The immune protection of OMP16-specific IgM against Brucella infection

Background: Brucellosis, a severe zoonotic infectious disease, poses substantial economic and health threats globally. The intracellular survival strategy of Brucella complicates disease control, highlighting the need for novel immunotherapeutic strategies such as antibody-based therapies and multi-epitope vaccines. Results: This study generated two IgM monoclonal antibodies (D3 and F5) against the conserved outer membrane protein OMP16 of Brucella using hybridoma technology. Peptide scanning and Western blot identified their linear epitopes (D3: 77TLSKQAQW84; F5: 120RDFLASRG127), which are highly conserved among major Brucella species. Integrated approaches-including molecular docking, alanine-scanning mutagenesis, and dot-blot assays-revealed key residues at the epitope interface that form stable bonds with antibody complementarity-determining regions (CDRs). Functionally, both antibodies activated the complement system, with F5 exhibiting significant complement-dependent bacteriolytic activity in vitro. Furthermore, in the presence of complement, D3 and F5 enhanced macrophage-mediated opsonophagocytosis and intracellular killing of Brucella abortus A19. In a mouse infection model, passive immunization with either antibody significantly alleviated infection-induced weight loss and splenomegaly and reduced bacterial load in the spleen. Conclusions: Our study underscores the role of IgM antibodies in combating Brucella infection, offers insights for antibody-based immunotherapy, and provides a theoretical foundation for developing multi-epitope vaccines based on the conserved epitopes and critical residues.