Brucella melitensis infection associated with Guillain–Barré syndrome through molecular mimicry of host structures

Brucella melitensis is a facultative intracellular bacterium that can survive inside macrophages and the causative agent of brucellosis. In the present study, we found that a lipooligosaccharide of B. melitensis has a GM1 ganglioside-like structure and shows a strong antibody response in mice. The cholera toxin B subunit, which binds to GM1 ganglioside specifically, reacted with the surface of B. melitensis. Immunization with B. melitensis induced the production of anti-GM1 ganglioside antibodies in mice and serum from immunized mice showed a cross-reaction with Guillain–Barré syndrome (GBS)-associated Campylobacter jejuni, but not non-GBS-associated C. jejuni. When B. melitensis was treated with a neuraminidase, antibody responses disappeared. B. melitensis immunization induced the production of anti-GM1 ganglioside antibodies in BALB/c mice but not in C57BL/6 and ddY mice, and for BALB/c mice, immunization with B. melitensis induced much greater production of anti-GM1 ganglioside than GBS-associated C. jejuni. Flaccid limb weakness was observed in B. melitensis immunized mice. These results suggest that B. melitensis is a new etiological agent for GBS and that immunological responses between it and GBS-associated C. jejuni in the mouse model may be different.