TLR2 agonist Pam3CSK4 enhances the antibacterial functions of GM-CSF induced neutrophils to methicillin-resistant Staphylococcus aureus.

A proliferation of studies have demonstrated that the toll-like receptor 2 (TLR2) pathway affects the chemotaxis, phagocytosis, and cytokine release of neutrophils when pathogens invade. Our previous studies have demonstrated that pretreatment with high doses of Pam3CSK4 (>25 µg/ml) improves the antimicrobial activity of neutrophils, however, short-lived neutrophils limit their therapeutic functions. Here, we used granulocyte macrophage-colony stimulating factor (GM-CSF) to generate neutrophils from murine bone marrow, and assessed their effect on the immune response against methicillin-resistant Staphylococcus aureus. As comparing with classical method of generating neutrophils directly from murine bone marrow, our findings show that pretreatment with Pam3CSK4 enhanced the phagocytic and killing activities against MRSA by the GM-CSF induced neutrophils (GM-CSF neutrophils). Chemotaxis of GM-CSF induced neutrophils was significantly increased after the pretreatment with Pam3CSK4. Furthermore, Pam3CSK4 pretreatment enhanced iNOS, CRAMP, TNF-α, IL-1ß, IL-10, and IL-6 expression. Finally, we observed that p38MAPK and Akt phosphorylation kinases were increased significantly in GM-CSF neutrophils pretreatment with Pam3CSK4 in a dose- and time-dependent manner, whereas p38MAPK inhibitor (SB2021190) and PI3K inhibitor (LY294002) attenuated the antimicrobial activities including phagocytosis, killing activity, respiratory burst, and the release of lactoferrin(LTF) by the GM-CSF induced neutrophils. Together, these findings suggest that pretreatment with Pam3CSK4 enhances the antibacterial function of GM-CSF neutrophils against MRSA, and this could be related to the p38MAPK and PI3K signaling pathways.

[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.

Control of Methicillin-Resistant Staphylococcus aureus Pneumonia Utilizing TLR2 Agonist Pam3CSK4.

The spread of methicillin-resistant Staphylococcus aureus (MRSA) is a critical health issue that has drawn greater attention to the potential use of immunotherapy. Toll-like receptor 2 (TLR2), a pattern recognition receptor, is an essential component in host innate defense system against S. aureus infection. However, little is known about the innate immune response, specifically TLR2 activation, against MRSA infection. Here, we evaluate the protective effect and the mechanism of MRSA murine pneumonia after pretreatment with Pam3CSK4, a TLR2 agonist. We found that the MRSA-pneumonia mouse model, pretreated with Pam3CSK4, had reduced bacteria and mortality in comparison to control mice. As well, lower protein and mRNA levels of TNF-α, IL-1ß and IL-6 were observed in lungs and bronchus of the Pam3CSK4 pretreatment group. Conversely, expression of anti-inflammatory cytokine IL-10, but not TGF-ß, increased in Pam3CSK4-pretreated mice. Our additional studies showed that CXCL-2 and CXCL1, which are necessary for neutrophil recruitment, were less evident in the Pam3CSK4-pretreated group compared to control group, whereas the expression of Fcγ receptors (FcγⅠ/Ⅲ) and complement receptors (CR1/3) increased in murine lungs. Furthermore, we found that increased survival and improved bacterial clearance were not a result of higher levels of neutrophil infiltration, but rather a result of enhanced phagocytosis and bactericidal activity of neutrophils in vitro and in vivo as well as increased robust oxidative activity and release of lactoferrin. Our cumulative findings suggest that Pam3CSK4 could be a novel immunotherapeutic candidate against MRSA pneumonia.