[The fragments of dead macrophages infected by Brucellasuis S2 strain activates the immune response against Brucella infection].

OBJECTIVE

To investigate the role of the dead macrophages infected by Brucella suis S2 strain in the initiation of immune response to Brucella.

METHODS

The mouse peritoneal macrophages were infected with Brucella suis S2 strain in vitro. After one hour, the cells were cultured in serum-free RPMI1640 medium for 5 days until all of them were dead because of starvation. The dead cell fragments and the bone marrow-derived dendritic cells (BMDCs) were co-cultured for 24, 48 and 72 hours, and then interleukin 12 (IL-12), tumor necrosis factor α (TNF-α) in the co-cultivation supernatant were detected by ELISA. The mouse macrophages marked by carboxyfluorescein diacetate succinimidyl ester (CFSE) were infected with Brucella suis S2 strain in vitro, and then were cultured without serum in the dark; the dead macrophages fragments and BMDCs labeled with anti-CD11c-PE were co-cultured for 1 hour away from light, and then the changes that BMDCs swallowed the fragments of macrophages were observed by laser scanning confocal microscopy. BALB/c mice were inoculated with the fragments of dead macrophages infected by S2 strain through abdominal cavity. After one week, a second immunization was done. The serum levels of IL-4, IL-2 and IFN-γ were detected with ELISA at 3 days post-secondary immunization.

RESULTS

The macrophages fragments infected by S2 strain could be swallowed by DCs. The level of TNF-α in BMDCs swallowing macrophages fragments infected by S2 strain was significantly higher than that in the control group, but the former did not secret IL-12. The levels of IL-2, IL-4 and IFN-γ in the sera from the mice inoculated with the macrophages fragments infected by S2 strain were dramatically higher than those in the control groups.

CONCLUSION

The dead macrophages infected by Brucella suis S2 strain can activate DCs to present antigen and induce the anti-Brucella immune response.