Phagocytosis by Lymnaea stagnalis haemocytes: a potential role for phosphatidylinositol 3-kinase but not protein kinase A

The molecular events that regulate phagocytosis, an important innate immune response, in invertebrate defence cells (haemocytes) are poorly understood. Lymnaea stagnalis haemocytes were used as a model to elucidate the role of cell signalling pathways in phagocytosis by molluscan defence cells. The phosphatidylinositol 3-kinase (PI3-K) inhibitor, LY294002, significantly impaired haemocyte phagocytic activity in a dose-responsive manner with 10 microM LY294002 reducing internalization of fluorescent-conjugated Escherichia coli by 62% (P < or = 0.001). In contrast, the protein kinase A (PKA) inhibitor KT5720 was without effect. Therefore, PI3-K, but not PKA, appears to control phagocytosis by haemocytes in these gastropod molluscs.