The Bartonella autotransporter CFA is a protective antigen and hypervariable target of neutralizing antibodies blocking erythrocyte infection

Abstract

Antibodies are key to the clearance of Bartonella bacteremia, but the mechanisms and targets of protective antibodies are unknown and bacterial evasion strategies remain elusive. We studied experimental Bartonella taylorii infection of mice, its natural host, and investigated protective immune responses. Clearance of bacteremia depended on specific antibodies that interfere with bacterial attachment to erythrocytes. Accordingly, antibodies were effective in the absence of complement and Fc-receptors. Moreover, they formed independently of B-cell hypermutation and isotype class switch. The cloning of neutralizing monoclonal antibodies (mAbs) led to the identification of the bacterial autotransporter CFA as a protective antibody target, and vaccination against CFA protected against Bartonella bacteremia. MAb binding mapped to a region of CFA that is hypervariable in both human- and mouse-pathogenic Bartonella strains, suggesting mutational antibody evasion. These insights further our understanding of Bartonella immunity and immune evasion and elucidate mechanisms driving high Bartonella prevalence in the wild.