Aim and Background: RNA interference has the role of gene silencing process that is triggered by double-stranded RNAs. Common to all cell types, is the production of 21-24 nucleotide small interfering RNA (siRNA), which guides the RNA-induced silencing complex (RISC) to identify and cleave target mRNA sequences. siRNA duplex are potent activators of innate immune system that induce high levels of cytokines and interferon. Toll-like receptors trigger the first line of innate immune response that is mediated by transcriptional induction of a large number of cellular genes. siRNA interact with cytoplasmic RNA sensors such as: Retinoic - acid Inducible Gene -I (RIG-I), RNA-Activated protein kinase R (PKR), Interferon Regulatory Factor (IRF) and 2’ -5’ oligo adenylate synthetase (2’ -5’ OAS), Nuclear Factor kappa B cell (NF-kB). siRNA modification are on the sugar, phosphate linkage, base, overhangs and termini nucleotides leading to increase half-life siRNA. This review article describes gene silencing and innate immune caused by siRNA.

Background: RNA interference-based gene silencing has recently been applied as an efficient tool for functional gene analysis. RORC2 is the key transcription factor orchestrating Th17 cells differentiation, the cells that are known as the pathogenic elements in various autoimmune diseases. The aim of this study was to design efficient siRNAs specific for RORC2 and to evaluate different criteria affecting their functionality.Methods: Three siRNA duplexes specific for RORC2 mRNA were designed. Th17 cells were produced from IL-6 and IL-1 treated cord blood CD4+T cells. The T cells were transfected with three different designed siRNAs against RORC2 and the expression of RORC2 gene was measured using quantitative real time PCR.Results: Different levels of RORC2 down regulation were observed in the presence of each of the designed siRNAs. Efficient siRNA with 91.1% silencing activity met the majority of the established bioinformatics criteria while the one with 46.6% silencing activity had more deviations from these criteria.Conclusion: The more bioinformatics criteria are considered, the more functionality were observed for silencing RORC2. However, the importance of the type of criteria per se should not be neglected. Although all recommended criteria are important for designing siRNA but their value is not the same.

The p75 pan-neurotrophin receptor (p75NTR) plays a pivotal role in linking the immune system with the nervous system. p75NTR is required for the development of several characteristic features of allergic asthma. Also p75NTR upregulated by reactive Schwann cells after peripheral nerve injury.Moreover p75NTR and RhoA play a critical role in the regulation of apoptosis. To determine whether the designed siRNA for p75NTR can downregulates both p75NTR and Rho-A at RNA level in rats and, if so, at what magnitude, Schwann cell apoptosis occurs.Isolation and purification of neonate Schwann cells were prepared from rat sciatic nerve. Specific siRNA duplex was designed for p75NTR.To investigate the role of siRNA-mediated knockdown of p75NTR, the gene expression in p75NTR was examined with reverse transcription–polymerase chain reaction (RT-PCR) and Real-Time RT-PCR. Schwann cell apoptosis was performed by Annexin and TUNEL assays after 24 hours. Following p75NTR Transfection siRNA, p75NTR gene, compared with control, was downregulated by 73%. Without using siRNA for Rho-A, Rho-A gene was downregulated by 89% at the same time. Based on Annexin assay, apoptosis of Schwann cells occurred in siRNA+ NGF and control+ NGF by 16.76%±2.27 and 92.39%±1.82, respectively.TUNEL data showed that apoptosis of Schwann cells occurred in siRNA and control by 12.91%±6.39 and 78.55%±11.85, respectively. Thus, p75-siRNA downregulated both p75NTR and Rho-A at RNA level in rats and showed a role on decreased cell apoptosis compared to the controls.