Objective   To explore the role of X-box binding protein 1 (XBP1) in immune function regulation of macrophage by low conceatration of corticosterone.    Methods   Peritoneal macrophages were isolated from adult male C57BL/6 mice

and then infected with XBP1-RNAi lentivirus or negative control lentivirus. The infection efficiency was observed by fluorescence microscopy. Mice peritoneal macrophages were collected in 3 and 5 d after infection and total RNA were extracted. RT-PCR analysis was performed to detect the effect of RNA interference. Furthermore

mice peritoneal macrophages were cultured in vitro and infected with XBP1-RNAi lentivirus or negative control lentivirus for 3 d

and then treated with low concentration of corticosterone (50 ng/ml) for 1 h. TNF-α concentration in the cell culture supernatant and phagocytosis of macrophages were determined by enzyme-linked immunosorbent assay (ELISA) and confocal microscopy

respectively.    Results   When the multiplicity of infection (MOI) was more than 6

the infection efficiency of XBP1-RNAi lentivirus was above 75% after infection 4 d. RT-PCR analysis confirmed that XBP1-RNAi lentivirus effectively inhibited the expression of XBP1 mRNA in mice peritoneal macrophages. Furthermore

after selectively silencing of the XBP1 gene

the enhancement of macrophage phagocytosis by low concentration of corticosterone was efficiently inhibited

phagocytic rate and phagocytic index of mice peritoneal macrophages were decreased markedly compared with that of negative control lentivirus group (P0.01). Meanwhile

the enhancement of TNF-α production by low concentration of corticosterone was also depressed

the concentration of TNF-α in the cell culture supernatant was significantly declined in XBP-RNAi lentivirus group

compared with the negative control lentivirus group (P0.01).    Conclusion   Selective silencing of XBP1 by RNA interference may effectively inhibit the enhancement of macrophage phagocytosis and TNF-α production by low concentration of corticosterone.