TLR9 and chlamydia trachomatis infectious disease: Human studies have revealed that genetic variants in the TLR1, TLR2, TLR4, and TLR9 genes can increase inflammation and are associated with the risk of chlamydial infection and the development of pelvic inflammatory diseases, raising questions about whether genetic variation at these loci can serve as a biomarker of chlamydial infection (Taylor et al. 2012, 2013; Verweij et al. 2016).