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Prophenoloxidase-Mediated Ex Vivo Immunity to Delay Fungal Infection after Insect Ecdysis
Jie Zhang1,2, Wuren Huang1, Chuanfei Yuan3,4
1Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
Frontiers in Immunology
|November 23, 2017
Summary
Insect prophenoloxidases (PPOs) in molting fluid provide crucial "ex vivo" immunity, preventing fungal infections on newly molted insects. This unique defense mechanism protects the vulnerable exoskeleton during the critical post-ecdysis period.
Area of Science:
- Insect immunology
- Innate immunity
- Biochemistry
Background:
- Animals possess skin immunity against airborne pathogens.
- Insects, unlike mammals, molt periodically, exposing a vulnerable cuticle.
- Newly molted insects must evade infection despite a thin, unsclerotized cuticle.
Purpose of the Study:
- To investigate the protective mechanisms of insects against airborne fungal pathogens post-ecdysis.
- To elucidate the role of prophenoloxidases (PPOs) in the molting fluid.
- To understand insect strategies for surviving infections after molting.
Main Methods:
- Purified and recombinant prophenoloxidases (PPOs) were used.
- PPOs were tested for binding to fungal spores (conidia) and targeting cell wall components (chitin, β-1,3-glucan).
- The effect of PPO pretreatment on fungal spore virulence and adhesion was assessed.
- A spore-secreted protease (BPS8) was identified and its interaction with PPOs studied.
Main Results:
- Plasma PPOs bind to fungal spores, targeting chitin and β-1,3-glucan.
- PPO treatment increased spore hydrophilicity, reduced adhesion, and decreased virulence of *Beauveria bassiana*.
- Protease BPS8 degrades PPOs at high concentrations but activates PPOs at low concentrations, inhibiting spore germination.
Conclusions:
- Insects utilize prophenoloxidases (PPOs) in molting fluids for 'ex vivo' immunity on the integument.
- This PPO-mediated defense protects against airborne fungal infections immediately after ecdysis.
- A balance between PPO activity and protease BPS8 regulation is crucial for post-molt survival.
