Sustained and differential antibody responses to virulence proteins of Brucella melitensis during acute and chronic infections in human brucellosis

Brucellosis is an important zoonotic disease caused primarily by the bacterial pathogens Brucella melitensis and B. abortus. The pathogens cause debilitating febrile illness that can progress into a long-lasting disease with severe complications in humans. Understanding the mechanisms by which the host immune system responds to the infection will provide important information on the pathogenesis and development of differential diagnostic assays. In this study, a protein microarray was used to evaluate the antibody responses of brucellosis patients at different infection stages. A total of 107 outer membrane proteins, surface-exposed or secreted proteins, and known or putative virulence-associated proteins of B. melitensis were successfully expressed in Escherichia coli and used to fabricate the protein microarray. Then, 99 serum samples from acute, chronic, primary infection, or relapse brucellosis patients were probed with the protein microarray. Antibodies to 66 of the proteins were detected at least in one serum sample. Among the antigens, the combination of BMEII0318, BMEII0513, BMEI0748, and BMEII1116 could be used as serodiagnostic antigens for brucellosis. Patients at different infection stages show distinct antibody profiles. The numbers of antibodies in the relapse patients were superior to those in the primary infection patients, and the response magnitude of antibodies in the chronic infection patients was higher than those in the acute brucellosis patients. The sustained and differential antibody profiles of patients at different infection stages have implications for the development of new serological methods for the accurate diagnosis of human brucellosis, and contribute to a more detailed understanding of the pathogenesis of chronic brucellosis.