BACKGROUND:Adipose stem cells can differentiate into bone cells, cartilage cells, smooth muscle cells, myocardial cells and nerve cells. Adipose-derived stem cells and mesenchymal stem cells have very similar biological properties, and they are also very close in terms of cellsurface marker expression profile. OBJECTIVE:To investigate the expression of human leukocyte antigen II in adipose-derived stem cells and its immunogenicity and immunomodulatory effect, and to explore the specific mechanism. METHODS:After isolation and culture, the adipose-derived stem cells were stimulated with interferon-γ, and the expression of human leukocyte antigen II was detected by flow cytometry, the expression of indoleamine 2,3-dioxygenase was determined by real-time PCR and western blot. Adipose-derived stem cells were used to stimulate lymphocytes, and the cellproliferation was observed. The lymphocytes were stimulated with phytohemagglutinin, and then 1×102-1×105 adipose-derived stem cells were added to inhibit the proliferation;meanwhile, adipose-derived stem cells, a third party, at a dose of 1×102-1×105 were added to the ongoing two-way mixed lymphocyte reaction, and the cellnumber was calculated as count per minute. RESULTS AND CONCLUSION:The expression of human leukocyte antigen II and indoleamine 2,3-dioxygenase was low in adipose-derived stem cells, but up-regulated with stimulation of interferon-γ. Adipose-derived stem cells could not stimulate lymphocyte proliferation, but could inhibit lymphocyte proliferation induced by phytohemagglutinin or al ogeneic lymphocytes, and interferon-γwas highly expressed in the supernatant of co-culture of adipose-derived stem cells and mixed lymphocytes. These results indicate that the adipose-derived stem cells have low immunogenicity and can inhibit cellproliferation of lymphocytes in vitro, and the addition of exogenous interferon-γcan enhance the immunosuppressive effects of adipose-derived stem cells.