In vitro evaluation of immunomodulatory activity of Bifidobacterium bifidum 791 in the cell model of innate and adaptive immunity

Over recent decades, multiple data were accumulated on immunotropic activity of Bifidum flora, based on effects of these bacteria on isolated lymphoid follicles, dendritic cells, B-cell aggregates, pro- and anti-inflammatory cytokines and chemokines, as well as participation of bifidoflora in the recognition of “non-self” during the development of microsymbiocenosis. The relevance of research in the field is associated both with fundamental issues of human host/microbiota symbiosis, but also with the prospects of practical application of the knowledge gained towards design of probiotics that affect the immune system. This article presents the results concerning effects of supernatant and bacterial cells of Bifidobacterium bifidum 791 (B. bifidum 791) strain in the model of human peripheral blood mononuclear cells (MNCs). We used the reference strain B. bifidum 791 (Russian Collection of Industrial Microorganisms from the GosNII Genetika Federal State Enterprise, Deposition No. AS-1247), which is used in production of the probiotic drug “Bifidumbacterin” (CJSC Ecopolis, Kovrov). Mononuclear cells (MNCs) were isolated from peripheral blood of 20 healthy donors. MNCs were stained with monoclonal antibodies for CD4, CD8, CD3, CD25, CD69, CD56 (Beckman Coulter, USA). Analysis of the cellular subsets was performed by multicolor flow cytometry with Cytomics FC500 instrument (Beckman Coulter, USA). The experiments were carried out in duplicate. The studies have shown that probiotic strains have an activating and modulating effect upon immunocompetent cells. The studied B. bifidum 791 strain had an immunomodulatory effect on the cells of nonspecific and adaptive immunity: it increased the percentage of CD69⁺ cells in the subpopulation of CD3⁺CD8⁺T lymphocytes, CD69 (%) and CD25 (%) NK cells, and promoted activation of cytotoxic lymphocytes. The supernatant of bifidobacteria had a more pronounced effect on MNCs. E.g., it increased the expression of CD69 by Th cells, induced the expression of CD25 by T cytotoxic cells, and increased the CD69 and CD25 expression (%) by NK cells compared to B. bifidum 791 bacterial cells. These data contribute to understanding the mechanisms of immunoregulatory influence of normobiota (in the Bifidobacteria models) by formation of symbiotic interactions “microbiota – host” and contribute to the development of a new research area, i.e., “infectious symbiology”. Further study of immunomodulatory activity of bifidoflora has the prospectives of searching and selection of Bifidobacteria strains, in order to create new targeted probiotic preparations.