Objective  To explore the main components of the A antigen of Brucella 104 M vaccine strain and screen the potential candidate proteins from the A antigen and provide evidence for the development of novel vaccine for Brucella.

Methods In this study, the main components of the A antigen of Brucella 104M vaccine strain were resolved using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Kaumas brilliant blue staining, horseshoe crab reagent detection of lipopolysaccharide, and lipopolysaccharide silver staining, and this protein was further resolved by western blotting with the serum of immunized sheep to select the part of blotted cuttings for enzymatic digestion of the proteins, and liquid chromatography-tandem mass spectrometry was used for further analysis. The virulence-associated proteins with Brucella A antigenic with score ≥0.6 or higher as potential vaccine candidates were screened by using antigen analysis tool-VaxiJen and virulence protein analysis tool - VirulentPred.

Results Brucella A antigen is a yellowish marshmallow-like, lightweight substance, mainly composed of proteins and lipopolysaccharides. Proteomic characterization of the A antigen showed that there were 1 142 proteins in the 104 M A antigen, including 172 proteins capable of reacting with sheep serum, and 87 proteins with VaxiJen antigenicity score ≥0.6, in which 38 were virulence-associated proteins.

Conclusion  The main components of the A antigen of Brucella 104M vaccine strain are proteins and lipopolysaccharides, and further experiments are needed to test the immunogenicity and level of protection of these proteins screened from A antigen in order to design a more effective and safer vaccine against brucellosis.