Five different adjuvants were examined for potentiation of humoral and cell-mediated immune (CMI) responses in cattle to a Brucella abortus soluble
antigen (BASA). Two separate experiments were performed involving a total of 64 steers, divided among six groups (Experiment 1) and 9 groups (Experiment 2). The adjuvants used were:
muramyl dipeptide, Freund's incomplete adjuvant,
dimethyl-dioctadecyl ammonium bromide (
DDA), Bordetella pertussis and Propionibacterium acnes. In each experiment, three groups received BASA (2 mg
protein) subcutaneously with adjuvant, one group received a reduced dose of B. abortus Strain 19 (S19), one group served as unvaccinated controls, and another group received BASA alone. Primary responses were studied following a single immunization in comparison to the single inoculation with S19. For each experiment serum antibody responses and CMI responses were sequentially determined over a period of 56 days. Antibody responses to B. abortus were measured using the
brucellosis card,
rivanol precipitation-plate agglutination,
complement fixation, and fluorometric immunoassay tests, and as well as with an
enzyme-linked
immunosorbent assay. The CMI response was measured using
antigen-specific lymphoproliferation (LP) and skin testing for delayed-type
hypersensitivity (DTH) to BASA (Experiment 2). Specific aspects of induced CMI responses investigated were macrophage activation (IL-1 production), helper T cell activation (IL-2 production), and release of soluble suppressor factor(s). In general, mean antibody responses were significantly higher (P less than 0.05) in immunized steers than in control steers and those receiving BASA alone. The LP responses to heat-killed B. abortus were generally higher in immunized groups than in the controls. The LP and DTH responses were greatest in the groups receiving S19 and BASA +
DDA. Increased induction of
IL-1 was largest in the group receiving BASA +
DDA whereas
IL-2 release was greatest in S19 vaccinated steers. Suppressor T cell responses were most obvious in the groups receiving S19, BASA + B.
pertussis, and P. acnes. These studies demonstrated that
DDA potentiates CMI responses to a soluble B. abortus
antigen and may be useful as an adjuvant for future
vaccines, particularly
subunit vaccines.