Sequential Immune Acquisition of Monoclonal Antibodies Enhances Phagocytosis of Acinetobacter baumannii by Recognizing ATP Synthase.

Objectives: The aim of this study was to prepare monoclonal antibodies (mAbs) that broadly target Acinetobacter baumannii and protect against infection by multi-drug-resistant (MDR) A. baumannii from different sources. Methods: mAb 8E6 and mAb 1B5 were prepared by sequentially immunizing mice with a sublethal inoculation of three heterogeneous serotypes of pan-drug-resistant (PDR) A. baumannii, ST-208, ST-195, and ST-229. Results: The cross-recognition of heterogeneous bacteria (n = 13) by two mAbs and potential targets was verified, and the in vitro antibacterial efficacy of mAbs was assessed. The median killing rate of mAb 8E6 against A. baumannii in the presence of complement and dHL-60 cells was found to be 61.51%, while that of mAb 1B5 was 41.96%. When only dHL-60 cells were present, the killing rate of mAb 8E6 was 65.73%, while that of mAb 1B5 was 69.93%. We found that mAb 8E6 and mAb 1B5 broadly targeted MDR A. baumannii on the ATP synthase complex and were equipped with an antibacterial killing ability by enhancing the innate immune bacteriolytic effect of ST-208 and ST-195 strains. Both monoclonal antibodies were validated to protect against respiratory infection at 4 and 24 h via enhancing the release of innate immune substances and inflammatory cytokines, effectively shortening the disease period in mice. Conclusions: mAb 8E6 and mAb 1B5 significantly enhanced the opsonization process of phagocytosis against A. baumannii strains prevalent in southern China by targeting ATP synthase antigens thereof, resulting in protective effects in mice.