Pathogen-Bound C-type Lectin and Ficolin Enhance Toll Receptor Signaling is activated through Spätzle1 Cleavage in response to White Spot Syndrome Virus (WSSV) in Penaeus monodon.

The dynamic interaction between immune recognition molecules and signaling pathways in the innate immune response of Penaeus monodon to White Spot Syndrome Virus (WSSV) infection is unveiled in this study. Through comprehensive gene expression profiling, we demonstrate significant upregulation of key immune genes, including a specific C-type lectin and a defined ficolin isoform, in WSSV-infected hemocytes, underscoring their pivotal roles in pathogen recognition and antiviral defense. Leveraging advanced molecular techniques, we successfully expressed, purified, and characterized these recombinant proteins, revealing their time-dependent expression and high-affinity binding to lipopolysaccharides (LPS). Intriguingly, pathogen-bound lectin and ficolin were found to modulate Spätzle1 cleavage and enhance its interaction with a functionally characterized Toll receptor variant, suggesting a sophisticated mechanism for immune activation. Computational analyses using HADDOCK and PDBePISA further elucidated the structural and energetic basis of Toll receptor interactions with cleaved Spätzle1 peptides, highlighting the critical role of hydrophobic, electrostatic, and hydrogen bonding interactions in complex stabilization. Temporal expression dynamics of MyD88 and TRAF6 following Spätzle1 injection revealed a robust, time-dependent activation of Toll-mediated signaling pathways, with peak expression at 24 hours post-injection. These findings not only deepen our understanding of crustacean immunity but also provide novel insights into the molecular mechanisms underlying pathogen recognition and immune modulation. The study positions this specific lectin and ficolin variants as key regulators of innate immunity, offering promising avenues for therapeutic interventions in aquaculture and beyond. By bridging molecular insights with functional validation, this work lays the groundwork for future research aimed at harnessing these immune molecules for sustainable disease management and immunotherapeutic applications.