Protective effect of TLR2/TLR9 agonists on pulmonary Acinetobacter baumannii infection in mice

To investigate the protective effect of Toll-like receptor (TLR) 2/TLR9 agonists, Pam₂ CSK₄ (Pam) and CpG ODN (CpG) on mice infected with Acinetobacter baumannii (Ab) in the lungs.

Female C57 mice (6~8 weeks old) were randomly divided into PBS, Pam, CpG and Pam+CpG groups. In 24 h after intranasal immunization with different doses of the corresponding agonists, the mice were given a lethal dose of Ab infection in the lungs, and the survival rates of the mice were observed. A sublethal dose lung infection model of Ab was then established, and the bacterial colonization in the blood, lungs, liver, kidneys and spleen was measured respectively in the mice after infection. HE staining was used to observe the pathological damages in the lungs and kidneys. The protective effect of the agonists in the immunized mice against Ab was examined at 1, 3 and 7 d after immunization to explore the protective time window. Pam + CpG was used to stimulate A549 cells and RAW264.7 cells to investigate the killing or phagocytic effects on Ab.

Compared to PBS, Pam + CpG treatment significantly improved the survival rate of the mice after a lethal dose of Ab lung infection (P<0.05, P<0.01), reduced bacterial colonization in the blood (P<0.01), lungs (P<0.01), liver (P<0.01), kidneys (P<0.01) and spleen (P<0.01) in the mice after sublethal challenge, and alleviated pathological damage caused by infection. Immunization at 1 or 3 d before infection significantly improved the survival rate (P<0.05), and the protective effect was the best in 3 d after immunization. Furthermore, compared to single PBS, Pam and CpG immunization, Pam+CpG significantly promoted the killing and phagocytic effects of A549 epithelial cells and RAW264.7 cells, respectively, against Ab (P<0.01).

Combined application of TLR2/TLR9 agonists exerts a significant protective effect on both lethal and sublethal infections of Ab, which might be by its promoting the killing or phagocytic effect of lung epithelial cells and macrophages against Ab.