Silica beads induce cellular and humoral immune responses in Galleria mellonella larvae and in isolated plasmatocytes, obtained by a newly adapted nylon wool separation method

Abstract

Intrahaemocoelic injection of silica beads into Galleria mellonella (wax moth) larvae provoked strong cellular and humoral reactions similar to those normally occuring during an antibacterial defence. The cellular reactions of the haemocytes—investigated by light and scanning electron microscopy—comprised degranulation of granular cells and phagocytosis by plasmatocytes. The humoral responses—measured in cell free haemolymph as the increase of antibacterial activity against Echerichia coli K12 D31 and of lysozyme activity against Micrococcus luteus cell walls—were significantly enhanced in comparison to controls. Only hydrophylic but not hydrophobic silica beads provoked strong reactions. Plasmatocytes (PLs), the main phagocytic haemocytes of G. mellonella, were isolated by using a newly adapted nylon wool column technique. PL monolayers, prepared from isolated cells, exhibited a high purity by consisting of at least 90% PL. Scanning electron microscopy studies revealed that 64% of the isolated PLs showed phagocytic activity against the sterile silica beads in vitro. Intrahaemocoelic injection of supernatants from monolayers with phagocytosing plasmatocytes into naive larvae led to a clearly higher antibacterial activity against E. coli in haemolymph of recipients than the injection of supernatants from monolayers with non-phagocytosing cells. The earlier supposition that haemocyte-released factors induce the humoral immune response is further supported by these results.