The Toll-like receptor 9 (TLR9) protein, also known as CD289, belongs to the family of Toll-like receptor (TLR) proteins which play a large role in pathogen recognition and the activation of innate immunity. Scientists using TLR9 antibodies have found that TLRs are highly conserved from Drosophila to humans, with a high degree of structural and functional homology1,2.