MAP kinases mediate phagocytosis and melanization via prophenoloxidase activation in medfly hemocytes

Area of Science:

• Insect immunology
• Invertebrate immune pathways

Background:

• Medfly (Ceratitis capitata) hemocytes exhibit phagocytosis of E. coli, a process linked to mitogen-activated protein (MAP) kinase signaling.
• Mammalian macrophages phagocytose pathogens differently than medfly hemocytes.

Purpose of the Study:

• To investigate the role of the prophenoloxidase (proPO) cascade in E. coli phagocytosis by medfly hemocytes.
• To determine if MAP kinase signaling influences proPO activation and its involvement in phagocytosis and melanization.

Main Methods:

• Identification and localization of proPO and prophenoloxidase-activating proteinases (PAPs) in medfly hemocytes using flow cytometry and immunocytochemistry.
• Assessment of E. coli phagocytosis inhibition using antibodies against proPO/PAPs and serine protease inhibitors.
• Evaluation of MAP kinase influence on PAPs secretion and subsequent proPO activation.

Main Results:

• ProPO and PAPs are constitutively expressed and associated with the hemocyte surface, unaffected by E. coli infection.
• E. coli phagocytosis is significantly inhibited by anti-proPO/PAPs antibodies and serine protease inhibitors, indicating proPO cascade involvement.
• ProPO activation is essential for melanization, and MAP kinases regulate PAPs secretion, controlling both phagocytosis and melanization.

Conclusions:

• The prophenoloxidase cascade, involving proPO and PAPs, plays a crucial role in E. coli phagocytosis and melanization in medfly hemocytes.
• MAP kinases are central regulators of this innate immune response, controlling PAPs secretion and subsequent proPO activation.