The Effect of Experimental BCG Antigen–Betulin-Derived Conjugates on the Guinea Pig Immunological Response

The immunopotentiating properties of BCG vaccine strain antigen conjugated with betulin derivatives have been evaluated. The experiments were carried out on agouti guinea pigs ( n = 20). The animals of the experimental groups ( n = 5) were immunized with the following antituberculosis drugs: group 1, with antigens of the BCG vaccine strain conjugated with betulinic acid; group 2, with BCG antigens conjugated with betulonic acid; and group 3, with the BCG vaccine. The animals of the control group ( n = 5) were injected with a saline solution. All the animals were infected with a virulent culture of Mycobacterium bovis (strain 8) on day 30 after the administration of antituberculosis drugs. The blood sampling for the assessment of the immune status was conducted on day 30 after the administration of drugs and day 30 after the infection with M. bovis . The designed conjugates were found to display immunopotentiating activity characterized by a 1.7–3.8-fold increase in the number of immunocompetent cells and an increase in the neutrophil functional activity observed to a greater degree in the guinea pig group 2. After infection with M. bovis some key parameters of the immune system, such as a T-lymphocyte count and the activity of enzymatic (myeloperoxidase) and nonenzymatic (cationic proteins) bactericidal systems of neutrophilic granulocytes significantly increased in groups 2 and 3, which implied the highest antituberculosis activity of the agents administered to these animals. The guinea pigs were euthanized 45 days after the infection with M. bovis . The next pathoanatomical experiments proved that the vaccine strain conjugates with betulonic acid and the BCG vaccine induced marked resistance against the pathogenic mycobacteria. The protection indexes for these agents were approximately the same and achieved 66 and 71%, respectively.