Multivalent Co-assembly of LL37-CpG nanoparticles: Enhanced immune response through activating multiple cell internalization pathways

Recent studies have demonstrated that the human antimicrobial peptide LL37 plays a critical role in immune regulation under both normal physiological conditions and during disease progression, as evidenced by its elevated levels observed in various chronic inflammatory diseases. A deeper understanding of its mechanism is essential for elucidating associated physiological and pathological processes, as well as for designing effective immune adjuvants and clinical therapeutics. In this study, we report that LL37 facilitates the assembly of unmethylated CpG dinucleotides (CpG ODNs), a clinically relevant immune adjuvant, into non-crystalline nanoparticles (NPs) with controlled size and zeta potential in a charge ratio-dependent manner. These assembled NPs enter cells via receptor-mediated macropinocytosis, coupled with LL37-mediated membrane penetration, thereby significantly enhancing cellular uptake of CpG compared to CpG alone, which enters cells through clathrin-mediated endocytosis. Consequently, the enhanced internalization of LL37-CpG NPs markedly boosts TNF-α production (>3.5-fold) in macrophages through interactions with lysosomal TLR9. This immunostimulatory mechanism offers an alternative perspective on how LL37 modulates nucleic acid assembly and activates immune cells, providing guidance for the application of peptide-CpG ODN complexes in vaccine adjuvants and immune modulation for disease treatment.