RASAL3 Is a Putative RasGAP Modulating Inflammatory Response by Neutrophils.

As first responder cells in host defense, neutrophils must be carefully regulated to prevent collateral tissue injury. However, the intracellular events that titrate the neutrophil's response to inflammatory stimuli remain poorly understood. As a molecular switch, Ras activity is tightly regulated by Ras GTPase activating proteins (RasGAP) to maintain cellular active-inactive states. Here, we show that RASAL3, a RasGAP, is highly expressed in neutrophils and that its expression is upregulated by exogenous stimuli in neutrophils. RASAL3 deficiency triggers augmented neutrophil responses and enhanced immune activation in acute inflammatory conditions. Consequently, mice lacking RASAL3 (RASAL3-KO) demonstrate accelerated mortality in a septic shock model via induction of severe organ damage and hyperinflammatory response. The excessive neutrophilic hyperinflammation and increased mortality were recapitulated in a mouse model of sickle cell disease, which we found to have low neutrophil RASAL3 expression upon LPS activation. Thus, RASAL3 functions as a RasGAP that negatively regulates the cellular activity of neutrophils to modulate the inflammatory response. These results demonstrate that RASAL3 could serve as a therapeutic target to regulate excessive inflammation in sepsis and many inflammatory disease states.

Bacterial Lipoteichoic Acid Attenuates Toll-Like Receptor Dependent Dendritic Cells Activation and Inflammatory Response.

Toll-like receptor (TLR) signaling is an indispensable factor in immune cells activation. Many TLR ligands have been identified, and were characterized the immunological functions such as inflammatory cytokine production in immune cells. However, the anti-inflammatory response in TLR ligand-mediated manner is poorly understood. In this report, we show that bacterial lipoteichoic acid (LTA), which is a TLR2 ligand from gram-positive bacteria including Staphylococcus aureus (S. aureus), suppresses TLR-mediated inflammatory response in dendritic cells (DCs). The TLR ligand-induced Tumor Necrosis Factor-alpha (TNF-α) production was suppressed in the bone marrow derived dendritic cells (BMDCs) by co-treatment of LTA. The cellular activation, which was characterized as upregulations of CD80, CD86 and major histocompatibility complex II (MHC II) expression, was also suppressed in the TLR ligand stimulated BMDCs in the presence of LTA. While LTA itself didn't induced both TNF-α production and upregulation of cell surface markers. The LTA mediated immunosuppressive function was abolished by TLR2 blocking in lipopolysaccharide (LPS)-stimulated BMDCs. Furthermore, LTA also showed the immunosuppressive function in the generation of IFN-γ+CD4+ T (Th1) cells by attenuation of antigen presenting activity in the BMDCs. In the imiquimod (IMQ)-induced acute skin inflammation, LTA suppressed the inflammation by downregulation of the activation in skin accumulated DCs. Thus, LTA is a TLR2 dependent immunological suppressor against inflammatory response induced by other TLR ligands in the DCs.

Immunization with a Bacterial Lipoprotein Establishes an Immuno-Protective Response with Upregulation of Effector CD4+ T Cells and Neutrophils Against Methicillin-Resistant Staphylococcus aureus Infection.

Staphylococcus aureus (S. aureus) is a commensal bacterium in the human body; however, the bacterium frequently generates serious inflammation and infectious diseases. Some strains of S. aureus, such as methicillin-resistant Staphylococcus aureus (MRSA), are still a serious problem in public health facilities. Thus, an effective protection strategy is eagerly expected for the prevention and cure of MRSA infection. Here, we report that a specific fraction of an S. aureus lipoprotein (SA-LP) established a protective response against MRSA infection. The fractionated S. aureus lipoprotein SA-LP-F2, which is contained in 30-50 kDa of crude S. aureus lipoprotein (SA-LP-C), effectively activated dendritic cells (DCs) and the SA-LP-F2-pulsed DCs generated IFN-γ+CD4+ T (Th1) and IL-17A+CD4+ T (Th17) cells by in vitro antigen presentation. The SA-LP-F2 immunization upregulated the Th1 and Th17 populations so that MRSA colonization on the skin was suppressed during the challenge phase with MRSA. By following the effector T cell upregulation, the neutrophil function, which was a substantial effector cell against MRSA, was also enhanced in the SA-LP-F2-immunized mice. Finally, we found that the protective effect of SA-LP-F2 immunization was maintained for at least 90 days because the immunized mice continued to show a protective response during the MRSA challenge period. In the MRSA challenge, reactivated Th1 and Th17 populations were maintained in the SA-LP-F2-immunized mice as compared to naive mice. In addition, the neutrophil population was also upregulated in the mice. The memory CD4+ T cell (central memory T; TCM and effector memory T; TEM) population was established by SA-LP-F2 immunization and was maintained at higher levels than usual. Taken together, our findings may provide a breakthrough in the establishment of an immunization strategy against MRSA infection.