COMPARISON OF IMMUNE-RESPONSES AND RESISTANCE TO BRUCELLOSIS IN MICE VACCINATED WITH BRUCELLA-ABORTUS-19 OR RB51

Immune responses and resistance to infection with Brucella abortus 230 8 (S2308) were measured in mice following vaccination with B. abortus 19 (S19) or the Lipopolysaccharide (LPS) 0-antigen-deficient mutant, s train RB51 (SRB51). Live bacteria persisted for 8 weeks in spleens of mice vaccinated with 5 x 10(6) or 5 x 10(8) CFU of SRB51, whereas bact eria persisted for 12 weeks in mice vaccinated with 5 x 10(6) CFU of S 19. Mice vaccinated with 5 x 10(6) or 5 x 10(8) CFU of SRB51 had incre ased resistance to infection with S2308 at 12, 16, and 20 weeks after vaccination, but the resistance was lower than that induced by vaccina ting mice with 5 x 10(6) CFU of S19. Spleen cells obtained from mice v accinated with S19 or SRB51 generally exhibited similar proliferative responses to S2308 bacteria or bacterial proteins (106 to 18 kDa) foll owing challenge of mice with S2308 at 12, 16, or 20 weeks after vaccin ation. Mice vaccinated with S19 had antibody to S2308 bacteria and S23 08 smooth LPS at 3, 8, and 12 weeks after vaccination. In contrast, mi ce vaccinated with either dose of SRB51 did not produce antibody to S2 308 smooth LPS. In addition, only mice vaccinated with the highest dos e of SRB51 (5 x 10(8) CFU) had antibody responses to S2308 bacteria, a lthough the responses were lower and less persistent than those in mic e vaccinated with S19. Collectively, these results indicate that SRB51 -vaccinated mice have similar cell-mediated immune responses to S2308 but lower resistance to infection with S2308 compared with S19-vaccina ted mice. The lower resistance in SRB51-vaccinated mice probably resul ted from a combination of rapid clearance of SRB51 and an absence of a ntibodies to S2308 LPS.