Tissue reaction and immunity in swine immunized with Actinobacillus pleuropneumoniae vaccines

These studies were done to develop a subunit vaccine for swine that would protect against disease, but not create unacceptable tissue reactions at the immunization site. Swine were used to evaluate the local effects of subunit vaccines prepared from extracts of Actinobacillus pleuropneumoniae serotype 1 containing one of a wide variety of adjuvants. The antigen was an anionic fraction of a saline extract of A. pleuropneumoniae (ANEX). The adjuvants used were vegetable oils (peanut, sesame, canola, or corn oils, vitamin E, or Lipposyn II emulsion); mineral oil (Marcol-52) and other materials (aluminum hydroxide, polyethylene glycol, Quil-A, Amphigen, or Emulsigen-Plus). Two types of experiments were done. In the 1st set of experiments, pigs were given multiple simultaneous injections in different sites and euthanized on days 1, 3, 7, 14, 21, or 28. Tissues were examined for gross and histopathological lesions. In the 2nd set of experiments, 48 pigs were allocated to 6 groups and vaccinated twice with a vaccine containing ANEX antigen combined with one of various adjuvants. Antibody responses and protection from challenge were evaluated. Among the adjuvants that were tested, mineral oils induced protective immunity, although the mineral oil Marcol-52 resulted in severe tissue reactions. The vegetable oils induced little protective immunity, and some of them were quite irritating. The response to the other materials ranged from little irritation or protection induced by the vaccine containing aluminum hydroxide to effective protection without irritation after vaccination with ANEX/Amphigen or ANEX/Emulsigen-Plus combinations. In conclusion, swine were protected against disease by a subunit vaccine that did not create unacceptable tissue reaction at the immunization site.