BACKGROUND:Transplantation of mesenchymal stem cells (MSCs) to multiple sclerosis (MS) is a new developed treatment to be given more and more attention.However,whether the MSCs function by cell replacement after going cross the blood-brain barricr or immune suppression needs further confirmation.OBJECTIVE:To establish a steady and effective method of Y chromosome in situ hybridization (ISH) and to detect the distribution of MSCs in a mouse model with MS.DESIGN,TIME AND SETTING:The observational study was performed at the Laboratory of Molecular Immunology,Institute of Healthy Science from September 2007 to February 2009.MATERIALS:A total of 30 C57BL/6 mice,aged 6-8 weeks and weighing 15-20 g,were selected.Female mice were used to establish experimental autoimmune encephalomyelitis (EAE).METHODS:Y chromosme specific DNA probe labled with digoxine (DIG) was designed and ISH was performed to confirm that the designed probe was Y chromosome specific and biologically sensitive.We transplanted the MSCs from male mice into the female EAE mice,and tracked the MSCs by Y chromosome ISH.MAIN OUTCOME MEASRUES:Distribution of MSCs in mice with EAE was observed under the optical and fluorescence microscope.RESULTS:The probe was confirmed to be Y chromosome specific and biologically sensitive.What's more,a steady and effective method of ISH was established.Some MSCs were detected in the periphery organs-spleen and lymph node of mice with EAE;seldom in spinal cord which indicated that MSCs might play its roles by immune suppression.CONCLUSION:Some MSCs were detected in the periphery organs-spleen and lymph node of mice with EAE,but seldom in spinal cord in the central nervous system.