Abstract: Objective  To study fluorescent M.bovis BCG survival in infected IFN-γ activated THP-1 derived macrophage and its killing mechanism whether correlated with autophagy. PMA THP-1 differentiation into macrophages. Methods  THP-1 cells were induced by PMA and differentiated into macrophages, and then were activated by IFN-γ. The macrophages were divided into 4 groups: control, IFN-γ activated, Rapamycin treated and 3-MA+IFN-γ treated, and then subjected to fluorescent BCG infection at MOI 10∶1 for 48 hours. The cells were lysed with hyperpure water. The cell lysate and the culture supernatant were collected and mixed. 10 μl mixtures in 4 groups were diluted with 10-fold serial dilution, then inoculated on MiddleBrook 7H10 agar plates with OADC and cultured at 37℃ biochemical incubator for 3 to 4 weeks. The colonies on plates were counted，and the survival rates were calculated. At different time points of infection process, the macrophages were lysed and extracted the proteins. The expression of an autophagy marker LC3B was detected by Western blot, monitoring the changes of autophagy level. Results  Compared to the control group(inactivated macrophages), BCG survivals both in IFN-γ activated macrophages and Rapamycin treated macrophages decreased remarkably, whereas the levels of autophagy increased remarkably； but BCG survival in 3-MA+IFN-γ treated macrophages did not decrease, and the level of autophagy also did not increase. Conclusion  During the macrophages were infected by M. bovis BCG, or the macrophages phagocytosed BCG strains,the interaction between the macrophages and BCG strains was complex. IFN-γ activated macrophages were able to killed BCG effectively,the killing mechanism was related with the autophagy.

Key words: BCG vaccine, Interferon type Ⅱ, Macrophages, Autophagy, Cell line, tumor