibit the activation of the prophenoloxidase cascade, but the reactions were only partly influenced by PTU, an inhibitor of phenoloxidase. These results suggest that an enhancing factor for both reactions is phenoloxidase itself or a component induced during the course of activation of the prophenoloxidase cascade, but not the melanised substance produced by the action of this reaction. For plasmatocytes, attachment to non-self was totally blocked by the absence of CaCl2 or by the presence of EDTA at concentrations greater than 20 mM, and phagocytosis was greatly enhanced by CaCl2, but suppressed by EDTA. These results suggest that calcium is a factor required for adhesion of plasmatocytes, and that it also functions to enhance their phagocytic action.