Hydrogen peroxide is produced by E. coli challenged haemocytes and regulates phagocytosis, in the medfly Ceratitis capitata. The active role of superoxide dismutase

Hydrogen peroxide (H 2O 2) participates as a second messenger in cell signaling. In this paper, the role of H 2O 2 was investigated, in Escherichia coli phagocytosis by the haemocytes of the medfly Ceratitis capitata. Block of H 2O 2 synthesis by specific enzymic inhibitors, namely N-ethylmaleimide (NEM) for NADPH oxidase and diethyldithiocarbamate (DDC) for SOD, resulted in the increase of E. coli phagocytosis. Immunoblot analysis, flow cytometry and confocal microscopy, revealed the constitutive expression of SOD, in the medfly haemocytes. Phagocytosis increased by small interfering RNA (siRNA) for SOD, revealing the active involvement of SOD and H 2O 2. Immunoblot analysis showed an increase of the ERK1/2 phosphorylation, in the presence of the above H 2O 2 synthesis enzymic inhibitors. In addition, confocal microscopy showed no co-localization of SOD with β integrin subunit. It appears that SOD participates in the regulation of bacterial phagocytosis, due to involvement of the produced H 2O 2 in the differential phosphorylation of MAP kinases.