Objective To explore the expression of beta 2 adrenergic receptors(?2-AR) in bone marrow cells and its significance and provide a scientific basis for the theory of hematopoietic regulation by nerve factors.Methods After bone marrow mononuclear cells were isolated from normal mouse bone marrow by the Ficoll density gradient centrifugation,the expressions of ?2-AR were studied by immunohistochemistry in bone marrow mononuclear cells,cultured bone marrow stromal cells,GM-CFUs,paraffin sections and smears of bone marrow.Mouse models of immune-mediated aplastic anemia(AA) were made by lymphocyte infusion.Mice were divided into 3 groups including animal model group,?2-AR antagonist (ICI 118551) group,and control group,and the expression of ?2-AR in bone marrow mononuclear cells at the 8 th day was detected by Western blotting.Results The positive expression of ?2-AR in cytoplasm or membrane of normal mouse bone marrow cells showed different brown by immunohistochemical staining.There were intensive positive expressions of ?2-AR in mononuclear cells(48%) and bone marrow stromal cells (68%),while progenitor cells only showed middle-positive(55%)or weak positive(45%),and other hematopoietic accessory cells were positive in varying degrees.The relative values of ?2-AR of bone marrow mononuclear cells in 3 groups were 1.03?0.31,1.72?0.29 and 1.41?0.35,respectively;the expression of ?2-AR in animal model group was more lower than that in control group(P