Maggot excretions/secretions inhibit multiple neutrophil pro-inflammatory responses

There is renewed interest in the use of maggots (Lucilia sericata) to aid in healing of chronic wounds. In such wounds neutrophils precipitate tissue damage rather than contribute to healing. As the molecules responsible for the beneficial actions of maggots are contained in their excretions/secretions (ES), we assessed the effects of ES on functional activities of human neutrophils. ES dose-dependently inhibited elastase release and H2O2 production by fMLP-activated neutrophils; maximal inhibition was seen with 5–50 μg of ES/ml. In contrast, ES did not affect phagocytosis and intracellular killing of Candida albicans by neutrophils. Furthermore, 0.5 μg of ES/ml already inhibited neutrophil migration towards fMLP. ES dose-dependently reduced the fMLP-stimulated expression of CD11b/CD18 by neutrophils, suggesting that ES modulate neutrophil adhesion to endothelial cells. ES did not affect the fMLP-induced rise in [Ca2+]i in neutrophils, indicating that ES act down-stream of phospholipase C-mediated activation of protein kinase C. In agreement, ES inhibited PMA-activated neutrophil functional activities. ES induced a rise in intracellular cAMP concentration in neutrophils and pharmacological activators of cAMP-dependent mechanisms mimicked their inhibitory effects on neutrophils. The beneficial effects of maggots on chronic wounds may be explained in part by inhibition of multiple pro-inflammatory responses of activated neutrophils by ES.