IMMUNE-RESPONSES AND RESISTANCE TO BRUCELLOSIS IN MICE VACCINATED ORALLY WITH BRUCELLA-ABORTUS RB51

Immune responses and resistance to infection with Brucella abortus 230 8 (S2308) were measured in mice following oral or intraperitoneal (i.p .) vaccination with strain RB51 (SRB51). Bacteria persisted in the par otid lymph node for 4 weeks following oral vaccination of mice with 5 x 10(8) or 5 x 10(6) CFU of SRB51. Bacteria did not appear in the sple en during 12 weeks after oral vaccination, whereas they did appear in the spleen for 8 weeks following i.p. vaccination of mice with SRB51 ( 5 x 10(8) or 5 x 10(6) CFU). Increased resistance to S2308 infection o ccurred at 12 to 20 weeks in mice vaccinated i.p. with SRB51 (5 x 10(8 ) or 5 x 10(6) CFU) but occurred at 12 weeks only in mice vaccinated o rally with SRB51 (5 x 10(8) CFU). Oral SRB51 vaccination induced lower levels of antibodies to the surface antigens of intact SRB51 bacteria that did i.p. vaccination. However, neither route of vaccination indu ced anamnestic antibody responses to the surface antigens of intact S2 308 bacteria after challenge infection of the vaccinated mice with S23 08. Mice vaccinated orally with SRB51 and challenged with S2308 at 12 to 20 weeks had lower and less persistent spleen cell proliferation an d production of gamma interferon in response to S2308 and certain immu nodominant S2308 proteins (32 to less than or equal to 18 kDa) than di d mice vaccinated i.p. with SRB51. However, mice vaccinated orally or i.p. with SRB51 and challenged with S2308 had similar spleen cell tumo r necrosis factor alpha production. These results indicate that oral v accination of mice with SRB51 was effective in inducing protective imm unity to S2308 infection, although the immunity was lower and less per sistent than that induced by i.p. vaccination. The lower protective im munity induced by oral vaccination may have resulted from lower and le ss persistent cell-mediated immunity and gamma interferon production i n response to S2308 and S2308 proteins.