[Effect of Bifidobacterium on the maturation and function of dendritic cell originating from blood monocyte]

To study in vitro whether the bifidobacterium plays a role in the functioning of dendritic cell (DC) stimulating the proliferation of T lymphocyte, and has effect on the generation of cytokine secreted by the DC deriving from the normal adult peripheral blood monocyte.

Normal adult immature DCs were generated in induction from monocyte cultured with granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin-4 (IL-4). On the 7th day of cell culture, immature DCs were exposed to various dosage heat-killed bifidobacteria (100 microg/mL, 10 microg/mL), while the control group was exposed to the culture without heat-killed bifidobacterrium, LPS at 1 microg/mL was added to some cultures as positive control. The morphology of DC was observed by phase-contrast microscope and electron microscope. On the 9th day of the culture, the immune function of DC stimulating the proliferation of allogeneic T lymphocytes was examined by MTT assay. At the same time, the level of IL-12 in DC culture and the level of IFN-gamma in DC and T lymphocyte co-cultured supernatant were analyzed by ELISA.

The phase-contrast microscope and electron microscope indicated that immature DCs stimulated by the heat-killed bifidobacterium had typical morphology characteristic to be similar to the morphology of mature DCs as positive control. The mixed leukocyte reaction (MLR) test showed that by the stimulation of the heat-killed bifidobacterium, the induced DCs could remarkably stimulate the proliferation of allogeneic T cells (P < 0.01), and the effect of high dosage (100 microg/mL bifidobacterium) experimental group was the strongest. After the stimulation of the heat-killed bifidobacterium, the level of IL-12 in culture supernatant of experimental group was higher than that of control group (P < 0.05). In the co-culture supernatant, the level of IFN-gamma in the control group was lower than that in the experimental groups (P < 0.05).

Bifidobacteria have effects on the differentiation, maturation and function of DC deriving from the monocyte: (1) The bifidobacterium can promote the maturation of DC morphology in vitro; (2) the bifidobacterium can promote the function maturation of DC by enhancing the ability to stimulate the T lymphocyte proliferation; (3) after the stimulation of the bifidobacterium, the level of IL-12 secreted by DC has been remarkably elevated, and the stimulated DC can promote the level of IFN-gamma secreted by T lymphocyte. The various dosages of bifidobacterium have different effect on the degree of DC maturation, and the that of the high dosage (100 microg/mL) bifidobacterium is the strongest.