Anti-Human IgG Fab Antibody [4A11] (A86804)

Intramuscular administration of inactivated influenza virus vaccine is the main vaccine platform used for the prevention of seasonal influenza virus infection. In clinical trials, inactivated H5N1 vaccines have been shown to be safe and capable of eliciting immune correlates of protection. However, the H5N1 vaccines are poorly immunogenic compared to seasonal influenza virus vaccines. Needle-free vaccination would be more efficient and economical in a pandemic, and the development of an effective and safe mucosal adjuvant will be an important milestone. A stabilized chemical analog of double-stranded RNA, PIKA, was previously reported to be a potent mucosal adjuvant in a murine model. While PIKA stimulates dendritic cells in vitro, little was known about its receptor and adjuvanting mechanism in vivo. In this study, we demonstrated that the immunostimulatory effect of PIKA resulted in an increased number of mature antigen-presenting cells, with the induction of proinflammatory cytokines at the inoculation site. In addition, coadministration of PIKA with a poorly immunogenic H5N1 subunit vaccine led to antigen sparing and quantitative and qualitative improvements of the immune responses over those achieved with an unadjuvanted vaccine in mice. The adjuvanted vaccine provided protection against lethal challenge with homologous and heterologous H5N1 wild-type viruses. Mice lacking functional TLR3 showed diminished cytokine production with PIKA stimulation, diminished antibody responses, and reduced protective efficacy against wild-type virus challenge following vaccination. These data suggest that TLR3 is important for the optimal performance of PIKA as an adjuvant. With its good safety profile and antigen-sparing effect, PIKA could be an attractive adjuvant for use in future pandemics.

Objective: Single-immunoglobulin interleukin-1 receptor-related (SIGIRR), which is also known as Toll/interleukin-1 receptor 8 (TIR-8), is a member of the TIR domain-containing family of receptors and was first characterized as an inhibitor of interleukin-1 receptor (IL-1R) and Toll-like receptor (TLR) signaling. In the Dextran sulfate sodium-induced colitis model, SIGIRR(-/-) mice were shown to have increased inflammation and to be more susceptible to endotoxin challenge. Increasing evidence implicates TLR and IL-1R signaling in the pathology of rheumatoid arthritis (RA). Therefore, the purpose of this study was to investigate the involvement of SIGIRR in regulating inflammation in disease-relevant models.

Methods: Primary human monocyte-derived macrophages and dendritic cells (DCs) were used to overexpress SIGIRR as well as to knock down endogenously expressed SIGIRR using small interfering RNAs. SIGIRR was also overexpressed in synovial cells derived from RA patients. To investigate the role of SIGIRR in vivo, zymosan-induced arthritis (ZIA) and collagen antibody-induced arthritis (CAIA) were induced in SIGIRR-knockout mice.

Results: SIGIRR overexpression inhibited TLR-induced cytokine production in macrophages and DCs, while SIGIRR knockdown resulted in increased cytokine production following TLR stimulation. Moreover, SIGIRR overexpression inhibited the spontaneous release of cytokines by human RA synovial cells. The role of SIGIRR as an inhibitor of inflammation was confirmed in vivo, since SIGIRR(-/-) mice developed a more severe disease in both the ZIA and CAIA models.

Conclusion: Our study is the first to show the expression pattern and function of SIGIRR in primary human cells. Furthermore, this investigation defines the role of SIGIRR in disease-relevant cell types and demonstrates that SIGIRR is a potential therapeutic target for RA.