FIG. 1.
Uterine inoculation of heifers with C. abortus increases preexisting anti-C. abortus serum antibody levels in a dose-dependent manner. Estrus was induced in a total of 32 Holstein heifers by injection with dinoprost tromethamine. A total of 30 heifers (6 heifers each per challenge dose of 0, 104, 105, 106, or 108 IFU) responded with estrus and were given a uterine challenge of C. abortus strain B577 via the cervix. Single serum samples were collected 3 to 5 weeks before and 7 to 9 weeks after inoculation. Median and quartile rlu values per second are shown for bovine Ig isotypes IgM, IgG, IgG1, and IgG2 in a chemiluminescent ELISA using C. abortus strain B577 EB lysate antigen. Asterisks indicate significantly different pre- and postchallenge serum antibody levels (P < 0.028 [Wilcoxon signed rank test]). The increase in antibody levels at high levels of challenge inocula suggests that these inocula sufficiently breached anti-C. abortus immunity to establish infections that resulted in substantial stimulation of the immune response to C. abortus.