Immunity to bovine reproductive infections.

Protective immune responses in the genital tract are robust, as shown by convalescent and vaccine-induced immunity. Systemic immunity is crucial for systemic infections that result in reproductive failure (such as brucellosis, leptospirosis, and the systemic forms of C. fetus and H. somnus infection). Although IgA responses can protect against sexually transmitted or venereal infections, systemically induced IgG antibody responses also protect. IgA responses can be induced by immunization of the genital tract, where inductive sites develop after antigenic stimulation. The common mucosal immune system can also be used to induce a genital IgA response, as shown by intranasal vaccination. Lastly, it is necessary to determine which antigens of each infectious agent are protective and which types of immune responses protect best.