Toll-like receptors (TLRs) play important roles in the immune responses against invading microorganisms. Development of TLR antagonists is recognized as a promising direction in suppressing the associated inflammatory reactions of the TLRs. Aptamers are single-stranded RNA or DNA molecules isolated through an in vitro selection process. Using a novel molecular evolution strategy that combines immunoprecipitation (IP) with systematic evolution of ligands by exponential enrichment (SELEX), we developed an IP-SELEX selection method to facilitate the screening of high-affinity aptamers for the Toll-like receptor 2 (TLR2). Also, human TLR2 functional aptamers were identified and characterized using NF-kappaB reporter assays. Among the functional aptamers, the most effective, AP177, with a dissociation constant of 73 pM, was characterized with TLR2-expressing cells challenged with bacterial cells and purified ligands. The aptamer could effectively antagonize TLR2, significantly inhibit NF-kappaB activity, and suppress the secretion of the cytokines by >80. In addition, the precise region within the functional aptamer that specifically bound TLR2 was resolved using aptamer microarray analysis. The results of functional assays showed that AP177 acted as a TLR2 antagonist and may hold therapeutic potential in the treatment of diseases related to dysregulated TLR2 immune responses.
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