The purpose of the work was to show possible manifestations of the "immunological memory" of neutrophils as a population of cells of the innate immunity system when studying the dynamics of phagocytosis activity of the test object C.diphtheriae var. gravis, tox + after repeated stimuli of the immune system of experimental rabbits by experimental diphtheria bacterial antigen drug. The drug was obtained by the authors’ method. Material and methods. The phagocytic activity of neutrophils in rabbit blood was examined by direct morphological method before administration of the test drug and on the second day, 3 hours after each vaccination. The activity indices of phagocytosis were calculated: microbial number, phagocytosis index, percentage of phagocytic neutrophils, and phagocytic number. Subsequently, at intervals of 1 month, similar studies were performed twice and the results obtained were evaluated using conventional statistical methods (p=0.05). Results and discussion. Studies showed that microbial number was significantly higher than its baseline 2.0 and 1.5 times, respectively. It should be noted that the indicators of the baseline rate of increase of microbial numbers with each administration of the drug, although they were significant, but decreased: the maximum value of this index was registered after the first vaccination – 180 %, after the second vaccination it was slightly lower – 170 %, after the third dropped to 120 %. Statistical processing of the results showed that all other indices of phagocytic activity of neutrophils under the influence of the first antigenic stimulus increased significantly by 2.8 times (phagocytosis index), by 1.5 times (phagocytic number), and by 2.0 times (phagocytic neutrophils) (t > 2, p = 0.05). When re-vaccinated compared with baseline levels of phagocytic activity in the first experiment, phagocytosis index increased by 51 %, phagocytic neutrophils – by 26 %, phagocytic number – by 46 % (t> 2, p = 0.05). There was no authentic difference between phagocytosis index and phagocytic neutrophils values after the first and second vaccinations (t <2, p = 0.05), but the level of phagocytic number was significantly higher (t = 2, p = 0.05). In relation to the indices obtained on the eve of the second vaccination, the phagocytosis index increased by 24 %, the phagocytic number – by 14% (t> 2, p = 0.05). The increase in phagocytic neutrophils was not significant (t <2, p = 0.05). With regard to the influence of the third antigenic stimulus, the dynamics of phagocytosis activity indices was similar. Their average values on the eve of all three vaccinations were much below than average levels after the vaccinations (t> 2, p = 0.05). The increase in the number of absorbed microbial cells in repeated vaccinations was provided not by increasing the number of phagocytic neutrophils, but by increasing their efficiency. The results of the experiment can be explained from the standpoint of the concept of trained innate immunity and epigenetic reprogramming of the innate immunity cells. Conclusion. Experimental bacterial diphtheria antigen drug stimulated the phagocytic activity of neutrophils in rabbit blood after the first, second and third vaccinations. Re-vaccination provides both increased neutrophils readiness for microbial cell uptake and a greater level of response. An increase in phagocytosis indices on the eve of repeated vaccinations and after them can indicate that the cells of the system of innate immunity save the information about antigenic stimulus obtained at the first administration of the test drug. The obtained results are promising for the design of a combined diphtheria vaccine with a bacterial component aimed at preventing colonization by the pathogen of the respiratory tract mucosa and toxic forms of diphtheria.
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