Probiotic bacteria have potential use as immunomodulators but comparative data on
their immunological effects are very limited. The aim of this study was to characterize
the effect of oral administration of probiotic strains, alone or as mixtures, on systemic
and organ-specific immune responses. For this purpose, healthy C57BL/6 mice were
perorally administered probiotics for 3 weeks. A total of five common probiotic strains,
Lactobacillus rhamnosus species GG (LGG) and LC705, Bifidobacterium breve 99
(Bb99), Propionibacterium freudenreichii Shermanii JS (PJS), and Escherichia coli Nissle
1917 (EcN), and two of their mixtures, were tested. Livers, spleens, and blood were
collected for investigation. A number of five treatments increased the abundance of
the natural killer (NK) cells. Bb99 had the most prominent effect on hepatic NK cells
(20.0 Å} 1.8%). LGG (liver: 5.8 Å} 1.0%; spleen: 1.6 Å} 0.4%), Bb99 (liver: 13.9 Å} 4.3%;
spleen: 10.3 Å} 3.7%), and EcN (liver: 8.5 Å} 3.2%; spleen: 1.0 Å} 0.2%) increased the
percentage of both the hepatic and splenic T-helper 17 cells. Moreover, LGG (85.5 Å}
3.0%) and EcN (89.6 Å} 1.2%) increased the percentage of splenic regulatory T-cells. The
tested mixtures of the probiotics had different immunological effects from their individual
components on cell-mediated responses and cytokine production. In conclusion, our
results confirm that the immunomodulatory potential of the probiotics is strain- and
organ/tissue-specific, and the effects of probiotic mixtures cannot be predicted based
on their single constituents.
Our study confirms that the immunomodulatory potential of probiotic bacteria is strain- and organ/tissue-specific. Therefore, the immunomodulatory properties of the probiotic candidates should not be extrapolated from the observations obtained with the other strains or even with the same strain in different target organ/tissue.