Abstract: Objective To observe the changes of immune cell populations in peripheral blood of mice with lymph node metastasis of pancreatic cancer. Methods C57BL/6J mouse syngeneic Panc02 pancreatic cancer cells were injected into intra-footpad . The FCM (fluorescence activated cytometry) was adopted to detect 13 immune cell populations in peripheral blood. Results Six weeks after injection, the lymph node metastasis rate was 65%. Compared to that of normal mice, in the peripheral blood of the mice with and without lymph node metastasis, the B lymphocytes（P<0.05，P<0.01） and T lymphocytes （P<0.05，P<0.01）were significantly decreased; however, the granulocytes（P<0.05，P<0.01）, myeloid derived suppressor cells (MDSC) （P<0.01，P<0.01）and M2 polarized tumor associated macrophages (TAM) （P<0.05，P<0.01 were significantly elevated. Compared with the tumor bearing mice without lymph node metastasis, in the peripheral blood of the tumor bearing mice with lymph node metastasis, the changes of the above immuen cell populations were more obvious（P<0.05）. Conclusion Pancreatic cancer with lmyph node metastasis can induce intensively systemic immunosuppression and the MDSC and M2 polarized TAM may play crucial roles. Immune reconstructions are potential important targets for the prevention and treatment of lymph node metastasis of pancreatic cancer.

Key words: Key Words：Pancreatic Cancer, Lymph node metastasis, Myeloid-derived suppressor cells, Tumor associated macrophages, Immune reconstruction