[Protective effect of pretreatment with TLR2 agonist Pam3Csk4 on mice challenged by methicillin-resistant Staphylococcus aureus].

OBJECTIVE

To evaluate the protective effect of pretreatment with Pam3Csk4, a Toll-like receptor 2 (TLR2) agonist, on mice against methicillin-resistant Staphylococcus aureus (MRSA) infection.

METHODS

Kunming mice were injected with Pam3Csk4 (25, 50, 100 μg/mice) via tail vein. 12 and 24 hours later, the mice were inoculated with live MRSA (7×10(10) CFU/kg, ATCC43300) via tail vein. All mice were observed at 2-hour intervals for the first 24 hours and 6-hour intervals for the rest time, and survival was monitored for at least 7 days. Bacterial burden in liver, spleen and kidney of the mice were estimated by colony counting on nutrient agar 6 hours after infection (3×10(8) CFU/mice, ATCC43300). In addition, 6, 12 and 24 hours after MRSA challenge, the concentrations of tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), interferon γ (IFN-γ) and IL-10 were measured by ELISA, and the mRNA levels of these cytokines were detected by fluorescence quantitative PCR (qPCR). Finally, 24 hours after being pretreated with Pam3Csk4, mRNA levels of CXC chemokine ligand 1 (CXCL1) and Fcγ receptor III (FcγRIII) in spleen of the mice were evaluated by qPCR.

RESULTS

Compared with normal saline-pretreated mice, we found that mice pretreated with the Pam3Csk4 (100 μg/mice) had higher survival in sepsis models caused by MRSA in dose- and time-dependent manners, and Pam3Csk4 (over 50 μg/mice)-pretreated mice had a survival rate more than 70%. In addition, the protein and mRNA levels of TNFα were markedly reduced in Pam3Csk4-pretreated mice at 6 and 12 hours, but not different from the controls at 24 hours post-infection. While IL-6 at protein and mRNA levels decreased in Pam3Csk4-pretreated mice only at 6 hours post-infection. Both protein and mRNA levels of IFN-γ greatly decreased in Pam3Csk4-pretreated mice compared with those of the control group. However, IL-10 level was unchanged between the two groups at all time points. Further studies showed that the mRNA levels of CXCL1 and FcγRIII were notably raised in spleen of the mice 24 hours after administered with Pam3Csk4 compared with normal saline-pretreated mice.

CONCLUSION

Our results suggest that Pam3Csk4 pretreatment can protect mice from challenged by MRSA.