TLR1 and Lyme disease: Indeed, the Lyme disease-causing bacterium Borrelia burgdorferi is endowed with potent ligands for these TLRs, including the outer surface protein A (OspA), a triacylated lipoprotein with strong TLR1/2 stimulatory activity [50] and flagellin, the natural ligand for TLR5.[51–53] The effects of Borrelia-derived TLR ligands on TLR2 and TLR5 triggering are still unclear and may depend on cell type.