A SMALL PHAGOCYTOSIS STIMULATING FACTOR IS RELEASED BY AND ACTS ON PHAGOCYTOSING GALLERIA-MELLONELLA HEMOCYTES IN-VITRO

We established an in vitro transfer system with monolayers of isolated plasmatocytes from Galleria mellonella, The plasmatocytes represent t he main phagocytically active haemocyte type in this lepidopteran inse ct. Plasmatocytes to which hydrophilic silica beads were added as a ph agocytosing agent served as 'donor' cells, Supernatants from these don or cultures were transferred to freshly prepared 'recipient' plasmatoc yte monolayers. Subsequently, FITC (fluorescein-isothiocyanate) labell ed ye ast cells were added to the recipient monolayers and the phagocy tic activity was determined using an FITC quenching assay with trypan blue. The phagocytic activity in plasmatocyte monolayers which receive d supernatants from phagocytically active donor cells was significantl y higher than the activity of cells receiving supernatants from non-ac tivated donor cells. Time course studies revealed that the inducing ca pacity of the donor cell supernatants was highest 2-4h after starting phagocytosis of the silica beads, Isolation of the responsible phagocy tosis stimulating factor is still underway, From our investigations we can conclude that it must be a very small (<500 Dal, hydrophobic, and heat-sensitive molecule. This allows us to speculate that it could be long to the eicosanoids or to the biogenic amines. In addition, we cou ld show that donor cell supernatants possess opsonic activity and that the injection of donor cell supernatant into intact larvae induces an antibacterial humoral response in vivo. Copyright (C) 1996 Elsevier S cience Ltd