Abstract: The acquired immunodeficiency syndrome caused by HIV-1 is spreading all over the world.The slow progress in AIDS therapy and vaccine partially imputes to be lack of appropriate animal models used to study AIDS pathogenesis and to evaluate vaccines.To find an animal model is an imperative task in HIV research.Tree shrew is widely used in biomedical research,and is susceptible to many medically important viruses.Whether tree shrew (Tupaia belangeri) can be infected by HIV-1 is a valuable approach.In present study,wild tree shrews from Yunnan Province were maintained in laboratory animal facility for more than 2 weeks before sacrifice.Tree shrew spleen and peripheral blood lymphocytes and monocytes/macrophages and human peripheral blood lymphocytes and monocytes were separately infected by 5 HIV-1 strains (HIV-1ⅢB,HIV-1JR-FL,HIV-1Ada-M,HIV-1Ba-L,HIV-1SF162),which use different coreceptors after the cells were activated by allogeneic lymphocytes,PHA and IL-2 for 72 h.The HIV-1 infected cells were then cultured in vitro for 15 days.The proliferation rates and viability of HIV-1 infected human immunocytes obviously dropped on day 15,but those of tree shrew immunocytes did not despite either infected or not infected by HIV-1.HIV-1 particles in the infected culture supernatant and proviral DNA in the cells were respectively detected by RT-PCR using primer sk145/431 and by PCR using primer sk68/69 on days 1,3,5,7,9,12,15 after infection with HIV-1.In addition,the expression of HIV-1 specific antigens on the tree shrew and human immunocytes after infection were detected by flow cytometry,for which an AIDS patient plasma was used as the first antibody,and FITC-conjugated sheep anti-human-IgG as the second antibody.HIV-1 RNA and proviral DNA were respectively found in the culture supernatant of the HIV-1 infected human immunocytes and in the infected cells.Using flow cytometry,HIV-1 specific antigens were also measurable on the surface of these cells.However,neither HIV-1 RNA in the supernatant from the infected HIV-1 tree shrew immunocytes nor the proviral DNA from the infected tree shrew immunocytes could be detected.The HIV-1 specific antigens were not demonstrated on the surface of the HIV-1 infected tree shrew immunocytes.Taken together,these experimental results suggested that the tree shrew immunocytes can not be in vitro infected by these HIV-1 strains.It seems to be caused by the structure differences of the HIV-1 receptors (CD4) and coreceptors (CCR5 or CXCR4) between human and tree shrew immunocytes.