Objective To explore the role of IL-1β in capillary leak syndrome by observing the alterations of AQP-1 expression,apoptosis,and ultrastructural of vascular endothelial cells under the action of IL-1β.Methods Umbilical vein endothelial cells (UVEC) in vitro were randomly allocated into 3 groups:time,concentration,and control.In the time group,UVECs were treated with culture medium containing 20 μg/L IL-1β for3 h(T1),8 h(T2),12 h(T3) and 24 h(T4).In the concentration group,UVECs were treated with culture medium containing 0.2 μg/L(C1),2 μg/L(C2) and 20 μg/L(C3) IL-1β for 24 h.In the control group,UVECs were treated with culture medium without IL-1β for 24 h.The changes of AQP-1 mRNA and protein expression were detected by real-time PCR and Western blot.Apoptosis was detected by flow cytometry,and cell ultrastructural changes were observed by electron microscopy.Results AQP-1 mRNA and protein expression of T1-T4 in the time group and C1-C3 in the concentration group were lower than those of the control group (P ＜ 0.05).The apoptotic rate was increased,and mitochondrial swelling,vacuolar degeneration,karyolysis and necrosis were observed under electron microscopy.These were more pronounced with time or concentration increases.Conclusions IL-1β can cause a decrease of AQP-1 mRNA and protein expression,increase in apoptotic rate and increase in damage to the cells'ultrastructure.This is an important reason for damage to the vascular endothelial barrier and may be associated with capillary leak syndrome.