Induction of immune and adjuvant immunoglobulin G responses in mice by Brucella lipopolysaccharide.

The immunogenic and adjuvant properties of Brucella abortus and Escherichia coli lipopolysaccharides (LPSs) were studied in endotoxin-responsive, athymic, and euthymic BALB/c mice and in responsive C3H/HeAu mice and congenic nonresponsive C3H/HeJ mice. Consistent with previous reports, E. coli LPS did not stimulate significant primary or secondary antibody responses in C3H/HeJ mice and induced the production of immunoglobulin M (IgM) and low levels of IgG in C3H/HeAu mice. In contrast, B. abortus smooth and rough LPS stimulated primary and secondary antibody responses and induced the production of IgM and high levels of IgG in both responsive and nonresponsive strains of C3H/He mice and in nude mice. When used as adjuvant, B. abortus LPS augmented the IgG plaque-forming-cell response of C3H/HeAu and BALB/c euthymic mice to the T-dependent antigen sheep erythrocytes. E. coli LPS augmented only the IgM plaque-forming-cell response in the same mouse strains. Neither B. abortus nor E. coli LPS was adjuvant for C3H/HeJ or nude mice. The dichotomy between the antibody and adjuvant responses of both C3H/HeJ mice and athymic mice to B. abortus LPS may be a function of the true thymus independence and dependence of these responses. In addition, the refractiveness of C3H/HeJ and nude mice to B. abortus LPS as adjuvant, but not as mitogen or polyclonal B cell activator, clearly dissociates these phenomena.