【Abstract】ObjectiveTo study Toll like receptor 4 (TLR4) expression on peripheral blood monocytes (PBMCs) during the early stage of human acute pancreatitis. MethodsThirty consecutive patients with acute pancreatitis admitted within 24 h of onset of abdominal pain were enrolled in this study. Another 20 healthy volunteers were included as control. Blood samples were collected by venipuncture on the day of admission and 3， 7 d after admission and PBMCs were isolated. TLR4 and CD14 expressions on PBMCs were detected by flow cytometry. Serum tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) were measured simultaneously. Correlations between these parameters were analyzed. ResultsTLR4 expression increased on the day of admission and then continued to decline for several days. On third day, TLR4 expression was almost normal compared with the normal control. The alteration of serum TNF-α was consistent with that of TLR4. ConclusionDuring the early stage of human acute pancreatitis, mononuclear-macrophages may be ignited through TLR4 (a door keeper of innate immune system), which lead to TNF-α production.