M28 family peptidase derived from Peribacillus frigoritolerans initiates trained immunity to prevent MRSA via the complosome-phosphatidylcholine axis

Methicillin-resistant Staphylococcus aureus (MRSA) represents a major global health threat due to its resistance to conventional antibiotics. The commensal microbiota maintains a symbiotic relationship with the host, playing essential roles in metabolism, energy regulation, immune modulation, and pathogen control. Mammals harbor a wide range of commensal bacteria capable of producing unique metabolites with potential therapeutic properties. This study demonstrated that M28 family peptidase (M28), derived from commensal bacteria Peribacillus frigoritolerans (P. f), provided protective effects against MRSA-induced pneumonia. M28 enhanced the phagocytosis and bactericidal activity of macrophages by inducing trained immunity. RNA sequencing and metabolomic analyses identified the CFB-C3a-C3aR-HIF-1α axis-mediated phosphatidylcholine accumulation as the key mechanism for M28-induced trained immunity. Phosphatidylcholine, like M28, also induced trained immunity. To enhance M28-mediated therapeutic potential, it was encapsulated in liposomes (M28-LNPs), which exhibited superior immune-stimulating properties compared to M28 alone. In vivo experiments revealed that M28-LNPs significantly reduced bacterial loads and lung damage following MRSA infection, which also provided enhanced protection against Klebsiella pneumoniae and Candida albicans. We first confirmed a link between complement activation and trained immunity, offering valuable insights into the treatment and prevention of complement-related autoimmune diseases.