Resistant silkworm strain block viral infection independent of melanization

Area of Science:

• * Insect immunology
• * Molecular entomology
• * Biochemistry

Background:

• * Melanization, driven by the prophenoloxidase-activating system (proPO), is a critical invertebrate immune defense.
• * The specific role of melanization in antiviral responses within the silkworm, Bombyx mori (B. mori), remains incompletely understood.

Purpose of the Study:

• * To investigate the relationship between melanization and viral infection susceptibility in Bombyx mori.
• * To compare melanization levels and antiviral mechanisms between susceptible (871) and resistant (871C) silkworm strains.
• * To elucidate the role of Serpins in regulating melanization and antiviral immunity.

Main Methods:

• * Comparative analysis of melanization extent in susceptible and resistant B. mori strains.
• * iTRAQ-based quantitative proteomics to identify differentially expressed proteins, particularly Serpins.
• * Enzymatic assays to assess prophenoloxidase (PO) activity.
• * Viral infection assays in hemolymph with and without PTU (a melanization inhibitor).

Main Results:

• * Susceptible silkworm strain (871) exhibited significantly higher melanization than the resistant strain (871C).
• * Several Serpins were upregulated in the resistant strain; Serpin-5, Serpin-9, and Serpin-19 were found to inhibit PO activity, suggesting melanization pathway inhibition.
• * Hemolymph from the susceptible strain reduced viral infection when melanization was induced (without PTU), while the resistant strain suppressed viral infection independently of melanization.

Conclusions:

• * The melanization pathway is inhibited in the resistant silkworm strain (871C).
• * Melanization effectively blocks viral infection in susceptible silkworms (871).
• * Resistant silkworms employ melanization-independent mechanisms to combat viral infections, expanding our understanding of insect antiviral strategies.