Objective To evaluate the role of phosphodiesterase 4B (PDE4B) in lipopolysaccharide (LPS)-induced release of inflammatory factors in rat microglias.Methods The pri mary cultured microglial cells were randomly divided into 5 groups (n =24 each) using a random number table:control group (group C),LPS group,vehicle group,mismatch small interfering RNA (siRNA) group and PDE4B-siRNA group.The cells were incubated for 48 h in C and LPS groups.The cells were transfected with lipofectaminTM RNAiMAX 1 μl for 48 h in vehicle group.In mismatch siRNA and PDE4B-siRNA groups,mismatch siRNA 2 μl and PDE4B-siRNA 2 μl were added to 100μl serum-free culture medium (final concentration of siRNA 20 nmol/L),respectively,lipofectaminTM RNAiMAX 1 μl was added simultaneously and the cells were then transfected for 48 h.The expression of PDE4B protein and mRNA was determined by Western blot and real-time PCR,respectively.The cells were cultured for 24 h in serum-free culture medium containing LPS 100 ng/ml in LPS,vehicle,mismatch siRNA and PDF4B-siRNA groups.Then the release of TNF-α and IL-1β was measured by ELISA and the expression of extracellular signalregulated protein kinase (ERK) and phosphorylated ERK (p-ERK) was detected by Western blot.Results Compared with C group,the expression of PDE4B protein and mRNA was significantly down-regulated in group PDE4BsiRNA (P ＜ 0.05),no significant changes were found in LPS,vehicle and mismatch siRNA groups (P ＞ 0.05),and the release of TNF-α and IU1β was increased and the expression of p-ERK was up-regulated in the other four groups (P ＜ 0.05).Compared with LPS group,the release of TNF-α and IL-1β was decreased and the expression of p-ERK was down-regulated in PDE4B-siRNA group,and no significant changes were found in vehicle and mismatch siRNA groups (P ＞ 0.05).There was no significant difference in ERK expression between the five groups (P ＞ 0.05).Conclusion PDF4B can promote LPS-induced release of inflammatory factors in rat microglias and activation of ERK is involved in the mechanism.