A CRP-like protein mediates antibacterial immunity in Pacific white shrimp, Litopenaeus vannamei.

C-reactive protein (CRP), an evolutionarily conserved short pentraxin, functions as a critical soluble pattern recognition receptor (PRR) in innate immunity and exhibits phylogenetic conservation from arthropods to mammals. In this study, we identified a CRP gene in Litopenaeus vannamei and designated it LvCRP. In vitro studies demonstrated that recombinant LvCRP (rLvCRP) exhibits broad-spectrum pathogen recognition through high-affinity binding to conserved bacterial surface components (LPS, PGN, and PCh), facilitated by its multimeric complex formation. Notably, rLvCRP activated and modulated complement-like proteins in crustacean immunity, highlighting its evolutionary connection to the complement system. In vivo investigations demonstrated that rLvCRP enhances host defense through two synergistic mechanisms: (1) augmenting hemocyte-mediated phagocytosis and pathogen clearance efficiency, and (2) coordinately upregulating key immune components including inflammatory factors, complement-like molecule, and downstream antimicrobial peptides (AMPs). Furthermore, rLvCRP promoted nuclear translocation of the NF-κB homolog LvDorsal in shrimp hemocytes and significantly enhanced survival rates during Vibrio infection, establishing its crucial regulatory role in antibacterial immunity. Collectively, these findings establish LvCRP as a pivotal immunomodulator that integrates pattern recognition, complement activation, and effector mechanisms, exhibiting dual functionality in both cellular (phagocytosis) and humoral (complement activation/AMP production) immunity. This study demonstrates the evolutionary significance of CRP as a multifunctional defense molecule in crustaceans and provides novel insights into invertebrate immune regulation.