Like TLR5 on Day 26, TLR9 is a protein that is primed to detect invading pathogens. TLR9 does this by watching for DNA that looks foreign. Normally, the two letters CG next to each other (aka CpG) are methylated in human DNA. Unmethylated CpGs are the norm in bacteria and viruses. TLR9 watches for DNA with unmethylated CpGs to mount an immune response.
Click here to see the sequence of Day 65, with TLR9 underlined.