Abstract— <p>A conjugate of gold nanoparticles (15 nm) with brucellin (a polysaccharide–protein complex isolated from the vaccine strain of Brucella) was obtained. Vaccination of white mice was carried out with the obtained conjugate. The preparation was administered intraperitoneally three times with an interval of seven days. After that, all animals were injected with a suspension of the cells of the <i>Brucella abortus</i> 82 vaccine strain. Using a cell proliferative test, it was demonstrated that phagocytic cells and splenocytes had higher metabolic activity in the group of animals immunized with the brucellin conjugate with gold nanoparticles as compared with the group immunized with the native antigen. Moreover, this trend was enhanced after the introduction of the vaccine strain. The highest titer of antibodies was observed in animals immunized with the brucellin conjugate with gold nanoparticles (1 : 2560 initially and 1 : 10 240 after stimulation with the vaccine strain). It is important that, during the opsonophagocytic reaction, the level of opsonizing antibodies was very high, which contributes to the neutralization of bacteria persisting in the animal organism.</p>