Objective:To explore the effect of bifidobacterium on the production and morphology of dendritic cells(DC) in vitro and in vivo.Methods: In vivo

the mice were administrated orally with live bifidobacteria

heat-killed bifidobacteria(1×109CFU/ml)

with spent culture supernatant(SCS) or saline normal respectively

and their intestinal samples were used to evaluate the production of intestinal DC by immunohistochemical method.In vitro

the monocyte was induced by heat-killed bifidobacterium alone

to find out whether it could change cell morphology and become DC

Phase-contrast microscope morphological observation was made.On the other hand

normal adult immature DCs were induced by monocyte cultured in granuloeyte macrophage-colony stimulating factor(GM-CSF) and interleukin-4(IL-4)

and they were exposed to various dosages of heat-killed bifidobacterium(100ug/ml

10ug/ml) in experimental groups on the 7th day

while the control group was exposed without heat-killed bifidobacterrium

LPS at 1ug/ml was added to some cultures as positive control.The morphology of DC was observed by phase-contrast microscope and electron microscope.Results: Under the microscope

DCs were present in the intestinal lamina propria of mice

the sizes of which were varied and the appearances were irregular.Counting showed that the bifidobacterium could increase the number of DCs in the small intestine of mice.There was significant difference between the control group and the live bifidobacterium group

the heat-killed bifidobacterium group and SCS group(P<0.05).The heat-killed bifidobacterium group was compared with the live bifidobacterium group and the SCS group

It was concluded that there was an obvious difference(P<0.05).In vitro

Monocyte could not changed the morphology of cells induced by the heat-killed bifidobacterium

but it could promote the maturation of the morphology of the immature DC

which is derived from the normal adult peripheral blood monocyte.Conclusion: The research shows that the bifidobacterium have an important effect on the differentiation?development and maturation of DC.It is not the sole function of bifidobacterium.The changes of the microenvironment in vivo have an effect on the differentiation and development of DC.