FIG. 1.

(A) Bacterial loads in the spleen 21 days after infection of C57BL/6 or Igh6^−/− mice with a mixed inoculum containing B. abortus 2308 (WT) and the virB mutant. Mice (n = 5) were inoculated i.p. with a 1:1 mixture of WT and virB mutant bacteria. The number of CFU of each bacterial strain was determined by differential plating. The significance of differences (P < 0.05) between the virB mutant and the WT was determined with the Student t test. (B) Bacterial loads in the spleens of Igh6^−/− mice after splenocyte transfer. Splenocytes from immunized or naïve C57BL/6 mice were transferred intravenously into 10 Igh6^−/− mice per group 2 days before they were inoculated i.p. with a 1:1 mixture of WT and virB mutant bacteria. Numbers of CFU from the spleens were determined 21 days after infection. The significance of differences (P < 0.05) between the virB mutant and the WT was determined by Student's t test.