Aptamers that bind to the human complement component receptor hC5aR1 interfere with hC5aR1 interaction to its hC5a ligand

The complement system plays an important role in inflammation and immunity. In this system, a potent inflammatory ligand is C5a, which initiates its effects by activating its core receptor C5aR1. Thus, compounds that interfere with the C5a–C5aR1 interaction could alleviate some inflammatory conditions. Consequently, several ligands that bind to either C5a or C5aR1 have previously been isolated and evaluated. In the present study, two RNA aptamers, aptamer 1 and aptamer 9, that specifically bind to hC5aR1 with much higher affinity than antibodies were isolated. These two aptamers were tested for their ability to interfere with the cognate ligand of hC5aR1, C5a, using a chemotaxis assay. Both aptamer 1 and 9 interfered with the C5a interaction, suggesting that the aptamers recognized the extracellular domain of hC5aR1 responsible for hC5a ligand binding. Considering the higher affinity of aptamers to the hC5aR1 and their interference with hC5a ligand binding, further study is warranted to explore not only their applications in the diagnosis of inflammatory diseases but also their usefulness in modulating hC5a and hC5aR1 interactions.